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334 Cards in this Set
- Front
- Back
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What is a hormone?
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A hormone is a small chemical messenger that transports a signal from one cell to another
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How is the hormone carried between cells?
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By the blood
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What are the eight locations of hormone secretion in the body?
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Pituitary gland, Pineal gland, thyroid, thymus, adrenal gland, reproductive organs (testes, ovary)
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What percentage of hormones are water soluble and therefore polar and hydrophillic?
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80%
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What are the two types of water-soluble hormones?
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Polypeptide hormones
Some amino acid derivatives |
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What are some examples of homrones that are amino acid derivatives?
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Neurotransmitters like dopamine, epinephrine and monosodium glutamate
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What are the type of hormones that are water INSOLUBLE, therefore APOLAR and HYDROPHOBIC?
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Steroid hormones, some dipeptide-like derivatives
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What are some examples of steroid hormones?
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Estrogen, testosterone
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What is the structure of estrogen, testosterone like?
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They are cholesterol derivatives, with many ring structures fused together
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How are steroid hormones transported?
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In the blood, but need a carrier because they are hydrophobic
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What is the carrier of steroid hormones?
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Human serum albumin
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What are two general mechanisms of hormone action?
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-Peptide or amine binds receptor on outside of cell, and acts through receptor without entering the cell
-Steroid or thyroid hormone enters the cell, and hormone/receptor complex acts in the nucleus |
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Why can steroid hormones cross the membrane?
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Since they are apolar, they can freely diffuse across the membrane and can either interact with factors in the cytoplasm, or be modified to be soluble in the aqueous cytoplasm
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What do nuclear hormone/receptor complexes generally act as?
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Transcription factors in the nucleus, that bind DNA to affect levels of transcription
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Which type of hormone has a faster action?
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The peptide and amine hormones are faster-acting than steroid and thyroid hormones
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Why do peptide and amine hormones act faster than steroid and thyroid hormones?
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Since peptide and amine hormones bind their receptor earlier, they initiate an extremely fast cascade in response
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What generally happens when peptide and amine hormones bind their receptor?
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Binding causes a conformational change, or dimerization, and this signals to the inside of the cell. Sometimes a second messenger is activated, and a signalling cascade within the cytoplasm is activated reseulting in action (ie. altered activity of a specific enzyme)
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What are the three classifications of hormones?
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Endocrine, Paracrine, Autocrine
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What are endocrine hormones?
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THey act on cells FAR away from the site of secretion through the intermediate of the bloodstream
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What is a key example of an endocrine hormone?
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Insulin
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What is the purpose of insulin?
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Insulin, which is secreted by the pancreas activates glucose uptake by several cell types such as adipocytes or liver cells
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What are paracrine hormones?
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They act on neighbour or nearby cells
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What is an example of a paracrine hormone response?
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During an immune response the macrophages (WBCS) are activated and when they bind to a T lymphocyte, they secrete IL-1 that stimulates maturation of the bound T lymphocyte
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What are autocrine hormones?
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Hormones that act on the same cell that released them, or the same type of cell
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What is an example of an autocrine hormone response?
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THe response of T-cells to IL-1 is enhanced by the T cells auto-stimulatory release of protein growth factor IL-2
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How do hormones exercise their actions?
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Hormones interact with SPECIFIC RECEPTORS, and only cells expressing the specific receptor will respond to the hormone. This results in activation of SPECIFIC SIGNAL TRANSDUCTION pathways and a response
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How do hormones bind their ligand?
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With high affinity
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What does it mean that a hormone binds its ligand with HIGH AFFINITY?
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Affinity refers to the strength of the interaction, ie. how tightly the hormone binds its receptor. Therfore if a hormone binds its ligand with high affinity, it is a very tight binding
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How is specificity for a hormone to its receptor acheived?
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Precise molecular complementarities between the signal (hormone) and receptor molecules
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What are two reasons for the high sensitivity of a given ligand?
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1-high affinity of receptor to ligand
2-cooperativity in receptor-ligand interactions and amplification of the signal by an enzyme cascade |
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What does it mean when a ligand has "high sensitivity"?
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We only need a small amount of hormone to trigger a response
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How is affinity expressed?
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Affinity is expressed as the dissociation constant, Kd
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What is Kd normally?
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10^-10 or less (nanomolar!)
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What does it mean to have a lower Kd?
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Higher affinity
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What does cooperativity result in?
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Large changes in receptor activation wih small changes in ligand concentration
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What are four key components of signal transduction?
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Specificity
Amplification, Desenstitization/Adaption Integration |
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How is specificity achieved?
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There is one molecule for each type of receptor (most of the time!)
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How is amplification achieved?
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Through activation of downstream effectors
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How is desensitization acheived?
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Activation of a negative feedback signal, to stop the response so it doesnt continue forever
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What is integration of hormone response?
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2 different ligands generate the same downstream response- 2 separate pathways initiated can interact once in the cell
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How does the shape of a receptor confer specificity?
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The signal molecule has a shape complementary to the receptor shape, and other signal molecules do not fit
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How is does a feedback circuit result in desensitization?
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The feedback circuit shuts off the receptor or removes it from the cell surface
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What is an example of a hormone that has a desensitization/adaption mechanism?
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Insulin!
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What are the six signalling mechanisms that eukaryotic cells use to transduce extracellular signals?
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1-Gated ion channels
2-Receptor enzymes 3-Membrane proteins that act through G proteins 4-Nuclear proteins that bind steroids and act as TF 5-Membrane proteins that attract and activate soluble proteins kinases 6-Adhesion receptors that carry information between the extracellular matrix and cytoplasm |
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How do gated ion channels work?
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Opens or closes in response to concentration of signal ligand. The binding results in a conformational change, and a pore opens that allows ions (ex: K+, Na+, Ca 2+) to enter the cell, and this results in the signal
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How do receptor enzymes work?
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Ligand binding to extracellular domain of the receptor stimulates an enzyme activity in the intracellular domain
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What is an example of a receptor enzyme?
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Insulin binds its receptor, which is a tyrosine kinase. A conformational change results in dimerization, the activation of the tyrosine kinase and and activation of a signal cascade by cross phosphorylation between the two monomers
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What is another name for G-protein coupled receptors?
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Serpentine receptors
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How do serpentine receptors work?
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External ligand binding to receptor activates an intracellular GTP binding protein (G), which regulates an enzyme that generates an intracellular second messenger, X
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What are some features of serpentine receptors?
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Alpha helices, zig zag across membrane, embedded
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What are some features of gated ion channel receptors?
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Helices that span the PM, have pores
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How do "off" and "on" receptors relate to each other?
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They are in EQUILIBRIUM. Hormone binds and shifts equilibrium to ON
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What is an example of an adhesion receptor?
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E cadherin- is on the cell surface, interacts with ECM proteins like collagen, fibronectin. Binding leads to a conformational change and signal transduction
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How should we measure hormone concentration?
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Indirectly
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Why should we measure hormone concentration indirectly?
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Hormones act at very low concentrations, so its hard to measure its concentrations directly.
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What is the hormone concentration range that hormones generally act at?
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Generally between 10^-12 and 10^-7 M
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What is an example of an indirect measurement approach to measure hormone concentration?
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Radioimmunoassay
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What is the basis of RIA?
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Use antibodies and radiactivity to measure amount of hormone
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What is an advantage of RIA?
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Prevents having to use bioassays, which are more difficult, time consuming, and less precise
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How are the hormones used in RIA altered?
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They are radiolabelled with radio-isotopes (I125)
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Which aa can I125 label?
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Tyrosine residues
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What type of antibodies are used in RIA?
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Anti-hormone antibodies
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What is the general procedure of RIA?
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If we have an unknown concentration of hormone, we will perform a binding concentration between cold hormone and a known amount of radiactively labelled hormone to a fixed amount of anti-H antibody
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What does it mean to have a "cold hormone"?
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It is NOT radiolabelled
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What is the first step of RIA?
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React radiolabelled homone with antioody. Measure radioactivity in free and bound forms
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What is done with the free/bound hormones?
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Separate bound/free hormones by column chromatography or filter binding assay. Can calculate counts of free hormone/bound
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What is done after the initial point of radiolabelled free/bound hormone is measured?
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Compete with increasing amounts of unlabelled hormones and perform same analysis as for labelled. Keep outcompeting in small amounts and can create a STANDARD CURVE
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What are the components of a standard curve used in RIA?
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It is cpm bound/ cpm free vs. concentration of unlabelled antigen
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What is the difference between Radio-receptor ligand assays and RIA?
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Same principle, except it uses the ligand and its receptor as measurable entities
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What can we determine with RRA?
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Ligand concentration, as well as receptor density, # of binding sites for hormone, and the affinity of a ligand for its receptor
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How does RRA work?
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A known concentration of radiolabelled hormone and receptor is mixed with an unknown concentration of unlabelled.
Measure bound hormone/vs unbound. Unlabelled hormone outcompetes labelled hormone binding to receptor |
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How is a Scatchard plot achieved?
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By manipulating data of RRA, can be used to find number and affinity constants
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What are the three major types of experiments used in the RRA?
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Kinetics
Saturation Inhibition |
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What is receptor/ligand binding described by?
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The laws of mass action
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What is kon?
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Forward rate constant, it is associated with second order reactions and depends on the concentrations of both unbound L and unbound R
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What is koff?
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Reverse rate constant. It is only affected by the concentration of bound ligands. It is first order because breakdown is of a single species, and depends only on time
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What are the units of kon?
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1/M*s
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What are the units of koff?
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1/s
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What is the goal of kinetics measurement experiments?
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To measure k on and k off
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What does saturation mean?
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Receptor concentration and affinity
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How is a saturation curve generated?
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Holding the amount of receptor constant and varyint the concentration of radioligand
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What is the difference between a saturation curve and kinetics curve?
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To generate a kinetcs curve, the amound of BOTH receptor and radioligand are held constant and the only variable is time
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What can we determine from a saturation experiment?
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Bmax and Kd
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What is Bmax?
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Receptor density or number of binding sites for hormone
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What is Kd?
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Represents the afffinity of the receptor. It is the DISSOCIATION CONSTANT, which is the ratio of concentrations at eqm.
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How can you define Kd?
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Concentration of ligand at which 1/2 of the binding sites are occupied
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What is Y?
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Fractional occupation of ligand binding sites
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What does a small Kd mean?
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Tighter binding, because more RL, and more complex
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What does a large Kd mean?
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Weaker binding, and therefore more free complexes
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What is Y% at Kd?
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0.5
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How is Kd calculated?
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Koff/kon
[R][L]/ [RL] {([RT] - [RL])/[L]} /[RL] |
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How is Y% calculated?
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[RL]/RT
[L]/ Kd + [L] |
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What is the equation used in a Scatchard plot?
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-B/Kd + Bmax/Kd
y=mx +b where x=B |
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What is the Y axis of a scatchard plot?
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B/F (bound ligand over free ligand)
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What is the X axis of a scatchard plot?
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[RL] (=B)
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What is the slope of a scatchard plot?
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-1/Kd
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What is a linear scatchard plot representative of?
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A hormone which binds a single receptor (like glucagon!)
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What does "inhibition" measure?
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Affinity of the same or competing ligand
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What is the variable in inhibition experiments?
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Nonradilabelled form of ligand or competitive drug
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What is Ki?
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[ ] of inhiitor at which you can 50% inhibition of receptor/hormone binding
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What is cooperative binding?
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When binding at one site affects binding at another
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What is an example of a protein that has a concave (increase then decrease) Scatchard plot?
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This is an example of POSITIVE cooperativity. Ane example of this is hemoglobin. When one O2 binds, it imporves the bniding at another site.
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What does a negative cooperativity Scatchard plot look like?
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Convex curve, where binding at one site reduces binding at another
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Defects in which components result in hormone related diseases?
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Either hormone secretion or in the receptor function
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What is type I diabetes?
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Insulin is absent
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What is type II diabetes?
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Insulin cannot stimulate target cells dispite availability
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How does Type I diabetes result?
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T cell mediated destruction of insulin producing beta cells of the islets of Langerhans within the pancrease
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Why does the body think the individual with Type 1 diabetes is starving?
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Even though blood glucose level is high, it is as though thse patients are starving since glucose cannot be taken up by the cells, due to the absence of insulin
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Which type of diabetes is considered the main disorder that affects carbohydrate metabolism?
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Insulin-independent diabetes (Type II)
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What is defected in Type II diabetes?
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The receptor
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Why do obese patients have a greater prevalence of type II diabetes?
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Fatty acid metabolism is thought to be a huge component of insulin resistance, because high levels of FFA promote insulin resistance. Additionally, adipocytes do not have enough receptors, and glucose is not taken up by these cells
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What is hypoglycemic shock?
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If you inject too much insulin, reduce glucose level dramatically in the blood
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When is insulin secreted?
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In resppse to high glucose in the body, for instance after eating a meal
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What does insulin do to glucose?
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Enhances glucose transport from the blood across the plasma membraen of muscle, liver, and fat cells
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How does insulin affect glycogen?
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Stimulates glycogen synthase
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How does insulin affect protein synthesis?
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Turns on specific genes, and therefore enhances protein synthesis
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How does insulin block gluconeogenesis?
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Inhibits formation of pyruvate carboxylase and fructose diphosphate
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At what concentration does insulin act?
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10^-11 to 10 -10 M (low nano molar range)
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What is the structure of insulin like?
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A small protein/peptide, 5.8 kDA, two polypeptide chains A and B joined by disulfide bonds
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How is insulin synthesized?
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As a preprohormone
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What happens to the preprohormone form of insulin?
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Proteolytic cleavage of signal sequence, and storage in vesicles/secretory granules in the pancrease. This is PROINSULIN
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What happens to proinsulin?
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It is cleaved again by proteolysis, to form mature insulin
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Where is mature insulin stored?
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In island of laagerhans cells in the pancrease
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What is the difference between the storage form of insulin, and the active form that is in the blood?
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In the storage form, it exists as a hexamer, but in the blood it acs as a monomer
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What are the structures of the A and B chain?
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Alpha helices
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What is at the center of the hexamer form of insulin and what does it do?
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At the center there is a zinc molecule, which is responsible for stabilizing the hexamer
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What does the Scatchard Plot of Insulin reveal?
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It is a curvilinear convex Scatchard plot, which indicates negative cooperativity
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How do insulin receptors recognize insulin?
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At low concentraions, very efficiently, and at high concentrations very inefficiently
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When is the maximum biological response, ie. when is insulin binding most efficient?
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When only 2% of available insulin receptors are coupled with insulin
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What is the "spare receptors" theory?
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You need a vast excess of receptors to have efficient insulin binding (because of negative cooperativity)
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What happens when insulin level is greater than the 2%?
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We need to slow down glucose uptake, which is a very fast process, to avoid having glucose levels drop too fast
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How is glucose uptake slowed once the 2% is achieved?
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Through negative cooperativity, the overal population of receptors changes conformation somehow to become less efficent at binding insulin, this allows enough time for our organism to counteract the insulin mediated glucose decrease and prevents hypoglycemic shock
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Why does a lower amount of functional receptors cause insulin insensitivity in type II diabetic patients?
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The receptors bind insulin normally, but since there are less "spare receptors" they get into a low affinity mode under 2%-> lower response to insulin
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What components of the insulin receptor allow this negative cooperativity to work?
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Insulin receptors have two DIFFERENT binding sites in their alpha subuninits, and insulin is an asymetric molecule. Consequently it binds to site 1 of receptor 1 and site 2 of recptor 2, causing a conformational change in which the other sites are disrupted.
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What happens to the beta subunits when insulin binds?
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The conformational change in the alpha subunits causes the beta subunits of the insulin receptor to also undergo a conformational change, bringing the kinase sites closer together!
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How does the insulin receptor exist?
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As a dimer, when then the two domains come together- activation. These two parts of the dimer form a V shaped molecule with an axis of symmetry between them.
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Which domain of the receptor does insulin interact with?
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The L1 domain
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In which domain of the insulin receptor is there the oonnection with the other component of the dimer?
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At the fibronectin domain
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What is the structure of the tyrosine kinase domain of the insulin recptor?
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It is a bilobar struture with active site in middle.
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What is the structure like of the tyrosine kinase domain of the insulin receptor when INACTIVE?
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There is an activation loop that folds in and blocks sites. The conformational change of the receptor causes the unfolding of the loop, and now its activated
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What happens in the activation loop of the TK domain of the IR?
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It gets phosphorylated by transferring the gamma phosphate from ATP to a tyrosine residue
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What are some downstream events that insulin stimulates?
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Metabolism (glucose transport and glycogen synthesis)
Cellular growth and differentiation (DNA/RNA/Protein synthesis) |
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What is IRS?
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Insulin Response Substrate that plays a key role in mediating the intracellular effects of insulin
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What are the key phosphorylation sites in the IR?
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1st-Y960
2nd- Y1158, Y1162 Y 1163 |
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What is the functionof phosphorylating Y960, and where is this tyrosine located?
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Y960 is in the JM domain of the IR, and it is necessary for appropriate substrate recognition, especially IRS1
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What is the function of Y1158, Y1162 Y 1163 and where are these tyrosines located?
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Y1158, Y1162 Y 1163 are located in the KD domain of the IR. These are autophosphorylated and releae the blockage of the active site, which enhances the tyrosine kinase activity of the receptor
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What are three important domains of the IRS1?
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PHD, PTB, and Cterminal region
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What is the PHD domain of the IRS1?
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Pleckstrine Homology Domain
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What is the purpose of the PHD?
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Serves to anchor the IRS proteins to membrane phosphoinositides and helps to localize the IRS proteins in close proximity to the insulin receptor
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What are phosphoinositides?
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phospholipids w/ modified headgroups
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What is the PTB domain?
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Phosphotyrosine Binding Domain
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What is the function of the PTB domain?
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It functions as a binding site to the motif containing the phosphorylated tyrosines of the JM region. Consequently, localizes the IRS1 to the IR
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What is the function of the C terminal domain of the IRS?
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IT contains multiple tyrosine phosphorylation motifs that serve as docking sites for SH2 domain containing proteins
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What are some examples of SH2 domain containing proteins that bind the Cterminal domain of the IRS?
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p85alpha
Grb2 |
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What are Sh2 domains?
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Sarc homology 2 proteins
That are small modular domains that bind to phosphotyrosine residues *common theme in cellular signalling |
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What is p85alpha a subunit of?
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PI3K
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What happens once IRS1 is localized to the JM domain of the IR?
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It is phosphorylated in 5 sites, these 5 sites serve as recruitment sites for additional proteins
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What is the first protein that binds to the IRS1 and what does it do?
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the Sh2 domain of p85alpha (subunit of PI3K) binds. Once it binds, it is active, and can recruit the p110 catalytic subunit of PI3K
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What does PI3K do?
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Phosphorylates PIP2 on position 6 to get PIP3
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What does PIP3 do?
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Recruits PKB (Akt)
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Once PKB (Akt) is recruited, what happens to it?
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It is phosphorylated by PKD1 in the membrane
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What does this phosphorylated PKB do?!?
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Recruits glucose transporter and therefore we get UPTAKE OF GLUCOSE!
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What are some other things that PKB phosphorylates?
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GSK3 (Glycogen synthase kinase) on its Ser residue, inactivating it
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What does inactivation of GSK3 result in?
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GSK3 normally phosphorylates GS, which inactivates it. Now, this inactivation is lifted, and GS can participate in glycogen synthesis.
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How exactly does PKB stimulate the transporter to come to the membrane?
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The glut transporter is located in internal membrane vesicles, and it is stimulated to move to the PM
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What else can the IRS1 pathway do?
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Activate gene expression through GRB2 and Ras
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How does IRS1 activate gene expression through Grb2 and Ras?
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Sh2 of Grb2 binds P of IRS1. SOS binds to Grb2 and Ras, causing GDP to switch for GTP. Activated Ras activates Raf-1-> MEK-> ERK
ERK moves to nucleus-> p's Elk1 TF Elk1 TF+ SRF-> stimulate transcription |
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What is the negative feedback loop to regulate IR activity?
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The IR activates serine/threonine kinases which start a negative feedback loop that inhibits the IR
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What is another way to inhibit the IR?
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THrough receptor mediated endocytosis. It can either be fused w/ lysosome and degraded, or recycled back to the surface
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How many glucose transporters exist?
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12 glucose transporters exist
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How do GLUT work?
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Glucose binds to the extracellular side of the GLUT
Conformational change of the GLUT Inside is open Releases glucose |
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What is the structure of GLUT1 like?
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12 helical segments span
Charged residues bind glucose |
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Where is GLUT1 located?
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In RBS (erythrocytes)
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What method was used to prove the ability of glucose transporter to translocate from the intracellular storage sites to the plasma membrane?
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immunofluorescence
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Describe this immunofluorescence experiment
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Differentiated adipocytes were transfected w/ Glut4-GFP construct and followed the pathway of movement by immuofluorescence microscopy
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What did the immunoflurescence microscopy show?
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Translocation of GLUT4 from the intracelllular storage sites to the PM
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Where does GLUT 4 regulate glucose transport?
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Adipocytes and muscle cells
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Under basal conditions, ie. with no insulin signal, where is the majority of GLUT4 located?
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It is excluded from the PM of adipose and muscle cells
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How is this exclusion of GLUT4 in adipose and muscle cells acheived?
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Efficient endocytosis and intracellular sequestration within insulin-responsive storage compartments
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What does insulin do to GLUT4 that is excluded from the PM?
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Insulin increases the exocytosis of GLUT4 and slightly inhibits endocytosis
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How large is the increase of GLUT4 transporters at the membrane due to insulin's effect?
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10-20 fold increase
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What are the three main players in insulin mediates activation of glucose transport?
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PDK1, PKB, PKC
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What is PDK1?
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Phospho-inositide-dependent protein kinase
It is a serine/threonine kinase |
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What is PKB?
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Protein kinase B
Serine/threonine kinase Contains a PHD |
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What is PKC?
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Protein kinase C
Serine/threonine kinase Contains a PHD |
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How do PDK1 and PKB interact?
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PDK1 is already prsent in the membrane, and phosphorylatse PKB
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What does PKC do?
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It is involved in mobilization of GLUT transporters
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What are lipid rafts?
|
Microdomains in the PM, function as a unit.
Consist of high levels of cholesterol and lipid sphinogmyelin. They organize different signalling molecules, activate actin, which somehow gets GLUT to the membrane |
|
|
How does insulin binding to IR result in GLUT4 recruitment?
|
Insulin binds, IRS gets phosphorylated, PI3K can convert PIP2 to PIP3. PIP3 interacts with PDK, p's PKB, PKC etc...downstream phosphorylation somehow results in GLUT4 recruitment to the membrane
|
|
|
What is the difference between GLUT2 and GLUT4?
|
GLUT2 is located in the beta islets of langerhans in the pancreas.
GLUT 2 acts as a sensor of glucose. It is different than GLUT4 in that it is a low affinity molecule |
|
|
How does the low affinity to glucose help GLUT2 act?
|
The low affinity of GLUT2 allows it to detect low levels of glucose- this allows the transporter to be controlled. We do not want glucose to be taken up into the pancreas, we just want cells to know they have to release insulin so that they can stimulate other cells to uptake glucose (ex by adipose cells using GLUT4)
|
|
|
What does the liver synthesize in response to insulin?
|
TGA and fatty acids
|
|
|
How does this synthesis work?
|
Excess glucose is oxidized to acetyl coA, which is used to synthesize fatty acids for export as TAGS in VLDLs to fat and muscle cells
|
|
|
What are the two forms that glucose is stored in?
|
Glycogen (liver and muscle)
TAGS (adipose tissue) |
|
|
What happens a few hours after food intake?
|
Slight decrease in glucose level in blood due to glucose oxidation by brain and other tissues
|
|
|
What does this slight decrease in blood glucose levels entail?
|
Insulin secretion needs to be controlled
|
|
|
How is the secretion of glucose controlled?
|
Glucagon
|
|
|
Which cells secrete glucagon?
|
Alpha cells in the isletes of langerhans of the pancreas
|
|
|
When is glucagon released?
|
In response to reduced levels of blood glucose
|
|
|
What does glucagon stimulate?
|
Glucose production and glycogen breakdown
|
|
|
What happens in the fasting state?
|
-Causes glucose transport to the brain
-Mobilizes FA from adipose cells to be converted to keton bodies -Causes glycogen breakdown -Gluconeogenesis |
|
|
What type of hormone is glucagon?
|
29 aa peptide hormone
|
|
|
What type of receptor is the glucagon receptor?
|
Hepta helical transmembrane receptor
Serpentine receptor |
|
|
What does the intracellular part of the Glucagon receptor contain?
|
A recruitment domain that binds to the heterotrimeric G proteins
|
|
|
What do G proteins consist of?
|
Three subunits: alpha, beta, gamma
|
|
|
What does binding of glucagon do to GPCRs?
|
Binding of glucagon causes a conformational change in the molecule, allows recruitment of complex of heterotrimeric G proteins by the C terminal portion, which is inside the cytosol (N terminal portion on outside in ECS)
Once recruited, the alpha subunit allows exchange of GDP for GTP, which recruits AC |
|
|
What are Gs proteins used for?
|
Coupled to the stimulation of AC
|
|
|
What are Gi proteins used for?
|
Inhibition of AC, activation of G proteins coupled in rectifying potassium channels
|
|
|
What are Gq proteins involved in?
|
Activation of phospholipase C
|
|
|
What is the main function of all G proteins?
|
Facilitate the replacement of GDP with GTP in nucleotide-binding pocket of GTP binding protein
|
|
|
Which subunits are conserved in all G proteins?
|
Beta and Gamma. Alpha subunit varies, to convey a different type of signal
|
|
|
Where is epinephrine produced?
|
In the adrenal glands
|
|
|
How does epinephrine affect glucose levels?
|
Increases blood glucose levels by increasing breakdown of glycogen in the liver and release lipids from fat cells
|
|
|
What else is epinephrine involved in?
|
Heart rate, contracting blood vessels, flight or fight response of the sympathetic nervous system
|
|
|
What type of hormone is epinephrine?
|
An amino acid derivative hormone (NOT A PEPTIDE HORMONE LIKE GLUCAGON OR INSULIN)
|
|
|
Which hormone does epinephrine often act with synergistically?
|
Glucagon
|
|
|
What type of receptor does epinephrine act with?
|
Beta adrenergic receptor (G protein coupled)
|
|
|
Which family does B adrenergic receptor belong to? What is characteristic of this family?
|
Serpentine or GPCRs, have 7 transmembrane helices
|
|
|
What does adenylate cyclase do?
|
Converts ATP to cAMP (second messenger molecule)
|
|
|
What happens to the alpha subunit once GTP is bound to the GR?
|
Dissociates and moves to adenylyl cyclase, activating it
|
|
|
What is the definition of receptor desensitization?
|
A receptor will no longer respond to its ligand after persistent exposure
|
|
|
How does desensitization of B adrenergic receptor work?
|
Once Galpha dissociates from Gbetagamma, the Gbetagamma recruits BARK
|
|
|
At what point can the G beta/gamma subunit recruit BARK?
|
Only when BARK has been phosphorylated by PKA, which was activated by cAMP, which was produced by AC which had been activated by Galpha
|
|
|
What does BARK do?
|
Phosphorylates Ser residues near the carboxy terminal of the beta adrenergic receptor
|
|
|
What does this phosphorylation by BARK do?
|
Blocks further binding of G proteins to the receptor
|
|
|
How is this block achieved?
|
Beta-arrestin bind the phosphorylated serine residues in the carboxy terminal of the beta-adrenergic receptor, which blocks the further association with G proteins
|
|
|
What else does beta-arrestin do?
|
It induces endocytosis of the beta-adrenergic receptor
|
|
|
What can happen to the endocytosed beta-adrenergic receptor?
|
Arrestin dissociated, and the receptor is de-phosphorylated and brought back to the cell surface
|
|
|
What is leptin?
|
A hormone that is important for energy metabolism and homeostasis balance
|
|
|
What is a key system that leptin is apart of?
|
The physiological system that helps maintain the body weight constant
|
|
|
What are the signal sthat are generated in proportion to fat stores able to do?
|
Influence appetite and energy expenditure in a regulated manner to regulate body weight
|
|
|
Describe an experiment to determine the function of leptin
|
Two mutated mice, one with mutation in an ob/ob gene and one with mutation in db/db gene were put in a parabiosis experiment
|
|
|
What is a parabiosis experiment?
|
Where the circulation of two animals is joined
|
|
|
What did the db/db mice produce?
|
A circulating factor that had no effect on their own weight, but triggered massive weight loss in WT mice and in ob/ob mice
|
|
|
What effect did the ob/ob mice have?
|
No effect on WT or db/db
|
|
|
What could one conclude from this experiment?
|
THere is a certain circulating factor that ob/ob mice are deficient in and db/db mice are not responsive to
|
|
|
What do the results suggest for the db/db mice?
|
the diabetes gene encodes the receptor for this circulating factor
|
|
|
What does a defect in the leptin gene, or the leptin receptor gene cause?
|
OBESTITY
|
|
|
What is leptin secreted by?
|
Adipocytes
|
|
|
What type of hormone is leptin?
|
It is a peptide hormone that is 16kDa, that is a 4 helix bundle with an extra small helix
|
|
|
What does leptin regulate?
|
Fuel stores and energy from nutrients
|
|
|
Where does leptin send signals reflecting the nutrional state?
|
The hypothalamus
|
|
|
How does food intake activate the secretion of leptin from adipocytes?
|
The adipocyte size increases, triggering the secretion of leptin
|
|
|
What are the TWO effects of leptin?
|
Inhibition of feeding and fat synthesis
Activation of fatty acid oxidation |
|
|
Where is leptin receptor expressed?
|
In the hypothalamus to regulate appetite
In other tissues to stimulate fatty acid oxidation |
|
|
For obese people, do they have a defect in the LR or just leptin?
|
Most have a defect in LR (leptin receptor)
|
|
|
How is leptin an antilipogenic hormone?
|
It prevents the generation of lipids
|
|
|
How does leptin prevent the loss of function and viability of cells due to fat overload?
|
Prevents accumulation of non-oxidative fatty acids, protects against lipotoxicity, etc
|
|
|
How was it determined that most obese people have a defect in leptin receptor and not leptin?
|
A radioimmonoassay was performed to measure the leptin level in the blood of obese people and they saw that there was a normal level of leptin
|
|
|
What type of receptor is LR?
|
One without an intrinsic kinase activity
|
|
|
What does LR recruit?
|
Cytoplasmic tyrosine kinase (Jak2 (janus kinase 2))
|
|
|
How is the LR different from the insulin receptor?
|
The insulin receptor has intrinsic enzyme (kinase) activity and the LR does not (needs to recruit Jak2)
|
|
|
What does recruitment of Jak2 by the LR result in?
|
Activation of transcription STAT proteins that regulate neuronal gene expression
|
|
|
What happens when leptin binds its receptor and how does this contrast with insulin?
|
Binding of leptin causes two leptin receptor monomers to come together as a dimer. Insulin receptors already exist as a dimer!
|
|
|
What happens once the Leptin-R monomers dimerize?
|
Recruits Jak2
|
|
|
What does Jak2 and what does this result in?
|
Jak2 autophosphorylates, eventually results in phosphorylation of tyrosine residues on the OB-R
|
|
|
What are the phosphorylated residues on the OB-R used for?
|
Docking of STAT proteins with their SH2 domain
|
|
|
What happens once Stat proteins dock?
|
STAT proteins get phosphorylated and they can homo or heterodimerize and goes to the nucleus, where the dimer acts as a TF to express a gene that tells the brain to STOP EATING
|
|
|
Where exactly does the STAT dimer bind in the genes?
|
Specific responsive elements in the promoter of their target genes
|
|
|
What other hormone does leptin have a cooperativity with?
|
Insulin
|
|
|
How does this leptin/insulin cooperativity work?
|
Leptin makes the cells of the liver and muscle more sensitive to insulin
|
|
|
How does this increased sensitivity of liver and muscle to insulin by leptin work?
|
There is cross-talk between the protein tyrosine kinases activated by leptin and those activated by insulin
|
|
|
Which substrate can insulin/letpin both trigger phosphorylation of?
|
IRS-2
|
|
|
What happens when IRS2 is phosphorylated in response to leptin/insulin triggered phosphorylation?
|
PI3-K is activated, which results in inhibition of food intake as well as incorporation of glucose in cells
|
|
|
What is an example of a hormone that has a gated ion channel receptor?
|
Acetylcholine
|
|
|
What is acetylcholine?
|
Neurotransmitter in the nervous system
|
|
|
What does acetylcholine act on?
|
Neurons and muscle cells
|
|
|
What physiological functions does acetylcholine have?
|
It is involved in synaptic plasticity (learning and emory)
|
|
|
What type of receptor is the acetylcholine receptor?
|
It is a nicotinic gated ion channel rcetptor
|
|
|
What type of molecule is acetylcholine?
|
It is NOT A PEPTIDE HORMONE OR AN AMINO ACID DERIVATIVE
It is a derivative of two small molecules (acetic acid and choline) |
|
|
What is the nicotininc acetylcholine receptor essential for?
|
The passage of an electrical signal from a motor neuron to a muscle fiber at the neuromuscular junction
|
|
|
How does acetylcholine result in muscle contraction?
|
Acetylcholine is released by the motor neuron, and diffuses to the motor neuron, where its receptor is located. Binding causes a conformational change, depolarization of the neuron (due to ion influx) and thus muscle contraction
|
|
|
Which ions does the acetylcholine receptor allow to pass through?
|
Na+ , Ca2+, and K+
|
|
|
How big is the nicotinic acetylcholine receptor?
|
290kDa (VERY LARGE)
|
|
|
How many subunits does it have?
|
Five: beta, gamma and delta
Two alpha |
|
|
Where does acetylcholine bind?
|
There is a binding site on each alpha subunit of the receptor
|
|
|
How are the five subunits of the acetylcholine receptor arranged?
|
A central transmembrane channel, which is lined with polar side of M2 helices
|
|
|
What does each acetylcholine receptor subunit have?
|
Four transmembrane helical segments (M1, M2, M3, M4)
|
|
|
Which subunits are hydrophobic?
|
M1, M3, M4
|
|
|
What is the function of having all the M2 helices of the subunits of the acetylcholine receptor facing inward?
|
They can interact with the positively charged ions
|
|
|
What do genetic defects of the Ach receptor result in?
|
Diseases in which muscles are periodically paralyzed or stiff
|
|
|
What is a disorder where the muscles are periodically paralyzed?
|
Hyperkalcemic periodic paralysis
|
|
|
What is a disorder where the muscles are periodically stiff?
|
Paramyotonia congenita
|
|
|
How does the stiffness in paramyotonia congenita result?
|
THe action potentials last longer, and the channel doesnt close as fast.
|
|
|
What are three types of hormones that mediate their action through a soluble intracellular receptor?
|
Steroid Hormones
Thyroid hormones Retinoid hormones |
|
|
What do steroid, thyroid and retinoid hormones do?
|
Affect important biological processes such as: metabolism, development, and growth and differentiation
|
|
|
How are thyroid and steroid hormones stimulated to be released?
|
Sensory input from the environment results in the secretion of a hormone from the hypothalamus, which triggers secretion of hormones from the anterior pituitary, which triggers the release of thryoid hormones from the thyroid, and steroid hormones from the testes/ovary/adrenals
|
|
|
What type of hormone are steroid hormones?
|
Hydrophobic cholesterol derivatives
|
|
|
What is one of the main effects of steroid hormones?
|
To coordinate biological and physiological responses for special biological purposes such as reproduction
|
|
|
Which steroid hormones do the adrenal glands produce?
|
Glucocorticoids
Mineralcorticoids |
|
|
Where do most steroid hormone producing cells obtain cholesterol from?
|
The diet
|
|
|
What does the hydrophobicity of steroid hormones allow them to do?
|
Readily diffuse across the PM
|
|
|
What are the three domains of steroid receptors?
|
Transcription activation, DNA binding, Hormone binding
|
|
|
What does the hormone binding domain define?
|
The type of hormone that can bind the receptor
|
|
|
What does the DNA binding domain of the steroid hormone receptor form and where does it bind on the DNA?
|
Forms two zinc fingers in tandem and binds HREs (Hormone Responsive Elements)
|
|
|
How does the transcription activation domain of the steroid hormone receptor act?
|
Activates by recruiting RNA pol II to activate transcription
|
|
|
How does the steroid hormone/receptor complex bind DNA?
|
As a dimer
|
|
|
What is the HRE composed of?
|
Two six nucleotide sequences
(either contiguous or separated by 3 nt) |
|
|
What recognizes the six nucleotide sequence?
|
1 zinc finger domain (composed of TWO zinc fingers) from each monomer of the dimer binds to 1 of the six nucleotide sequences
|
|
|
How is the receptor kept in the cytoplasm until steroid hormone binds?
|
A HSP protein (Hsp90) binds the receptor, hiding the NLS
|
|
|
How does steroid hormone binding allow the complex to move to the nucleus?
|
It releases hsp90 binding, allowing the complex to go to the nucleus after dimerization, by exposing the NLS
|
|
|
What are thyroid hormones responsible for?
|
Key regulators of metabolism and development and have pleotropic effects on many organs
|
|
|
What stimulates the release of thyroid hormone? (TH)
|
Thyroid stimulating hormone released by the pituitary
|
|
|
Which hormones does the thryroid gland produce?
|
T3 (triiodothyronine)
T4 (thyroxine) |
|
|
What type of hormones are T3 and T4?
|
Metabolic stimulators, derived from tyrosines. THey are water insoluble even though they are derived from proteins
|
|
|
What are T3 and T4 NOT?
|
Cathecolamines
|
|
|
How is T3 and T4 stored?
|
In Thyroglobulin-Tyr
|
|
|
How is thyroglobulin-tyr stored?
|
In colloid spheres surrounded by thyroid follicular cells, after post translational modification w/ sugars
|
|
|
How are t3 and t4 released from thyroglobulin?
|
Thyroglobulin-tyr is iodinated and then cleaved by proteolysis to yield T3 and T4
|
|
|
What type of protein is thyroglobulin?
|
660 kDa protein (140 tyrosine residues)
|
|
|
How many residues in the thyroglobulin are iodinated?
|
20
|
|
|
How are two of these iodinated tyrosines used to make T3 and T4?
|
they are oxidatively coupled to yield T3 and T4 upon proteolysis
|
|
|
How are T3 and T4 transported through the blood?
|
Thyroxine binding protein, prealbumin and albumin
|
|
|
What are the three domains of the T3 receptor?
|
Modulator, DNa binding, hormone binding
|
|
|
What does the T3/Receptor complex do?
|
Induces transcription of specific genes through binding to thyroid hormone responsive elements (TRE)
|
|
|
What is the main product of thyroid secretion?
|
T4
|
|
|
How is T3 produced?
|
Local deiodination occurs in peripheral tissues, yielding T3, the biologically active form of thyroid hormone
|
|
|
Which gene contains the TREs?
|
Thyroid hormone responsive genes (THRG)
|
|
|
What are the four phases of the cell cycle?
|
G1, S, G2, M
|
|
|
What is G1 phase?
|
Rna and protein synthesis
|
|
|
What is S phase?
|
DNa synthesis (doubles DNA) , Rna and protein synthesis
|
|
|
What is G2 phase?
|
Continuation of RNA and protein synthesis
|
|
|
What is M phase?
|
mitosis and cytokinesis
|
|
|
What is Go phase?
|
Terminally differentially differentiated cells withdraw here for an indefinite amount of time, can reenter at G1
|
|
|
Where and what is the restriction point?
|
At the end of G1, cells that pass this are committed to going through S phase
|
|
|
What are the main players that control the cell cycle in response to extracellular stimuli?
|
CDKs, that associate with cyclins
|
|
|
Where is cyclin-e-cdk2 active?
|
G1-S
|
|
|
Where is cyclin b-cdk1 active?
|
M phase
|
|
|
Where is cyclin a-cdk2 active?
|
S-M phase
|
|
|
What are two ways that CDK is regulated in the cell cycle?
|
Phosphorylation and proteolysis
|
|
|
How is CDK activated?
|
Phosphorylating Thr 160 and removing phosphate on Tyr 15
|
|
|
What are two key targets that CDK phosphorylates?
|
phosphatase
DBRP |
|
|
How does phosphorylating of phosphatase work?
|
It removes more of the inhibitoryphosphates on Tyr 15, therefore further activating CDK
|
|
|
What is DBRP?
|
Destruction Box Recognizing Protein
-triggers ubiquitin molecules to be targeted to cyclin, which is degraded by the proteosome, leaving CDK inactive |
