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89 Cards in this Set
- Front
- Back
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What is the endoplasmic reticulum?
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continuous network of flattened sacs, tublues, and associated vesicles that stretch throughout the eukaryotic cell's cytoplasm
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What are the sacs in the ER called
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ER cristnae
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The space in the ER encolsed by the sacs and the tubules is called
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ER lumen
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what does the ER synthesize?
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proteins and lipids, including triglyserols, cholesterol, and related compounds
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Does the smooth ER have ribosomes or the rough ER?
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rough ER
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Functions of the ER:
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-processes of proteins
-Drug detoxification, carbohydrate metabolism -Membrane biosynthesis -Calcium storage – Ca2+ are pumped into the ER, then released in response to extracellular signals |
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What moves the proteins and lipids from the ER to the golgi for further processing?
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transition vesicles, transition elements play a roll in transiton vesicle function
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What are some differences in in the rough ER and the smooth ER?
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Rough ER forms flattened sheets, smooth ER forms tubular structures.
Rough ER transition elements resemble the smooth ER. |
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THe ER is the main source of what?
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membrane lipids which are restricted to one monolayer of the ER membrane
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What do flippases do?
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catalyze the translocation of phospholipids through the ER membrane.
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Phospholipid exchange proteins:
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in ER
in the cytosol and conveys phospholipid molecules from the ER to the outer mitochondrial and chloroplast membrane. |
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In the rough ER, what do the attached ribosomes do?
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responsible for synthesizing both membrane bound and soluble proteins
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What happens to proteins in the ER?
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they are synthesized and glycosylated
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What carries proteins to the golgi?
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transition vesicles
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Compartmentalization of the steps of glycosylation and subsequent modification of proteins:
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ER - proteins are synthesized and glycosylated
transition vesicles carry proteins to the golgi golgi: proteins and moved and sorted in the golgi golgi - glycosylated proteins are modified at many steps defferent vesicles are formed depending on their contents -lysosomes -secretory protein |
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N-linked glycosylation:
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cytosol: synthesis of core oligosaccharide
flippase: core oligosaccharide is moved into the ER lumen ER: core oligosaccharide is modified ER: core oligosaccharide is transferred to proteins and modified |
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oligosaccharide
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a saccharide polymer containing a small number (typically three to ten) of component sugars, also known as simple sugars.
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exocytosis:
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releases intracellular molecules to the extracellular medium
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endocytosis:
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imports extracellular molecules by forming vesicles from the plasma mambrane
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collagen biosynthesis from the ER
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1. collagen translation to produce procollagen
2. hydroxylation of selected proline and lysine residues 3. addition of N-linked oligosaccharides 4.The 3 alpha helix chains assemble to form a triple helix (9 helical sequences of amino acids are at the ends of the triple helix structure) 5. procollagen moves to the Golgi via vesicles from smooth ER |
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collagen biosynthesis in the golgi
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1.Carbohydrate side chains are modified (e.g.,
removal of mannose attachment) 2. Protein is packaged into transport vesicle |
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collagen biosynthesis in the extracellular matrix
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1. movement of the vesicle to the plasma membrane
2. secretion of procollagen to ECM area by exocytosis 3. cleavage of the collagen ends 4. collagen assembles into collagen fibrils 5. collagen assembles into collagen fibers |
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lysosome function
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1. isolates digestive enzymes from the cell
2. degrades major classes of macromolecules 3. degrades extracellular materials brought into the cell by endocytosis 4. digests damaged or unnecessary materials 5. intracellular structure, macromolecules |
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production of lysosomal proteins in the golgi
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1. addition of mannose-6-phosphate to soluble lysosomal enzymes
2. mannose-6-phosphate binds to receptor 3. tagged enzyme is packaged into vesicle |
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Targeting of soluble lysosomal enzymes to endosomes and lysosomes be a mannose-6-phosphate tag:
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1. ER-lysosome enzyme is synthesized and carbohydrate is added
2. in golgi-mannose is phosphorylated by sequential activity of 2 enzymes 3.golgi- mannose-6-phosphate binds to receptor and the tagged enzymes are packaged in transport vesicles. 4. endosome-low ph in late endosome causes of enzyme and receptor |
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Lysosome - associated diseases:
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I-cell disease and Lysosome storage diseases
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I-cell disease
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-proteins are released into the extracellular medium
-lack mannose-6-phosphate residues -defective phosphotransferase |
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lysosome storage diseases
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-often involve a missing enzyme which results in harmful accumulation of a lipid of polysaccharide
Tay-Sachs-cannot cleave N-acetylglalactosamine from the CHO portion of the ganglioside glycolipids; lysosomes fill with membrane fragments |
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RER - After biosynthesis, how do membrane bound proteins remain anchored?
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they stay bound by hydrophobic regions and then soluble proteins are released
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The rough ER is the site for what?
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the initial steps of addition and processing of the carbohydrate groups of glycoproteins, polypeptide folding, recognition and removal of misfolded polypeptides and assembly of multimeric proteins
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RER-What happens to proteins before going to the golgi?
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they are degraded by proteasomes
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What happens in the SER
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drug detox
carb metabolism calcium storage steroid biosynthesis |
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constitutive secretion
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after budding from TGN some vesicles move directly to the cell surface where they immediately fuse with the membrane
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exocytosis process
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1. vesicles move to cell surface
2. membrane of vesicle fuses with plasma mambrane 3. plasma membrane pulls apart and vesicle is forced to exterior part of the cell 4. membrane integrates into plasma membrane 5. glycoprotiens and glycolipids that remain anchored to plasma membrane face the extracellular space |
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polarized secretion
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occurs when one set of enzymes or proteins are released on one side of the cell
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fluid phase endocytosis
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pinocytosis for nonspecific internalization of extracellular fluid
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lysosome
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organelle containing digestive enzymes capable of degrading all the major classes of biological macromolecules.
digests damaged, unnecessary structures single membrane bounded which is crucial for contained hydrolytic enzymes |
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physical signal factors that can be received by cells
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heat, gravity, wounding, light
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chemical signal factors that can be received by cells
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extracellular molecules produced by the organism - hormones, signals
signals from environment-food, toxins |
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chemical messengers received by cells
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hormones, growth factors, ligand
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hormones
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produced in one part of the organism but exert an effect at a distance
eg. endocrine |
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growth factors
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released locally and act on nearby tissue
eg. paracrine |
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ligand
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a molecule traveling a short or long distance that binds to a receptor
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overall flow of information during cell signaling:
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1. receptor-ligand binding-ligand is primary messenger, binds to receptor in plasma membrane
2. signal transduction-second messengers, small molecules that relay information in the cell 3. cellular response in cytosol 4. changes in gene expression - mucleus |
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signal transduction
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ability fo the cell to translate a receptor-ligand interaction to changes in its behavior or gene expression
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high receptor affinity
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almost all the receptors are occupied at a low concentration of ligand
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low receptor affinity
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requires a relatively high concentration of ligand for most of the receptors to be occupied
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dissociation constant (kd)
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defines affinity
concentration of free ligands needed to produce a state in which half of the receptors are bound to ligands |
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smaller kd
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high affinity for ligands
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larger kd
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low affinity for ligands
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kd value range
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10^-4 to 10^-9mM
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Receptor Down-regulation
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caused by changes in properties or cellular location of the receptor
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How is receptor down-regulation regulated?
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1. removal of the receptor from the cell surface
2. lowered affinity of the receptor for its ligand 3. changes that render the receptor to be unable to initiate changes in cell function |
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G-protein linked receptors
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- causes change in receptor conformation by activating particular gene protein
- activated gene protein binds to target protein such as enzyme altering the targets activity - g-protein linked receptors initiate singal transduction in the cell |
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examples of g-protein linked receptors
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olfactory receptors
norepinephrine receptors hormone receptors |
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G-protein activation is the binding of what
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GTP
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what other molecules does activated G-protein activate?
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andenylyl cyclase
protein kinases phospholipase C |
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Structure of G-linked receptors
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- each g-linked receptor has a 7 transmembrane a helices
-N-terminus of protein is exposed to extracellular fluid -C-terminus resides in the cytosol -extracellular fluid has a unique binding site while cytoplasmic site interacts w/ G protein |
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G-protein activation
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-messenger binds to receptor causing conformational change on G-protein binding site
-Ga releases GDP and aquires GTP -Ga with GTP releases to initiate signal transduction events |
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the 2 classes of G-proteins?
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heterotrimeric - 3 subunits
monomeric - 1 subunit ras |
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Gprotein activation/inactivation cycle:
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1. ligands bind, the receptors activate Gprotein causing Ga to release GDP and aquire GTP
2. the Ga & Gbg subunits separate and begin signal transduction 3. The GTP-Ga hydrolyzes and becomes inactive 4. inactive GDP-Ga recombines w/Gbg to form inactive heterotrimeric G-protein |
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ROles of G proteins and cyclic AMP in signal transduction
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adenylate cyclase
- activated Gprotein activates adenylyl cyclase - cAMP (snd messenger) produced -cAMP activates cAMP dependent protein kinase A(PKA) |
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Role of IP3 and DAG in signal transduction
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Phospholipase C
-G-protein activates phospholipase C cleaving PIP2(generates IP3) -diacylglycerol and IP3 are released (2nd messengers) - activation of protien kinase C, release of calcium, and many response pathways |
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Receptor Tyrosine Kinases Initiate a Signal Transduction Cascade Involving PLC
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1. Receptor aggregates after ligand binding
2. Receptor undergoes autophosphorylation at tyr residues on the cytoplasmic tail 3. Proteins with SH2 domains associated with receptor 4. Phospholipase C binding cleaves InsP3 and DAG from the membrane -InsP3 activates a Ca channel in ER |
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Receptor Tyrosine Kinases Initiate a Signal Transduction Cascade Involving Ras and MAP Kinase
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1. Receptor aggregates after ligand binding
2. Receptor undergoes autophosphorylation at tyr residues on the cytoplasmic tail 5. GRB2 activates Sos which activates Ras by helping it release GDP and acquire GTP 6. Ras pathway – activation of MAPK and results in the formation of AP-1 transcription factor 7. AP-1stimulates expression of genes needed for cell growth |
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How can hormonal signals be classified?
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distance traveled
animals - chemical properties plants - growth regulators |
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what do hormones regulate?
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growth and development, rates of body processes, concentrations of substances, responses to stress and injury
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Insulin signaling pathway
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1. Insulin binds to the receptor activating phosphorylation of IRS-1 (insulin receptor substrate-1)
2. IRS-1 activates the Ras-MAPK transduction pathway 3. IRS-1 activates PI (phosphatidyl inositol) 3 kinase converting PIP2 to PIP3 4. PIP3 recruits protein kinases to inner surface of the membrane phosphorylating Akt 5. Akt catalyzes the phosphorylation of other kinases leading to recruitment of GLUT4 to the membrane and glycogen synthesis |
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Apoptosis by absence of survival factors
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1.Occurs when survival factors are no longer present
2.Death-promoting proteins accumulate which trigger the release of cytochrome c 3.Cytochrome c forms a complex with other proteins resulting in the activation of the initiator caspase. 4. The initiator caspase activates the executioner caspase |
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Apoptosis by cell death signals
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1. Ligand binds to death receptor on the target cell causing recruitment of adaptor proteins
2. Initiator procapsase proteins cluster-activating them 3. Initiator capsases activate the executioner caspase which activates apoptosis |
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All cells regulate their electrical properties
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- currents through membranes
- potentials across membranes - neurons are highly specialized in these functions - electrical excitability - rapid transmission of information - through body - along axons - between cells - via synapses |
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two subsystems
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cns and pns
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Voltage gated ion channels
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- key to electrical excitability
- voltage sensors - respond to changes in membrane potential - can be multimeric (V-gated K+) or monomeric (V-gated Na+) - gates are all-or-none - inactivation gates |
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Patch clamp
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- allows recording of currents through individual ion channels
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The squid giant axon and action potentials
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- motor neuron for swimming
- up to 1mm in diameter - model neuron - record with an intracellular electrode - stimulate to elicit action potentials |
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The Action Potential
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- an action potential propagates gradually down an unmyelinated axon
- channel inactivation prevents AP reversal |
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The Electrical Synapse
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- physical connection between cytoplasm of two neurons
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The Chemical Synapse
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- physical gap between cells
- pre- and post-synaptic specializations - message carried by neurotransmitters - action potential converted to chemical signal at axon terminal |
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important signal transduction electrical signals
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membrane potential
electrical excitability action potential synaptic transmission |
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membrane potential
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unequal distribution of charged ions in and out of the biological membrane
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electrical excitability
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ability to execute ans action potential in response to stimuli
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action potential
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large electrical depolarization and repolarization of a biological membrane
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synaptic transmission
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transmission mode of nerve impulses from presnaptic neurons to postsynaptic neurons
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synapse
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junction between pre and post synaptic neurons
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The Chemical Synapse - Signal Transduction
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- ionotropic receptors - ligand gated channels
- metabotropic receptors - intracellular signals |
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where does glycolysis occur?
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cytoplasm of the cell
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where and what does kreb cycle do?
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occurs in the mitochondrial matrix and degrades pyruvate to carbon dioxide.
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where does Oxidative phosphorylation occur?
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Oxidative phosphorylation occurs on the inner membrane produces almost 90% of the ATP generated by respiration.
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Chemiosmosis in mitochondrial matrix:
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energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work.
As hydrogen ions flow down their gradient, they cause the cylinder portion and attached rod of ATP synthase to rotate. The spinning rod causes a conformational change in the knob region, activating catalytic sites where ADP and inorganic phosphate combine to make ATP. |
