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231 Cards in this Set
- Front
- Back
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At its most basic level glycolysis converts each molecule of glucose into?
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two smaller molecules of pyruvate
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the formation of pyruvate also produces two types of activated carrier molecules?
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ATP and NADH
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what are the parts of acetyl-CoA?
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pyruvate converted into CO2 plus a two-carbon acetyl group, attached to Coenzyme A
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what is oxidative phosphorylation?
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phosphorylation of ADP to form ATP
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does glycolysis use oxygen to produce ATP?
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no
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for every molecule of glucose that enters glycolysis what is the net gain of ATP?
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two molecules
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for every molecule of glucose that enters glycolysis what is the net gain of NADH?
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two molecules
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in anaerobic conditions what can happen to pyruvate and NADH
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pyruvate is converted into products that are excreted from the cell
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what are fermentations?
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anaerobic energy-yelding pathways
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what are the products of pyruvate decarboxylation?
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molecule of CO2 (waste product), a molecule of NADH, and aceytl CoA
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in the oxidation of fatty acid into acetyl coA how many molecules of NADH and FADH2 are produced?
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1 of each
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what are the major end products of the citric acid cycle?
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CO2 ad NADH
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is O2 directly used in the citric acid cycle?
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no, but it is needed for NADH to get rid of its electrons and thus regenerate the NAD+ that is necessary to keep the cycle going
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each turn of TCA produces how many FADH2, NADH,a and GTP molecules?
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3 NADH, 1 FADH2, and 1 GTP
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where does the oxygen atom required to make CO2 from the acetyl groups entering TCA come from?
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3 molecules of water
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where is the electron transport chain located?
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embedded in the inner membrane of the mitochondrian
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what happens to the electrons at the end of the electron transport chain?
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passed to molecules of oxygen gas --> these reduced oxygen molecules combine with with protons to form water
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where does oxidative phosphorylation occur in bacteria?
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plasma membrane
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how is sugar stored?
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as glucose subunits in the large, branched polysaccharide glycogen
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compared to glycogen how much energy does the oxidation of a gram of fat release
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about twice as much energy
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where are fat and starch stored in plant cells?
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chloroplast
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what do mitochondria use as fuels?
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fatty acids and pyruvate
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what does pyruvate come from?
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glucose and other sugars
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where do fatty acids come from?
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fats
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what is the energy released during the passage of electrons along the electron transport change used for?
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harnessed to pump protons across the inner mitochondrial membrane
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what does the proton gradient across the inner mitochondrial membrane do?
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drives the synthesis of ATP to complete the chemiosmotic mechanism
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NADH + 1/2O2 + H+ ->
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NAD+ + H2O
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where is the electron transport chain located?
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inner mitochondrial membrane
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what are the three respiratory enzyme complexes?
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NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase
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which is the oxygen requiring step of cellular respiration?
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the last step, performed by cytochrome oxidase
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what does NADH dehydrogenase do?
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first step of electron transport, hydride ion is removed from NADH and is converted into a proton and two high energy electrons: H- -> H+ + 2e-
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in the electron transport chain each transfer is what type of reaction?
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oxidation-reduction
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what is the formula that each respiratory enzyme complex goes through to use the energy released by electron transfer?
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H2O --> H+ + OH-
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the energetically favorable flow of electrons along the electron-transport chain does what to protons?
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pumps protons across the membrane and out of the matrix, creating an electrochemical proton gradient across the inner mitochondrial membrane
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the electrochemical gradient causes it to be more favorable for H+ to flow where?
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back into the mitochondrial matrix
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what does the electrochemical gradient across the inner mitochondrial membrane drive?
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ATP synthesis by oxidative phosphorylation
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what does ATP synthase do?
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creates a hydrophilic pathways across the inner mitochondrial membrane that allows protons to flow down their electrochemical gradient
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how many protons are needed to pass through the ATP synthase to generate a molecule of ATP?
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about 3
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what two things can ATP synthase do?
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harness the flow of protons down their electrochemical gradient to make ATP or use the energy of ATP hydrolysis to pump protons across a membrane
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what gradient moves pyruvate and phosphate (Pi) into the matrix?
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pH gradient made by H+
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what gradient drives the ADP-ATP exchange?
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voltage gradient because ADP only carries a -3 charge while ATP carries a -4 charge
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in bacteria what is responsible for the movement of the flagellum?
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H+ flow
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how many molecules of ATP are produced by each pair of electrons donated by the NADH produced in mitochondria during oxidative phosphorylation?
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about 2.5 molecules
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In cytosol: glucose -->
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2 pyruvate + 2NADH + 2ATP
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in mitochondrian (pyruvate dehydrogenase and citric acid cycle):
2 pyruvate --> |
2 acetyl CoA + 2 NADH
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in mitochondrian (pyruvate dehydrogenase and citric acid cycle): 2 acetyl CoA -->
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6 NADH + 2 FADH2 + 2 GTP
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net result in mitochondrian: 2 pyruvate -->
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8 NADH + 2 FADH2 + 2 GTP
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in mitochondrian (fatty acid oxidation and citric acid cycle): palmitoyl CoA -->
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8 acetyl CoA + 7 NADH + 7 FADH2
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in mitochondrian (fatty acid oxidation and citric acid cycle): 8 acetyl CoA -->
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24 NADH + 8 FADH2 + 8 GTP
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net result in mitochondrian: palmitoyl CoA -->
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31 NADH + 15 FADH2 + 8 GTP
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what is one way that protons can be pumped across membranes?
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transfer of electrons
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NADH <-->
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NAD+ + H+ + 2e-
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what is redox potential?
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voltage difference between a redox pair; a measure of the tendency of a given system to donate electrons or to accept electrons
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what does ubiquinone do in the mitochondrial respiratory chain?
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picks up electrons from the NADH dehydrogenase complex and delivers them to the cytochrome b-c1 complex
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how many electrons can quinones carry?
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up to two
|
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what is the redox potential of NADH/NAD+
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-320 mV; strong tendency to donate electrons
|
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|
what is the redox potential of H2O/O2?
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+820 mV; strong tendency to accept electrons
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inside NADH dehydrogenase electrons are passed between what type of groups?
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iron-sulfur centers
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what protein contains one or more heme groups?
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cytochromes
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what does cytochrome oxidase receive its electrons from?
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cytochrome c (it oxidizes it)
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what is the reaction that cytochrome oxidase assists in?
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4e- + 4H+ + O2 --> 2H2O
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what is a very important job of cytochrome oxidase concerning O2?
|
it holds O2 tightly so that when O2 picks up one electron and becomes the superoxide radical O2- (dangerously reactive) it will not cause damage to DNA, proteins, and lipid membranes before the other four electrons are there
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what do chloroplasts produce?
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ATP and NADPH
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what happens in the photosynthetic electron transfer reactions (light reactions)
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energy derived from the sunlight energizes an electron in the green organic pigment chlorophyll; electrons move along an electron-transport chain
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what happens in the carbon fixation reactions (dark reactions)
|
ATP and NADPH produced by light reactions drive the conversion of CO2 to carbohydrate
|
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what do longer wavelengths mean in terms of energy?
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lower energy
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what are light absorbing chlorophylls held in?
|
photosystems
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what is the central reaction of photosynthetic carbon fixation?
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an atom of inorganic carbon is converted to organic carbon; CO2 + ribulose 1,5-bisphosphate --> two molecules of 3-phosphoglycerate
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carbon fixation is performed by what enzyme?
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ribulose bisphosphate carboxylase
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what is the process called that regenerates ribulose 1,5 bisphosphate
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carbon fixation cycle (calvin cycle)
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how many molecules of glyceraldehyde-3-phosphate are produced for every 3 molecules of CO2 that enter the Calvin cycle?
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only 1
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what is glyceraldehyde-3-phosphate used for?
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starting material for the synthesis of many sugars, and organic molecules
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for every molecule of CO2 converted to carbohydrate how much ATP and NADPH are consumed?
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3 molecules of ATP and 2 molecules of NADPH
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what is nitrogen fixation?
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reduction of N2 to ammonia by addition of hydrogen
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what is the major job of the ER?
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new-membrane synthesis
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what are endosomes?
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sort ingested molecules and recycle some back to the plasma membrane and send some to lysosomes
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what are peroxisomes?
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single membrane; contain enzymes used in a variety of oxidative reactions that break down lipids and destroy toxic molecules
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what do nuclear transport receptors do?
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bind to the nuclear localization signal and help direct the new protein to the pore by interacting with the nuclear pore fibrils
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what role to chaperone proteins play in transferring proteins across the two membranes of chloroplasts and mitochondrian?
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help to pull them across the membranes
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what two kinds of proteins are transferred from the cytosol to the ER?
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water soluble proteins (completely translocated), prospective transmembrane proteins (partly translocated)
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where are water soluble proteins that enter the ER destined for?
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secretion or lumen of an organelle
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where are transmembrane proteins destined for?
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ER membrane, membrane of another organelle, or the plasma membrane
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what directs proteins to the ER?
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an ER signal sequence
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what type of ribosomes make proteins that are destined for the ER?
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membrane-bound ribosomes on RER
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what two components aid the ER signal sequence to find the ER membrane?
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signal recognition particle (binds to the ER signal sequence when it is exposed on the ribosome), SRP receptor (recognizes the SRP)
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what happens when an SRP binds to a signal sequence?
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causes protein synthesis by the ribosome to slow down
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how does a polypeptide enter the lumen of the ER?
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through a translocation channel in the ER membrane
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what end is the signal sequence usually on for soluble proteins?
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N-terminal
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does the signal peptide remain bound to the translocation channel while the protein chain is threaded through the membrane?
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yes
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when does the signal peptide get cleaved? how?
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during translocation, cleaved off by a signal peptidase located on the luminal side of the ER membrane
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how do transmembrane proteins differ in their translocation process from soluble proteins?
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they have an N-terminal signal sequence that initiates translocation (like soluble proteins) but they have an additional sequence of hydrophobic amino acids (stop-transfer sequence)
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what is a stop transfer sequence?
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an additional sequence of hydrophobic amino acids that are located on transmembrane proteins
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what type of bonds are formed when a stop transfer sequence is located in a protein?
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forms an alpha helical membrane spanning segment
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what is a start transfer sequence?
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an internal signal sequence found in some transmembrane proteins, it is never removed from the polypeptide
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what is the secretory pathway?
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starts with the biosynthesis of proteins on the ER membrane and their entry into the ER, leads through the Golgi apparatus to the cell surface
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what is a more inward endocytic pathway responsible for?
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ingestion and degradation of extracellular molecules, moves materials from the plasma membrane, through endosomes, to lysosomes
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what are coated vesicles?
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vesicles that bud from membranes with distinctive protein coat on their cystolic surfaces
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after a coated vesicles buds from its parent organelle what happens?
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it sheds its coat, allowing its membrane to interact directly with the membrane to which it will fuse
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what is the function of the coat on coated vesicles?
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shapes the membrane into a bud, helps to capture molecules for onward transport
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how are clathrin-coated vesicles formed?
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start of as clathrin-coated pit, form basketlike network on the cystolic surface of the membrane, the GTP binding protein dynamin assembles as a ring around the neck of each invaginated coated pit, dynamin causes ring to constrict, pinches off the vesicle
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what is the role of adaptins?
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secure the clathrin coat to the vesicle membrane and help select cargo molecules for transport
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what do adaptins bind to?
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cargo receptors that have certain cargo molecules bound to them
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what are the two types of adaptins?
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ones that bind cargo receptors in the plasma membrane and one s that bind cargo receptors in the golgi apparatus
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what type of vesicles are involved in transporting molecules between the ER and the golgi and from one part of the golgi to another?
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COP-coated vesicles
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what are SNAREs on the vesicle called?
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v-SNAREs
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what are SNAREs on the target membrane called?
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t-SNAREs
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for two lipid bilaryers to come in contact and intermix during the fusion of a vesicle what must happen?
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water must be displaced from they hydrophilic surface of the membrane
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why is it necessary to have specialized proteins that assemble at the fusion site of vesicle to a new membrane?
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they forma fusion complex that provides the means to cross the energy barrier
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what role do v-SNAREs and t-SNAREs play in membrane fusion
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they wrap around each, acting like a winch that pulls the two membranes into close proximity
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what happens to most proteins when they enter the ER?
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they are chemically modified
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what are the membrane enclosed sacs of the golgi called?
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cisternae (each stack contains 3-20)
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what is the entry face of the golgi called?
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cis face (adjacent to the ER)
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what face of the golgi points towards the plasma membrane?
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the trans face
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what is the constitutive exocytosis pathway sometimes referred to as?
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the default pathway, because unlike the pathway to lysosomes or the ER it does not require a particular signal sequence
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where does the regulated exocytosis pathway act?
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only in cells that are specialized for secretion
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what happens to secretory vesicles when they bud off of the trans end of the golgi?
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accumulate near the plasma membrane, wait for an extracellular signal that will stimulate them to fuse with the plasma membrane and release their contents
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how do proteins destined for secretory vesicles get grouped together?
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they contain special surface properties that cause them to aggregate with one another under ionic conditions (acidic pH and high Ca2+)
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what are the two types of endocytosis?
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pinocytosis (cellular drinking) and phagocytosis (cellular eating)
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what does the binding of antibody coated bacteria to surface receptors on phagocytic cells do?
|
induces the phagocytic cell to extend sheetlike projections of the plasma membrane, called pseudopods
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what are pseudopods
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sheet like projections of the plasma membrane that engulf bacteria and fuse at their tips to form a phagosome
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what mechanism allows eukaryotic cells to continually ingest bits of their plasma membrane?
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pinocytosis
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what generally carries out the process of pinocytosis?
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clathrin-coated pits
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what is receptor mediated endocytosis?
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happens when specific macromolecules bind to complementary receptors on the cell surface and enter the cell as receptor-macromolecule complexes in clathrin-coated vesicles
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how is cholesterol transported in the blood?
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bound to protein in the form of particles called low density lipoproteins (LDL)
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how do cholesterol molecules get into cells
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the LDL binds to receptors on cell surfaces and receptor-LDL complexes are ingested by receptor mediated endocytosis and delivered to endosomes
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why do endosomes cause LDL to dissociate from its receptor?
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the interior of endosomes is more acidic than the surrounding cytosol or extracellular fluid
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where is LDL taken?
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to lysosomes to be broken down, cholesterol escapes into the cytosol for new membrane synthesis
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what are early endosomes?
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endosomes directly under the plasma membrane
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what are late endosomes?
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endosomes near the nucleus
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how do early endosomes mature?
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vesicles within them fuse, either with one another or a preexisting late endosome
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how is the interior of an endosome compartment kept acidic? (pH 5-6)
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by an ATP driven H+ pump in the endosomal membrane that pumps H+ into the endosome lumen from the cytosol
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what is the purpose of endosomes?
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act as the main sorting station in the inward endocytic pathway
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what does the acidic environment in endosomes do?
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causes many receptors to release their bound cargo
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what happens to the receptors after they enter the endosome?
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most are returned to the same plasma membrane domain from which they came, some travel to lysosomes, some proceed to a different domain of the plasma membrane (transcytosis)
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what are lysosomes?
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membranous sacs of hydrolytic enzymes that carry out controlled intracellular digestion of both extracellular materials and worn-out organelles
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what pH are enzymes in lysosomes optimally active?
|
acidic conditions of ~5
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which direction are H+ (protons) pumped by ATP-driven H+ pumps in lysosomes?
|
into the lysosome to maintain its acidic pH
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why are lysosomal membrane proteins usually highly glycosylated?
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they protect the proteins from digestion by the lysosomal proteases
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how are proteins destined for the lysosome recognized?
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while in the ER and cis Golgi they are tagged with a mannose-6-phosphate so in the trans Golgi they are recognized by a mannose-6-phosphate receptor, they are delivered to the lysosome via late endosomes
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what is an autophaosome?
|
it is a organelle enclosed by a double membrane which then fuses with lysosomes for degradation
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where do paracrine signals act?
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locally, remaining in the neighborhood of cells that secrets them
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what are hormones?
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signals sent throughout the body by secreting them into the bloodstream
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what are the cells that produce hormones?
|
endocrine cells
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what are local mediators usually used for?
|
many of the signal molecules that regulate inflammation at the site of an infection or control cell proliferation in a healing wound
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what are contact dependent signaling cell used for?
|
play an important role in tissues in which adjacent cells that are initially similar are destined to become specialized in different ways
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what happens to cells if they receive no signals?
|
they usually die
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what is the final outcome of a signaling chain?
|
response of the cell
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what are the 5 functions of signaling cascades?
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transform the signal into a molecular form suitable for passing the signal along, relay the signal from the point in the cell at which it is received to the point at which the response is produced, many amplify the signal received, can distribute the signal and each step can be modulated by other factors
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what two classes do extracellular signal molecules fall into?
|
too large or too hydrophilic to cross the plasma membrane of the target cell, small enough or hydrophobic enough to slip easily through the plasma membrane
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how does nitric oxide act in a cell?
|
diffuses readily out of the cell that generates it and enters neighboring cells
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what does nitric oxide do?
|
triggers smooth muscle relaxation in a blood vessel wall
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why is nitroglycerine to treat patients with angina?
|
nitroglycerine is quickly converted to NO which rapidly relaxes coronary blood vessels and increases blood flow to the heart
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what happens when NO binds to the enzyme guanylyl cyclase in a cell?
|
stimulates the formation of cyclic GMP from the nucleotide GTP, this forms the next link in the signaling chain that leads to the cell's ultimate response
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can steroid proteins cross over the plasma membrane into the cell
|
yes
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what do hormones do when they bind to hormone receptors
|
cause hormone receptors to make large conformational changes that activates the protein allowing it to promote or inhibit the transcription of a selected set of genes
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what are the three large families of cell surface receptor proteins?
|
ion channel linked receptors, G protein linked receptors, and enzyme linked receptors
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what is the resulting signal from an ion channel linked receptor?
|
resulting signal is a flow of ions across the membrane which produces an electrical current
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what happens when G protein linked receptors are activated?
|
activate a class of membrane bound protein which is then released to migrate in the plane of the plasma membrane initiating a cascade of other effects
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what happens when enzyme linked receptors are activated?
|
act as enzymes or are associated with enzymes inside the cell
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what are ion channel linked receptors responsible for?
|
rapid transmission of signals across synapses in the nervous system
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|
what is a characteristic of phosphoenolpyruvate (PEP?
|
it is a very high energy molecule
|
|
|
what does lactate dehydrognase do?
|
it converts (ferments) pyruvate to lactate (in animals)
|
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what does pyruvate decarboxylase do?
|
it converts (ferments) pyruvate to ethanol (in bacteria and yeast)
|
|
|
how does glycogen enter glycolysis?
|
as glucose-1-phosphate after conversion by glycogen phosphorylase
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which two enzymes in glycolysis are inhibited by high [ATP]?
|
phosphofructokinase and pyruvate kinase
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how does pyruvate enter the mitochondrial matrix?
|
through an H+/pyruvate symporter
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what is pyruvate dehydrogenase?
|
multiprotein complex in mitochondrial matrix catalyses the oxidative decarboxylation of pyruvate using the covalently bound coenzyme A
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from acetyl CoA what does the TCA cycle produce?
|
3 NADH, 1 FADH2, 1GTP, and 2CO2
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|
each pyruvate yields:
|
4NADH, 1FADH2, 1 GTP, and 3CO2
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|
Glucose + 10 NAD+ + 2FAD+ + 4ADP + 4Pi -->
|
6CO2 + 10 NADH + 2 FADH2 + 4 ATP
|
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|
what is unique about coenzyme Q?
|
completely dissolved in the lipid bilayer and a true mobile electron carrier
|
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|
what does a more negative E0' mean?
|
lower the compound's affinity for e- and the better an e- donor it is
|
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|
where are 2FEe2S type and 4Fe4S type iron-sulfur centers found?
|
in complexes I, II, and III
|
|
|
how many protons are transported across the membrane if 2 electrons are donated?
|
4 protons
|
|
|
at the end of the respiratory chain two electrons are accepted by what? to form what?
|
oxygen to form water
|
|
|
what is the chemiosmotic coupling hypothesis?
|
the electron transport chain in the mitochondria inner membrane generate the electrochemical [H+] gradient which could be tapped to drive ATP synthesis
|
|
|
what is proton motive force?
|
pmf is the energy stored in the proton gradient available to do work- synthesize ATP
|
|
|
what are some functions of the rough ER?
|
protein folding, assembly of multiple protein subunits, disulfide bond formation, protein modification, protein quality control
|
|
|
what are some functions of the golgi apparatus?
|
receive newly made proteins from ER, protein and lipid modification, dispatch proteins from the trans-Golgi network to appropriate destination
|
|
|
what are some functions of lysosomes?
|
degrade worn-out organelles, degrade macromolecules and particles taken into the cell by endocytosis
|
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what are the functions of endosomes?
|
sort the ingested molecules, recycle some of the ingested molecules back to the plasma membrane
|
|
|
what are functions of peroxisomes?
|
lipid breakdown, destroy toxic molecules
|
|
|
do proteins transported through nuclear pores remain folded?
|
yes
|
|
|
does transport through nuclear pores require energy?
|
yes- in the form of GTP
|
|
|
where are proteins destined for mitochondria, chloroplasts, and peroxisomes usually synthesized?
|
on free ribosomes in the cytosol
|
|
|
what do most proteins targeted for peroxisomes have?
|
PTS1 signal at extreme C-terminus (Ser-Lys-Leu)
|
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the ER serves as an entry point for all proteins destined for what organelles as well as itself?
|
golgi apparatus, endosomes, lysosomes, and plasma membrane
|
|
|
what determines the specificity of vesicle docking?
|
SNAREs
|
|
|
what are some types of modification in the ER?
|
formation of disulfide bonds, protein glycosylation
|
|
|
what does the constitutive exocytotic pathway do?
|
supplies newly made lipids and proteins to the plasma membrane and carries proteins to the cell surface for secretion
|
|
|
where and how do secretory proteins aggregate?
|
in the Golgi network under acidic pH and high [Ca2+]
|
|
|
what are second messengers?
|
molecules that relay signals received at receptors on the cell surface to target molecules in the cell
|
|
|
what is the structure of G protein-linked receptors?
|
seven pass transmembrane receptor protein, a single polypeptide chain that threads back and forth across the lipid bilayer 7 times
|
|
|
what signals do G protein linked receptors respond to?
|
hormones, local mediators, and neurotransmitters
|
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|
what happens when a neurotransmitter binds to an ion-channel-linked receptor?
|
it alters its conformation so as to open or close a channel for the flow of specific ions (Na+, K+, Ca2+, Cl-) across the plasma membrane
|
|
|
what are molecular switches?
|
proteins which are switched from an inactive to active state when a signal is received
|
|
|
what happens to proteins whose activity is turned on or off by phosphorylation?
|
the switch is thrown in one direction by a protein kinase, which tacks a phosphate group onto the switch protein, and in the other direction by a protein phosphatase which plucks the phosphate off
|
|
|
how are GTP-binding proteins switched on and off?
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switch between an active and inactive state according to whether they have GTP or GDP bound to them
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what are some proteins that are part of the seven pass transmembrane receptor family?
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rhodopsin, olfactory receptors in the vertebrate nose, and the receptors that participate in mating rituals of single cell yeasts
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what happens when an extracellular signal molecule binds to a seven-pass transmembrane receptor?
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the receptor undergoes a conformational change that enables it to activate a G protein located on the underside of the plasma membrane
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what is the general structure of all G-proteins?
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composed of three protein subunits- alpha, beta, gamma, unstimulated the alpha has GDP bound to it, beta and gamma are tethered to the plasma membrane by short lipid tails
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what happens when an extracellular ligand binds to its receptor in G-protein linked receptors?
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activates a G protein causing the alpha subunit to lose some of its affinity for GDP, which it exchanges for a molecule of GTP, alpha subunit detaches from the B and gamma units
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how is the signal in G protein linked receptors turned off?
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alpha subunit has an intrinsic GTP-hydrolyzing activity, eventually hydrolyzes its bound GTP back to GDP
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what does the pertussis toxin do?
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alter the alpha subunit of a different type of G protein, locks the G protein into its inactive GDP bound state
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what happens when acetylcholine binds to a receptor on a heart muscle cell?
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the subunits dissociate, the By complex binds to the intracellular face of a K+ channel in the heart muscle cell plasma membrane, allows K+ to flow out of the ell
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what are the most frequent target enzyme for G proteins?
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adenylyl cyclase (produces cyclic AMP), and phospholipase C (produces inositol trisphosphate and diacylglycerol)
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what is the Gs protein in charge of?
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activated G protein alpha subunit switches on the adenylyl cyclase causing a dramatic and sudden increase in the synthesis of cyclic AMP from ATP
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what eliminates the signal of Gs?
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cyclic AMP phosphodesterase rapidly converts cyclic AMP to ordinary AMP
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what is released from the adrenal gland when we are frightened or excited?
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adrenaline, binds to a class of G-protein-linked receptors that are present on many types of cells
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what enzyme does cyclic AMP activate?
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cyclic-AMP-dependent protein kinase (PKA)
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what does activated PKA do in the cell?
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catalyzes the phosphorylation of particular serines or threonines on certain intracellular proteins
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what would cause a slow response from an activated cyclic AMP cascade?
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a response that involves changes in gene expression, ex.increase in amount of intracellular cyclic AMP concentration in hypothalamus causes the production and secretion of a peptide hormone called somatostatin
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signal molecule + G protein linked receptor --> activation of adenylyl cyclase --> converts ATP to cyclic AMP -->
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activates PKA --> moves into nucleus --> phosphorylates specific gene regulatory proteins --> stimulate transcription of a whole set of target genes
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what does phospholipase C do once it is activated by a G protein?
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cleaves a lipid molecule, inositol phospholipid, that is a component of the cell membrane
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what two molecules are made when the sugar-phosphate head is removed from inositol phospholipid?
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inositol 1,4,5- trisphosphate (IP3) and diacylglycerol (DAG)
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what does inositol 1,4,5-trisphosphate (IP3) do? how does diacylglycerol (DAG) help?
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diffuses into the cytosol, encounters ER, binds to and opens Ca2+ channels that are embedded in ER, Ca2+ rushes out into the cytosol, diacylglycerol helps recruit and activate a protein kinase (protein kinase C- PKC), PKC phosphorylates a set of intracellular proteins
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how is the low concentration of free Ca2+ in the cytosol maintained
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by membrane-embedded pumps that actively pump Ca2+ out of the cytosol
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what does the Ca2+ responsive protein calmodulin do?
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undergoes conformational change when it binds to Ca2+ which allows it to wrap around a wide range of target proteins in the cell, altering their activities
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what are some important targets of calmodulin? what do they do?
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Ca2+/calmodulin-dependent protein kinases (CAM-kinases), when they are activated they influence other processes in the cell by phosphorylating selected proteins
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what is the largest class of enzyme linked receptors?
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tyrosine protein kinase (phosphorylates tyrosine side chains on selected intracellular protenis)
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what is the form of enzyme linked receptors?
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a single alpha helix
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what happens when a signal molecule binds to an enzyme linked receptor?
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causes two receptor molecules to come together in the membrane, forming a dimer, contact between two intracellular receptor tails activates their kinase function (each receptor phosphorylates the other)
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what does phosphorylation of receptor tails do to an enzyme linked receptor?
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triggers the assembly of an elaborate intracellular signaling complex on the receptor tails
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what removes the signal from enzyme linked receptors?
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protein tyrosine phosphatases, remove the phosphates that were added in response to the extracellular signal
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what are some intracellular signaling proteins that receptor tyrosine kinases recruit?
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activate phosphatidyl-inositol 3-kinase (PI 3-kinase) which phosphorylates inositol phospholipids, this becomes a docking site for protein kinase B (PKB) which phosphorylates target proteins on serines and threonines
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what is Ras
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a small protein that is bound by a lipid tail to the cytoplasmic face of the plasma membrane
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what family is Ras a member of?
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monomeric GTP-binding proteins
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when is Ras active?
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when bound to GTP (inactive when GDP is bound)
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in its activated state what does Ras promote?
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activation of a phosphorylation cascade in which a series of protein kinases phosphorylate and activate one another in sequence
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what is the cascade that Ras starts referred to as?
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MAP-kinase cascade (final kinase in the chain is MAP-kinase) Ras --> MAP-kinase-kinase-kinase --> MAP-kinase-kinase --> MAP kinase
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what does MAP-kinase do at the end of the MAP kinase cascade?
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phosphorylates certain gene regulatory proteins on serines and threonines altering their ability to control gene transcription and thereby causing a change in the pattern of gene expression
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