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40 Cards in this Set
- Front
- Back
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Difference between myoglobin and hemoglobin
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Myo - single chain, 1 heme group and found in muscle
Hemo-tetramer, 4 heme groups, rbc |
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What is P50 value?
Does myoglobin have a higher or lower P50 than hemoglobin? |
P50 is the pressure of 02 when 50% of protein is bound to o2
Lower P50 which means myo binds o2 more tightly |
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cooperativity--
in binding curves what signals positive cooperativity? |
coupling of conformational changes between two widely separated binding sites
--a foot at the bottom of the graph |
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Why is the binding of the first o2 the slowest in Hb?
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Affinity of hemoglobin for successive oxygen molecules increases because fewer salt bridges need to be broken
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What shifts Hb binding curves to the right of Mb binding curves?
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Hb has allosteric regulation by 2,3 BPG . 2,3 BPG stabilizes deoxyHb
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Where is 2,3 BPG most likely to be bound to Hb?
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In the tissues
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What would happen if Hb didnt have 2,3 BPG?
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1. Hb binding curve would lie closer to Mb
2. HbO2 would not give up oxygen as readily at the partial pressures of oxygen found in tissues |
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What is the Bohr effect?
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low pH stabilizes deoxyHb -- like CO2. lower pH produced by carbonic acid leads to the protonation of several key enzymes that form ion pairs that further stabilize deoxyHb. So it shifts the curve to the right and more o2 is released
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Why is protein folding represented as a descent into an energy well?
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funnel represents the free energy change as folding progresses but pathway must avoid local minima (bumps in the funnel)
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What drives protein folding?
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entropy driven (proteins collapse rapidly around hydrophobic side chains with the release of bound water molecules) and non covalent forces
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What assists in folding proteins?
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1. molecular chaperones or heat shock proteins - that inhibit or reverse formation of improperly folded proteins. 2. protein disulfide isomerase (PDI) that shuffles disulfides ina protein until a stable disulfide is formed 3. prolyl cis-trans isomerase that catalyzes the interconversion of the cis and trans conformations of proline
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What primarily drives protein folding?
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primary structure
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What does resolution mean?
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accuracy and detail - the smaller the number the better
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atomic level techniques to see protein structure-- name 2
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X- ray crystallography and NMR
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X-ray cystalography
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uses electron density to generate an atomic model, observes heavy atoms, need to grow a crystal of the protein - resolution has the greatest effect on model accuracy (lower is better)
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NMR -
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determines relative distances between protons to generate an atomic model -only works on small proteins --number of constraints determines accuracy (more is better)
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How does enzymes work?
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Work by stabilizing the transition state by forming non covalent bonds with the reactant
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What are enzymes made out of?
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Mostly protein but some RNA
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What are the 6 classes of enzymes?
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1. Isomerase/mutase
2. lyase 3. ligase 4.oxidoreductase 5.transferase 6. hydrolase |
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What do isomerases or mutases do?
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A to B - catalyzes structural changes within a single moleucle
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lyases do what?
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promote lysis of a substate
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ligases do what?
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join 2 substrates together - most common
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oxidoreductases-
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promote oxidation/reduction reactions
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What is the michaelis-menten equation?
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vo= vmax [s]/Km +[S]
vo=velocity at substrate conc vmax= maximal velocity at enzyme conc Km=the M-M constant - a characteristic of the enzyme at specific temp and pH |
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transferasese -
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promote group transfer
A+B---- C+D |
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hydrolases--
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promote group transfer reactions to water (h20 is always an reactant)
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What is the formula for finding Km?
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Km= 1/2 Vmax OR Km=(k_-1 +k_2 /k_1) a ratio of the rate constants
Km is a substrate level |
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What is Kcat?
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the turnover number. The number of reactions per time
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What does Km mean?
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is an approximate dissociation constant for ES-- the smaller the value of Km the tighter the binding of S to E -- value varies widely and depends on specific substrate, pH, temp, and ionic strength
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What ratio provides a measure of efficiency of different enzymes?
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Kcat/km -- this ratio when used to compare the SAME enzyme with different substrates provides a measure of the specifity of the enzyme
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T/F Enzymes display stereospecifity.
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T - they act on a single stereoisomer and/or produce a single stereoisomer
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How are enzyme's actives sites specific?
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active sites have a shape and functional group specific for each enzyme and is essential for function
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How does enzymes stabilize the transition state?
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1. active site matches the shape of the transition state leading to the product
2. active site possesses functional groups that interact more strongly with the transition state structure than with the substrate |
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What structure does enzymes bind to stronger?
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the transition state
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How does hydrophilic and phobic interactions speed up enzymatic reactions?
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Hydrophilic --binding and selectivity, acid-base catalysis, covalent bond formation or breaking
non polar(hydrophobic) - provides van der Waals interactions (binding and selectivity) |
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In the enzyme lysozyme - what aa needs to be protonated and what needs to be deprotonated?
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Glu=protonated and Asp =deprotonated for the enzyme to be active
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What type of amino acids can add an phosphate group?
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basic, polar, and oxygen containing
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In allosteric oligomeric enzymes R and T mean what?
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R=relaxed -active
T=tense -inactive |
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what are the 2 classes of cofactors?
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coenzymes (organic molecules) and essential ions
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How does a cosubstrate bind?
prosthetic group? |
loose association -
prosthetic - covalent binding tightly bound by non covalent interactions |
