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21 Cards in this Set
- Front
- Back
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How many ATP molecules does 1 round of glycolysis yield?
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2
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Why does glucose need help crossing cellular membranes? How does it achieve this?
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It's polar.
Glucose transporters allow for facilitated diffusion of glucose. |
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How would Km of glucose transporters differ among the general cell population, liver cells, pancreatic cells, muscle cells, and fat cells?
Why do they differ? |
All cells: ~1mM
Liver, pancreas: ~15-20mM Muscle/fat: ~5mM Liver stores glucose, functions at high concentrations of glucose (after eating). Pancreas secretes insulin (high concentration when eating). |
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What reaction do glucose transporters catalyze?
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Gout-->Gin
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How is the concentration of glucose within the cell kept low?
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Gin is phosphorylated via glucose hexokinase (ATP-->ADP) to form Glucose-6-P, which keeps glucose transporters from recognizing them!
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What reaction does phosphoglucose isomerase catalyze? How do its reactants structurally differ from its products?
What are the specific requirements of the enzyme? And how are they obtained? |
G-6-P<-->Fructose-6-P
Differ in position of carbonyl PIM needs open chain form. Although ring position is favored both G6P and F6P, the rings constantly close and open in a dynamic equilibrium. |
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What's the free energy change for G-6P<-->F6P?
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None; no energy needed for conversion
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Towards which reaction is hexokinase driven and why?
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Towards formation of G6P+ADP+H+ because ATP hydrolysis is hugely favorable.
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What are the requirements of a committed step?
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Strongly energetically favorable (not easily reversed)
Specific to pathway |
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What chemical step proceeds the formation of F-6P? Which enzyme catalyzes this?
How is it a committed step? |
F-6P + ATP ---> F-1,6-BP + ADP + H+
Phosphofructokinase Strongly favors formation of F-1,6-BP; F-6P only goes to one PW (specific PW) |
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What product marks the end of stage 1? How many ATPs have been used?
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F-1,6-BP; 2 ATPs
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What is the first step of stage 2 in glycolysis? What enzyme catalyzes it? What is the free energy change?
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F-1,6-BP <--> DHAP + GAP
Aldolase ~0 |
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What is the role of TIM?
Describe its mechanism. |
DHAP<-->GAP
Glutamate acts as an acid and takes H off of DHAP, Carbonyl oxygen then removes H from Histidine forming an enediol intermediate. The histidine then takes back an H from enediol, enediol kicks down electrons and takes back H from glu. Now is GAP. |
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Why would enediol dissociation from TIM be unfavorable? How is it prevented?
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Enediol is very reactive and can be hydrolyzed in aqueous solution (wasted reactant).
TIM employs a conformational change that prevents its dissociation. |
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What is the first reaction of stage 3 in glycolysis? What enzyme catalyzes it?
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GAP + P + NAD+ <--> NADH + 1,3-BPglycerate
VIA Glyceraldehyde-3P DH |
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What challenges does Glyceraldehyde-3P DH face in its reaction? How does it overcome them?
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While oxidation is favorable, dehydration is not, requires a large deltaG to overcome.
So it breaks the reaction into two steps--with thioester intermediate. |
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Describe the mechanism of Glyceraldehyde-3P DH.
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Cysteine acts as nucleophile and attacks GAP forming hemithiocetal. Histidine takes an H from OH on hemithioacetal kicks down electrons and then hemi reduces NADH while itself becomes oxidized, forming thioester intermediate. A second NAD+ enters and kicks out NADH. Phosphate enters and phosphorylates thioester intermediate, which pops off of cysteine.
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Why doesn't Glyceraldehyde-3P DH allow water into its active site?
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Thioster can be hydrolyzed.
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What reaction does phosphoglycerate kinase catalyze? Why does this occur twice?
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1,3-BPglycerate + ADP-->ATP + 3-phosphoglycerate
Need two ATPs to pay for initial kinase reactions in stage one |
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What is the net ATP formation for 1 round of glycolysis?
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2
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Where does glycolysis occur?
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Cytoplasm.
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