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21 Cards in this Set

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How many ATP molecules does 1 round of glycolysis yield?
2
Why does glucose need help crossing cellular membranes? How does it achieve this?
It's polar.

Glucose transporters allow for facilitated diffusion of glucose.
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).
What reaction do glucose transporters catalyze?
Gout-->Gin
How is the concentration of glucose within the cell kept low?
Gin is phosphorylated via glucose hexokinase (ATP-->ADP) to form Glucose-6-P, which keeps glucose transporters from recognizing them!
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.
What's the free energy change for G-6P<-->F6P?
None; no energy needed for conversion
Towards which reaction is hexokinase driven and why?
Towards formation of G6P+ADP+H+ because ATP hydrolysis is hugely favorable.
What are the requirements of a committed step?
Strongly energetically favorable (not easily reversed)

Specific to pathway
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)
What product marks the end of stage 1? How many ATPs have been used?
F-1,6-BP; 2 ATPs
What is the first step of stage 2 in glycolysis? What enzyme catalyzes it? What is the free energy change?
F-1,6-BP <--> DHAP + GAP
Aldolase
~0
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.
Why would enediol dissociation from TIM be unfavorable? How is it prevented?
Enediol is very reactive and can be hydrolyzed in aqueous solution (wasted reactant).

TIM employs a conformational change that prevents its dissociation.
What is the first reaction of stage 3 in glycolysis? What enzyme catalyzes it?
GAP + P + NAD+ <--> NADH + 1,3-BPglycerate

VIA Glyceraldehyde-3P DH
What challenges does Glyceraldehyde-3P DH face in its reaction? How does it overcome them?
While oxidation is favorable, dehydration is not, requires a large deltaG to overcome.

So it breaks the reaction into two steps--with thioester intermediate.
Describe the mechanism of Glyceraldehyde-3P DH.
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.
Why doesn't Glyceraldehyde-3P DH allow water into its active site?
Thioster can be hydrolyzed.
What reaction does phosphoglycerate kinase catalyze? Why does this occur twice?
1,3-BPglycerate + ADP-->ATP + 3-phosphoglycerate

Need two ATPs to pay for initial kinase reactions in stage one
What is the net ATP formation for 1 round of glycolysis?
2
Where does glycolysis occur?
Cytoplasm.