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Biochemistry Exam II > Glycolysis > Flashcards

Glycolysis Flashcards

1
Q

overview of glycolysis

A

involves a sequence of rxns that metabolize 1 molecule of glucose to 2 molecules of pyruvate and generates 2 ATP
(Anaerobic)
Under aerobic conditions can produce more ATP

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2
Q

Fates of Glucose

A

pyruvate-> ethanol, lactate, complete oxidation (CO2, H2O)

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3
Q

__ is the only fuel the brain can use under conditions of nonstarvation and RBCs can use at all.

A

glucose

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4
Q

What process can salvage and resynthesize glucose from pyruvate and lactate?

A

gluconeogenesis

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5
Q

Sources of glucose in diet

A

disaccharides (sucrose/lactose)

starch

gylcogen

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6
Q

Glucose uptake occurs via what protein carrier?

A

Glucose transporters (GLUTs)

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7
Q

GLUT1

A

ubiquitous but expressed highly in brain and RBCs

High affinity

unregulated

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8
Q

GLUT2

A

Main transporter in liver

low affinity

unregulated

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9
Q

GLUT3

A

main transporter in neurons

high affinity

unregulated

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10
Q

GLUT4

A

present in skeletal muscle, heart and adipose tissue

insulin dependent

regulated by insulin

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11
Q

Two stages of Glycolysis

A
  1. trapping of glucose and its cleavage into 2 interconvertible 3-carbon molecules
  2. generation of ATP
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12
Q

first stage of glycolysis

A

begins with the phosphorylation of glucose by hexokinase and ends with the isomerization of dihydroxyacetone phosphate to glyceraldehyde 3-phosphate (GAP)

5 steps, 3 rxns, no ATP generation, 2 ATP used

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13
Q

Step 1

A

Glucose phosphorylated to glucose-6-phosphate (G6P). ATP consumed. Enzyme hexokinase (in all tissues) and glucokinase (in liver)

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14
Q

Step 2

A

G6P isomerized to fructose-6-phosphate (F6P). Enzyme phosphoglucoisomerase

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15
Q

Step 3

A

F6P phosphorylated to fructose-1,6-bisphosphate (F1,6BP). ATP consumed. Enzyme phosphofructokinase (rate limiting enzyme of glycolysis)

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16
Q

Step 4

A

F1,6BP broken down to glyceraldehyde-3phosphate (G3P) and dihydroxyacetone phosphate (DHAP). Enzyme is aldolase

17
Q

Step 5

A

DHAP isomerized to G3P. Enzyme triose phosphate isomerase

18
Q

Second stage of glycolysis

A

Energy harnessed in GAP used to form ATP

19
Q

GAPDH step

A

 Oxidative phosphorylation of GAP to form 1,3-BPG  Reduce NAD+ to NADH  1,3-BPG has high phosphoryl- transfer potential  NADH contains a pair of “high energy” electrons  Sent to electron transport chain (ETC), play role in oxidative phosphorylation (OXPHOS)

20
Q

Phosphoglycerate kinase/mutase step

A

 The kinase converts 1,3 BPG to 3-PG  ADP is phosphorylated to form ATP and 3-PG  Via substrate transfer  The mutase moves phosphate from 3rd to 2nd position (2-PG)

21
Q

Enolase/Pyruvate kinase step

A

 Dehydration of 2-PG by enolase forms PEP, an enol with high phosphoryl-transfer potential (unstable)  Then, Pyruvate kinase transfers phosphoryl group from PEP to ADP to form ATP  PEP is converted from unstable enol to pyruvate, a stable ketone  This step is irreversible

22
Q

Fates of Pyruvate

A

 Pyruvate can be reduced to lactate, with the regeneration of NAD+  Pyruvate can be oxidized aerobically via the citric acid cycle after first undergoing an oxidative decarboxylation to form acetyl CoA  Yeast and some other microorganisms can convert pyruvate to ethanol – maintain redox balance

23
Q

Regeneration of NAD+

A

when pyruvate is converted to lactate, NADH is converted to NAD+. this NAD+ goes back and works in the reaction with GAP.

24
Q

Sucrose

A

disaccharide of glucose and fructose

25
Q

Lactose

A

disaccharide of glucose and galactose

26
Q

Fructose and galactose are converted into

A

glycolytic intermediates

27
Q

Fructose

A

quickly turned to fat in times of high energy

28
Q

Major regulatory enzymes of Glycolysis

A

– Hexokinase
– Phosphofructokinase
– Pyruvate kinase

29
Q

Regulation of Glycolysis in Muscle

A

Goal: To generate ATP during activity  ATP levels regulate glycolysis

at rest glyc is inhibited and during exercise it is stimulated (contraction)

30
Q

Regulation of Glycolysis in Liver

A

Goal: To maintain blood glucose levels  To provide building blocks for other pathways (in response to biochemical diversity and need)

Enzymes: phosphofructokinase, glucokinase, pyruvate kinase

31
Q

Phosphofructokinase

A

Activated by F-2,6-BP  Inhibited by citrate

32
Q

Glucokinase

A

No hexokinase in liver  Glucokinase is not inhibited by glucose 6-phosphate – Glucose permanently trapped

33
Q

Pyruvate kinase

A

regulated by allosteric effectors and covalent modification

34
Q

Excessive fructose consumption

A

can lead to pathological conditions

Biochemistry Exam II (7 decks)

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