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BIOCH 200 > Glucose and Glycolysis > Flashcards

Glucose and Glycolysis Flashcards

1
Q

What is the function of glycolysis?

A

To convert glucose to pyruvate
To convert 2ADP to 2ATP
To reduce 2 molecules of NAD+ to NADH

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2
Q

Where does glycolysis take place?

A

In the cytosol

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3
Q

What is the net reaction of glycolysis?

A

Glucose + 2ADP + 2Pi –> 2 Pyruvate + 2 ATP + 2 NADH + 2H + 2H20.

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4
Q

What are the two stages of glycolysis?

A
  1. Hexose/Energy input.

2. Triose/Energy payout.

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5
Q

How many molecules of ATP are formed in the triose stage?

A

4 ATP

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6
Q

How many molecules of ATP are consumed in the hexose stage?

A

2 ATP.

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7
Q

What step does hexose become two triose molecules?

A

Step 4.

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8
Q

Which steps of glycolysis are coupled to the utilization of ATP?

A

Steps 1 and 3; drive the reaction forward.

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9
Q

What is step 6 coupled to?

A

The synthesis of reducing agents NADH

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10
Q

What occurs in the first step of glycolysis?

A

ATP phosphoryl group is transferred to the oxygen atom of glucose, producing G6P and ADP.
PHOSPHORYLATION.

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11
Q

What enzyme catalyzes step one?

A

Hexokinase.

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12
Q

Is step one reversible? why/why not?

A

No, hexokinase quickly phosphorylates glucose to prevent glucose from diffusing back out of the reaction.

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13
Q

What occurs in the second step of glycolysis?

A

G6P is converted into F6P, a keto-isomer.

ISOMERIZATION.

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14
Q

Is step two reversible?

A

Yes, the free energy change is near zero so it is a near-equilibrium reaction.

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15
Q

What occurs in the third step of glycolysis?

A

A phosphoryl group of ATP is transferred to F6P, producing F-1,6-P.
PHOSPHORYLATION

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16
Q

What enzyme is active in step three.

A

PFK-1.

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17
Q

What step in glycolysis is the rate-determining step?

A

Step three (PFK-1).

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18
Q

Is step three reversible?

A

No, it is metabolically irreversible. There is a large negative free energy change.

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19
Q

What occurs during step four of glycolysis?

A

F-1,6-P is cleaved into GAP and DHAP.

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20
Q

Is step four reversible?

A

Yes, the free energy change is near zero.

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21
Q

What occurs in step five of glycolysis?

A

DHAP molecule is converted to GAP

ISOMERIZATION.

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22
Q

Is step five reversible?

A

Yes, the free energy change is near zero.

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23
Q

What occurs in step six of glycolysis?

A

GAP is oxidized and phosphorylated to produce 1,3-BPG.

OXIDATION, PHOSPHATE ADDITION.

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24
Q

What are the products of step six?

A

1 NADH

1,3-BPG

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25
Q

What step is of glycolysis produces the most energy?

A

Step 6; formation of NADH.

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26
Q

What is the free energy change of step 6?

A

Oxidation: very negative.
Phosphorylation: very positive.

In total, near zero but driven forward by formation of NADH and coupling with next reaction.

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27
Q

What occurs in step seven of glycolysis?

A

A phosphoryl transfer from 1,3-BPG to ADP creates 3-PPG and ATP.

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28
Q

What is substrate level phosphorylation?

A

The formation of ATP by the transfer of a phosphoryl group from a ‘high energy’ compound to ADP.

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29
Q

Is step 7 reversible?

A

Yes.

30
Q

What occurs in step eight of glycolysis?

A

3-PPG is converted into 2-PPG.

ISOMERIZATION.

31
Q

Is step 8 reversible?

A

Yes.

32
Q

What occurs in step nine of glycolysis?

A

2-PPG is dehydrated to PEP.

33
Q

What enzyme is activated in step nine?

A

Enolase.

34
Q

What are the products of step nine?

A

Phosphoenolpyruvate and water.

35
Q

What does enolase require to operate?

A

Magnesium ions (2).

36
Q

Is step nine reversible?

A

Yes.

37
Q

What occurs in step ten?

A

SBL of ADP, phosphoryl transfer from PEP to ADP to form pyruvate.
PHOSPHORYLATION

38
Q

What enzyme is active in step ten?

A

Pyruvate kinase.

39
Q

Is step ten reversible?

A

No; pyruvate kinase is heavily regulated.

40
Q

What net free energy change is essential for glycolysis to operate? Is this requirement satisfied? Which particular reactions play the biggest role?

A

Negative.
Yes, net negative energy change.
Steps 1, 3, and 10 have the largest negative energy change.

41
Q

What is hexokinase regulated by?

A

Product inhibition via G6P.

42
Q

What is PFK-1 regulated by?

A

Inhibited via feedback inhibited by ATP/Citrate

Activated by AMP and F-2,6-BP. Feedback inhibition by PEP.

43
Q

What is pyruvate kinase regulated by?

A

Feed-forward activated by F-1,6BP

Inhibited by ATP via product inhibition.

44
Q

Can glycolysis operate under anaerobic conditions?

A

Yes.

45
Q

What is 2ADP equal to?

A

1 AMP and 1 ATP

46
Q

What step is the dehydration step?

A

Step 9: 2-PPG to PEP.

47
Q

What does glycogen require to break glycosidic bonds?

A

Inorganic phosphate, NOT ATP.

48
Q

What is glycogen synthesized from?

A

G6P

49
Q

What five routes can pyruvate take?

A
  1. Enter the CAC as acetyl-CoA.
  2. Carboxylated to oxaloacetate, CAC intermediate.
  3. Reduction to ethanol.
  4. Reduction to lactate.
  5. Converted to alanine.
50
Q

What fates of pyruvate require oxygen?

A

Carboxylation to oxaloacetate and conversion to Acetyl-CoA for CAC.

51
Q

What fates of pyruvate occur in anaerobic conditions?

A

Reduction to ethanol and lactate.

52
Q

How is pyruvate reduced to ethanol?

A
  1. Decarboxylated to acetaldehyde.

2. Reduced to ethanol via alcohol dehydrogenase; coupled to oxidation of NADH.

53
Q

What is fermentation?

A

A process where electrons from glycolysis in the form of NADH are passed to organic molecules such as ethanol/lactate.

54
Q

How is pyruvate reduced to lactate?

A
  1. Transfer of a hydride ion from NADH produces Lactace and NAD+.
55
Q

Is pyruvate reduction to lactate reversible?

A

Yes.

56
Q

What is the net effect of lactate formation?

A

To maintain the flux of the glycolytic pathway and the production of ATP. ONLY IN OXIDATIVE ENVIRONMENT.

57
Q

What effect does lactate have on the blood after excretion from muscle?

A

Lowers pH, inducing T-state and increasing oxygen unbinding.

58
Q

What kind of transporter moves lactate out of muscles?

A

Proton-lactate symporter.

59
Q

What are the pros of lactate formation?

A

Increased oxygen unloading in muscles.

Metabolic fuel for cardiac tissues in aerobic conditions.

60
Q

What is the main substrate of CAC?

A

Acetyl-CoA

61
Q

What converts pyruvate to acetyl-CoA?

A

Pyruvate Dehydrogenase Complex PDC/PDH

62
Q

What are the products of PDH?

A

Acety-CoA, NADH, and CO2

63
Q

Where does the pyruvate dehydrogenase reaction occur?

A

Inside the mitochondrial matrix.

64
Q

How is pyruvate transferred to the matrix?

A

Pyruvate translocase (Proton symport)

65
Q

Explain the pyruvate dehydrogenase reaction:

A

Pyruvate is decarboxylated, the acetyl group is transferred to SH-CoA to form a thioester (high energy) bond.

The carboxyl group is reformed at CO2 and a hydrogen from the SH-CoA reduces NAD+

66
Q

What is coenzyme A?

A

Derivative of vitamin B attached to adenosine nucleotide, contains a reactive thiol (SH) group.

67
Q

Is the formation of acetyl-CoA reversible?

A

No, it is a significant committed step in carbohydrate metabolism.

68
Q

What are the three main cofactors involved in pyruvate dehydrogenase reaction?

A

Coenzyme A, NAD+ and FAD.

69
Q

What are the advantages of multienzyme complexes?

A
  • Faster reaction times.
  • Limits side reactions.
  • Controlled as a single unit.
70
Q

How is PDH regulated?

A

NADH inhibits PDH (product inhibition)
Acetyl-CoA inhibits PDH (product inhibition)
Calcium activates PDH.

Activated by NAD+ and Coenzyme-A

71
Q

How does protein kinase regulate PDH?

A

Protein kinase is activated by NADH and Acetyl-CoA; phosphorylates and shuts ‘off’ PDH.

72
Q

How does protein phosphatase regulate PDH?

A

Activated by Calcium, activated PDH via dephosphorylation.

BIOCH 200 (7 decks)

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