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Biochemistry II > Glycolysis I > Flashcards

Glycolysis I Flashcards

1
Q

What are the first five metabolic intermediates in glycolysis?

A
  1. Glucose
  2. Glucose-6-phosphate
  3. Fructose-6-phosphate
  4. Fructose-1,6-bisphosphate
  5. Glyceraldehyde-3-phosphate (and diacylglycerol)
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2
Q

What enzyme catalyzes the formation of glucose to glucose-6-phosphate?

A

Hexokinase

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3
Q

Hexokinase catalyzes what type of reaction?

A

A phosphorylation

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4
Q

What is the mechanism for hexokinase?

A

A phosphoryl transfer:

The hydroxyl group of glucose C6 acts as a nucleophile and attacks the gamma phosphate of ATP

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5
Q

What enzyme catalyzes the formation of fructose-6-phosphate from glucose-6-phosphate?

A

Phosphohexoisomerase

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6
Q

What is the mechanism of phosphohexoisomerase?

A

An aldo-keto isomerization

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7
Q

Is the first step of glycolysis reversible?

A

No

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8
Q

Is the second step of glycolysis - the aldoketo isomerization of glucose-6-phosphate to fructose-6-phosphate - reversible? If so, what is the reverse mechanism?

A

Yes, it is reversible

  1. General base 1 deprotonates C1 of fructose-6-phosphate; electrons flow to form C1-C2 alkene and hydroxyl group at C2 via deprotonation of general base 2
  2. The ENEDIOL intermediate is formed
  3. General base 2 deprotonates hydroxyl group at C1, forming the C1 carbonyl, and protonating the C1-C2 alkene from general base 1 to form glucose-6-phosphate
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9
Q

What is the second step of glycolysis?

A

The aldo-keto isomerization of glucose-6-phosphate to fructose-6-phosphate via phosphohexoisomerase

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10
Q

What is the third step in glycolysis?

A

The phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate by phosphofructokinase-1

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11
Q

Is the third step in glycolysis reversible?

A

No

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12
Q

Like the first step of glycolysis, the third step of glycolysis requires what cofactor?

A

ATP

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13
Q

What is the mechanism of phosphofructokinase-1?

A

Phosphoryl transfer:

The C1 hydroxyl of C1 functions as a nucleophile and attacks the gamma phosphate of ATP

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14
Q

Why are the first and third steps of glycolysis irreversible?

A

Because they are phosphoryl transfers from ATP

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15
Q

What is the fourth step of glycolysis?

A

The formation of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate via aldolase from fructose-1,6-bisphosphate

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16
Q

What reaction does aldolase catalyze?

A

The making/breaking of carbon-carbon double bonds:

The formation of glyceraldehyde-3-phosphate and dihydroxylacetone phosphate from fructose-1-6-bisphosphate

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17
Q

What is the mechanism of aldolase?

A

The making and breaking of C=C bonds:

  1. The nitrogen of lysine (in active site of aldolase) attacks the carbonyl carbon of fructose-1,6-bisphosphate, forming a hydroxyl group in the process
  2. A hydrogen atom on the nitrogen of lysine “kicks back” and forms a double bond between the nitrogen and carbon, ultimately releasing water
  3. The oxygen atom of an aspartate residue (in active site of aldolase) acts as a general base, deprotonating the oxygen of hydroxyl group on C4, causing the bond between C3 and C4 to break and yielding glyceraldehyde-3-phosphat and an ENAMINE intermediate
  4. The lone pair on nitrogen “kicks back” and causes the alkene between C2 and C3 to deprotonate the aspartic acid residue
  5. A water molecule deprotonates and forms a hydroxyl group that acts as a nucleophile, attacking the carbon of the enamine
  6. The hydroxyl group “kicks back,” forming a carbonyl group that then kicks out the lysine residue and forming dihydroxyacetone phosphate
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18
Q

What two amino acid residues are crucial to the functioning of aldolase?

A

The lysine and aspartate residues

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19
Q

In the fourth step of glycolysis, aldolase contains a lysine residue that functions first as a _________________.

A

Nucleophile

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20
Q

Aldolase catalyzes a __________________ reaction, meaning that one of its byproducts is a water molecule.

A

Dehydration

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21
Q

The aspartate residue in aldolase functions first as a _________________ ______________, deprotonating C4 of the intermediate.

A

General base

22
Q

Which amino acid residue in aldolase is responsible for triggering the C=C breakage?

A

Aspartate

23
Q

The immediate products of aldolase’s cleavage of fructose-1,6-bisphosphate are glyceraldehyde-3-phosphate and an ________________ intermediate.

A

Enamine

24
Q

Because an enamine is unstable, the lone pair on nitrogen reforms a double bond with carbon and the alkene deprotonates what amino acid residue in aldolase?

A

Aspartic acid

25
Q

What acts as a nucleophile to reduce the nitrogen-carbon double bond in step 4 of glycolysis?

A

Water

26
Q

What is the last electron movement catalyzed by aldolase?

A

Oxygen kicks back, forming the carbonyl, and kicks out the lysine residue, thereby reforming the catalyst and forming dihydroxyacetone phosphate

27
Q

The fifth step of glycolysis does what?

A

Transforms dihydroxyacetone phosphate to glyceraldehyde-3-phosphate

28
Q

What enzyme catalyzes the isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate?

A

Triose phosphate isomerase

29
Q

What mechanism does triose phosphate isomerase catalyze?

A

An aldo-keto isomerization

30
Q

In the forward direction of glycolysis, the aldo-keto isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate is __________________.

A

Reversible

31
Q

Which step of glycolysis is catalytically perfect?

A

Step 5 - the aldo-keto isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate by triose phosphate isomerase

32
Q

What is the mechanism for triose phosphate isomerase?

A

An aldo-keto isomerization in which a ketone (dihydroxyacetone phosphate) isomerizes into an aldehyde (glyceraldehyde-3-phosphate)

  1. General base 1 deprotonates C1
  2. An alkene forms between C1 and C2
  3. A hydroxyl group forms at C2 via general base 2
  4. General base 2 deprotonates the hydroxyl at C1
  5. The alkene deptronates general base 1, thereby forming glyceraldehye-3-phosphate
33
Q

What does Glc stand for?

A

Glucose

34
Q

What does HX stand for?

A

Hexokinase

35
Q

What is the name of this structure?

A

Glucose

36
Q

What does G6P stand for?

A

Glucose-6-phosphate

37
Q

What is the name of this structure?

A

Glucose-6-phosphate

38
Q

What does PHI stand for?

A

Phosphohexoisomerase

39
Q

What does F6P stand for?

A

Fructose-6-phosphate

40
Q

What is the name of this structure?

A

Fructose-6-phosphate

41
Q

What does PFK-1 stand for?

A

Phosphofructokinase-1

42
Q

What does F16P stand for?

A

Fructose-1,6-bisphosphate

43
Q

What is the name of this structure?

A

Fructose-1,6-bisphosphate

44
Q

What does ALD stand for?

A

Aldolase

45
Q

What does DHAP stand for?

A

Dihydroxyacetone phosphate

46
Q

What does GAP stand for?

A

Glyceraldehyde-3-phosphate

47
Q

What does TIM stand for?

A

Triose phosphate isomerase

48
Q

What is the name of this strucutre?

A

Dihydroxyacetone phosphate

49
Q

What is the name of this structure?

A

Glyceraldehyde-3-phosphate

50
Q

Which steps of the “energy investment phase” of glycolysis are reversible?

A

Step 2 (G6P to F6P via PHI)

Step 4 (F16P to DHAP and GAP via ALD)

Step 5 (DHAP to GAP via TIM)

51
Q

Which steps of the “energy investment phase” of glycolysis are irreversible?

A

Step 1 (Glc to G6P via HX)

Step 3 (F6P to F16P via PFK-1)

52
Q

Why are steps 1 and 3 of glycolysis irreversible?

A

Because they require ATP

Biochemistry II (19 decks)

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