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Biochemistry Exam 2 > Chapter 16: Glycolysis > Flashcards

Chapter 16: Glycolysis Flashcards

1
Q

Why is glycolysis important?

A

Central pathway for production of:

  • energy (ATP)
  • carbons for biosynthetic pathways (fatty acids and amino acids)
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2
Q

Glucose is the most _____ hexose and has a strong tendency to exist in __________.

A

Stable

Ring formation

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3
Q

Overview: Glucose is converted into…

A

2 pyruvate and 2 ATP via 10 enzymatic steps

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4
Q

Glycolysis is present…

A

In all organisms and is an anaerobic process

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5
Q

In mammals, _____ and _____ can only use glucose as carbon and energy source.

A

Brain and RBCs

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6
Q

The brain cannot ______ and can only use _____.

A

Cannot store fuel

Can only use glucose

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7
Q

RBCs do not have ________. Only way for them to generate ATP is through ________.

A

Mitochondria

Glycolysis

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8
Q

In eukaryotic cells, glycolysis takes place in the _______.

A

Cytoplasm

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9
Q

Glycolysis consists of 2 stages:

A

Stage 1: traps glucose in the cell and destabilizes it (NO ATP generated and actually consumes 2 ATP/glucose)
Stage 2: oxidizes the 3-carbon compounds to pyruvate while generating ATP (ATP harvested)

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10
Q

What are the 3 irreversible steps of glycolysis?

A
  1. ) Glucose —> Glucose 6-phosphate by hexokinase
  2. ) Fructose 6-phosphate —> Fructose 1,6-biphosphate by PFK
  3. ) Phosphenolpyruvate —> Pyruvate by Pyruvate kinase
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11
Q

Stage 1, step 1 of glycolysis (enzyme, catalyst, etc.)

A

Glucose —> Glucose 6-phosphate by hexokinase

*Uses 1 ATP

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12
Q

Why is stage 1, step 1 important? 2 reasons.

A

Glucose 6-phosphate cannot diffuse through the membrane
and
Phosphoryl group destabilizes glucose and facilitates its further metabolism

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13
Q

Stage 1, step 2 of glycolysis (enzyme, catalyst, etc.)

A

Glucose 6-phosphate is isomerized to Fructose 6-phosphate by phosphoglucose isomerase

  • Conversion of aldose to ketose
  • 6 carbon ring -> 5 carbon ring
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14
Q

Stage 1, step 3 of glycolysis (enzyme, catalyst, etc.)

A

Fructose 6-phosphate is phosphorylated to Fructose 1,6-biphosphate by PFK

  • Irreversible reaction
  • Requires 1 ATP
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15
Q

What’s special about PFK?

A

Allosteric enzyme and key regulator for glycolysis

Catalyzes the irreversible reaction

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16
Q

Stage 2, step 4 of glycolysis (Enzyme, catalyst, etc.)

A

Fructose 1,6-biphosphate is hydrolyzed into GAP and DHAP by aldolase

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17
Q

In stage 2, step 4, which isomer is on the direct pathway of glycolysis and which is unusable?

A

GAP - direct

DHAP - unusable but readily converted so that 3-carbon fragment is not wasted

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18
Q

What catalyst interconverts DHAP into GAP?

A

Triose phosphate isomerase
Ketose –> Aldose
*Rapid, reversible reaction

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19
Q

Stage 2, step 5 of glycolysis (Enzyme, catalyst, etc.)

A

GAP –> 1,3-BPG by glyceraldehyde 3-phosphate dehydrogenase

  • Redox reaction
  • NO energy extracted at this point and 2 ATP have been invested
  • NAD+ required
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20
Q

1,3-BPG is an _____________ with a ____________.

A

Acyl phosphate with a high phosphoryl-transfer potential

*High tendency to donate a phosphoryl group to become more stable

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21
Q

Stage 2, step 6: catalyst - glyceraldehyde 3-phosphate dehydrogenase has a 2-step process

A

1.) Exergonic - releases energy (thermodynamically favorable)
2.) Endergonic - uses energy (unfavorable)
Steps occur in succession
*Does not use ATP

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22
Q

Stage 2, step 7 of glycolysis (enzyme, catalyst, etc.)

A

1,3-BPG (higher phosphoryl potential than ATP) –> 3-phosphoglycerate + ATP by phosphoglycerate kinase

  • Called substrate-level phosphorylation
  • First ATP producing reaction, makes up for the 2 lost
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23
Q

Stage 2, step 8 of glycolysis (Enzyme, catalyst, etc.)

A

3-phosphoglycerate –> 2-phosphoglycerate by phosphoglycerate mutase
*Rearrangement

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24
Q

Stage 2, step 9 of glycolysis (enzyme, catalyst, etc.)

A

2 phosphoglycerate –> phosphoenolpyruvate by enolase

*Introduces a double bond

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25
Q

Stage 2, step 10 of glycolysis (enzyme, catalyst, etc.)

A

Phosphoenolpyruvate —> Pyruvate + ATP by pyruvate kinase

*Irreversible reaction

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26
Q

Net reaction of glycolysis

A

2 molecules of ATP generated in the conversion of glucose to 2 molecules of pyruvate

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27
Q

Deficiencies associated with glycolytic enzymes

A
  1. ) Hemolytic anemia (Destruction of RBCs - causes bleeding, lysing)
  2. ) Exercise-induced muscle cramps and muscle weakness - not enough energy for exercising
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28
Q

Erythrocytes (RBCs) lack…

A

Mitochondria and therefore rely on glycolysis to function

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29
Q

What enzymes are involved in exercise-induced muscle problems?

A

PFK
Aldolase
Phosphoglycerate kinase

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30
Q

What must be regenerated in order for glycolysis to proceed?

A

NAD+ - only limited amounts in the cell

*Comes from the vitamin niacin - which is essential in our diets, but we cannot make

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31
Q

There are 3 ways to regenerate NAD+

A
  1. ) Ethanol (No O2 present)
  2. ) Lactate (No O2 present)
  3. ) Acetyl CoA (if O2 present)
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32
Q

Ethanol - Alcoholic fermentation - what organisms are responsible for this process?

A

Yeast and other microorganisms

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33
Q

What are the two steps of alcoholic fermentation (ethanol)?

A
  1. ) Decarboxylation of pyruvate by pyruvate decarboxylase (1 C released as CO2)
  2. ) Reduction of acetaldehyde to ethanol + NADH by alcohol dehydrogenase

Pyruvate —> Acetaldehyde —> Ethanol

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34
Q

Lactate - Lactic acid fermentation - what’s involved?

A

Lactate is formed from pyruvate in many microorganisms and in muscle when oxygen is limited during exercise

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35
Q

Lactic Acid fermentation reaction

A

Pyruvate —> Lactate by lactate dehydrogenase using NADH

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36
Q

Which two ways of regeneration of NAD+ allow the operation of glycolysis in anaerobic conditions?

A

Lactate and ethanol regeneration methods

37
Q

Fructose is mainly metabolized by the ________ using the __________ pathway.

A

Liver

Fructose 1-phosphate pathway

38
Q

Fructose cannot directly enter the glycolytic pathway, therefore it enters glycolysis as…

A

Glyceraldehyde 3-phosphate (GAP)

39
Q

METABOLISM OF FRUCTOSE: The reaction from fructose —> glyceraldehyde 3-phosphate

A
  • Fructose —> Fructose 1-phosphate by fructokinase
  • Fructose 1-phosphate —> Glyceraldehyde + Dihydroxyacetone phosphate by Fructose 1-phosphate aldolase
  • Glyceraldehyde —> GAP by Triose kinase
40
Q

METABOLISM OF GALACTOSE: The reaction of galactose –> glucose 6-phosphate

A
  • Galactose —> Galactose 1-phosphate by galactokinase

- Galactose 1-phosphate —> Glucose 6-phosphate by phosphoglucomutase

41
Q

Galactose is converted into __________ by the ___________ pathway.

A

Glucose 1-phosphate

Galactose-glucose interconversion pathway

42
Q

Galactose enters glycolysis as…

A

Glucose 6-phosphate

43
Q

Lactose-intolerance or hypolactasia is caused by…

A

Deficiency of the enzyme lactase - cleaves lactose into galactose and glucose
-Causes water imbalance -> diarrhea

44
Q

What are the 5 major reactions in glycolysis?

A
  1. ) Phosphoryl transfer
  2. ) Phosphoryl shift
  3. ) Isomerization
  4. ) Dehydration
  5. ) Aldol cleavage
45
Q

What is phosphoryl transfer?

A

Kinases - transfer of phosphoryl groups from ATP

46
Q

What is phosphoryl shift?

A

Mutases - shift of a phosphoryl group

47
Q

What is isomerization?

A

Isomerases - aldose is converted to a ketose or vice versa

48
Q

What is dehydration?

A

Dehydrogenases - Elimination of water

49
Q

What is aldol cleavage?

A

Aldolases - split of carbon-carbon bond

50
Q

Enzymes are controlled by 3 different mechanisms (What are they and how fast are they?)

A
  1. ) Reversible allosteric control - milliseconds
  2. ) Regulation by reversible phosphorylation - seconds
  3. ) Transcriptional control - hours (more long-term; increases or decreases enzyme amounts)
51
Q

What is the major controller of the glycolytic pathway?

A

PFK (Inhibit PFK, inhibit glycolysis)

52
Q

PFK: what activates and inhibits it?

A

PFK activated by low levels of ATP by AMP
PFK inhibited by high levels of ATP

*Controlled differently in the liver than in the muscles

53
Q

What inhibits hexokinase?

A

Glucose 6-phosphate

54
Q

What inhibits pyruvate kinase? What stimulates it?

A

Pyruvate kinase inhibited by ATP and alanine

Pyruvate kinase stimulated by Fructose 1,6-biphosphate

55
Q

In the LIVER, what inhibits and activates PFK?

A

PFK is inhibited by citrate

PFK is activated by fructose 2,6-bisphosphate

56
Q

The livers main function is to…

A

Maintain blood glucose levels

57
Q

Liver vs. Muscle/Brain

A

Liver - glucokinase - NOT inhibited by glucose 6-phosphate (lower affinity for glucose)
Muscle/brain - hexokinase - Inhibited by glucose 6-phosphate (higher affinity for glucose)

58
Q

When glucose levels are high, glucose goes to?

A

Liver

59
Q

When glucose supply is limited, glucose goes first to the _____ and _____.

A

Brain and muscle

60
Q

Functions of GLUT1 and GLUT 3

A
  • Present in nearly all mammalian cells
  • Responsible for basal glucose uptake
  • Transport glucose at NORMAL blood glucose levels
61
Q

Function of GLUT2

A
  • Present in the liver and pancreatic beta-cells

- Has a very high Km for glucose only after each meal

62
Q

Function of GLUT4

A
  • Transports glucose into muscle and fat cells

* Insulin-responsive glucose transporter (activated by insulin)

63
Q

Function of GLUT5

A
  • Present in SI

- Functions as a fructose transporter

64
Q

Which situation do cancer cells prefer? Glycolysis or Oxygen?

A

Glycolysis (Will die if O2 present)

65
Q

Cancer cells obtain ATP by metabolizing _______ to ______ even in the presence of ______. This process is termed the…

A

Glucose –> Lactate
Even in presence of O2
Termed: Warburg effect

66
Q

Hypoxia-inducible transcription factor (HIF-1) increases the expression of most ________ and ________.

A

Glycolytic enzymes and glucose transporters GLUT1 and GLUT3

67
Q

What stimulates HIF-1?

A

Exercise - this enhances the ability to generate ATP anaerobically

68
Q

Which glycolytic enzymes catalyze reactions that consume ATP?

A

Hexokinase and phosphofructokinase-1

69
Q

Which glycolytic enzyme converts dihydroxyacetone phosphate to glyceraldehyde 3-phosphate?

A

Triose phosphate isomerase

70
Q

Which reaction is catalyzed by enolase?

A

2-phosphoglycerate → phosphoenolpyruvate

71
Q

When oxygen is limiting (anaerobic conditions) during intense exercise, the skeletal muscle converts pyruvate into:

A

Lactate

72
Q

How does insulin increase glucose uptake in skeletal and heart muscle?

A

It stimulates delivery of vesicles containing GLUT4 to the plasma membrane

73
Q

Which glycolytic enzyme is directly inhibited by high concentrations of glucose 6-phosphate?

A

Hexokinase

74
Q

Fructose enters the glycolytic pathway as:

A

Glyceraldehyde 3-phosphate

75
Q

Which compounds allosterically activate phosphofructokinase-1?

A

AMP and fructose 2,6-bisphosphate

76
Q

Which of the following enzymatic reactions is NOT carried out during glycolysis?

  • Aldol Cleavage
  • Dehydration
  • Isomerization
  • Oxidative Decarboxylation
  • Phosphoryl Transfer
A

Oxidative Decarboxylation

77
Q

The substrate for the enzyme enolase is:

A

2-phosphoglycerate

78
Q

T or F: Glycolysis occurs in the mitochondria

A

False

79
Q

The glycolytic enzyme _________________ is allosterically activated by high concentrations of fructose 1,6-bisphosphate.

A

Pyruvate kinase

80
Q

Which reaction is catalyzed by triose phosphate isomerase?

A

Dihydroxyacetone phosphate → glyceraldehyde 3-phosphate

81
Q

. During the Cori Cycle, the contracting skeletal muscle accumulates _______________, which serves as a precursor for ________________ in liver.

A

Lactate; gluconeogenesis

82
Q

Phosphofructokinase-1 is the major control point of glycolysis and is allosterically inhibited by high levels of:

A

ATP

83
Q

Fructose enters the glycolytic pathway after it is converted to the glycolytic intermediate:

A

Glyceraldehyde 3-phosphate

84
Q

A defect in the enzyme phosphoglycerate kinase leads directly to accumulation of:

A

1,3-bisphosphoglycerate

85
Q

The glycolytic enzyme _________________ is the major control point of glycolysis and is allosterically activated in liver by high levels of______________.

A

Phosphofructokinase; fructose 2,6-bisphosphate

86
Q

T or F: Cancer cells convert glucose to acetyl CoA during hypoxia.

A

False

87
Q

Which of these enzymes uses NAD+ as co-factor?

A

Glyceraldehyde 3-phosphate dehydrogenase

88
Q

A powerful allosteric activator of phosphofructokinase (PFK) in liver is:

A

Fructose 2,6-bisphosphate

Biochemistry Exam 2 (10 decks)

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