Chapter 16: Glycolysis Flashcards Preview

Biochemistry Exam 2 > Chapter 16: Glycolysis > Flashcards

Flashcards in Chapter 16: Glycolysis Deck (88):
1

Why is glycolysis important?

Central pathway for production of:
-energy (ATP)
-carbons for biosynthetic pathways (fatty acids and amino acids)

2

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

Stable
Ring formation

3

Overview: Glucose is converted into...

2 pyruvate and 2 ATP via 10 enzymatic steps

4

Glycolysis is present...

In all organisms and is an anaerobic process

5

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

Brain and RBCs

6

The brain cannot ______ and can only use _____.

Cannot store fuel
Can only use glucose

7

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

Mitochondria
Glycolysis

8

In eukaryotic cells, glycolysis takes place in the _______.

Cytoplasm

9

Glycolysis consists of 2 stages:

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)

10

What are the 3 irreversible steps of glycolysis?

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

11

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

Glucose ---> Glucose 6-phosphate by hexokinase
*Uses 1 ATP

12

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

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

13

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

Glucose 6-phosphate is isomerized to Fructose 6-phosphate by phosphoglucose isomerase
*Conversion of aldose to ketose
*6 carbon ring -> 5 carbon ring

14

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

Fructose 6-phosphate is phosphorylated to Fructose 1,6-biphosphate by PFK
*Irreversible reaction
*Requires 1 ATP

15

What's special about PFK?

Allosteric enzyme and key regulator for glycolysis
Catalyzes the irreversible reaction

16

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

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

17

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

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

18

What catalyst interconverts DHAP into GAP?

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

19

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

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

20

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

Acyl phosphate with a high phosphoryl-transfer potential
*High tendency to donate a phosphoryl group to become more stable

21

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

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

22

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

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

23

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

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

24

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

2 phosphoglycerate --> phosphoenolpyruvate by enolase
*Introduces a double bond

25

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

Phosphoenolpyruvate ---> Pyruvate + ATP by pyruvate kinase
*Irreversible reaction

26

Net reaction of glycolysis

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

27

Deficiencies associated with glycolytic enzymes

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

28

Erythrocytes (RBCs) lack...

Mitochondria and therefore rely on glycolysis to function

29

What enzymes are involved in exercise-induced muscle problems?

PFK
Aldolase
Phosphoglycerate kinase

30

What must be regenerated in order for glycolysis to proceed?

NAD+ - only limited amounts in the cell
*Comes from the vitamin niacin - which is essential in our diets, but we cannot make

31

There are 3 ways to regenerate NAD+

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

32

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

Yeast and other microorganisms

33

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

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

34

Lactate - Lactic acid fermentation - what's involved?

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

35

Lactic Acid fermentation reaction

Pyruvate ---> Lactate by lactate dehydrogenase using NADH

36

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

Lactate and ethanol regeneration methods

37

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

Liver
Fructose 1-phosphate pathway

38

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

Glyceraldehyde 3-phosphate (GAP)

39

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

-Fructose ---> Fructose 1-phosphate by fructokinase
-Fructose 1-phosphate ---> Glyceraldehyde + Dihydroxyacetone phosphate by Fructose 1-phosphate aldolase
-Glyceraldehyde ---> GAP by Triose kinase

40

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

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

41

Galactose is converted into __________ by the ___________ pathway.

Glucose 1-phosphate
Galactose-glucose interconversion pathway

42

Galactose enters glycolysis as...

Glucose 6-phosphate

43

Lactose-intolerance or hypolactasia is caused by...

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

44

What are the 5 major reactions in glycolysis?

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

45

What is phosphoryl transfer?

Kinases - transfer of phosphoryl groups from ATP

46

What is phosphoryl shift?

Mutases - shift of a phosphoryl group

47

What is isomerization?

Isomerases - aldose is converted to a ketose or vice versa

48

What is dehydration?

Dehydrogenases - Elimination of water

49

What is aldol cleavage?

Aldolases - split of carbon-carbon bond

50

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

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

51

What is the major controller of the glycolytic pathway?

PFK (Inhibit PFK, inhibit glycolysis)

52

PFK: what activates and inhibits it?

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

What inhibits hexokinase?

Glucose 6-phosphate

54

What inhibits pyruvate kinase? What stimulates it?

Pyruvate kinase inhibited by ATP and alanine
Pyruvate kinase stimulated by Fructose 1,6-biphosphate

55

In the LIVER, what inhibits and activates PFK?

PFK is inhibited by citrate
PFK is activated by fructose 2,6-bisphosphate

56

The livers main function is to...

Maintain blood glucose levels

57

Liver vs. Muscle/Brain

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

When glucose levels are high, glucose goes to?

Liver

59

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

Brain and muscle

60

Functions of GLUT1 and GLUT 3

-Present in nearly all mammalian cells
-Responsible for basal glucose uptake
*Transport glucose at NORMAL blood glucose levels

61

Function of GLUT2

-Present in the liver and pancreatic beta-cells
-Has a very high Km for glucose *only after each meal*

62

Function of GLUT4

-Transports glucose into muscle and fat cells
*Insulin-responsive glucose transporter (activated by insulin)

63

Function of GLUT5

-Present in SI
-Functions as a fructose transporter

64

Which situation do cancer cells prefer? Glycolysis or Oxygen?

Glycolysis (Will die if O2 present)

65

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

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

66

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

Glycolytic enzymes and glucose transporters GLUT1 and GLUT3

67

What stimulates HIF-1?

Exercise - this enhances the ability to generate ATP anaerobically

68

Which glycolytic enzymes catalyze reactions that consume ATP?

Hexokinase and phosphofructokinase-1

69

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

Triose phosphate isomerase

70

Which reaction is catalyzed by enolase?

2-phosphoglycerate → phosphoenolpyruvate

71

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

Lactate

72

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

It stimulates delivery of vesicles containing GLUT4 to the plasma membrane

73

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

Hexokinase

74

Fructose enters the glycolytic pathway as:

Glyceraldehyde 3-phosphate

75

Which compounds allosterically activate phosphofructokinase-1?

AMP and fructose 2,6-bisphosphate

76

Which of the following enzymatic reactions is NOT carried out during glycolysis?
-Aldol Cleavage
-Dehydration
-Isomerization
-Oxidative Decarboxylation
-Phosphoryl Transfer

Oxidative Decarboxylation

77

The substrate for the enzyme enolase is:

2-phosphoglycerate

78

T or F: Glycolysis occurs in the mitochondria

False

79

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

Pyruvate kinase

80

Which reaction is catalyzed by triose phosphate isomerase?

Dihydroxyacetone phosphate → glyceraldehyde 3-phosphate

81

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

Lactate; gluconeogenesis

82

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

ATP

83

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

Glyceraldehyde 3-phosphate

84

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

1,3-bisphosphoglycerate

85

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

Phosphofructokinase; fructose 2,6-bisphosphate

86

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

False

87

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

Glyceraldehyde 3-phosphate dehydrogenase

88

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

Fructose 2,6-bisphosphate