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GI > Glycolysis > Flashcards

Glycolysis Flashcards

1
Q

Represent the three most abundant six-carbon sugars in most people’s diets

A

Glucose, Fructose, and Galactose

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2
Q

Because of their structural similarity, fructose and galactose metabolism are able to integrate into

-only requires a few enzymatic steps

A

Glucose Metabolism

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3
Q

The bulk of glucose’s chemical energy remains untapped as glycolysis ends with the formation of

A

Pyruvate

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4
Q

Fully oxidized to CO2 and H2O in the citric acid cycle

A

Pyruvate

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5
Q

The conversion of glucose to pyruvate takes place in which two stages?

A
  1. ) Energy investment stage

2. ) Energy generation stage

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6
Q

While in the energy investment stage phosphorylated intermediates are made at the expense of

A

ATP

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7
Q

In the energy generation phase, substrate level phosphorylation generates how many ATP per glucose molecule?

A

2

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8
Q

At the end of glycolysis, we also see the production of

A

2 NADH

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9
Q

In the first stage of glucose metabolism, two high-energy ATP molecules are consumed in the production of

A

Fructose 1,6-bisphosphate

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10
Q

This ‘energy investment’ phase includes two of the 3 enzymatic steps critical to regulation of flux through glycolysis, both of which are

A

Phosphorylation reactions

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11
Q

Highly hydrophilic compounds, unable to diffuse passively across the hydrophobic barrier of the cytoplasmic membrane

A

Sugars

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12
Q

Function to move glucose down its concentration gradient into the interior of the cell

A

GLUT1-GLUT5

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13
Q

Primarily involved in glucose uptake from the blood

A

GLUT1, GLUT3, and GLUT4

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14
Q

Found in the liver, kidney and pancreas, and can transport glucose into and out of cells

A

GLUT2

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15
Q

Allows for insulin regulated uptake and storage of glucose in fat and muscle during times of sufficient blood glucose

A

GLUT4 insulin sensitivity

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16
Q

Recall that a low Km value implies

A

High receptor affinity for a substrate

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17
Q

Have low Km values and no insulin sensitivity to insure a constant basal uptake of glucose

A

GLUT1 and GLUT3

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18
Q

Has a higher Km, and will more easily take in glucose during periods of high blood glucose

A

GLUT2

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19
Q

In Pancreatic B cells this GLUT-2 mediated uptake results in insulin secretion which allows the activation of

A

GLUT4

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20
Q

Has a lower Km then GLUT-2, and will insure that skeletal and adipose tissue extract glucose from the blood faster than the liver

A

GLUT4

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21
Q

Unusual in that it is the primary transporter for fructose (instead of glucose) in the small intestine and the testes

A

GLUT5

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22
Q

Phosphorylation of intracellular glucose helps to maintain a ‘downhill’ gradient of sugar from outside to inside the cell, and it traps the phosphorylated sugar

A

Inside of the cell

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23
Q

The first covalent modification to intracellular glucose is the addition of a phosphate onto the #6 carbon, making

A

Glucose-6-phosphate (G-6-P)

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24
Q

This reaction is catalyzed by one of two enzymes, depending upon the tissue in question. These are referred to as

A

Isoenzymes

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25
Q

Functions in most tissues, and has a low Km and a low Vmax, but a broad specificity for six carbon sugars

A

Hexokinase

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26
Q

Located in the liver and in the pancreas, and has a high Km and a high Vmax

A

Glucokinase

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27
Q

Permits the liver to respond to high concentrations of blood sugar that are obtained following a meal

A

The high Km of glucokinase in the liver

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28
Q

Plays a central role in the regulation of blood glucose, and this capacity of glucokinase helps it to diminish the hyperglycemia that follows a meal

A

Liver

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29
Q

Serves peripheral tissues by permitting them to metabolize only the quantity of glucose that meets their immediate needs, but also to be able to do so efficiently, even at lower blood glucose concentrations

A

Low Km of Hexokinase

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30
Q

Consistent with this role hexokinase expression is not effected by

A

Insulin

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31
Q

Importantly, high levels of G6P inhibit

A

Hexokinase

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32
Q

Glucokinase is not inhibited by its product, but it is inhibited by

-Binds to the glucokinase regulatory protein

A

Fructose 6-phosphate

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33
Q

This inhibition is reversed under conditions either of high intracellular glucose or

A

Fructose-1-phosphate

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34
Q

Glucokinase expression is positively influenced by

A

Insulin

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35
Q

GLUT-1 & 3 expressing cells insure a steady input of glucose into the cytosol where it can be “secured” by phosphorylation via

A

Hexokinase (which also has a low Km)

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36
Q

This process is inhibited in times of glucose excess by

-Ensures that cells do not make more glucose than metabolically necessary

A

G6P

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37
Q

A similar rationale can be seen with the GLUT-2 expressing liver. During glucose excess insulin will trigger increased

A

Glucokinase Expression

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38
Q

Because glucokinase does not have feedback inhibition it will be able to take in excess glucose even though its transporter and glucokinase have higher

A

Km’s

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39
Q

Regardless of which kinase is used, synthesis of glucose 6 phosphate from glucose and ATP is an

A

Irreversible Reaction

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40
Q

Following the isomerization of glucose 6-phosphate to fructose 6-phosphate, a second, tightly regulated, phosphorylation takes place, catalyzed by the enzyme

A

Phosphofructokinase-1 (PFK-1)

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41
Q

This Reaction catalyzed by PFK-1 produces

A

Fructose 1,6-bisphosphate

42
Q

The most influential and regulatory step in glycolysis

A

The PFK-1 production of F-1,6-BP

43
Q

The PFK-1 production of F-1,6-BP is an

A

Irreversible reaction

44
Q

PFK-1 is negatively regulated by

A

ATP and Citrate

45
Q

This is logical as both of these compounds, when present in the cell at high concentrations, are indicative of an

A

Energy Rich State

46
Q

PFK-1 is also inhibited by

A

Low pH

47
Q

PFK-1 is POSITIVELY regulated by

A

AMP and Fructose-2,6-BP

48
Q

An allosteric activator of PFK-1

A

Fructose-2,6-BP

49
Q

Intracellular levels of fructose 2,6-bisphosphate are altered by the variable action of a dual function enzyme called

A

PFK-2/FBP-2

50
Q

PFK-2/FBP-2 has two different

A

Catalytic activities

51
Q

Responsible for the synthesis of fructose 2,6-bisphosphate, from fructose 6-phosphate and ATP

A

PFK-2 (a kinase)

52
Q

Catalyzes essentially the reverse of this reaction, production of fructose 6 phosphate and Pi from fructose 2,6-bisphosphate

A

FBP-2 (a phosphatase)

53
Q

The PFK-2/FBP-2 itself is regulated by

A

Phosphorylation or Dephosphorylation

54
Q

Signal transduction cascades beginning with insulin and glucagon, on cellular membrane receptors, and ending with protein kinase and phosphatase activities regulate

A

Phosphorylation and dephosphorylation of PFK-2/FBP-2

55
Q

During the well-fed state, glucagon levels decrease and insulin levels rise. These changes lead to

A

Dephosphorylation of PFK-2/FBP-2

56
Q

Dephosphorylation of PFK-2/FBP-2 leads to active

-hence more Fructose-2,6-BP

A

PFK-2

57
Q

Elevated levels of fructose 2,6-bisphosphate activate

A

PFK-1

58
Q

Thus the rate of glycolysis in the liver is

A

Increased

59
Q

Fructose 2,6-bisphosphate acts as an intracellular signal, indicating that glucose is

A

Abundant

60
Q

During fasting and starvation, glucagon levels rise and insulin levels decrease. These changes lead to

A

Phosphorylation of PFK-2

61
Q

This leads to an inactivation of

A

PFK-2

62
Q

Reduced levels of fructose 2,6-bisphosphate inhibit the activity of PFK-1, thus the rate of

A

Liver glycolysis

63
Q

Subject to regulation on a local, intracellular level via ATP, AMP, H+, and citrate, small molecule indicators of the local and immediate metabolic/physiologic state

A

PFK-1

64
Q

Also subject to regulation on a larger, organ scale via insulin and glucagon, with fructose 2,6-bisphosphate as an intermediary

A

PFK-1

65
Q

Splits fructose 1,6 bisphosphate into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate

A

Aldolase A

66
Q

Catalyzes the interconversion of these three-carbon compounds

A

Triose Phosphate Isomerase

67
Q

Glyceraldehyde 3-phosphate is then recruited by glyceraldehyde 3-phosphate dehydrogenase to produce

A

1,3-BPG

68
Q

This intermediate leads to the first production of

A

ATP

69
Q

Action of the isomerase permits us to start with one molecule of glucose, and proceed on with two molecules of

A

1,3-BPG

70
Q

Take note that in order to oxidize glyceraldehyde 3-phosphate, glyceraldehyde 3-phosphate dehydrogenase requires

A

NAD+

71
Q

The phosphate on carbon #1 of 1,3 bisphosphoglycerate is transferred to

A

ADP

72
Q

The phosphate on carbon #1 of 1,3 bisphosphoglycerate is transferred to ADP by

-produces ATP and phosphoglycerate

A

Phosphoglycerate Kinase

73
Q

This reaction is

A

Reversible

74
Q

3-phosphoglycerate is ocnverted into 2-phosphoglycerate by

-Reversible and unregulated

A

Phosphoglycerate Mutase

75
Q

Converts 2-phosphoglycerate into phosphoenolpyruvate, with the release of one molecule of water

A

Enolase

76
Q

Participates in the second substrate level phosphorylation in glycolysis, and the production of a second ATP molecule

A

Phosphoenolpyruvate

77
Q

Dephosphorylates phosphoenolpyruvate, producing ATP and pyruvate

-An IRREVERSIBLE reaction

A

Pyruvate Kinase

78
Q

Regulation of this step takes a somewhat unusual form. Fructose 1,6-bisphosphate acts in a feed-forward manner to stimulate

A

Pyruvate Kinase

79
Q

Liver pyruvate kinase is itself subject to direct phosphorylation, causing

A

Inactivation

80
Q

The phosphorylation (inctivation) and Dephosphorylation (activation) of pyruvate kinase is mediated by

A

Glucagon and Insulin respectively

81
Q

The decreased breakdown of PEP is also helpful during glucagon-induced

A

Gluconeogenesis

82
Q

Subject to local, intracellular regulation by fructose 1,6 bisphosphate and it’s also subject to higher order regulation via protein phosphorylation/dephosphorylation and the hormones insulin and glucagon

A

Pyruvate Kinase

83
Q

Glycolysis will come to a halt without the ability to recycle

A

NADH to NAD+

84
Q

What are the two mechanisms by which cells can replenish NAD levels?

A
  1. ) Oxidative phosphorylation

2. ) Conversion of Pyruvate to Lactate

85
Q

Without oxidative phosphorylation, the cell converts pyruvate to lactate using

A

Lactate dehydrogenase

86
Q

The conversion of pyruvate to lactate by lactate dehydrogenase also does what?

A

Oxidizes NADH to NAD+

87
Q

If rates of production exceed blood-mediate clearance, high levels of lactate can drop the

A

Local pH

88
Q

The cramping that occurs during heavy exercise is the consequence of rapid local production of

A

Lactate

89
Q

Lactate is eventually taken up by liver, via the circulatory system, and re-converted to pyruvate via the reversible lactate dehydrogenase reaction. This muscle/blood/liver handoff has been designated the

A

Cori Cycle

90
Q

The process of oxidative phosphorylation is able to take each NADH produced in aerobic glycolysis and generate

A

3 ATP

91
Q

Which produces more ATP per glucose molecule, aerobic or anaerobic glycolysis?

A

Aerobic

92
Q

What are the three enzymes that catalyze the three irreversible reactions in glycolysis?

A

Gluco/Hexokinase, PFK-1, and pyruvate kinase

93
Q

We see feedback inhibition of hexokinase by

A

G6P

94
Q

Neither insulin nor glucagon actually enters the cells that are responsive to

A

Them

95
Q

Glucagon signaling typically stimulates

A

Phosphorylation

96
Q

Insulin signaling typically stimulates

A

Dephorphorylation

97
Q

Leads to disruption of glycolysis and the build up of glycolytic intermediates

A

Pyruvate Kinase Deficiency

98
Q

Cell dehydration, contraction, and crenation (echinocytes), leading to premature destruction of the erythrocyte are a sign/symptom of

A

Pyruvate Kinase deficiency

99
Q

An Increased offloading of O2 into tissues due to increased 2,3-BPG is a sign/symptom of

-results in improved exercise performance in these patients relative to others with similarly low Hgb

A

Pyruvate kinase deficiency

100
Q

How can we treat the hemolytic anemia seen with pyruvate kinase deficiency?

A

Transfusions, supplemental folic acid, splenectomy

GI (59 decks)

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