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Biochemistry II > Ch. 14 Glycolysis and Gluconeogenesis > Flashcards

Ch. 14 Glycolysis and Gluconeogenesis Flashcards

1
Q

What does carbohydrate metabolism entail?

A

Carbohydrates are broken down into CO2 and water by a series of reactions.

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2
Q

What is the most abundant organic molecule on Earth?

A

Glucose.

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3
Q

How is glucose stored in the cell?

A

Glucose can be polymerized into glycogen and/or starch for storage.

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4
Q

What happens if glucose is oxidized? Reduced?

A

Oxidizing glucose produces CO2. Reducing glucose produced fatty acids.

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5
Q

What does it mean that glucose is a “branch point” in metabolism?

A

Glucose can either be used to produce energy or stored for later use.

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6
Q

What is glycolysis (big picture)?

A

The conversion of glucose to two 3C molecules called pyuvate.

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7
Q

What kind of a sugar is glucose and what does this mean?

A

Glucose is an aldohexose. It is a 6C sugar with an aldehyde.

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8
Q

Why is glycolysis considered a central pathway for biochemistry?

A

There is divergence and convergence in the pathway. Metabolites leave the pathway (divergence) and metabolites enter the pathway (convergence).

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9
Q

What is the basic overview of glycolysis (10)?

A
  1. Phosphorylate 6C sugar (glucose)
  2. glucose-6-phsophate → fructose-6-phosphate
  3. phosphorylate fructose-6-phosphate
  4. 1,6 fructose bisphosphate cleaved to form two 3C molecules
  5. interconversion to glyceraldehyde-3-phosphate (GAP)
  6. GAP oxidized and phosphorylated with inorganic phosphate → 1,3 bisphosphoglycerate
  7. Phosphate from 1,3 bisphosphoglycerate transferred to ADP (x2)
  8. 3-phosphoglycerate → 2-phosphoglycerate
  9. 2-phosphoglycerate dephosphorylated to produce ATP (x2)
  10. two pyruvate produced
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10
Q

How do you name/define each step of glycolysis?

A

Define each step by naming the enzyme involved or naming both the substrate AND product of the step.

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11
Q

How is glycolysis broken up?

A

Into two parts; first five steps (1-5) and the last five steps (6-10).

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12
Q

What does glycolysis produce and what is the ΔG?

A

Produces 4 ATP per glucose, but burns 2 ATP throughout the process, so the net yield is 2 ATP per glucose.

Glucose → Pyruvate ΔG°= -107.8 kJ/mol
(~30% efficient)

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13
Q

How are enzymes usually named?

A

Usually named after the substrate and what the reaction is.

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14
Q

What is the first step of glycolysis?

A

Hexokinase Step:
-Glucose is taken up into the cell by glucose transporters.
-We burn 1ATP (PRIMING REACTION) because phosphorylation of glucose by hexokinase occurs and has a net ΔG°= -16.7 kJ/mol
-Glucose becomes “activated”

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15
Q

What is the rationale of the hexokinase step of glycolysis?

A

By converting glucose to glucose-6-phosphate, glucose is captured in the cell and [glucose] in the cell stays low. Glucose transporters don’t move glucose-6-phosphate.

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16
Q

What is hexokinase and what does it do?

A

An enzyme that is unidirectional (strongly -ΔG), regulated, and phosphorylates glucose to glucose-6-phosphate.

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17
Q

What inhibits hexokinase (1)?

A

Glucose-6-phosphate inhibits hexokinase.
FEEDBACK INHIBITION AT PLAY

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18
Q

What is the second step of glycolysis?

A

Phosphoglucomutase Step:
-Glucose-6-phosphate gets isomerized to fructose-6-phosphate

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19
Q

What is the rationale behind the phosphoglucomutase step of glycolysis?

A

C1 is now an alcohol instead of an aldehyde, and as such can be phosphorylated.

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20
Q

What is the ΔG of the phosphoglucomutase reaction and what does this mean?

A

ΔG=0 so the reaction is bidirectional, at equilibrium, reversible, and NOT regulated.

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21
Q

What is the third step of glycolysis?

A

Phophofructokinase (PFK) Step:
-Burn 1 ATP (PRIMING REACTION) to phosphorylate fructose-6-phosphate at C6 to produce fructose-1,6-bisphosphate

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22
Q

What is the ΔG of the phosphofructokinase reaction and what does this mean?

A

ΔG is negative, so it is a unidirectional enzyme that is regulated.

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23
Q

What regulates phosphofructokinase (4)?

A
  1. ATP inhibits PFK (and inhibition at this step inhibits the hexokinase step too).
  2. AMP stimulates PFK, which means PFK can sense the energy status of the cell.
  3. Citrate inhibits PFK, which directly links glycolysis to the Krebs Cycle.
  4. Fructose-2,6-bisphosphate activates PFK

FEEDBACK INHIBITION AT PLAY

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24
Q

What is the rationale of the phosphofructokinase step?

A

The 6C molecule produced will be broken into two 3C molecules each containing a phosphate group.

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25
What is the fourth step of glycolysis?
Fructose Bisphosphate Aldolase Step: -fructose 1,6 bisphosphate is cleaved to two 3C molecules each containing a phosphate group -produces dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3 phosphate (G3P)
26
What is the ΔG of the fructose bisphosphate aldolase reaction and what does this mean?
ΔG=0 so its a reversible reaction, at equilibrium, bidirectional, and NOT regulatory.
27
What is the rationale of the fructose bisphosphate aldolase step?
Carbonyl group at C2 draws electrons and makes the bond weaker/more breakable.
28
What is the fifth step of glycolysis?
Triose Phosphate Isomerase: -conversion of DHAP to G3P -produces two phosphorylated 3C molecules that are the same
29
What is the ΔG of the triose phosphate isomerase reaction and what does this mean?
ΔG=0 so the reaction is reversible, at equilibrium, bidirectional, and NOT regulatory.
30
What is the rationale for the triose phosphate isomerase step?
Only G3P goes on in the glycolysis pathway, so converting DHAP to G3P maintains one pathway.
31
What is the sixth step of glycolysis?
Glyceraldehyde-3-Phosphate Dehydrogenase Step: -two G3P molecules get oxidized -NAD gets reduced to NADH
32
What is the ΔG for the glyceraldehyde-3-phosphate dehydrogenase step?
ΔG=0 so the reaction is reversible, at equilibrium, bidirectional, and NOT regulatory.
33
What is the rationale for the glyceraldehyde-3-phosphate dehydrogenase reaction?
Inorganic phosphate is added to each 3C molecule to produce 1,3 bisphosphoglycerate which is used in the next step.
34
What is the seventh step of glycolysis?
Phosphoglycerate Kinase Step: -1,3 bisphosphoglycerate is dephosphorylated and the inorganic phosphate is directly added to ADP to produce ATP and 3-phosphoglycerate -SLP causes us to break even here (one per molecule)
35
What is the ΔG of the phosphoglycerate kinase reaction and why is it an outlier?
ΔG is "﹣" but the reaction is bidirectional (NOT unidirectional). Products are favored.
36
What is the rationale for the phosphoglycerate kinase step?
Becuase products are favored, the concentration of 1,3 BPG is kept low. This pulls the previous three reactions forward.
37
What is substrate level phosphorylation?
Phosphate comes from a metabolite and is directly placed onto ADP to form ATP.
38
What is the eighth step of glycolysis?
Phosphoglycerate Mutase Step: -3-phosphoglycerate is isomerized to 2-phosphoglycerate
39
What is the ΔG of the phosphoglycerate mutase reaction?
ΔG=0 so reaction is reversible, bidirectional, at equilibrium, and NOT regulated.
40
What is the rationale for the phosphoglycerate mutase step?
Prepares the molecule for the next reaction.
41
What is the ninth step of glycolysis?
Enolase Step: -2-phosphoglycerate converted to phosphoenolpyruvate (PEP) and water
42
What is the ΔG of the enolase reaction?
ΔG=0 so the reaction is reversible, bidirectional, at equilibrium, and NOT regulated.
43
What is the rationale for the enolase reaction?
The dehydration reaction makes the phosphate group a good leaving group for the next reaction.
44
What is the tenth step of glycolysis?
Pyruvate Kinase Step: -PEP is dephosophorylated and the phosphate group is transfered to ADP -SLP (now +2 ATP)
45
What is the ΔG for the pyruvate kinase reaction?
ΔG=﹣23 kJ/mol so the reaction is unidirectional and regulated.
46
What is pyruvate kinase allosterically inhibited by (3)?
Pyruvate kinase is ALLOSTERICALLY inhibited ny ATP, acetyl CoA, and alanine. (feedback inhibition)
47
How does an allosteric inhibitor/stimulator work?
Binds at a site other than the active site, but impacts binding of ligands at the active site.
48
What is pyruvate kinase allosterically stimulated by (2)?
Pyruvate kinase is ALLOSTERICALLY stimulated by AMP and fructose-1,6-bisphosphate.
49
What does inhibition of pyruvate kinase cause?
Inhibition causes a buildup of PEP, which causes a buildup of 2-phsophoglycerate, which keeps building up down the line.
50
What is the net reaction for glycolysis?
glucose + 2 ADP + 2 Pᵢ + 2 NAD⁺ → 2 pyruvate + 2 ATP + 2 NADH + 2 H⁺ + 2 H₂O
51
How and where do glycogen and starch converge with glycolysis?
Convergence occurs at phosphoglucomutase step (#2). 1. glycogen/starch phosphorylase cleaves storage molecule to produce glucose-1-phosphate 2. glucose-1-phosphate is converted to glucose-6-phosphate VERY easily by phosphoglucomutase 3. phosphoglucomutase is bidirectional!
52
Why is glycogen or starch convergence advantageous for organisms?
You bypass the hexokinase step which means you get a net production of 3 ATP instead of 2. (50% increase)
53
Do only glycogen and starch converge onto glycolysis?
No. Every single carbohydrate converges onto glycolysis.
54
Why is glycolysis so well regulated?
Pyruvate is significantly more toxic to cells than other metabolites, so it can't be allowed to buildup.
55
What happens to NAD/H when cells are under anaerobic conditions?
NADH can't be oxidized back to NAD so redox reactions can no longer occur. This leads to a buildup of metabolites = cell toxicity.
56
Why does fermentation occur?
It is how cells can produce NAD under anaerobic conditions and put glycolysis back in play.
57
What does fermentation in eukaryotes look like (chemical equation)?
pyruvate + NADH + H⁺ → lactate + NAD
58
Lactic acid is also toxic to a degree, so how does our body handle it?
Lactate is circulated to the liver where it is converted to glucose, further keeping glycolysis in play.
59
What does fermentation in yeast look like (chemical equation)?
pyruvate  ↔️ CO₂ + acetaldehyde + NADH ↔️ NAD + ethanol
60
Why can't humans perform yeast fermentation?
We only have alcohol dehydrogenase, we don't have pyruvate decarboxylase.
61
What is gluconeogenesis?
The process of making glucose from pyruvate; exact opposite of glycolysis
62
Where does gluconeogenesis take place?
Almost entirely done in the liver.
63
Why do we need to make glucose when we get it in our diet?
Some cells and tissues like your brain and RBCs exclusively use glucose, so we would run out of glucose if we depended only on dietary intake.
64
How do the seven non-regulatory enzymes of glycolysis play into gluconeogenesis?
They work in both directions, so they will function in both glycolysis and gluconeogenesis.
65
How do they three regulatory enzymes of glycolysis play into gluconeogenesis?
They don't. The cell needs a way to overcome the regulatory enzymes because they only work in one direction.
66
What is the first step of gluconeogenesis?
Pyruvate produced in the cytosol will end up in the mitochondrial matrix via pyruvate transporters on the inner mitochondrial membrane.
67
What does the first step of gluconeogenesis "undo/line up" with in glycolysis?
Pyruvate Kinase Step (#10)
68
What is the second step of gluconeogenesis?
Pyruvate in the mitochondrial matrix is carboxylated by pyruvate carboxylase to produce oxaloacetate.
69
What is pyruvate carboxylase?
A regulatory enzyme that is ONLY found in the in the mitochondrial matrix. It carboxylates pyruvate to oxaloacetate in gluconeogenesis.
70
How is pyruvate carboxylase activated (1)?
It is activated by acetyl CoA because when [acetyl CoA] is high, the cell is in a high energy state; and anabolism can occur.
71
What is the third step of gluconeogenesis?
Oxaloacetate in the mitochondrial matrix is reduced to form malate via malate dehydrogenase.
72
What is the fourth step of gluconeogenesis?
Malate is transported out of the mitochondrial matrix into the cytosol by malate transport proteins in the inner mitochondrial membrane.
73
What is the fifth step of gluconeogenesis?
Malate is reoxidized to oxaloacetate in the cytosol by malate dehydrogenase.
74
Why does step five of gluconeogenesis occur? It seems like a waste of time...
There are no oxaloacetate transporters in the mitochondrial membrane, so it needs to be converted to malate to leave the mitochondria.
75
What is the sixth step of gluconeogenesis?
Oxaloacetate is decarboxylated and phosphorylated to make phosphoenolpyruvate (PEP)
76
What is burned in step six of gluconeogenesis?
One GTP per pyruvate (2 total per glucose molecule)
77
Why does the decarboxylation in step six occur?
Decarboxylation is energy favorable, and when combined with the hydrolysis of a phosphoanhydride bond, drives the reaction forward.
78
What is the seventh step of gluconeogenesis?
Glycolysis steps 9, 8, 7, 6, 5, and 4 occur in the reverse directions.
79
What is the eighth step of gluconeogenesis?
The enzyme fructose-1,6-bisphosphotase dephosphorylates fructose-1,6-bisphosphate to fructose-6-phosphate.
80
What does the eighth step of gluconeogenesis "undo/line up" with in glycolysis?
Phosphofructokinase (PFK) Step (#3)
81
What is fructose-1,6-bisphosphotase?
A regulatory enzyme that is unidirectional (ΔG=-16.7 kJ/mol) and dephosphorylates fructose-1,6-bisphosphate.
82
How is fructose-1,6-bisphosphotase inhibited (2)?
It is inhibited by AMP and fructose-2,6-bisphosphate. You can't make glucose if you don't have any energy (aka [AMP] is high).
83
What is the ninth step of gluconeogenesis?
Fructose-6-phosphate undergoes step 2 of glycolysis in the reverse direction.
84
What is the tenth step of gluconeogenesis?
Glucose-6-phosphotase converts glucose-6-phosphate to glucose.
85
What does the last step of gluconeogenesis "undo/line up" with in glycolysis?
Hexokinase Step (#1)
86
What is glucose-6-phosphotase (2 roles/functions)?
A regulatory enzyme that converts G6P to glucose via substrate level control/regulation. It is unidirectional and ΔG is "﹣". It is also a transport protein that binds G6P, removes phosphate, and transports glucose into the ER.
87
What is the substrate level regulation of glucose-6-phosphotase?
When [G6P] is high, the enzyme is active and when the [G6P] is low, the enzyme is inactive.
88
What is the rationale for the last step of gluconeogenesis?
It keeps the cytosolic [glucose] low (sequestered in the ER) and it is involved in bulk flow vesicular transport.
89
What is the main role of the liver?
The liver maintains BGL.
90
What is the net reaction of gluconeogenesis?
2 pyruvate + 4 ATP + 2 GTP + 2 NADH + 2H⁺ + 6 H₂O → glucose + 4 ADP + 2 GDP + 6 Pᵢ + 2 NAD⁺ ΔG = ﹣15.6 kJ/mol
91
What kind of a process is gluconeogenesis? Glycolysis?
Gluconeogenesis is anabolic and glycolysis is catabolic.
92
Why is it okay that gluconeogenesis consumes energy.
It's an anabolic process, so it will only occur when the cell is in a high energy state and has ATP/GTP to spare.
93
What is the Cori Cycle?
How lactic acid is cycled in the liver. 1. lactate travels to the liver via the bloodstream 2. lactate is up-taken into the liver by receptors 3. lactate in the liver is converted to pyruvate 4. liver performs gluconeogenesis
94
What is a futile cycle?
A cycle where glycolysis and gluconeogenesis happen at the same time. Cells NEVER allow this to happen.
95
Why do cells never allow a futile cycle to occur?
Glycolysis produces 2 ATP while gluconeogenesis burns 6 ATP/GTP. You would lose 4 ATP and gain nothing.
96
Catabolism is inhibited by ______________ and stimulated by ________________.
Inhibited by high energy molecules (ATP, GTP, Acetyl CoA). Stimulated by low energy molecules (AMP, ADP, NAD⁺)
97
Anabolism is inhibited by ______________ and stimulated by ________________.
Inhibited by low energy molecules. Stimulated by high energy molecules.

Biochemistry II (11 decks)

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