Chapter 16: Glycolysis

Question 1

Where does galactose enter the glycolytic pathway?

Answer 1

Galactose is converted in the liver to Glucose-6-phosphate

Question 2

Fructose metabolism

Answer 2

Fructose is converted to fructose‑6‑phosphate in most tissues

Is converted to fructose‑1‑phosphate in the liver by the enzyme fructokinase

Fructose‑1‑phosphate is then cleaved by fructose‑1‑phoshate aldolase into DHAP and G3P

Question 3

Glycolysis

Energy investment phase intermediates

Answer 3

Intermediates

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1. Glucose
2. Glucose 6-phosphate
3. Fructose 6-phosphate
4. Fructose 1,6-bisphosphate
5. Glyceraldehyde 3-phosphate (G3P)
   
   • Dihydroxyacetone phosphate (DHAP)
   • DHAP converts to second molecule of G3P

Question 4

Glycolysis

Energy investment phase enzymes

Answer 4

Enzymes

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1. Hexokinase
2. Phosphoglucoisomerase
3. Phosphofructokinase
4. Aldolase
5. Triose phosphate isomerase

• Converts DHAP to G3P

Question 5

Glycolysis

Energy payoff phase intermediates

Answer 5

Intermediates

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1. 1,3-Bisphosphoglycerate (BPG)
2. 3-Phosphoglycerate (PG)
3. 2-Phosphoglycerate (PG)
4. Phosphoenolpyruvate (PEP)
5. Pyruvate

Question 6

Glycolysis

Energy payoff phase enzymes

Answer 6

Enzymes

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1. Glyceraldehyde 3-phosphate dehydrogenase
2. Phosphoglycerokinase
3. Phosphoglyceromutase
4. Enolase
5. Pyruvate kinase

Question 7

Glycolysis

All enzymes

Answer 7

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1. Hexokinase
2. Phosphoglucoisomerase
3. Phosphofructokinase
4. Aldolase
5. Triose phosphate isomerase
6. Glyceraldehyde 3-phosphate dehydrogenase
7. Phosphoglycerokinase
8. Phosphoglyceromutase
9. Enolase
10. Pyruvate kinase

Question 8

Glycolysis

All intermediates

Answer 8

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1. Glucose
2. Glucose 6-phosphate
3. Fructose 6-phosphate
4. Fructose 1,6-bisphosphate
5. Glyceraldehyde 3-phosphate (G3P)
   
   • Dihydroxyacetone phosphate (DHAP)
   • DHAP converts to second molecule of G3P
6. 1,3-Bisphosphoglycerate (BPG)
7. 3-Phosphoglycerate (PG)
8. 2-Phosphoglycerate (PG)
9. Phosphoenolpyruvate (PEP)
10. Pyruvate

Question 9

Step 1 of glycolysis

Answer 9

Hexokinases transfers a phosphoryl group to carbon-6 utilizing one ATP

Traps glucose WITHIN the cell

IRREVERSIBLE

Question 10

Step 2 of glycolysis

Answer 10

Phosphoglucose isomerase isomerizes glucose 6-phosphate to fructose 6-phosphate

Converts an aldose to a ketose

Question 11

Step 3 of glycolysis

Answer 11

Phosphofructokinase transfers a phosphoryl group to carbon-1 utilizing one ATP

IRREVERSIBLE

Question 12

Step 4 of glycolysis

Answer 12

Aldolase performs a reverse aldol reaction that cleaves fructose-6-phosphate into DHAP and G3P

Generates an aldehyde and ketone

Question 13

Step 5 of glycolysis

Answer 13

Triose phosphate isomerase isomerizes DHAP to a second molecule of G3P

Question 14

Step 6 of glycolysis

Answer 14

Glyceraldehyde 3-phosphate dehydrogenase oxidizes G3P via the addition of a phosphate group to carbon-1 forming 1,3-BPG

NAD⁺ gets reduced which produces one molecule of NADH

Question 15

Step 7 of glycolysis

Answer 15

Phosphoglycerate kinase transfers the phosphoryl group on carbon-1 to ADP

Forms one molecule of ATP from each 1,3-BPG; total two ATP per each glucose molecule

Question 16

Step 8 of glycolysis

Answer 16

Phosphoglycerate mutase moves the phosphoryl group from carbon-3 of 3-PG to carbon-2 forming 2-PG

Question 17

Step 9 of glycolysis

Answer 17

Enolase performs a dehydration elimination reaction

Generates a resonance stabilized phosphoenolpyruvate molecule

Question 18

Step 10 of glycolysis

Answer 18

Pyruvate kinase transfers phosphoryl group to ADP

Forms one molecule of ATP from each phosphoenopyruvate; total two ATP per each glucose molecule

IRREVERSIBLE

Question 19

Phosphofructokinase regulation

Answer 19

Inhibited by an over-accumulation of ATP

Stimulated by high ratio of AMP:ATP

Most important control mechanism of glycolytic pathway

Question 20

Hexokinase regulation

Answer 20

Inhibited by an over-accumulation of glucose-6-phosphate

Question 21

Pyruvate kinase regulation

Answer 21

Inhibited by an over-accumulation of ATP

Stimulated by fructose 1,6-bisphosphate in a feed-forward mechanism

Question 22

Glucose transporters in the liver and pancreatic β cells

Answer 22

GLUT2

Highest K_m of all glucose transportes at 15−20mM to remove excess glucose from the blood

Question 23

Glucose transporters in muscle and fat cells

Answer 23

GLUT4

Relatively low K_m of 5mM to ensure adequate uptake of glucose

Question 24

Warburg effect

Answer 24

Rapidly growing tumors obtain ATP by metabolizing glucose to lactate even in the presence of oxygen, a process termed aerobic glycolysis

Question 25

Gluconeogenesis

Answer 25

Reverse process to glycolysis Bypasses irreversible steps Gly-1, Gly-3, & Gly-10 **Gly-10** * Pyruvate carboxylase (PC) * Phosphoenolpyruvate carboxykinase (PEPCK) **Gly-3** * Fructose 1,6-bisphosphatase (FBPase) **Gly-1** * Glucose 6-phosphatase (G6Pase)

Question 26

Step 1 of gluconeogenesis

Answer 26

**Pyruvate carboxylase (PC)** uses ATP to make *oxaloacetate* from pyruvate Occurs in the mitochondiral matrix; oxaloacetate is subsequentally transported out of the mitochondria to the cytoplasm

Question 27

Step 2 of gluconeogeneisis

Answer 27

**Phosphoenolpyruvate carboxykinase (PEPCK)** transfers a phosphate to oxaloacetate to form *phosphoenolpyruvate*

Question 28

Step 9 of gluconeogenesis

Answer 28

**Fructose-1,6-phosphatase (FBPase)** removes a phosphate from fructose-1,6-bisphosphate to form *fructose-6-phospate* Stimulate by **glucagon** and an increase in **ATP** Inhibited by **insulin** and an increase in **AMP**

Question 29

Step 11 of gluconeogenesis

Answer 29

Glucose 6-phosphate is transported into the lumen of the *endoplasmic reticulum* **Glucose-6-phosphatase** dephosphorylates glucose-6-phosphate to glucose G6Pase is an integral membrane protein on the inner surface of the endoplasmic reticulum

Question 30

Hypoglycemic response

Answer 30

**Glucagon** stimulates PKA **FBPase** is activated to stimulate gluconeogenesis Glycolysis is inhibited

Question 31

Hyperglycemic response

Answer 31

**Insulin** stimulates phosphoprotein phosphatase **Phosphofructokinase** is activated which stimulates glycolysis Gluconeogenesis is inhibited

Question 32

Process to catabolize lactic acid

Answer 32

**Cori cycle-** when muscles are under anaerobic conditions and produce lactate, it can be transported to the liver and used in gluconeogenesis