Lecture 7 - Glycolysis

Question 1

What inhibits hexokinase?

Answer 1

G-6-P

Question 2

What enzyme controls the entry of G6P into the glycolysis pathway?

Answer 2

PFK-1

Question 3

What inhibits PFK1? Activates?

Answer 3

Allosteric inhibition: ATP

Allosteric activation: AMP

Question 4

What are the relative Km values of hexokinase and glucokinase? Where is each found?

Answer 4

Hexokinase lower Km than Glucokinase. RBCs need glucose! Glucokinase - liver, Hexokinase - most everywhere else

Question 5

List the glycolysis substrates in order.

Answer 5

Glucose > G6P > F6P > F1,6B > G3P > 1,3BPG > 3PG > 2PG > PEP > P

Question 6

Where does glycolysis occur?

Answer 6

Cytoplasm

Question 7

Source of ATP for blood cells?

Answer 7

Anaerobic glycolysis. They have no mitochondria!

Question 8

List the glycolysis enzymes in order.

Answer 8

Hexokinase, PHI, PFK1, Aldolase, Triose phosphate isomerase, Glyceraldehyde 3-phosphate dehydrogenase, Phosphoglycerate kinase, Phosphoglycerate mutase, Enolase, Pyruvate kinase
(H-PHI-PFK1-A-TPI-G3PDH-PGK-PGM-E-PK)

Question 9

What is the primary fuel used the the heart under normal conditions?

Answer 9

Fatty acids: 60-80%

Note: Glucose is 20-30%, only 2% of total ATP used from glycolysis! This is significant for ischemia since

Question 10

What are the glucose transporters in the heart? What is significant about the dominant class of glucose transporters in the heart?

Answer 10

GLUT1 (10%) and GLUT4 (90%). GLUT4 is insulin dependent.

Question 11

What enzymes are directly involved in generating substrates for the Lactate dehydrogenase?

Answer 11

G3P Dehydrogenate (produces NADH) and pyruvate kinase (produces pyruvate)

Question 12

G6P can enter other pathways besides glycolysis. List these.

Answer 12

Glycogen, pentose phosphate, blood glucose (liver)

Question 13

What two groups of cells rely solely on anaerobic glycolysis?

Answer 13

RBCs and lens cells (eye)

Question 14

What enzyme allows G6P to be released from the cell? Where is this enzyme found?

Answer 14

G6P phosphatase, found in liver and renal cortex

Question 15

What type of glucose transporter is found in the liver?

Answer 15

GLUT2 (constitutively active - not insulin regulated)

Question 16

What step in glycolysis is heavily regulated and irreversible (a committed step)?

Answer 16

Conversion of F6P to F1,6B by PFK1

Question 17

Where does arsenate inhibit ATP production? How does it inhibit?

Answer 17

Substitutes for Pi in rxns. 2nd PO4 at the G3P DH step.

Question 18

What 2 steps in glycolysis are not reversible?

Answer 18

F1,6BP, Pyruvate kinase

Question 19

Explain the types of lactic acidosis.

Answer 19

Type A: Occurs when there is evidence of poor oxygen perfusions
Type B: No evidence ox depletion, liver dysfunction, ox phos uncoupling

Question 20

Define lactic acidosis.

Answer 20

acidosis - persistant high lactate levels > 5mM in presence of low pH

Question 21

How do cytosolic NADH electrons enter the mitochondrial matrix (pathway common in all tissues)?

Answer 21

G3P phosphate shuttle (present in all tissues)

Question 22

What is the ATP/NADH ratio through the G3P shuttle?

Answer 22

1.5ATP/NADH

Question 23

How do cytosolic NADH electrons enter the mitochondrial matrix (pathway present in heart, liver, kidney)

Answer 23

Malate-aspartate shuttle

Question 24

What is the ATP/NADH ratio for the malate-aspartate shuttle?

Answer 24

2.5ATP/NADH

Question 25

What specific interaction allow the malate-aspartate system to “drop off” its electrons in the mitochondrial matrix?

Answer 25

Malate + NAD(+) => Oxaloacetate + HADH
(Malate is oxidized, NADH goes to ETC)
(See page 402 in Mark’s)

Question 26

What enzyme is responsible for converting oxaloacetate to aspartate within the context of the Malate-aspartate shuttle?

Answer 26

alpha-keto-glutarate

Question 27

List the key regulated steps in glycolysis.

Answer 27

1) Hexokinase (glucokinase in liver)
2) PFK1
3) Pyruvate kinase
4) Pyruvate dehydrogenase

Question 28

What regulates Hexokinase function?

Answer 28

Inhibited by presence of G6P

Question 29

What regulates Glucokinase function?

Answer 29

Induced by insulin

Question 30

What regulates PFK1

Answer 30

Induction: AMP, fructose-2,6bisP
Inhibition: ATP, acidosis, citrate

Question 31

What regulates pyruvate kinase?

Answer 31

+ fructose-1,6-bisP

• ATP
• cAMP dependent kinase (glucagon in liver)

Question 32

What regulates pyruvate dehydrogenase?

Answer 32

• NADH
• Acetyl CoA
  + ADP

Question 33

Explain the function of GKRP.

Answer 33

Translocates glucokinase between the cytoplasm and the nucleus (in nucleus GK is inactive, cytoplasm its active).

Question 34

Explain the regulation of GKRP.

Answer 34

• Fructose-6-P inhibits GKRP by aiding it in binding GK

- Glucose & fructose-1-P block GKRP-GK interactions activating GK

Question 35

What is the effect of insulin on glucokinase?

Answer 35

Increases number of GK units

Question 36

What is the effect of G6P on glucokinase?

Answer 36

Not a lot. Liver needs to be able to synthesize glycogen even when blood glucose is elevated.

Question 37

What is the role of PFK-2?

Answer 37

Deal functions:

1) KINASE: Phosphorylates F6P to F2,6BP
2) PHOSPHATATSE: F2,6BP to F6P

Question 38

What is the significance of F2,6BP?

Answer 38

• Most potent activator of PFK-1

- Most potent inhibitor of fructose-1,6-bisphosphatase (gluconeogenesis in liver)

Question 39

What is the effect of PFK2 phosphorylation in the heart?

Answer 39

Kinase activity activated > F2,6BP increased > glycolysis

Question 40

What is the effect of PFK2 phosphorylation in the liver?

Answer 40

Kinase activity inhibited > F2,6BP decreased > Gluconeogenesis can occur

Question 41

Pyruvate dehydrogenase function

Answer 41

Oxidizes pyruvate following glycolysis > Acetyl-CoA for TCA

Question 42

Dichloroacetate

Answer 42

Inhibits PDH kinase, activated PDH

Question 43

Effect of increased PDH activity

Answer 43

Increased Acetyl-CoA into TCA. Heart uses more glucose.