Glycolysis: Functions, pathways, energetics, regulation- Lecture 61

Question 1

What is the overall reaction of glycolysis?

Answer 1

C6H12O6 + 2NAD+ + 2 Pi –> 2 CH3COCOOH (pyruvate) + 2 ATP + 2 NADH

Question 2

Gycolysis is the only source of energy for ________ and a major source of energy for _________.

Answer 2

RBCs and normally for the brain

Embryonic tissue, retina, adrenals, some immune cells, exercising muscles

Question 3

What is the first step of glycolysis?

Answer 3

Glucose + ATP –> Glucose-6-Phosphate + ADP + Pi

via hexokinase

Question 4

Which steps in glycolysis are irreversible?

Answer 4

1, 3, and 10

Question 5

What is the second step of glycolysis?

Answer 5

G6P –> Fructose 6-P

via phosphoglucoisomerase

Question 6

What is the third step in glycolysis?

Answer 6

F6P + ATP –> F1,6bisP + ADP
via phosphofructokinase
RATE LIMITING

Question 7

What regulates the rate limiting step of glycolysis (not in the liver)?

Answer 7

the third step of glycolysis is catalyzed by PFK which is…
inhibited by ATP and citrate
stimulated by AMP, Pi, NH4, F1,6bisP

Question 8

What kinds of sites does PFK have?

Answer 8

two substrate binding sites (ATP, F6P)
two allosteric inhibitory sites
four allosteric activator sites

Question 9

What regulates the rate limiting step of glycolysis (in the liver)?

Answer 9

the third step of glycolysis is catalyzed by PFK which is…
insulin stimulates
glucagon inhibits

Question 10

What is the fourth step of glycolysis?

Answer 10

F1,6bisP < —- > DHAP + G3P

via aldolase

Question 11

What is the fifth step of glycolysis?

Answer 11

DHAP < —- > G3P
via tripse phosphate isomerase
*note that after this you have two G3P products which can continue (so everything after this step should be doubled)

Question 12

What is the sixth step of glycolysis?

Answer 12

G3P + NAD+ + Pi < —- > 1,3 bis phosphoglyceric acid + NADH
via gluceraldehyde 3-P dehydrogenase
Note: oxygen independent

Question 13

_____ is a high energy compound that “traps” energy that would have otherwise been ______.

Answer 13

1,3 bis PGA

released as heat

Question 14

What is the seventh step of glycolysis?

Answer 14

1,3 bis PGA + ADP < —- > 3 PGA + ATP

via phosphoglycerate kinase

Question 15

What is substrate level phosphorylation?

Answer 15

the transfer of energy to a high energy intermediate which can produce ATP

Question 16

_____ is highly sensitive to poisoning by heavy metals such as _____.

Answer 16

Phosphoglycerate kinase (enzyme of glycolysis 7)
Hg, Cd, Pb

Question 17

What effect does arsenic have on the body?

Answer 17

competes with Pi for G3P in the G3PDH reaction to form arseno-3-phophoglyceric acid rather than 1,3 bisP that releases energy as heat rather than as ATP
glycolysis continues, but no ATP is produced- this is a problem in RBCs who use this as their only source for ATP –> anemia

Question 18

RBCs have a mutase which converts small amounts of ______ into ________, an important allosteric effector of hemoglobin that regulates _____.

Answer 18

1,3 bis P
2,3 bis P
oxygen affinity

Question 19

What is the eighth step of glycolysis?

Answer 19

3 phosphoglycerate < —- > 2-phosphoglycerate

via phosphoglyceromutase

Question 20

What is the ninth step of glycolysis?

Answer 20

2PGA < —- > Phosphoenolpyruvate (PEP)+ H2O

via enolase

Question 21

Enolase is inhibited by ______.

Answer 21

fluoride

Question 22

What is the tenth step of glycolysis?

Answer 22

PEP + ADP –> Pyruvate + ATP

via pyruvate kinase

Question 23

Which steps of glycolysis participate in substrate level phosphorylation?

Answer 23

seven and ten

Question 24

How is pyruvate kinase regulated?

Answer 24

inhibited by ATP, NADH, and acetyl CoA
stimulated by F1,6 bis P
inhibited by glucagon(Epi) cAMP-PKA phosphorylation
stimulated by insulin

Question 25

What is the net ATP yield for one mol of glucose through glycolysis?

Answer 25

net 2 ATP | 2 ATP consumed, 4 ATP produced

Question 26

Describe fructose metabolism in the liver.

Answer 26

1. Fructose + ATP --> Fructose 1P via fructokinase 2. Fructose 1P --> Glyceraldehyde + Dihydroxyacetone P via aldolase 3. Glyceraldehyde + ATP --> Glyceraldehyde 3P + ADP via triose kinase 4. G3P -->--> Pyruvate

Question 27

What is hereditary fructose intolerance?

Answer 27

Aldolase B in liver is replaced by aldolase A which cannot react with Fructose 1P

Question 28

Describe the pathway of galactose metabolism.

Answer 28

1. Galactose + ATP --> Galactose 1P + ADP via galactokinase 2. Galactose 1P + UDP-glucose --> Glucose 1P + UDP-galactose via galactose 1P uridylyltransferase 3. glucose 1P --> glucose 6P via phosphoglucomutase 4. Glycolysis (other tissues) or return to glucose (liver)

Question 29

What is galactosemia?

Answer 29

mainly deficiency of galactose 1P resulting in accumulation or toxic galactose 1P uridylytransferase in liver, may also be caused by deficiency of galactokinase