Quiz 7

Question 1

what is hexokinase inhibited by

Answer 1

G6P and ADP (products)

Question 2

what is glucokinase inhibited by? What is it not inhibited by? What is it induced by?

Answer 2

NOT inhibited by G6P and ADP
Repressed by glucagon
Inducible transcriptionally by high carb diet and insulin

Question 3

what kind of reaction is aldose G6P to ketose F6P

Answer 3

acid base catalysis (phosphoglucoisomerase)

Question 4

What is PFK inhibited by

Answer 4

citrate and ATP (high E signals)

Glucagon (hormonal)

Question 5

what is PFK stimulated by? what is it repressed by?

Answer 5

AMP, Pi, NH4, F 1,6 bis P (product, weird!)

Insulin stimulates as well (hormonal)

Question 6

what are the binding sites on PFK?

Answer 6

there are 8
2 for substrates (ATP and F6P)
2 allosteric inhibitory (ATP and citrate)
4 allosteric activation (AMP, Pi, NH4, F 1,6 BP)

Question 7

how is hormonal of PFK accomplished

Answer 7

complex system with fructose 2,6 BP which is a powerful activator. F 2,6 BP formed from F6P + F2,6 bis phosphokinase. Broken down by F2,6bisphosphosphatase.

• Kinase activated in dephosphorylated form, phosphatases inactivated in dephosphorylated form.
• insulin promotes dephosphorylated form, glucagon and epinephrine promote phosphorylated form

Question 8

how are glucagon and epinephrine able to act in glycolysis pathway

Answer 8

via cAMP-PKA pathway.

Question 9

what does Glyceraldehyde 3 Phosphate dehydrogenase (G3PDH) have that is necessary

Answer 9

reactive thiol sites to catalyze the transfer of a high energy group phosphate to G3P - this is why thiol reacting compounds like heavy metals are dangerous because they inhibit glycolysis at this step

Question 10

how is the high energy trapped in the first transfer of P to ADP in glycolysis

Answer 10

Oxidation of aldehyde on C1 of G3P to carb acid on C1 of 3PGA was trapped in high energy intermediate 1,3 bis PGA which is what gives off the ATP. If we didn’t trap this energy, it would just get released as heat

Question 11

what are the three irreversible steps of glycolysis

Answer 11

hexokinase (Glucose to G6P)
PFK (F6P to F1,6 BP)
PK (Phosphoenol pyruvate to pyruvate)

Question 12

what is enolase inhibited by

Answer 12

fluoride

Question 13

how is PK regulated

Answer 13

inhibited by ATP, NADH, and Acetyl CoA (signs of high energy)
Stimulated by Fructose 1.6 BP which is its product

*Also regulated by glucagon – cAMP – PKA phosphorylation which inhibits its activity. Insulin stimulates it via dephosphorylation

Question 14

sucrose is metabolized to

Answer 14

glucose and fructose

Question 15

what does fructose become

Answer 15

Fructokinase turns it into Fructose 1-P. Aldolase B can turn this into DHAP or glyceraldehyde. Glyceraldehyde becomes G3P with triose kinase and ATP

Question 16

why would you have hereditary fructose intolerance

Answer 16

because you dont have aldose B which is the only thing that can cleave Fructose 1P to DHAP and glyceraldehyde.

Question 17

what is lactose metabolized to

Answer 17

glucose and galactose

Question 18

what does galactose become

Answer 18

galactokinase turns it into galactose 1P. Uridyl transferase turns it into Glucose 1P. Phosphoglutamutase turns this into G6P.

Question 19

what is wrong in galactosemia

Answer 19

uridyl transferase is deficient so high levels of galactose 1P accumulate

Question 20

will high levels of pyruvate inhibit the H or M isoform

Answer 20

H

Question 21

what enzymes are important in the pyruvate to ethanol rection

Answer 21

PTT/Vitamin B1 is cofactor for pyruvate decarboxylase, removes CO2
ALcohol Dehydrogenase turns acetaldehyde into ethanol (and oxidizes NADH to NAD)

Question 22

how is PDH regulated

Answer 22

E1 inhibited by ATP
E2 inhibit by product inhibition of Acetyl CoA
E3 product inhibition by NADH

Also has hormonal control – PDH kinase phosphorylates E1 and inhibits its activity. NOT mediated by cAMP PKA and not effected by glucagon or epinephrine.

Question 23

what does PDH phosphatase do

Answer 23

dephosphorylates E1-P and activates E1. STRONGLY increased by insulin. Insulin stimulates glucose to pyruvate

Question 24

where does insulin stimulate glucose to pyruvate

Answer 24

GK, PFK, PK, PDH

Question 25

what can succinyl coA be pulled out to form

Answer 25

heme

Question 26

what can OAA be pulled out to form

Answer 26

glucose, aspartate, asparagine, pyrimidines

Question 27

what can citrate be pulled out to form

Answer 27

fatty acids

Question 28

what can alpha KG be pulled out to form

Answer 28

glutamate, glutamine, proline, ornithine

Question 29

what happens if OAA is removed from cycle

Answer 29

OAA is not regenerated and the cycle stops as acetyl CoA accumulates - anaplerotic rxns can replenish OAA that is pulled out or deficient

Question 30

what reactions can replenish OAA

Answer 30

1. Pyruvate carboxylase - contains biotin (the vit B used to carry CO2 in enzymatic rxns). ATP is necessary for this carboxylation. VERY stimulated by acetyl CoA
2. Many AA care catabolized to TCA intermediates
3. PEP carboxynase converts PEP (glycolysis) to OAA

Question 31

what are there NO carriers for in the mitochondria

Answer 31

OAA, alpha GP, DHAP, NADH/NADPH

Question 32

what can malate be exchanged for in the mitochondria

Answer 32

Dicarboxylate carrier
Tricarboxylate carrier
Alpha keto glutarate carrier