Energy metabolism of major nutrients flashcards

Question 1

Allosteric enzyme regulation

Answer 1

Intermediate or product binds to site other than the active site and inhibits reactions. Fast and versatile regulation.

Question 2

What are triglycerides are made of?

Answer 2

3 fatty acids + glycerol

Question 3

Sources of pyruvate

Answer 3

Glucose, glycerol, and some amino acids

Question 4

Pathways pyruvate can enter

Answer 4

If anaerobic conditions can be made into 1. Reduced to Lactate (end product of glycolysis) or 2. Converted to ethanol (in yeast and bacteria). If aerobic conditions can be made into 1. Irreversible Oxaloacetate by pyruvate carboxylase (start of gluconeogenesis) or 2. Irreversibly made into Acetyl CoA by pyruvate dehydrogenase complex (PDH) which enters TCA cycle

Question 5

Steps of PDH

Answer 5

Irreversible, takes place in mitosol 1. Pyruvate enters E1–decarboxylation to yield CO2 and reduces pyruvate to enolic form of acetyl group 2. E2 oxidizes enol into an acetyl group (by reduction of lipoic acid) which attaches to CoA 3. E3 re-oxidizes lipoic acid and reconstructs FAD to allow for the next reaction, produces NADH which goes to terminal oxidation

Question 6

How many enzymes and coenzymes in PDH?

Answer 6

3 enzymes, 5 coenzymes, and 2 regulatory enzymes

Question 7

3 products of PDH

Answer 7

Acetyl CoA, CO2, NADH Products also inhibit complex with feedback inhibition

Question 8

3 reactants in PDH

Answer 8

1. Pyruvate 2. NAD+ 3. Coenzyme A (CoASH)

Question 9

4 forms of regulation in PDH

Answer 9

1. Feedback inhibition 2. Phosphorylation and dephosphorylation of enzymes 3. Regulating protein kinase and phosphoprotein phosphatase 4. Calcium

Question 10

PDH deficiency

Answer 10

Incompatible with life if gone but possible to have reduced activity

Question 11

What stimulates/inhibits protein kinase?

Answer 11

Stimulates: ATP, Acetyl CoA, NADH Inhibits: Pyruvate (when glycolysis active PDH active)

Question 12

Congenital lactic acidosis

Answer 12

X linked “dominant” (more common in Ashkenazi jews). PDH mostly inhibited which causes buildup of lactate. May respond to ketogenic (low glucose) diet.

Question 13

How does glycerol get metabolized?

Answer 13

Converted to pyruvate which becomes Acetyl CoA

Question 14

How do amino acids get metabolized?

Answer 14

Some converted to pyruvate which becomes Acetyl CoA and some deaminated and oxidized to produce Acetyl CoA directly

Question 15

3 pathways Acetyl CoA can enter

Answer 15

1. Complete oxidation in TCA cycle 2. Conversion into ketone bodies in the liver 3. Biosynthesis of sterols and long fatty acid chains in the cytosol

Question 16

3 sources of Acetyl CoA (AcCoA)

Answer 16

1. PDH 2. Some amino acids 3. beta-oxidation of fatty acids

Question 17

Why step-wise catabolism of AcCoA?

Answer 17

Highly reduced high energy bond molecule. If we broke it down all at once we would blow up.

Question 18

Citrate synthase

Answer 18

Reacts with AcCoA to produce isocitrate

Question 19

How many atoms of C enter Kreb’s cycle? How many lost?

Answer 19

2 C atoms enter, 2 C lost in form of CO2

Question 20

How many NADH, FADH, and GTP are produced from one turn of TCA cycle?

Answer 20

3 NADH, 1 FADH, 1 GTP

Question 21

What 3 Kreb’s cycle steps produce 1 NADH each?

Answer 21

1. Isocitrate dehydrogenase (also produces CO2) 2. alpha-ketoglutarate dehydrogenase (also produces lipoic acid and CO2) 3. Malate dehydrogenase

Question 22

What Kreb’s cycle step produces 1 FADH?

Answer 22

Succinate dehydrogenase

Question 23

What Kreb’s cycle step produces 1 GTP?

Answer 23

Succinyl-CoA-synthase (to Succinate). This uses substrate-level phosphorylation and this step can go back and forth

Question 24

Energetics produced during TCA cycle?

Answer 24

3 NADH–>NAD+ = 9 ATP FADH2–>FAD = 2 ATP GDP + Pi–> GTP = 1 ATP TOTAL: 12 ATP per acetyl CoA oxidized

Question 25

5 regulators of TCA cycle

Answer 25

1. Supply of AcCoA transport and beta-oxidation of fatty acids 2. Regulation of PDH 3. Supply of NAD+ and FAD 4. Availability of ADP+Pi and oxygen (to make ATP) 5. Regulation of enzymes Rule of thumb: Inhibition downstream means inhibition of everything upstream of it

Question 26

Arsenic poisoning

Answer 26

Affects enzymes that use lipoic acid as a cofactor (PDH, alpha-ketoglutarate DH)

Question 27

Fumarase deficiency

Answer 27

Autosomal recessive with reduced enzyme activity and inhibits all steps upstream. Neurological impairment, encephalomyopathy, dystonia.

Question 28

When there is a need for other nutrients how can TCA cycle be used?

Answer 28

Certain intermediates can go through anabolic reactions to be turned into fatty acids, sterols, amino acids (which can make neurotransmitters), heme (through succinyl CoA to ALA synthase and glycine)

Question 29

Pyruvate carboxylase

Answer 29

Converts pyruvate to oxaloacetate which is what joins with Acetyl CoA in the first step of TCA cycle. Also main enzyme in gluconeogenesis.

Question 30

Oxaloacetate

Answer 30

Intermediate of TCA cycle which reacts with Acetyl CoA to produce citrate in the first step of TCA cycle

Question 31

beta-oxidation

Answer 31

Oxidative degeneration of fatty acids. Fatty acids are cleaved into 2 carbon units to yield Acetyl CoA to enter into TCA cycle. With each cleavage 1 NADH and 1 FADH are formed.

Question 32

Which enzymes are regulated by Succinyl CoA?

Answer 32

1. Citrate synthase 2. alpha-ketoglutarate dehydrogenase (the intermediate comes back to inhibit earlier steps when TCA cycle is full)