Lecture 29 - Lipid Metabolism II COPY

Question 1

What is the most energy dense fuel used by the body?

L29 S4

Answer 1

TAGs which are contain about 6.75 times as much energy as carbohydrates

Question 2

Where do TAGs come from?

L29 S8

Answer 2

• intestines (dietary)
• liver (de novo)
• adipocytes (de novo)

Question 3

What are the enzymes responsible for TAG breakdown?

L29 S10

Answer 3

Adipose triglyceride lipase (ATGL):
-breaks down TAG to DAG

Hormone sensitive lipase (HSL):
-breaks down DAG to MAG

MAG lipase:
-breaks down MAG to fatty acid and glycerol

Question 5

What are the major regulators of mobilization of fatty acids?

L29 S10

Answer 5

Promotes:

• hunger
• exercise
• glucagon
• epinephrine

Inhibits:

• fed state
• insulin

Question 6

What are the main steps of fatty acid breakdown and where does each step take place?

L29 S15

Answer 6

Activation and trapping of fatty acid (cytosolic)

Beta-oxidation (mitochondrial)

Question 7

What is acyl-CoA synthase and what is it the mechanism?

L29 S16

Answer 7

Converts fatty acid to acyl-CoA using ATP and CoA.

2 steps:

• cleavage of ATP to form acyl adenylate (acyl + AMP) and pyrophosphate
• replacement of AMP with CoA to form acyl-CoA

Question 8

How does acyl-CoA get into the mitochondria?

L29 S17

Answer 8

• cytosolic carnitine acyltransferase I attaches acyl to carnitine removing CoA
• acyl carnitine goes through translocator in mitochondrial membranes
• mitochondrial matrix carnitine acyltransferase II removes acyl from carnitine and replaces CoA
• carnitine is recycled to cytoplasm to be reused

Question 9

What are the 4 steps of β-oxidation and what enzyme catalyzes each step?

L29 S19

Answer 9

• oxidation (acyl CoA dehydrogenase)
• hydration (enoyl CoA hydratase)
• oxidation (3-hydroxyacyl CoA dehydrogenase)
• thiolysis (acetyl CoA acetyltransferase)

Question 10

What is the reaction catalyzed by acyl CoA dehydrogenase?

L29 S20

Answer 10

Oxidation of β carbon using FAD+ to form trans fatty enoyl CoA and FADH2.

FADH2 is used by complex 2 of ETC to generate 2 ATP

Question 11

What is the reaction catalyzed by enoyl CoA hydratase?

L29 S20

Answer 11

Enoyl-CoA + H20 -> β hydroxyl acyl CoA

Question 12

What is the reaction catalyzed by β hydroxy acyl CoA dehydrogenase?

L29 S20

Answer 12

β-hydroxyacyl CoA + NAD+ -> β-ketoacyl CoA + NADH

NADH is used by complex I of ETC to generate 3 ATP

Question 13

What is the function of acyl CoA acyl transferase (or ketothiolase)?

L29 S21

Answer 13

Attaches CoA at β ketone and cleaves acetyl CoA from chain (shortens by 2C)

Question 14

What molecules are produced by fatty acid break down that are used to generate energy?

L29 S23

Answer 14

• FADH2 (2 ATP through complex 2)
• NADH (3 ATP through complex I)
• Acetyl CoA (through TCA cycle)

Question 15

How much ATP is generated by breaking down palmitic acid (16C)?

L29 S24

Answer 15

• 7 FADH2 x 2 ATP (14 ATP)
• 7 NADH X 3 ATP (21 ATP)
• 8 acetyl CoA x 12 ATP (96 ATP)

Minus 2 ATP used during breakdown
——————————————————
Net ATP 129

Question 16

What molecule is needed for acetyl CoA to be used in the TCA cycle?

L29 S25

Answer 16

Oxaloacetate is needed with acetyl CoA for used by citrate synthase.

Low carb will result in low acetyl CoA

Question 17

What are ketone bodies, where are they produced and what are they used for?

L29 S27

Answer 17

Ketone bodies:

• acetoacetate
• β-hydroxybutyrate
• aceton

Produced in the liver through excessive β-oxidation

Provide energy in peripheral tissues during fasting condition and for the brain during starvation

Question 18

What is perilipin and what regulates it?

L29 S12

Answer 18

Proteins that coat lipid droplets and regulate lipolysis

Regulated by PKA and PP1

PKA phosphorylates allowing access for lipolysis enzymes (ATGL and HSL)
PP1 dephosphorylates reversing this