Metabolism VII: TAGs, FAs, and Ketone Bodies

Question 1

_______ account for 90-95% of dietary fat.

Answer 1

triacylglycerols

Question 2

Fatty acids account for ______ of biologically available energy.

Answer 2

95% (we get a lot of ATP dollars in fatty acid synthesis!)

Question 3

When there is a need for substrates for energy production, fatty acids are mobilized from what/where?

Answer 3

they are mobilized from TAGs in adipose tissue

Question 4

Hormone-sensitive triacylglycerol lipase (HSTL) is activated by what?

Answer 4

cAMP-dependent protein kinase A

Question 5

What is phosphorylated at the same time as HSTL? What is it necessary for?

Answer 5

perilipin, which is necessary for HSTL to translocate to the surface of the fat droplet and hydrolyze TAGs (it is essential for the mobilization of fats in adipose tissue)

Question 6

Which tissues/organs are good users of fatty acids?

Answer 6

liver, renal cortex, heart, skeletal muscle

Question 7

Which tissues do not / cannot use fatty acids as an energy source?

Answer 7

RBCs (lack mitochon.), brain, nervous system, adrenal medulla, lens

Question 8

Each cycle of beta-oxidation generates…

Answer 8

1 acetyl-CoA, 1 NADH, 1 FADH2

Question 9

How much total ATP is formed from beta oxidation?

Answer 9

106

Question 10

What is the function of carnitine? What does a carnitine deficiency result in?

Answer 10

Carnitine transports long-chain fatty acids into the MT matrix for beta-oxidation. Inhibition of transport results in inhibition of FA oxidation and therefore decreased production of ATP.

Question 11

What is the only known inhibitor of CPT-1?

Answer 11

malonyl-CoA

Question 12

Fatty acids are transported into the mitochondria as _________ for oxidation.

Answer 12

acylcarnitines

Question 13

Broadly describe what beta-oxidation is.

Answer 13

It is the catabolic process by which fatty acid molecules are broken down in the mitochondria to generate acetyl-CoA (which enters CAC to generate energy) as well as NADH and FADH2 (which are used in ETC to generate energy)

Question 14

What is the significance of NADH and FADH2 to the electron transport chain?

Answer 14

They are electron carriers that travel down the ETC to release their electrons and facilitate the end result of massive energy production.

Question 15

Why does malonyl-CoA inhibit CPT-1?

Answer 15

It is a product of the rxn catalyzed by Ac-CoA carboxylase (rate-lim. enzyme in FA biosynthesis). FA biosynthesis is counterproductive to FA breakdown, which is why malonyl-CoA (an indicator of FA biosynthesis) inhibits CPT-1 and thus the process of beta-oxidation.

Question 16

Ketone bodies are synthesized from ______ in _________ when there is a high rate of ____________.

Answer 16

acetyl-CoA; liver mitochondria; beta-oxidation of fatty acids

Question 17

What are the 3 main ketone bodies?

Answer 17

• acetone (simplest)
• acetoacetic acid
• beta-hydroxybutyric acid

Question 18

True or false: Ketone body biosynthesis occurs only in the liver, but ketone bodies cannot be utilized in the liver.

Answer 18

True!

Question 19

Where does ketone body utilization occur?

Answer 19

in the mitochondria of muscle, brain, and certain other tissues (heart, renal cortex).

Question 20

What does acetoacetate succinyl-CoA transferase (aka thiophorase) do?

Answer 20

It is involved with conversion of ketone bodies to acetyl-CoA, which is used in the TCA to generate energy (this is how tissues derive energy from ketogenesis). It does this by transferring CoA from succinyl-CoA to acetoacetate to ultimately produce acetyl-CoA.

Question 21

What is the rate-limiting enzyme in ketone biosynthesis?

Answer 21

HMG-CoA synthase (only found in liver)

Question 22

Where do ketone bodies partition?

Answer 22

• urine

- lungs (specifically acetone, but lungs blow acetone off quickly)