Ch. 17 Fatty Acid Metabolism

Question 1

Do all cells burn fatty acids?

Answer 1

No. All cells can burn glucose, but not all cells can burn fatty acids.

Question 2

What are triacylglycerides (TAGs)?

Answer 2

long term energy storage molecules (fatty acids)

Question 3

What is the energy stored in a TAG vs carbohydrates and why (3)?

Answer 3

TAGs store more energy than carbohydrates because they have more carbon, there is no water accompanying TAGs, and TAGs are reduced so there are more levels of oxidation to get to CO₂.
(carbohydrates are partially oxidized)

Question 4

How is the majority of energy stored in humans?

Answer 4

Mostly fat. Humans store ~50X more energy in fat than glycogen.

Question 5

What will fatty acids be metabolized to?

Answer 5

acetyl-CoA which will then go into the citric acid cycle.

Question 6

What are the two ways fatty acids can be acquired?

Answer 6

Through your diet/eating and from adipose cells.

Question 7

What is the mechanism of acquiring fatty acids from eating/diet? (7)

Answer 7

1. ingested fats mix with bile salts to solubilize them
2. lipases cleave FAs from glycerol backbone to produce FFAs
3. FFAs taken up by epithelial cells in digestive system
4. FFAs reassemble into TAGs
5. TAGs are assembled into chylomicrons
6. epithelial cells secrete chylomicrons into bloodstream
7. adipose cells (storage) and muscle cells (use) have receptors that bind chylomicrons

Question 8

What are bile salts?

Answer 8

Bile salts are amphipathic so they form micelles. Their precursor is cholesterol. They solubilize fats.

Question 9

What are chylomicrons?

Answer 9

A phospholipid MONOlayer with a completely hydrophobic interior containing TAGs and cholesterols. A way to make TAG and cholesterol soluble.

Question 10

What are apolipoproteins?

Answer 10

Proteins embedded in the phospholipid monolayer of chylomicrons that allow a receptor to bind to the chylomicron (“address label”)

Question 11

What is the mechanism of acquiring fatty acids from adipose cells? (6)

Answer 11

1. adipose cells receive signal via a receptor
2. signal transduction cascade occurs
3. adenylyl cyclase activates PKA which leads to activation of lipases in adipose cells
4. active lipases produce FFAs from TAGs
5. serum albumen binds FFAs and makes them soluble in the bloodstream
6. cells recognize, bind, and internalize serum albumen

Question 12

What is serum albumen?

Answer 12

A protein that binds FFAs and makes them soluble in cells.

Question 13

Where does β-oxidation take place?

Answer 13

In the mitochondrial matrix.

Question 14

How do FFAs get into the mitochondrial matrix to undergo metabolism?

Answer 14

It gets converted to acyl CoA and transported by an antiporter.

FFA + CoA + ATP → acyl CoA + AMP + PPᵢ

Question 15

What does the conversion of FFA to acyl CoA cost?

Answer 15

It costs two phosphoanhydrides to “activate” FFA to acyl CoA. (energy investment)

Question 16

Is acyl CoA soluble and where can it go?

Answer 16

It is free to diffuse through the cytosol and does. It can diffuse through the outer mito. membrane, but NOT the inner mito. membrane (no transport protein)

Question 17

How does acyl CoA get through the inner mitochondrial membrane?

Answer 17

A carnitine group is added to acyl CoA to produce acylcarnitine. Carnitine:Acylcarnitine translocase transports it across the membrane.

Question 18

What is the carnitine:acylcarnitine translocase?

Answer 18

An antiporter in the inner mito. membrane that transports acylcarnitine into the matrix while simultaneously transporting carnitine out of the matrix.

Question 19

What does the enzyme on the translocase do?

Answer 19

enzyme on the antiporter immediately cleaves carnitine off the acyl group and reattatches the FFA to CoA

Question 20

What is β-oxidation?

Answer 20

a spiral pathway of fatty acid metabolism; kind of circular but every revolution the fatty acid gets two carbons shorter

Question 21

What does each revolution of β-oxidation produce?

Answer 21

Every revolution produces acetyl-CoA, FADH₂, and NADH

Question 22

What is the β-oxidation net reaction of ONE revolution?

Answer 22

Rₙ-CoA + NAD⁺ + FAD + CoA + H₂O → acetyl-CoA + NADH + H⁺ + FADH₂ + Rₙ_₂-CoA

Question 23

How do you determine the number of revolutions a fatty acid will undergo and why?

Answer 23

of revolutions = (# of C / 2) - 1
The last revolution produces acetyl-CoA so subtract 1.

Question 24

What are the total products for β-oxidation and the citric acid cycle? (one round)

Answer 24

β-oxidation: (C/2) acetyl-CoA, (C/2)-1 NADH, and (C/2)-1 FADH₂
Citric Acid Cycle (for one acetyl-CoA): 3NADH, 1 FADH₂, and 1 GTP/ATP

Question 25

What is the NADH and FADH₂ conversion factor for ATP?

Answer 25

1 NADH = 3 ATP 1 FADH₂ = 2 ATP

Question 26

Why does fatty acid metabolism need regulation?

Answer 26

Acetyl-CoA can either go into the citric acid cycle (catabolism in mitochondria) or fatty acid synthesis (anabolism in cytosol).

Question 27

What is the main regulatory mechanism for fatty acid metabolism?

Answer 27

Carnitine:Acylcarnitine Translocase is the main regulatory enzyme.

Question 28

How is Carnitine:Acylcarnitine Translocase inhibited?

Answer 28

Inhibited my malonyl-CoA which is synthesized from acetyl-CoA. Inhibition of this enzyme means there is no feedstock for β-oxidation (literally denying substrate).

Question 29

What else is regulated in β-oxidation (2) and how?

Answer 29

Two enzymes in β-oxidation are inhibited by high [NADH]/[NAD⁺] ratios. (feedback inhibition; if there is a lot of NADH you don't need more)

Question 30

What are ketone bodies?

Answer 30

Something that acetyl-CoA can be converted to in the liver. There are three major ketone bodies. (NOT produced from anything other than acetyl-CoA)

Question 31

Can all tissues use ketone bodies as fuel/energy?

Answer 31

No. Only some tissues can use ketone bodies as fuel.

Question 32

Which cells can use ketone bodies (2)? Which cannot (1)?

Answer 32

Brain and muscle can use them. The liver CANNOT use them.

Question 33

What is the pathway to make ketone bodies? (3)

Answer 33

1. two acetyl-CoA come together to produce acetoacetyl-CoA via thiolase 2. acetoacetyl-CoA and acetyl-CoA produce HMG-CoA (which is a precursor to cholesterol synthesis) 3. HMG-CoA is converted to acetoacetate (and from there can become any other ketone body)

Question 34

Why are ketone bodies important?

Answer 34

The brain needs something to use if glucose runs out. Ketone bodies are what it can use.