Lipid Metabolism

Question 1

PPARs

Answer 1

nuclear hormone receptors which bind directly to hormones which diffuse into the nucleus, then change conformation and initiate transcription.

Question 2

Saturated fatty acids can bind to some PPARs and thereby increase the expression of genes involved in. . .

Answer 2

Saturated fatty acids can bind to some PPARs and thereby increase the expression of genes involved in cholesterol and fat synthesis.

Question 3

Unsaturated fatty acids can bind to some PPARs and thereby increase the expression of genes involved in. . .

Answer 3

breakdown of fat and repression of fat and cholesterol synthesis.

Question 4

Diets that include high amounts of ___ and ___ may promote fat synthesis

Answer 4

Diets that include high amounts of saturated and trans fats may promote fat synthesis, which can lead to insulin resistance and cardiovascular disease.

Question 5

The rate-limiting step of fatty acid synthesis

Answer 5

Acetyl-CoA carboxylase

Question 6

The fatty acids produced in lipogenesis will be packaged into triglycerides and exported from the liver in the form of ___.

Answer 6

The fatty acids produced in lipogenesis will be packaged into triglycerides and exported from the liver in the form of VLDL.

Question 7

β-oxidation provides. . .

Answer 7

Acetyl-CoA

NADH

FADH₂

Question 8

______ are more atherogenic (lead to formarmation of plaques in arteries) than cholesterol itself.

Answer 8

Saturated fats and trans fats are more atherogenic (lead to formarmation of plaques in arteries) than cholesterol itself.

Question 9

Palmitate and Stearate

Answer 9

Question 10

“Essential” fatty acids

Answer 10

Linoleic acid and α-linolenic acid

Question 11

Humans do not have the machinery to introduce ____ into oleic acid.

Answer 11

Humans do not have the machinery to introduce the second double bond into oleic acid.

We therefore need to get polyunsaturated fats in the diet.

Question 12

Important α-linolenic acid derivatives

Answer 12

EPA and DHA

Question 13

Linoleic acid

Answer 13

Question 14

α-linolenic acid

Answer 14

Question 15

In the fed state, excess glucose is. . .

Answer 15

. . . converted into fat by the liver and sent to adipose tissue for storage.

Question 16

Acetyl-CoA traverses the mitochondrial membrane in the form of. . .

Answer 16

citrate

Question 17

For efficient synthesis of fatty acids from glucose, ____ are required.

Answer 17

For efficient synthesis of fatty acids from glucose, mitochondria are required.

This is for two reasons: 1. PDH is only present in the mitochondrial matrix, and 2. the main source of Acetyl-CoA for fatty acid synthesis comes from citrate which traverses the mitochondrial membrane.

Question 18

Acetyl-CoA Carboxylase mechanism

Answer 18

Question 19

Malonyl CoA inhibits. . .

Answer 19

beta oxidation

This ensures that lipogenesis and lipolysis are not occuring simultaneously.

Question 20

Regulation of Acetyl-CoA Carboxylase

Answer 20

Question 21

Fatty acid biosynthesis mechanism

Answer 21

Question 22

Reaction catalyzed by hormone sensitive lipase

Answer 22

Hydrolysis of the first of the three acyl chains on a triacylglyceride, producing one fatty acid and a diacylglyceride.

Question 23

Hormone sensitive lipase regulation

Answer 23

Question 24

Perlipin

Answer 24

Protein on the adipocyte lipid droplet membrane which, when activated by glucagon -> PKA phosphorylation, enables hormone sensitive lipase to access lipid droplets.

Question 25

Charging of fatty acids prior to the beginning of β-oxidation

Answer 25

Question 26

Rate limiting step for β-oxidation

Answer 26

Movement of fatty acids to the mitochondrial matrix

Question 27

Carnatine transport

Answer 27

Question 28

Regulatory role of malonyl CoA

Answer 28

Question 29

β-oxidation mechanism

Answer 29

Question 30

Comparing products of glucose and fatty acid metabolism

Answer 30

Question 31

Why couldn't you just run the cell on β-oxidation without ever using the TCA cycle or PDH?

Answer 31

**Lack of enough CoA** However, this can be partially overcome in times of excessive β oxidation by **using fatty acids to make ketone bodies**.

Question 32

After a one to two day fast, ____ begins to accumulate in the liver greater than the level that is needed to meet energy needs.

Answer 32

After a one to two day fast, **acetyl-CoA** begins to accumulate in the liver greater than the level that is needed to meet energy needs. This is what **triggers ketogenesis**

Question 33

Context of ketogenesis

Answer 33

Question 34

Circulating ketone bodies are important for maintaining ____ during periods of starvation.

Answer 34

Circulating ketone bodies are important for maintaining **muscle mass** during periods of starvation. They reduce the demand on amino acids for carbon skeletons, allowing muscle to avoid degradation for brain fuel.

Question 35

Ketone body biosynthesis

Answer 35

Takes place in the mitochondrial matrix

Question 36

\_\_\_\_ is shared by both the ketone body biosynthetic pathway and the steroid biosynthetic pathway.

Answer 36

**HMG-CoA Synthase** is shared by both the ketone body biosynthetic pathway and the steroid biosynthetic pathway.

Question 37

Ketone bodies are _____ and can be thought of as _____ forms of fatty acids.

Answer 37

Ketone bodies are **hydrophilic** and can be thought of as **water-soluble** forms of fatty acids.

Question 38

Ketone body utilization

Answer 38

Question 39

Only cells expressing ____ may harness ketone bodies as an energy source.

Answer 39

Only cells expressing **thiophorase** may harness ketone bodies as an energy source.

Question 40

Propionyl CoA metabolism

Answer 40

Question 41

Major steps in propionyl CoA metabolism

Answer 41

1. **Carboxylation** by **propionyl-CoA carboxylase** and **biotin** 2. **Enantiomerization** by **methylmalonyl-CoA racemase** 3. **Reorganization** to **succinyl-CoA** by **methylmalonyl-CoA mutase** and **cobalamine** 4. Conversion to **malate via the TCA cycle** 5. **Oxidative decarboxylation** to **pyruvate** and **CO₂** by **malic enzyme**, also producing **NADPH**