Metabolism 6 - Lipid Metabolism

Question 1

What is the structure of palmitate?

Answer 1

It is a 16 carbon fatty acid. Has a hydrophylic carboxylic acid head and a hydrophobic hydrocarbon tail.

Question 2

What are the two forms of fatty acids?

Answer 2

Fatty acids can be saturated (all single bonds) or unsaturated (some souble bomds which create a kink and mean that when stored the triaglycerol compounds will be liquid).

Question 3

What type of cells store fatty acids?

Answer 3

Adipocytes store fatty acids as triaglycerol compounds.

Question 4

What are the three primary sources of fat?

Answer 4

The diet, de novo synthesis (liver) and storage in adipocytes.

Question 5

What is the function of bile salts?

Answer 5

Bile salts in the intestine act as an emulsifier, which aids digestion and fat absorption. They also aid digestion of fat soluble vitamins.

Question 6

Where are bile salts generated, stored and used?

Answer 6

They are generated in the liver, stored in the gallbladder and used in the intestine.

Question 7

What disease is caused by a lack of bile salts?

Answer 7

Steatorrhea occurs - fatty stools as the majority of fat passes through the gut undigested and unabsorbed.

Question 8

What is orlistat?

Answer 8

A drug ehich inhibits gastric and pancreatic lipases, which reduces the absorption of fat. It is used to treat obesity, but can cause abdominal pain, urgency to defecate, increased flatus and steatorrhea.

Question 9

What is another name for fatty acid metabolism?

Answer 9

B-oxidation

Question 10

Where does fatty acid metabolism occur?

Answer 10

In the mitochondria, primarily in the liver. It cannot occur in the brain.

Question 11

Summarise beta oxidation

Answer 11

1) Fatty acids converted to acyl coA by acyl coA synthetase. Uses HS-CoA and converts ATP to AMP.
2) There is then oxidation using FAD, hydration, oxidation using NAD and thiolysis.
3) This produces aceyl coA and an acyl coA two carbons shorter than the origional

Question 12

What is the carnitine shuttle?

Answer 12

The shuttle which transports acyl CoA into the mitochondria, after it is generated at the outer mitochondrial membrane. Carnitine is converted to acyl carnitine, which travels through a translocase and is converted back to carnitine. The first stage uses Acyl CoA, and the second makes it. The enzymes used are both carnitine acyltransferase (I is first and then II inside the mitochondria).

Question 13

What are the enzymes used in the beta oxidation cycle?

Answer 13

3-hydroxyacyl CoA hydrolase, L-3-hydroxyacyl CoA dehydrogenase, B-ketothiolase.

Question 14

What happens if an odd chain fatty acid undergoes beta-oxidation?

Answer 14

Propionyl coA is produced in the final stage, which must be converted to succinyl coA. Succinyl coA can enter the TCA cycle.

Question 15

What is the overall reaction of B-oxidation of palmitate, and how many cycles occur?

Answer 15

There are 7 cycles to break down a 16 carbon chain.

Palitoyl coA + 7FAD + 7NAD+ +7H2O + 7CoA —> 8 acetyl coA + 7FADH2 + 7NADH

Question 16

What conditions are required for acetyl coA from B-oxidation to enter the krebs cycle?

Answer 16

B-oxidation and carbohydrate metabolism must be balanced, as oxaloacetate is needed for the entry of acetyl coA.

Question 17

What happens when fat breakdown predominates (during fasting)?

Answer 17

Acetyl coA forms acetoacetate, D 3-hydroxybutyrwte and acetone (ketone bodies) which can be respired in the brain, alongside glucose.

Question 18

What enzymes are used in fatty acid synthesis?

Answer 18

Acetyl coA carboxylase and fatty acid synthesase (which has 7 different activities)

Question 19

What activities occur following each round of elongation?

Answer 19

Reduction and dehydration by the act of ketoreductase, dehydratase and enol reductase.

Question 20

Summarise the stages of lipgenesis.

Answer 20

1) 3C species malonyl coA is formed by the reaction of acetyl coA with HCO3. This uses ATP and acetyl coA carboxylase.
2) Malonyl coA is transferred to ACP to form Malonyl ACP. This is catalysed by malonyl coA-ACP transferase
3) Acetyl from the CoA species is converted to ACP using Acetyl-CoA-ACP transferase
4) 2 molecules of acetyl ACP react to form malonyl ACP making acetoacyl ACP
5) Reduction, dehydration, reduction occurs
6) Final products: palmitate and ACP

Question 21

What are the differences between synthesis and degradation of fatty acids?

Answer 21

Synthesis uses ACP, degradation uses CoA
Synthesis uses NADPH, degradation uses FAD/NAD+
Synthesis occurs in the cytoplasm, degradation takes place in the mitochondrial matrix.

Question 22

What enzymes are used for desaturation of fatty acids?

Answer 22

Fatty acyl-coA desaturases

Question 23

What is MCADD?

Answer 23

Medium chain acyl-coenzyme A dehydrogenase deficiency (MCADD) is where the enzyme that catalyses the initial step of B-oxidation. When diagnosed patients cant fast for more than 10-12 hours, and need a high carb diet.

Question 24

What is primary carnite deficiency?

Answer 24

This is an autosomal recessive disorder where a non functional carnitine transporter is non functional, and carnitine cannot be transported into the cell. Carnitor is used as a supplement.