Biochemistry: lipids

Question 1

What is xanthelasma?

Answer 1

• A yellow deposit of cholesterol underneath the skin; usually occurs on or around the eyelids
• Results from high levels of cholesterol in the bloodstream
• They precipitate and deposit in blood vessels

Question 2

Describe the structure of cholesterol.

Answer 2

• A white crystalline solid
• Contains very few polar groups; water insoluble
• Belongs to the steroid chemical group

Question 3

What does cholesterol stacking lead to?

Answer 3

• Form cholesterol crystals in the urine, precipitate in the blood; potential heart disease

Question 4

Describe the synthesis of cholesterol.

Answer 4

• Synthesised in the liver
• Acetic acid becomes activated to acetyl coA and then combines via a series of steps using multiple enzymes to produce mevalonic acid

Question 5

What are fatty acids?

Answer 5

Carboxylic acids with an aliphatic chain which is either saturated or unsaturated

Question 6

What are the fatty acid isomers?

Answer 6

Cis: contains a double bond, does not stack, associated with healthy foods

Trans: straight chained fatty acid, can stack, unhealthy

Question 7

What are triglycerides and how are they formed?

Answer 7

• A type of lipid found in the blood
• Stored in fat cells
• Formed from three fatty acids and a glycerol molecule

Question 8

What are lipoproteins?

Answer 8

Complex particles with a central core containing cholesterol esters and triglycerides surrounded by free cholesterol, phospholipids and apolipoproteins.

Question 9

What does the formation of lipoproteins into a sphere allow for?

Answer 9

• An unreactive transport of lipids; due to small surface area

Question 10

What are the five major classes of circulating lipoproteins?

Answer 10

1. Chylomicrons
2. Very low-denisity lipoproteins
3. Low-density lipoproteins (unhealthy)
4. Intermediate density lipoproteins
5. High-density lipoproteins (healthy)

Question 11

Describe fat absorption.

Answer 11

1. Fats form an emulsion in the intestine
2. Achieved primarily by bile secretions
3. The emulsions form tiny particles called micelles
4. Micelles approach the cells of the intestinal wall and collapse
5. Fats and triglycerides are absorbed into the epithelial cells

Question 12

What is the role of bile salts?

Answer 12

Helps produce an emulsion from fats and intestinal aqueous juices in the intestine

Question 13

What is the advantage of an emulsification?

Answer 13

Tiny droplets have a larger surface area for lipase to work on

Question 14

How are lipoproteins made?

Answer 14

• Fatty acids and triglycerides become incorporated into chylomicrons in the Golgi body
• Chylomicrons pass primarily into the lymph system and then into the systemic bloodstream
• Chylomicrons can be metabolised in the body to generate other lipoproteins

Question 15

How do lipoproteins contribute to heart disease?

Answer 15

• Lipids are transported through the blood
• The low density lipoproteins begin to ‘stick’ to blood vessel walls - damaged