Fat Metabolism

Question 1

what are lipids ? (4 points)

Answer 1

1. includes fats and oils
2. composed predominantly (but not exclusively) of Carbon, Hydrogen and Oxygen atoms
3. atoms are linked by non-polar covalent bonds
4. lipids are non-polar and have a very low solubility in water

Question 2

what are the 4 sub-classes of lipids ?

Answer 2

1. fatty acids
2. triglycerides
3. phospholipids
4. steroids

Question 3

state 3 reasons to why fats are important

Answer 3

1. energy storage (triglycerides –> adipocytes)
2. membrane structure (phospholipids)
3. hormones and signalling compounds (steroids)

Question 4

what, in essence, are fatty acids ?

Answer 4

a fatty acid is a carboxyl group bound to a hydrocarbon

Question 5

what is the difference between cis and trans fats ?

Answer 5

1. cis double bond = both H in same orientation (side) of the bound carbon atoms
2. trans double bond = H atoms are on opposite sides if the bound carbon atoms

Question 6

‘triglycerides are stored in adipocytes’ - state 3 facts to describe this statement

Answer 6

1. food intake: adipocytes synthesise and store triglycerides
2. non-food intake: adipocytes release fatty acids and glycerol into the blood
3. used by other cells to provide energy for ATP synthesis

Question 7

state 3 facts about steroids

Answer 7

1. four interconnected rings of carbon atoms
2. insoluble in water
3. examples: cholesterol, steroid hormones

Question 8

state, and explain, the 3 places where fatty acids come from

Answer 8

1. adipose tissue: fat storage cells can release fats when needed
2. de novo synthesis: made from carbohydrates and some amino acids
3. diet: about 30-40% of calories in the diet come from fats

Question 9

what does the pancreas secrete for lipid digestion ?

Answer 9

the pancreas secretes digestive enzymes (including lipases) as well as bicarbonate

Question 10

what does the liver secrete for lipid digestion ?

Answer 10

the liver secretes bile (detergent –> emulsifies lipids)

Question 11

what are the following for fats in the body:

1) total bontent (kg)
2) energy content per gram
3) total body energy content (kcal)
4) percentage of total energy content

Answer 11

1. 15.6 Kg
2. 9 kcal / gram
3. 140,000 kcal
4. 78%

Question 12

what are the following for proteins in the body:

1) total bontent (kg)
2) energy content per gram
3) total body energy content (kcal)
4) percentage of total energy content

Answer 12

1. 9.5 Kg
2. 4 kcal / gram
3. 38,000 kcal
4. 21%

Question 13

what are the following for carbohydrates in the body:

1) total bontent (kg)
2) energy content per gram
3) total body energy content (kcal)
4) percentage of total energy content

Answer 13

1. 0.5 Kg
2. 4 kcal / gram
3. 2000 kcal
4. 1%

Question 14

state the 3 steps of fat metabolism

Answer 14

1. lipid mobilisation of adipose tissue
2. activation and transport
3. fatty acid oxidation

Question 15

explain, in brief, the first step of fat metabolism (2 points)

Answer 15

1. triglycerides are degraded to fatty acids and glycerol

2. released from adipose tissue and transited to energy releasing tissue

Question 16

explain, in brief, the first second of fat metabolism

Answer 16

in energy requiring tissue, fatty acids are activated and transported into the mitochondria for degradation

Question 17

explain, in brief, the first third of fat metabolism

Answer 17

fatty acid oxidation produces Acetyl CoA, which is then processed into the CTA

Question 18

briefly explain the reaction, and state the enzyme, of the first reaction of fat metabolism

Answer 18

1) fatty acid + CoA + ATP —> Acetyl CoA + AMP + PPi

2) Acetyl CoA synthetase

Question 19

briefly explain the reaction, and state the enzyme, of the second reaction of fat metabolism

Answer 19

1) carnitine + Acyl CoA —-> acylcarnitine + CoA

2) carnitine acyltransferase

Question 20

briefly explain the reaction, and state the enzyme, of the third reaction of fat metabolism

Answer 20

1) Acyl CoA + E-FAD —-> Trans-Δ²-enoyl CoA + E-FADH2

2) Acetyl CoA dehydrogenases

Question 21

briefly explain the reaction, and state the enzyme, of the fourth reaction of fat metabolism

Answer 21

1) trans-Δ-enoyl CoA + H2O —-> L-3-hydroxyacyl CoA

2) enol CoA hydratase

Question 22

briefly explain the reaction, and state the enzyme, of the fifth reaction of fat metabolism

Answer 22

1) L-3-hydroxyacyl CoA + NAD+ —-> 3 ketoacyl CoA + NADH + H+
2) L-3-dehydroxyacyl CoA dehydrogenase

Question 23

briefly explain the reaction, and state the enzyme, of the sixth reaction of fat metabolism

Answer 23

1) ketoacyl CoA + CoA —-> Acetyl CoA + Acetyl CoA (shortened by 2C)
2) B-ketothiolase

Question 24

what are ketone bodies (2 points)

Answer 24

1. energy rich

2. water soluble

Question 25

state the cellular location of: 1) fat synthesis, 2) fat breakdown

Answer 25

1) cytoplasmic

2) mitochondria

Question 26

state the coenzyme(s) of: 1) fat synthesis, 2) fat breakdown

Answer 26

1) NADP+/NADPH

2) NAD+/NADH, FAD/FADH

Question 27

state the enzyme characteristics of: 1) fat synthesis, 2) fat emulsification

Answer 27

1) a single polypeptide chain (fatty acid synthase)

2) not covalently linked

Question 28

state what the intermediaries are bound to in: 1) fat synthesis, 2) fat emulsification

Answer 28

1) acetyl carrier protein (ACP)

2) Acetyl CoA

Question 29

state the names of the 3 steps of fatty acid biosynthesis (in order)

Answer 29

1. carboxylation of Acetyl CoA and linkage to ACP
2. elongation
3. removal of ACP