Lipid Metabolism

Question 1

What is the main form of fat storage in animals?

Answer 1

Triglycerides

Question 2

Are triglycerides found in cell membranes?

Answer 2

No

Question 3

What are the four main steps of fatty acid oxudation?

Answer 3

• Lipolysis
• Activation
• Transport to mitochondria
• β-oxidation

Question 4

What happens during lipolysis?

Answer 4

Triglycerides are hydrolysed into glycerol and 3 fatty acids

Question 5

Where does lipolysis occur and what enzyme regulates it?

Answer 5

Regulated by hormone sensitive lipases and occurs in the cytoplasm

Question 6

What happens to glycerol after lipolysis?

Answer 6

It enters glycolysis or gluconeogenesis

Question 7

How are fatty acids activated for oxidation?

Answer 7

By binding CoA to form fatty acyl-CoA

Question 8

What enzyme actiavtes fatty acids?

Answer 8

Acyl-CoA synthase

Question 9

What energy molecules are used during fatty acid activation?

Answer 9

ATP –> AMP + 2 inorganic phosphate

Question 10

How are fatty acyl-CoAs trasnported into mitochondria?

Answer 10

Via the carnitine shuttle system

Question 11

Where does β-oxidation occur?

Answer 11

In the mitochondria

Question 12

What is removed from fatty acids during β-oxidation?

Answer 12

Two carbon units per cycle

Question 13

What are the four steps of one β-oxidation cycle?

Answer 13

• Dehydrogenation
• Hydration
• Oxidation
• Thiolysis

Question 14

What does dehydrogenation in the β-oxidation cycle produce?

Answer 14

FADH2

Question 15

What does oxidation in the β-oxidation cycle produce?

Answer 15

NADH

Question 16

What does thiolysis in the β-oxidation cycle produce?

Answer 16

Actetyl-CoA

Question 17

What are the products of one β-oxidation cycle?

Answer 17

• 1actetyl CoA
• NADH
• FADH2

Question 18

What happens to the acetyl-CoA produced in β-oxidation?

Answer 18

It enters the citric acid cycle and is oxidised for ATP production

Question 19

How much ATP is produced from each round of β-oxidation?

Answer 19

About 14 ATP

Question 20

Why do lipids yield more energy per carbon than carbohydrates?

Answer 20

Fatty acids produce around 7 ATP per carbon while glucose produces around 5.3 ATP per carbon

Question 21

What happens to odd-chain fatty acids during oxidation?

Answer 21

Produce propionyl-CoA

Question 22

What is the fate of propionyl-CoA in metabolism?

Answer 22

Converted into succinyl-CoA which enters the citric acid cycle and can be used in gluconeogenesis

Question 23

Where does fatty acid synthesis occur in the cell?

Answer 23

In the cytoplasm

Question 24

What is the first step required for fatty acid synthesis to begin?

Answer 24

Transport acteyl-CoA from the mitochondria to the cytoplasm

Question 25

How is acteyl-CoA transported from mitochondria to cytoplasm?

Answer 25

As citrate

Question 26

What enzyme converts acetyl-CoA to malonly-CoA?

Answer 26

Acetyl-CoA carboxylase

Question 27

What molecule carries intermediates in fatty acid synthesis?

Answer 27

Acyl Carrier Protein ACP

Question 28

What are the 5 steps of fatty acid chain assembly?

Answer 28

- Loading acetyl-Coa and Malonyl-CoA onto ACP - Condensation to form acetoacetyl-ACP - Reduction of ketone to alcohol - Dehydration to form double bonds - Reduction to convert double bond to single

Question 29

What is the final product of standard fatty acid synthesis?

Answer 29

Palmitate

Question 30

How many NADPH are used to synthesise one palmitate molecule?

Answer 30

14 NADPH

Question 31

What are the two main sources of NADPH for fatty acid synthesis?

Answer 31

- Citrate transport system - Pentose phosphate pathway

Question 32

What enzyme adds carbons to fatty acids after synthesis?

Answer 32

Elongase

Question 33

What enzyme introduces double bounds in fatty acids after synthesis?

Answer 33

Desaturase

Question 34

What three hormones are involved in the regulation of lipid metabolism?

Answer 34

- Arenaline - Glucagon - Insulin

Question 35

What effects does adrenaline have on lipid metabolism?

Answer 35

- Increase oxidation effect - Decrease synthesis effect

Question 36

What effects does glucagon have on lipid metabolism?

Answer 36

- Increase oxidation effect - Decrease synthesis effect

Question 37

What effects does insulin have on lipid metabolism?

Answer 37

- Decrease oxidation effect - increase synthesis effect

Question 38

What are the three ketone bodies produced during ketogenesis?

Answer 38

- Acetoacetic acid - 3 hydroxybutyric acid - Acetone

Question 39

What triggers the formation of ketone bodies?

Answer 39

An excess of acetyl-CoA that cannot be oxidised by the citric acid cycle

Question 40

Where does ketogenesis occur?

Answer 40

In the mitochondria of liver cells

Question 41

What are the two ways acetoacetic acid can be converted during ketogenesis?

Answer 41

- Reduced to 3 hydroxybutyric acid - Spontaneously decaboxylate to acetone

Question 42

What determines whether acteyl-CoA enters the citric acid cycle or ketogenesis?

Answer 42

The mitochondrial concentration of oxaloacetate

Question 43

What does high oxaloacetate concentration favor?

Answer 43

Oxidation - entering the citric acid cycle

Question 44

What does low oxaloacetate concentration favor?

Answer 44

Ketogenesis

Question 45

When is oxaloacetate concentration low?

Answer 45

During fasting or a low carbohydrate diet

Question 46

What are the two common precursors for triacylglycerol and phospholipid synthesis?

Answer 46

- Fatty acyl-CoA - Glycerol 3 phosphate

Question 47

How are fatty acids activated for metabolism?

Answer 47

By forming CoA thioester bond

Question 48

What is fatty acid activation for metabolism catalysed by?

Answer 48

Acyl-CoA synthetase

Question 49

What pathway provides glycerol 3 phosphate for lipid synthesis?

Answer 49

Glycolysis or gluconeogenesis

Question 50

How is triacylglycerol synthesised?

Answer 50

Glycerol-3-phosphate is esterified with three fatty acyl-CoAs

Question 51

How are phospholipids synthesised from diaglycerol?

Answer 51

A polar head group is added to diacylglycerol

Question 52

What two components combine to form sphingosine in sphingolipid synthesis?

Answer 52

- Palmitoyl-CoA - Serine

Question 53

What molecule is a precursor for both cholesterol and many other lipid soluble biomolecules?

Answer 53

Isopentenyl pyrophosphate

Question 54

Outline the simplified pathway of cholesterol synthesis starting from acetyl-CoA?

Answer 54

- Acetyl-CoA - Mevalonate - Isopentenyl pyrophosphate - Squalene - Cholesterol

Question 55

What are three situation that can lead to excess ketone body production?

Answer 55

- Starvation - Diabetes mellitus - High glucose demand in ruminants

Question 56

What are clinical signs of ketosis?

Answer 56

- Acetone smell on breath - Ketoacidosis - Hypoglycemia - Decreased milk production - Loss of appetite - Diarrhoea