Lipid Metabolism

Question 1

What are the three classes of lipids ?

Answer 1

1) fatty acid derivatives - for example phospholipids and triacylglycerols (TAGs).
2) vitamins eg A , D, E and K
3) hydroxy-methyl-glutaric acid derivatives ( c6 compound) for example ketone bodies

Question 2

In a healthy 70kg man, what is the energy content of triacylglycerols?

Answer 2

-600,000kJ

Question 3

I’m an obese 135 kg man , what is the energy content of triacylglycerols ?

Answer 3

-3,000,000kJ

Question 4

Where are Tag’s stored

Answer 4

Adipose tissue

Question 5

When are TAG’s actually used ?

Answer 5

During starvation period , in prolonged exercise , during pregnancy

Question 6

Storage/mobilisation is under …. control

Answer 6

Hormonal

Question 7

Are tags hydrophobic or hydrophilic

Answer 7

Hydrophobic

Question 8

Outline the process by which dietary fats are metabolised

Answer 8

1) bile salts in the small intestine emulsify fats , forming mixed micelles.
2) Pancreatic lipases hydrolyse fats in the small intestine extracellulary.
3) fatty acids and glycerol are recombined into triacylglycerols.
4) they are transported as triacylglycerols by lipoproteins called chylomicrons.
5) released into circulation via the lymphatic system
6) carried to adipose tissue where it is stored as TAGs ( fat mobilisation is hormonally controlled , eg they are metabolised when glucagon and adrenaline are high and insulin is low)
7) carried to consumer tissues as albumin - fatty acid complex

Question 9

What two cells/tissues do not require triacylglycerols ?

Answer 9

1) cells without mitochondria for example red blood cells

2) not the brain as fatty acids do not easily pass through the blood brain barrier

Question 10

Outline the TAG cycle in the adipose tissue

Answer 10

1) when glucose undergoes glycolysis , glycerol-1-phosphate undergoes esterfication with fatty acyl CoA to make triglycerides. This then undergoes lysis which produces fatty acids on albumin and glycerol.

Question 11

Define amphipathic

Answer 11

Contains both hydrophilic and hydrophobic groups

Question 12

Where does fatty acid catabolism occur

Answer 12

In the mitochondria

Question 13

What is the first step of fatty acid metabolism ?

Answer 13

ACTIVATION OF FATTY ACID

Question 14

Outline the process by which fatty acids are activated and where in a cell does this occur ?

Answer 14

• occurs in the cytoplasm ( not mitochondria).
• they are activated by combining with coenzyme A.
• this is aided by the enzyme fatty acyl coA synthase.
• coA+ fatty acid + ATP = AMP +2pi+ fatty-acyl-coA.

Question 15

What is the second step of fatty acid metabolism - after they have been activated ?

Answer 15

Fatty acyl coA cannot cross the inner mitochondria so they have Carnitine shuttle help.

• this transports fatty acyl coA across the inner membrane.

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Question 16

What is the 3rd step of fatty acid metabolism - after they have been transported across the inner mitochondrial membranes?

Answer 16

.Beta oxidation of fatty acids occur.

• this makes acetyl coA and FADH2 and NADH.
• acetyl coA can then enter Krebs cycle and FADH2 and NADH can enter oxidative phosphorylation

Question 17

How many carbon units are removed per beta oxidation cycle ?

Answer 17

2C

Question 18

Is ATP produced during beta oxidation ?

Answer 18

No

Question 19

Does beta oxidation require the presence of O2?

Answer 19

Yes;

Question 20

How is glycerol then metabolised ?

Answer 20

• transported to the live .
• glycerol kinase converts glycerol into glycerol phosphate ( using ATP).
• this can then be used to make TAGs
• or it is oxidised to make dihydroxyacetone phosphate (DHAP) which is an intermediate that can enter glycolysis. This in turn makes NADH.

Question 21

What are the three main types of ketone bodies produced in the body ?

Answer 21

1) acetone (liver)
2) acetoacetate (liver)
3) B-hydroxybutyrate (liver)

Question 22

What is the normal concentration of ketone bodies in plasma ?

Answer 22

Less than 1mM

Question 23

What concentration of ketone bodies would be present in plasma during starvation period

Answer 23

2-10 mM

Question 24

At what concentration would plasma ketone bodies rise to in someone who has untreated type 1 diabetes ?

Answer 24

More than 10mM

Question 25

How are ketone bodies synthesised ?

Answer 25

• begins with acetylcoA (ch3-coA)
• synthase converts acetyl coA into hydroxymethylglutaryl (HMG-coA)
• lyase enzyme then converts HMG-coA into ketone bodies.

Question 26

How is cholesterol produced in the liver ?

Answer 26

Begins with acetyl coA

• synthase converts acetyl-coA into hydroxylmethylglutaryl (HMG-coA)
• HMG reductase then converts HMG-coA into mevalonate then into cholesterol.

Question 27

When is cholesterol metabolism activated?

Answer 27

• when insulin levels in the blood are high as we are in a fed state.
• insulin /glucagon ratio is high.

Question 28

When are ketone bodies metabolised - under what conditions ?

Answer 28

• when insulin/glucagon ratio is low.
• so when glucagon concentration is high.
• this means we are in a starvation state,

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Question 29

Ar are ketone bodies water soluble or non soluble ?

Answer 29

Water soluble

Question 30

What is ketonuria?

Answer 30

Excretion of higher amounts of ketone bodies - associated with diabetes and starvation.

Question 31

Ketosis vs ketoacidosis

Answer 31

Ketosis is where during periods of starvation - our body metabolises ketones as fats are used instead of glucose (1-2mM) whereas ketoacidosis is where there is dangerously higher levels of ketones in the plasma ( above 10mM).

Question 32

What is a characteristic smell of someone with ketoacidosis ?

Answer 32

• nail varnish breath due to acetone.

Question 33

ImportantAcne of malonyl- coA

Answer 33

Inhibits the carnithine shuttleto ensure that newly synthesised fatty acids are not transported into the inner mitochondria and used for beta-oxidation.

Question 34

In a TAG, what would the reference ‘ 18:3’ represent ?

Answer 34

18 carbons

3 double bonds