Lipid Metabolsim

Question 1

What are the 3 classes of lipids?

Answer 1

Fatty acid derivatives
(Fatty acids, triacylglycerols, phospholipids, eicosanoids)
Hydroxyl-methyl-glutaric acid derivatives / HGM compounds (ketone bodies, cholesterol, cholesterol esters, bile acids and salts)
Vitamins (A, D, E, K) - cannot be made in the body

Question 2

What is the main function of triacylglycerols?

Answer 2

Fuel storage for prolonged aerobi exercise, stress situations such as starvation, during pregnancy and insulation

Question 3

Storage of triacylglycerols is under normal control. Name the hormone that promotes the storage of fat?

Answer 3

Insulin

Question 4

Storage of triacylglycerols is under normal control. Name the hormones that reduced the storage of fat?

Answer 4

Glucagon
Adrenaline
Cortisol
Growth hormone 
Thyroxine

*hormones that are causing processes to happen that require energy

Question 5

What is the first stage of triacylglycerol metabolism?

What are the products? What does this process require?

Answer 5

Hydrolyses by pancreatic lipase in the small intestine

Glycerol and fatty acids are produced

Requires bile salts and (protein factor) colipase

Question 6

Where is glycerol metabolised?

Answer 6

In the liver

Question 7

*fact

Answer 7

Arachidonic acid is an important polyunsaturated fatty acid (essential fatty acid) as it is the starting point for the synthesis of the eicosanoids, which are a family of signaling molecules in the body, including prostaglandins.

Question 8

What is stage 2 of lipid metabolism?

Answer 8

Catabolism of fatty acids

Question 9

What is lipolysis and why does it occur?

Answer 9

It is when adipose tissue triacylglycerols are hydrolysed by the enzyme hormone-sensitive lipase to release fatty acid and glycerol

It happens when the body is subjected to stress situations ie aerobic exercise, starvation, lactation

Question 10

Why hormones effect lipolysis and how?

Answer 10

Activated by; adrenaline, glucagon, growth hormone, cortisol, thyroxine

Inhibited by; insulin

Question 11

What is the enzyme that catalyses the lipolysis reaction?

Answer 11

Hormone sensitive lipase

Question 12

How are fatty acids transported around the body?

Answer 12

Bound non covalently to albumin - called non esterified fatty acids (NEFA) or free fatty acids (FFA)- in the blood

Question 13

By what process are fatty acids oxidised to release energy and where does it occur?

Answer 13

Beta oxidation

In mitochondria

Question 14

Why does beta oxidation of fatty acids not occur in the CNS?

Answer 14

Because fatty acids do not readily cross the blood-brain barrier

Question 15

In order to be oxidised, fatty acids need to be activated. How are they activated?

Answer 15

By linking to coenzyme A via the S atom forming a high energy of hydrolysis bond

Question 16

How does activated fatty acid get into mitochondria?

Answer 16

By using the special transport system that uses carnitine to shuttle the fatty acid

*this system plays an important role in regulation the rate of fatty acid oxidation by controlling their entry into mitochondria

Question 17

What inhibits the transport of activated fatty acid into the mitochondria for metabolism? Why?

Why is this process important?

Answer 17

Malonyl CoA

It is an intermediate in the synthesis of fatty acids

It prevents fatty acids newly synthesised in the cytoplasm from being immediately transported into the mitochondria and being oxidised.

Question 18

How would someone who has a defective mitochondrial fatty acid transport system present?

Answer 18

With a poor exercise tolerance

Unusually large amounts of triacylglycerols in their muscles cells

Question 19

Is beta oxidation of fatty acids an aerobic or anaerobic process?

Answer 19

Aerobic, it cannot occur in the absence of oxygen since this is require for stage 4 of catabolism to re-oxidise the NADH and FAD2H formed.

Question 20

Where is the major site of lipid synthesis in the body and name an important intermediate in lipid biosynthesis?

Answer 20

Liver

Acetyl-CoA

Question 21

What are the 3 ketone bodies produced in the body? How are they produced?

Answer 21

Acetoacetate -synthesises in the liver from acetyl CoA

Acetone- arises form the spontaneous decarboxylation of acetoacetate

Beta-hydroxybutyrate - synthesised in the liver from acetyl CoA

Question 22

The normal concentration of ketone bodies in circulation is low (<1mmol/L) but this can increase. What two situations would it increase and what are the names given to these types of raised ketone body conc.

Answer 22

Starvation - physiological ketosis

Untreated type 1 diabetes- pathological ketosis

Question 23

What do you call it when there are ketone bodies in urine?

Answer 23

Ketonuria

Question 24

What causes ketoacidosis?

Answer 24

Acetoacetate and beta-hydroxbutyrate - relatively strong organic acids, when present in the plasma they can cause acidosis

Question 25

Where might acetone be excreted? How can this be used to diagnose diabetes (type 1)

Answer 25

Via the lungs The characteristic smell of acetone (nail varnish remover) can often be smelt on the breath of someone with diabetes (untreated)

Question 26

What enzymes are used in the synthesis of ketone bodies and how are these controlled?

Answer 26

Lyase and reductase- controlled by insulin/glucagon ratios

Question 27

When the insulin;glucagon ratio falls what is the effect on lyase and reductase (enzymes involved in the synthesis of ketone bodies)? What is result on the overall production of ketone bodies

Answer 27

Lyase-activated Reductase-inhibited Ketone body formation is activated.

Question 28

When the insulin;glucagon ratio increases, what is the effect on lyase and reductase (enzymes involved in the synthesis of ketone bodies)? What is synthesised?

Answer 28

Lyase-inhibited Reductase- activated Ketone body formation is inhibited and cholesterol synthesis occurs

Question 29

What two things are needed for the synthesis of ketone bodies to occur?

Answer 29

- fatty acids to be available for oxidation in the liver following excessive lipolysis in adipose tissue -this supplies the substrate - the plasma insulin/glucagon ratio to be low, usually due to a fall in plasma insulin- this activates the lyase and inhibits the reductase

Question 30

Why are ketone bodies wanted in the body?

Answer 30

They are important fuel molecules that can be used by all tissues containing mitochondria They provide spare glucose in early starvation/diabetes They are converted to acetyl- CoA and this is subsequently oxidised via stage 3 of catabolism (TCA cycle)

Question 31

Give an example of an essential polyunsaturated Fatty acid

Answer 31

Linolenic acid

Question 31

What are the broad steps involved in beta oxidation?

Answer 31

Activation- energisation of molecule in cytoplasm Moving- conversion to molecule that is capable of being transported into mitochondria (use carnitine shuttle) Acetyl CoA production- cleaving and oxidising 2 carbons with every cycle

Question 32

How do statin drugs work and when would you use them?

Answer 32

They are used to inhibit the action of the HMG-CoA reductase enzyme which converts HMG-CoA into cholesterol. It is used to treat hypercholesterolemia

Question 33

What is a test for diabetes

Answer 33

Checking for ketonuira (ketone bodies in urine)

Question 34

Outline the process by which triacylglycerols would be used to generate energy in the patient during exercise

Answer 34

1) broken down by hormone sensitive lipase, hydrolyses TAGs 2) fatty acid transported bound to albumin to tissues 3) released and activated- bound to CoA 4) moved into mitochondria by carnitine shuttle 5) beta-oxidation occurs 6) acetyl CoA produced enter the TCA cycle