Lipids

Question 1

Main functions of lipids

Answer 1

Formation and maintenance of cell membranes: phospholipid and cholesterol.

Energy storage: triglycerides.

Formation of hormones, vitamins and bile acids: steroids and fatty acids.

Electrical insulation in neurones.

Thermal insulation in adipose tissue.

Question 2

Short term, labile energy sources

Answer 2

ATP

Redox agents: NAD, FAD

Ionic transmembrane gradients.

Creatine phosphate.

Though these are energy sources, they are not stable and do not last long.

Question 3

Formation of fatty acids from glucose.

Answer 3

Glucose is broken down into acetyl-CoA during the link reaction of aerobic respiration.

Acetyl CoA is then converted to fatty acids using ATP.

Question 4

Fatty acid synthesis from Acetyl CoA

Answer 4

This occurs in the cytosol in a great reducing environment:

Acetyl-CoA is used to make fatty acids using ATP, reducing power from electrons and fatty acid synthase.
Also produces CO2 and releases CoA.

2 carbons are added at a time to form fatty acids. Fatty acid chains are 16-20 carbons long with an even number of carbons.

Question 5

Beta oxidation of fatty acids

Answer 5

The break down of fatty acids back to acetyl-CoA, which occurs in the mitochondria.

Fatty acid chain is shortened 2 carbon at a time to from acetyl-CoA and ATP.
Hence why fatty acids are storage for energy.

Question 6

Fatty acids

Answer 6

Storage of energy: breaks down to release ATP in beta oxidation.

Structure: Hydrocarbon chain attached to carboxylic acid.
50 % of fatty acids are unsaturated- mono/polysaturates.

Forming double bonds is energy consuming so some fatty acids are essential, only obtained from diet.

Question 7

Fat mobilisation

Answer 7

The breakdown of fatty acids to acteyl-CoA and ATP, 2 carbons at a time.

Question 8

Triglycerides

Answer 8

Lipid molecule: contains even number of carbons, 16-20 carbons long.

Composed of 3 fatty acids attached to a glycerol molecule.

Cannot enter cells on its own, must be broken down before being transported.

Question 9

Statins

Answer 9

Drugs that blocks the conversion of Acetyl-coA into cholesterol.

This treats hypercholesterolemia and reduces risk of coronary heart disease.

Blocks HMG-CoA reductase, the first enzyme used to make cholesterol.

Examples:
Simvastatin
Pravastatin

Question 10

Carbohydrates in the brain

Answer 10

Glycogen cannot be stored in neurones, can only be stored in astrocytes.

Neurones get their energy source from ketone bodies.

Question 11

Cholesterol

Answer 11

Vitamin D precursor

Either obtained from diet of made in the liver (very energy consuming).

Most of cholesterol (75%) in the plasma undergoes esterification.

Too much in the blood increases risk of coronary heart disease due to hypercholesterolemia.

Question 12

Cholesterol esters

Answer 12

Made by reacting cholesterol with fatty acids, using LCAT enzyme.

Question 13

Acetyl-CoA transport in plasma

Answer 13

Cannot be transported in plasma, has to be hydrolysed first

Question 14

Ketone bodies

Answer 14

The following water soluble molecules:
Acetoacetate
Beta-hydroxybutyric acid
Acetone (one of the product of the breakdown of the previous ketone bodies)

They are a major source of energy that can last for 5 hours and are made from acetyl-CoA during fasting.

Question 15

Diabetics and ketone bodies

Answer 15

Diabetic people do not utilise glucose as their cells are unresponsive.

This leads to energy being produced from the breakdown of ketone bodies. But ketone bodies only last 5 hours so if it is not used, it is wasted.

This can cause weight loss in diabetic people as food being eaten is not used for energy.

Question 16

Acetone

Answer 16

A type of ketone body excreted by the kidneys.

Question 17

Unsaturated fatty acids

Answer 17

Contain C=C and make membrane more fluid due to the ‘kink’.

Fatty acids that are contain cis c=c are less flexible as they have an angle of 123 degrees.

This gives prevents them from packing more tightly and gives them a lower melting point than trans fats.

Trans fats have 132 degrees and look linear. They can pack more tightly.

Question 18

Exogenous lipid transport

Answer 18

Transporting lipid from the gut to the liver and periphery tissues,.

Fatty acids are absorbed in the small intestines and packaged into chylomicrons.

The liver and peripheries, like adipose and muscle tissue, take up chylomicrons and increase the concentration of lipids in the plasma.

Question 19

Endogenous lipid transport

Answer 19

Transporting lipid from the liver to periphery tissue.

Liver packages lipids in very low density lipoproteins (VLDL) and transports to adipose and muscle tissue.

Question 20

Reverse cholesterol lipid transport

Answer 20

Transporting lipid from periphery to the liver. This indicates that lipid levels are low.

Lipids are packaged into high density lipoproteins which are taken up by the liver.

Question 21

Bile production- lipid transport

Answer 21

Method of transporting lipid from the liver to the gut.

Bile is released from the liver and gallbladder into the cystic duct in the duodenum, in the small intestines.

Bile emulsifies fats in the intestines, facilitating its absorption.

Question 22

Very low density lipoprotein. (VLDL)

Answer 22

Transports cholesterol and triglycerides from the liver to the muscle and adipose tissue- Endogenous transport.

After the triglycerides are released then VLDL becomes intermediate density lipoprotein (IDL).

Question 23

High density lipoprotein (HDL)

Answer 23

Transports lipids from periphery to the liver.

High concentrations reduces the risk of developing cardiovascular diseases.

High density- smaller amount of lipids carried as there are more particles per given area compared to LDL and VLDL.

High levels in the blood indicate that cholesterol is being recycled.

Question 24

What happens during starvation

Answer 24

Lack of glucose present leads to the increase of ketogenesis:

Excess beta oxidation occurs which produces excess acteyl-CoA

Too much acetyl-CoA being produced compared to its use in the Kreb’s cycle.

Question 25

Lipoproteins

Answer 25

Soluble structures that store lipids.

Contains apolipoproteins which carries lipids, like apoE.

Question 26

Chylomicrons

Answer 26

Lipoproteins that carry exogenous lipids to the liver and periphery- exogenous transport.

Question 27

Hypercholesterolaemia

Answer 27

High fasting levels of plasma cholesterol.

This increases the risk of atherosclerosis.

Influenced by environmental (consuming too much cholesterol) and genetic factors.

Question 28

Lipoprotein protease

Answer 28

Enzyme that breaks down triglycerides into fatty acids and glycerol.

Located in the cell membrane of capillary walls.

Allows TG to be moved into cell as it cannot be transported in plasma.