Lipipd Transport

Question 1

Why must lipids be transported bound to carried in the blood?

Answer 1

They are hydrophobic/insoluble in water

Question 2

How are the majority of lipids transported in the blood?

Answer 2

Via lipoprotein particles

Question 3

What do lipoproteins usually consist of?

Answer 3

Phospholipid
Cholesterol
Cholesterol esters
Proteins
TAGs

Question 4

What is normal plasma glucose levels?

Answer 4

5mmol/L

Question 5

What is the normal amount of cholesterol in blood plasma?

Answer 5

Less than 5mmol/L

Question 6

Describe the structure of phospholipids

Answer 6

2 non polar hydrophobic fatty acid tails
Polar hydrophilic phosphate head

Question 7

What are the functions of cholesterol?

Answer 7

Regulates membrane fluidity
Precursor of corticosteroids (steroid hormones)
Precursor of bile acids

Question 8

What form is cholesterol transported in around the body?

Answer 8

As cholesterol ester

Question 9

What enzyme catalyses the formation of cholesterol esters?

Answer 9

LCAT

Question 10

Describe the structure of a lipoprotein

Answer 10

Phospholipid monolayer with small amount of cholesterol
Peripheral Apolipoproteins on outside of phospholipid monolayer
Integral apolipoproteins embedded in phospholipid monolayer
Cargo inside lipoprotein = TAG, cholesterol ester, fat soluble vitamins

Question 11

Give 2 examples of integral apolipoproteins

Answer 11

ApoA
ApoB

Question 12

Give 2 examples of Peripheral Apolipoproteins

Answer 12

ApoC
ApoE

Question 13

How are lipoproteins classified?

Answer 13

By density

Question 14

What are the 5 classes of Lipoproteins?

Answer 14

Chylomicrons
VLDL
IDL
LDL
HDL

Question 15

What is the function of Chylomicrons and VLDLs?

Answer 15

Transport TAG

Question 16

Where do Chylomicrons transport Triacylglycerols from and to?

Answer 16

Dietary TAG from the small intestine to adipose tissue

Question 17

Where do VLDLs transport Triacylglycerols from and to?

Answer 17

TAGs synthesised in the liver to adipose tissue

Question 18

What is the function of IDLs, LDLs and HDLs?

Answer 18

Transporting cholesterol

Question 19

Where does IDLs and LDLs transport chosterol from and to?

Answer 19

Cholesterol synthesised in the liver to tissues requiring cholesterol

Question 20

What is IDL in relation to LDL?

Answer 20

A short lived precursor of LDL

Question 21

Where do HDLs transport cholesterol from and to?

Answer 21

From cholesterol laden tissues back to the liver to be metabolised to bile salts for excretion

Question 22

What are Apolipoproteins?

Answer 22

They are the particular complement of associated proteins to a lipoprotein particle

Question 23

What are the 2 roles of apoproteins?

Answer 23

Structural - packaging water insoluble lipids
Functional - act as ligands for cell surface receptors, Co factors for enzymes

Question 24

What Apolipoprotein is added to Chylomicrons containing TAGs before they enter the lymphatic system?

Answer 24

ApoB(-48)

Question 25

Once Chylomicrons containing TAGs enter the blood, what 2 apoproteins are added?

Answer 25

ApoC ApoE

Question 26

What is lipoprotein lipase?

Answer 26

Enzyme which breaks down TAG in lipoprotein particle to release fatty acids

Question 27

Which Apolipoprotein on Chylomicrons binds to Lipoprotein Lipase on adipocytes and muscle ?

Answer 27

ApoC

Question 28

Wha happens to ApoC when the TAG content of a Chylomicron has been reduced to about 20%?

Answer 28

ApoC dissociates Leaves Chylomicron remnant

Question 29

What happens to Chylomicron remnants?

Answer 29

Return to liver ApoE binds to LDL receptor Chlyomicron remnant taken up by receptor mediated endocytosis

Question 30

What Apolipoproteins are added to VLDL when in the blood?

Answer 30

ApoB ApoC ApoE

Question 31

What happens to VLDL when it reaches the endothelial cells in muscle and adipose?

Answer 31

Binds to lipoprotein lipase Fatty acids released and are taken up by muscle for energy production, in adipose fatty acids re synthesised into TAG for storage

Question 32

How do cells that need cholesterol obtain cholesterol?

Answer 32

Express LDL receptor and when LDL binds it takes it up via receptor mediated endocytosis

Question 33

Why are LDLs not efficiently cleared by the liver? (Have the longest half life)

Answer 33

Do not have ApoC or ApoE Liver LDL receptor has a high affinity for ApoE

Question 34

What is the clinical relevance of high levels of LDL?

Answer 34

LDL susceptibility to oxidative damage due to its long half life Oxidised LDL taken up by macrophages forming foam cells in intima of blood vessel Foam cells form fatty streaks contributing to the formation of atherosclerotic plaques Leads to atherosclerosis

Question 35

What are the 6 classes of Hyperlipoproteinaemias?

Answer 35

I IIa IIb III IV V

Question 36

What are the clinical signs of Hypercholesterolaemia?

Answer 36

Xanthelasma Tendon Xanthoma Corneal Arcus

Question 37

What happens in hypercholesterolaemia?

Answer 37

Cholesterol gets deposited in various areas of the body

Question 38

What is Xanthelasma?

Answer 38

Yellow patches on eyelids

Question 39

What is Tendon Xanthoma?

Answer 39

Nodules on tendon

Question 40

What is corneal arcus?

Answer 40

Obvious white blueish circle around eye

Question 41

What happens when an atherosclerotic plaque grows and then ruptures?

Answer 41

Blood flow is reduced Once ruptured thrombosis occurs causing clotting Leads to stroke or myocardial infarction

Question 42

How are Hyperlipoproteinaemias initially treated?

Answer 42

Diet - reduce cholesterol and increase fibre Lifestyle - more exercise, stop smoking

Question 43

What is the next step if the initial approach to treating Hyperlipoproteinaemia doesn’t work?

Answer 43

Statins - inhibit HMG-CoA REDUCTASE so inhibit cholesterol synthesis Bile salts sequestants- more bile salts makes liver use up more cholesterol by producing more bile acids