BIOC Lecture 10: Lipid Transport

Question 1

What are endogenous lipids?

Answer 1

lipids that are naturally synthesized within the body

Question 2

Where are most TAG’s made?

Answer 2

In the liver

Question 3

What are the two ways to make TAG’s?

Answer 3

• From the degradation of fatty acids
• Derive from a 3C molecule in the glycolysis pathway
  These two ways make glycerol 3-phosphate backbone

Question 4

What needs to be removed to make a TAG?

Answer 4

Phosphate

Question 5

What is the structure of cholesterol?

Answer 5

4 sterol ring structure with a hydrocarbon tail

Question 6

What is every carbon molecule in cholesterol derived from?

Answer 6

Acetyl CoA (it is the building block)

Question 7

What is cholesterol most commonly found in the form of?

Answer 7

Cholesterol ester for storage

Question 8

How is a cholesterol ester made?

Answer 8

Fatty acid added to hydroxyl group

Question 9

Where does cholesterol come from?

Answer 9

Meat and animal products such as dairy - not plants

Question 10

How are cholesterol levels regulated?

Answer 10

The body shuts down its own cholesterol synthesis pathway when levels are high from the diet

Question 11

How does the body shut down its cholesterol synthesis pathway?

Answer 11

By cholesterol feeding back to inhibit the enzyme HMG CoA reductase

Question 12

How does the cholesterol synthesis pathway work?

Answer 12

• Acetyl CoA (from FFA’s, AA’s and glucose) gets converted into HMG CoA
• HMG CoA is converted into mevalonate, catalysed by the enzyme HMG CoA reductase

Question 13

Is cholesterol soluble?

Answer 13

Very insoluble

Question 14

What tissues have the greatest demand for cholesterol?

Answer 14

Liver and reproductive tissues

Question 15

What is the only way to get rid of cholesterol?

Answer 15

Steroid ring cannot be degraded - excreted as bile

Question 16

What is cholesterol a major component of?

Answer 16

Membranes and lipoproteins

Question 17

What are cholesterol precursors to?

Answer 17

• Steroid hormones
• Bile acids
• Vitamin D

Question 18

What is cholesterol important for the transport of?

Answer 18

Fat soluble vitamins

Question 19

Why are cholesterol important for neuronal function?

Answer 19

Part of the myelin sheet that insulates our nerves

Question 20

What are plasma lipoproteins?

Answer 20

particles that transport lipids, including cholesterol and triglycerides, through the bloodstream

Question 21

What is the structure of plasma lipoproteins?

Answer 21

• Single phospholipid layer
• Polar heads point outwards
• Apolipoproteins embedded in phospholipid layer
• Packaged in the middle are hydrophobic lipids (cholesterol esters and TAG’s)

Question 22

What are the 4 main lipoprotein classes?

Answer 22

• Chylomicrons
• VLDL
• LDL
• HDL

Question 23

Which lipoproteins are TAG rich?

Answer 23

Chylomicrons and VLDL

Question 24

Which lipoproteins are cholesterol rich?

Answer 24

HDL and HDL

Question 25

Which lipoproteins are the densest?

Answer 25

HDL because of its high protein content, and low lipid content

Question 26

Where are both forms of ApoB synthesised?

Answer 26

In ER in enterocytes

Question 27

How are lipoproteins assembled?

Answer 27

Using different apolipoproteins, including ApoB48 and ApoB100

Question 28

What is ApoB?

Answer 28

A lipid binding protein which comes in 2 different forms

Question 29

What are the two different forms of ApoB?

Answer 29

ApoB48 and ApoB100

Question 30

What does ApoB serve as the receiver of?

Answer 30

Lipids

Question 31

How are chylomicrons assembled? (First Step)

Answer 31

Lipids combine with apoB via MTP in ER to form chylomicrons (ApoB particle)

Question 32

How are chylomicrons assembled? (Second Step)

Answer 32

The chylomicron already produced + TAG via MTP creating a larger chylomicrons (larger ApoB)

Question 33

What is MTP?

Answer 33

Microsomal triglyceride transfer protein

Question 34

Where do chylomicrons go for maturation?

Answer 34

To golgi

Question 35

Where are chylomicrons secreted from?

Answer 35

Intestinal cells entering the bloodstream via the lymphatic system

Question 36

What appearance can chylomicrons give?

Answer 36

Give plasma a “milky” appearance after a fat-rich meal due to high TAG content

Question 37

What do lipoproteins solubilise?

Answer 37

Lipids for transport in blood to tissues

Question 38

What system do lipoproteins provide?

Answer 38

A delivery system for shifting lipids in and out of cells

Question 39

What are the important functions of apoproteins?

Answer 39

• Assembly (apoB)
• Ligands for cell surface receptors (apos B and E)
• Enzyme cofactors

Question 40

What hydrolyses lipids?

Answer 40

Lipoprotein and hepatic lipases

Question 41

What factors affect lipid levels?

Answer 41

• Diet (SAFA increases, PUFA decreases TAG + LDL)
• Drugs
• Genetics
• Disease

Question 42

What do statin drugs inhibit?

Answer 42

HMG-CoA
- Which lowers cholesterol levels and increases LDL receptor activity

Question 43

What do ezetimibe drugs do?

Answer 43

Blocks cholesterol absorption from intestine, less cholesterol uptake in body, also upregulates LDL receptors

Question 44

What drug do PUFA’s act similarly to?

Answer 44

Fibrates

Question 45

What do both PUFA’s and fibrates do?

Answer 45

Both activate a transcription factor known as PPAR

Question 46

What is the function of PPAR?

Answer 46

• When activated, switches on genes, one of them being lipoprotein lipase (LPL)
• LPL hydrolyzes the TAG which lowers the TAG content in your VLDL particles and therefore lower TAG levels in the blood

Question 47

What is familial hypocholesterolemia (FH) caused by?

Answer 47

Defects in LDLR causing elevated LDL cholesterol

Question 48

What do defects in apoB or MTP cause?

Answer 48

Low blood cholesterol levels

Question 49

What do defects in LPL or ApoCII cause?

Answer 49

Elevated TAG levels