15. Lipids

Question 1

What role do fats have besides energy production?

Answer 1

1. Make cell membranes - phospholipids + cholesterol

2. Essential fatty acids (omega 3 + 6) are precursors for eicosanoids e.g. prostaglandins, leukotrienes, thromboxanes.

Question 2

Identify 4 things cholesterol is used to make.

Answer 2

1. Membranes
2. Vitamin D
3. Steroid hormones
4. Bile salts

Question 3

Omega 3 + 6 are precursors for BOTH inflammatory and anti-inflammatory molecules.
True or False?

Answer 3

TRUE

Question 4

How are lipids in the diet transported around the body in circulation?
How are they then used for energy and storage?

Answer 4

Lipids are packaged into chylomicrons inside intestinal epithelial cells.
These then pass through the lymphatic system through the thoracic duct and enter circulation via the subclavian vein, bypassing the liver.

In circulation, lipoprotein lipase breaks down triacyclglycerols in chylomicrons into fatty acids + glycerol which is absorbed my muscle (energy) and adipose tissue (storage).

The chylomicron remnants take cholesterol to the liver.

Question 5

Fatty acids can be used by brain tissue.

True or False?

Answer 5

FALSE
cannot pass blood brain barrier.
only glucose (and ketone bodies).

Question 6

Liver synthesised fats (triglycerides + cholesterol) enter circulation via VLDLs.
Where do LDL + HDL come from?

Answer 6

Once the VLDL’s deliver triacylglycerols to tissues, they shrink and become LDL’s (mainly cholesterol).

Once this cholesterol is delivered to cells, it becomes a HDL.
This travels around the body picking up excess cholesterol to return to the liver.

Question 7

For oxidation to take place, fatty acids must first be activated to form fatty acyl CoA.
Where does this take place?

Answer 7

Cytosol

Question 8

Where does beta oxidation take place?

Answer 8

Mitochondria matrix

Question 9

Beta oxidation of fatty acids can only be done in aerobic conditions.
True or False?

Answer 9

TRUE

completely aerobic process

Question 10

What are the products of each cycle of beta oxidation?

Answer 10

Acetyl CoA
NADH
FADH2

these feed into the electron transport chain and Krebs cycle.

Question 11

Overall, how much ATP is produced from each molecule of palmitoyl CoA?

Answer 11

108 ATP

Question 12

What is the control point of beta oxidation?

Answer 12

Malonyl CoA

high conc inhibits carnitine, therefore fatty acids cant enter mitochondria.

(ensures that fatty acid breakdown doesn’t happen when energy levels are high)

Question 13

What are ketone bodies formed from, where, and under what conditions?

Answer 13

Made from excess acetyl CoA.
In mitochondria of liver cells.
During periods when the body relies on fatty acid oxidation for energy (e.g. fasting, uncontrolled diabetes).

Question 14

Ketone bodies can be used as an energy source by brain tissue.
True or False?

Answer 14

TRUE

Question 15

What is the risk with high levels of ketone bodies?

Answer 15

Ketoacidosis

affects blood pH, leading to coma and death.

Question 16

What diseases can high levels of cholesterol lead to?

Answer 16

Cardiovascular disease

Alzheimer’s disease

Question 17

What are the 2 sources of cholesterol?

Answer 17

Diet
Synthesis (mainly) - in almost all tissues, mainly in liver + intestine

Question 18

Plant sterols increase cholesterol uptake in the gut.

True or False?

Answer 18

FALSE

they inhibit uptake - lowering plasma cholesterol levels.

Question 19

Cholesterol uptake from LDL is via receptor mediated endocytosis.
How is cholesterol uptake regulated by cells?

Answer 19

LDL receptor synthesis depends on how much cholesterol in the cell.
If cholesterol levels are high, there will be a lack of receptors.
Preventing the uptake of cholesterol.

Question 20

What reaction controls the rate of cholesterol biosynthesis and where does it take place?

Answer 20

HMG CoA > Mevalonate
HMG CoA reductase.

Occurs in cytosol + SER (smooth endoplasmic reticulum)

Question 21

What is cholesterol synthesis controlled by?

Answer 21

1. HMG CoA reductase.
2. cholesterol levels - high levels inhibit
3. energy levels - insulin increases synthesis / glucagon inhibits

Question 22

Cholesterol is broken down to fatty acyl CoA and recycled.

True or False?

Answer 22

FALSE

cholesterol cannot be broken down, it is only excreted in faeces (via bile).

Question 23

High blood cholesterol increases risk of heart disease.

True or False?

Answer 23

TRUE

Question 24

Which of these fats increase LDL levels?

1. saturated fat
2. monounsaturated fat
3. trans fat
4. polyunsaturated fat
5. dietary cholesterol

Answer 24

1. saturated fat
2. trans fat
3. dietary cholesterol (less so than the other two)

Question 25

Is a blood cholesterol value above 5mM considered high?

Answer 25

Yes.

5 is the target, 4 if at risk.

Question 26

Atherosclerosis is when plaque builds up in your arteries.

What effect do LDL and HDL have on the risk of developing this disease?

Answer 26

↑ LDL = ↑ risk

↑ HDL = ↓ risk

Question 27

People with familial hypercholesterolaemia and Tangier disease are at an increased risk of coronary disease.
Why?

Answer 27

familial hypercholesterolaemia = Lack of LDL receptors

Tangier disease = lack of HDL

Question 28

Which of these diseases does high cholesterol not cause?
Alzheimer's disease
Atherosclerosis
Coronary disease
Non-alcoholic steatohepatitis
Sepsis

Answer 28

Sepsis

Question 29

Alcoholic and non-alcoholic steatohepatitis BOTH result in the accumulation of lipid droplets in hepatocytes, leading to inflammation + fibrosis.
True or False?

Answer 29

TRUE