Introduction to lipids

Question 1

Give some examples of lipids and their functions

Answer 1

Phospholipids & cholesterol: cell membranes
Triglyceride is a key energy store
Steroids and fatty acids play regulatory roles as hormones, vitamins and bile acids

Question 2

How is energy stored short term in cells?

Answer 2

ATP, redox agents, ionic transmembrane agents and creatine phosphate

Question 3

How is energy stored long term?

Answer 3

Stored as carbohydrates and fats

Question 4

Give an overview of how acetyl Co-A acts as an energy mediator

Answer 4

Sugars and starches turn into glucose which can be reversibly converted to form glycogen.
Glucose can either form lactic acid or acetyl CoA
The acetyl CoA form citric acid and ATP or reversibly into fatty acids. Acetyl CoA can be prevented from turning into cholesterol by statins

Question 5

What does the brain constantly require form the plasma?

Answer 5

Glucose or ketone bodies

Question 6

What happens in the citric acid cycle?

Answer 6

Acetyl CoA combines with oxaloacetate to form citric acid which then combines with oxygen to release energy and CO2

Question 7

Describe fatty acid synthesis

Answer 7

Leads to fatty acids with an even number of carbon atoms and consumes ATP

Question 8

Describe beta oxidation

Answer 8

A way of breaking down fats by fat mobilization

Shortens fatty acids by 2 carbons at a time and produces acetyl CoA and ATP

Question 9

Describe the structure of a fatty acid

Answer 9

Carbon chain with a COOH group attached
Most are 16-20 carbons long
50% have carbon carbon double bonds

Question 10

Why are essential fatty acids required?

Answer 10

Mammals lack the ability to make double bonds so some double bonded fatty acids are taken in through the diet

Question 11

Which chemical group does a fatty acid contain before bound to glycerol?

Answer 11

Acyl group

Question 12

What is cholesterol?

Answer 12

Essential component of the cell plasma membrane

Precursor of steroid hormones, bile salts and vitamin D

Question 13

Where is cholesterol obtained?

Answer 13

Liver or diet

Question 14

There is major emphasis on the recycling of cholesterol. State 2 ways in which it is recycled

Answer 14

Bile salts

Endogenous pathway

Question 15

How is cholesterol amphipathic as the free alcohol?

Answer 15

Both hydrophobic and hydrophilic

Question 16

Is a cholesterol ester hydrophilic or hydrophobic?

Answer 16

Hydrophobic

Question 17

What percentage of cholesterol is esterified?

Answer 17

75%

Question 18

How is cholesterol broken down?

Answer 18

By lipases to form glycerol and fatty acids

Question 19

List some steriods

Answer 19

Cholesterol
Vitamin D
Cortisol
Testosterone

Question 20

What is acetyl CoA?

Answer 20

Main energy production precursor

Question 21

What are ketone bodies? State them

Answer 21

Soluble chemicals made by acetyl CoA during fasting
Acetoacetic acid & beta-hydroxybutyric acid
Acetone is eliminated as waste

Question 22

Cis carbon-carbon double bonds create a kink. What does this kink do?

Answer 22

Lowers melting temperatures

Question 23

State the 4 pathways of lipid transport

Answer 23

From gut (digestive tract) to liver & periphery
(Periphery for lipids = muscle and adipose tissue)
From liver to periphery
From periphery to liver
From liver into digestive tract

Question 24

What is the exogenous pathway?

Answer 24

From gut to liver. Lipids are packaged into chylomicrons in the small intestine and these are taken up by the liver or periphery

Question 25

What is the endogenous pathway?

Answer 25

From liver to periphery

Lipid from liver packaged into VLDL

Question 26

What is reverse cholesterol transport?

Answer 26

From periphery to liver
Occurs when lipid supplies in liver are being exhausted
Thus a sign of reduced body lipid
HDL in blood indicates reverse path activity

Question 27

Describe bile production

Answer 27

From liver into gut
Cholesterol converted into bile acids
Most bile acids are reabsorbed by gut
Returned to the liver and recycled

Question 28

Describe LDL

Answer 28

Most Dangerous lipoprotein
LDL contents get incorporated into atheromas
LDL in blood may be “storage” for cholesterol that “cannot be stored elsewhere”
Excess LDL accumulates in atheromas
LDL is eventually “left-over” after periphery absorbs endogenous TG from VLDL from liver

Question 29

What is HDL?

Answer 29

The good lipoprotein

Increased HDL and lower CV risk

Question 30

Give the name for when lipids are transported from fat cells to the liver

Answer 30

Reverse cholesterol transport

Question 31

Describe VLDL

Answer 31

Signifies risk of atheroma
Used to transport endogenous cholesterol and TG from Liver to adipose and muscle
After TG is removed by periphery from VLDL, leaves over IDL
IDL is intermediate step in pathway where VLDL becomes LDL

Question 32

Describe chylomicron

Answer 32

Not usually associated with CV risk
Normally high after fat-containing meals
Carries lipids from gut to periphery
For exogenous lipids