Lipids

Question 1

Functions of lipids

Answer 1

Phospholipids & cholesterol - cell membranes

TG = key energy store

Steroids and fatty acids play regulatory roles as hormones, vitamins and bile acids

Question 2

Cellular energy - short-term storage

Answer 2

ATP (and other phosphate bonds)
Redox agents (NADH, FADH2)
Ionic transmembrane gradients
H+ across mito memb, Na+ across Plasma Membrane
All of the above are labile

Question 3

Limit on ATP stored

Answer 3

Some energy is stored intracell as creatine phosphate

Question 4

Carbohydrate as energy

Answer 4

Sugars are absorbed from gut into blood stream

Sugars absorbed by liver and stored as glycogen
Via hepatic portal vein

Also sugars stored throughout body as glycogen:
Glucose spike leads to insulin

Glycogen is broken down into glucose when more is needed

No glycogen in brain: it needs glucose or ketone bodies from plasma constantly

Question 5

Citric acid cycle

Answer 5

A-CoA + Oxalo-acetic acid -> Citric acid (6C)

Citric acid + O2 -> Oxalo-acetic acid + CO2 + ATP

Question 6

Fatty Acid Synthesis

Answer 6

Acetyl-CoA + ATP + e- (ATP) -> fatty acid + CO2 + CoA

Question 7

Fatty Acids

Answer 7

Simple straight C chain + COOH 16-20Cs

50% have double bonds

Question 8

Cholesterol

Answer 8

Essential component of cell membranes
precursor of bile acids, steroid hormones and vitamin D

Sources: from diet OR made in liver
A major emphasis on recycling
Bile salts
Endogenous pathway

Question 9

Cholesterol esters

Answer 9

75% of plasma cholesterol is esterified

Broken down by lipase to free cholesterol & FA

Question 10

Acetyl-Coenzyme A

Answer 10

Main energy production precursor

Cannot be transported in plasma

Question 11

Ketone

Answer 11

“Ketone bodies” are 3 soluble chemicals

Made from acetyl-CoA during fasting
By liver
Last for only 5 hours

During fasting, major energy source

Question 12

Acetoacetic acid & beta-hydroxybutyric acid

Answer 12

Acetone is a waste product
Made spontaneously by decarboxylation
eliminated by kidney

Question 13

Kink(veg)

Answer 13

Lowers melting temperature

Question 14

Fats

Answer 14

Saturated fats are bad
- Increase LDL

Trans unsaturated fats are bad

Cis unsaturated fats are either
Monounsaturated
Polyunsaturated
Health information on these changes but they are probably good for you
Lower melting temperature b/c of kink

Question 15

Exogenous Pathway

Answer 15

From gut to liver (and to periphery)

Diet and packaged into chylomicrons in small intestine

Question 16

Endogenous Pathway

Answer 16

From liver to periphery
Peripheral lipids stored in adipose & muscle

Endogenous = made by the body

Lipid from liver packaged into VLDL

Question 17

Reverse Cholesterol Transport

Answer 17

From periphery to liver

Occurs when lipid supplies in liver are being exhausted

HDL in blood indicates reverse path activity

Question 18

Bile production

Answer 18

From liver into gut (and gall bladder)
- Bile released into cystic duct

Cholesterol converted into bile acids

• Bile is necessary to digest fats in diet
• Emulsifies fats

Most bile acids are reabsorbed by gut
- Returned to the liver and recycled

Question 19

Lipoprotein lipase

Answer 19

Metabolises TG -> fatty acids + glycerol
Because TG cannot go through cell membrane
Cell surface-linked enzyme in capillary walls
In order to remove triglycerides from VLDL and to move the TG across the capillary membrane, TG must first be metabolised via lipoprotein lipase

Question 20

Lipoprotein particles

Answer 20

In plasma

Soluble and carry lipids

Question 21

Apolipoproteins

Answer 21

Proteins in LP particles that can hold lipids

Question 22

Lipid identified by density

Answer 22

Lipid is much less dense than protein
TG are very low density
Cholesterol is midway between TG and protein

Question 23

LDL

Answer 23

LDL contents get incorporated into atheromas
LDL in blood may be “storage” for cholesterol that “cannot be stored elsewhere”
Excess LDL accumulates in atheromas

Left over LDL absorbs endogenous TG from VLDL from liver

Question 24

HDL

Answer 24

Increased HDL -> lower CV risk

lipid transport from fat cells to liver

Question 25

VLDL

Answer 25

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

Question 26

IDL

Answer 26

Results from VLDL losing TG to periphery

IDL will become LDL

Question 27

Chylomicrons

Answer 27

Not usually associated with CV risk
Normally high after fat-containing meals

Carries lipids from gut to periphery
For exogenous lipids

Question 28

Hypercholesterolaemia

Answer 28

High fasting levels of plasma cholesterol

Increased risk of arteriosclerosis
HDL reduces risks

Due to a combination of environmental and genetic factors

Question 29

Statins

Answer 29

Drugs used to treat hypercholesterolaemia
Block endogenous cholesterol synthesis
By Blocking HMG-CoA Reductase
The entry step into cholesterol synthesis

Question 30

Metabolic syndrome

Answer 30

Group of risk factors that occur together, leading to increased risk for CAD, stroke, and type 2 diabetes

Main causes
Insulin resistance
Central obesity
Waist circumference

Question 31

Endothelial injury due to

Answer 31

raised LDL
‘toxins’ eg cigarette smoke
hypertension
haemodynamic stress

Question 32

Endothelial injury causes

Answer 32

platelet adhesion, PDGF release, VSMC proliferation and migration
insudation of lipid, LDL oxidation, uptake of lipid by VSMC and macrophages
migration of monocytes into intima

Stimulated VSMC produce matrix material

Foam cells secrete cytokines causing
further VSMC stimulation
recruitment of other inflammatory cells