lipids in health & disease

Question 1

what are the 2 lipids?

Answer 1

cholesterol & triacylglyceride

Question 2

what is function of cholesterol in plasma membrane?

Answer 2

• cholesterol helps maintain structure and fluidity of cell membrane
• OH group interacts with polar head groups of membrane phospholipids; rest of molecule embedded along with e.g. TG fatty acid chains, Helps to provide barrier to H+, Na+, solutes

Question 3

how does cholesterol help cell signalling?

Answer 3

• helps form lipid “rafts” that form bridges between receptor proteins & second messengers

Question 4

what does cholesterol act as precursor molecule for?

Answer 4

for bile/bile acids = important in digestion & absorption of fat-soluble vitamins, vitamin D and steroid hormones

• they also act as building blocks for lots of hormones and molecules etc

Question 5

what is the biggest alternative source of energy from glucose?

Answer 5

triglycerides

Question 6

what are lipoproteins?

Answer 6

proteins that are required for triglycerides and cholesterol to be carried around the body

= they bury the hydrophobic parts of lipids (triglyceride & glucose) so not exposed to water that surrounds proteins in blood

Question 7

what is exogenous cycle of lipid metabolism?

Answer 7

1. fat you consume in meal is absorbed in small intestine
2. then packages into lipoproteins called chylomicron (large particles that transport dietary fats through blood stream)
3. as chylomicrons circulatem, the particles encounter lipoprotein lipase (LPL) which acts on them and removes triglycerides resulting in chylomicron remnants which are taken up by liver = exogenous cycle

Question 8

what is endogenous cycle of lipid metabolism?

Answer 8

anticlockwise from liver, in liver - very low density lipoproteins (VLDL) particles are produced and leave liver and series of changes similar to chylomicron particles like removal of triglycerides →intermediate density lipoproteins (IDL) → low density lipoproteins (LDL)

Question 9

what means build up of LDL?

Answer 9

if balance of lipid pathways not equal

• HDL does reverse cholesterol transport
• if 2 processes unbalanced then can lead to build up of LDL
• too much LDL can lead to altered LDL which

Question 10

what happens if not enough LDL cleared?

Answer 10

it accumulates and gets chemically modified (oxidised) and aggregates.

This then acts as a trigger for macrophages to do what they do – mediate inflammation and swallow stuff including LDL itself.

Inflammation inhibits reverse cholesterol transport, thus exacerbating the imbalance and a feed-forward or vicious circle of increasing LDL and increasing inflammation

Question 11

how do statins work?

Answer 11

They interfere with cholesterol synthesis in the liver cell, which then expresses more LDL receptors in an attempt to get more cholesterol into the cell

= fool liver cell into thinking they don’t have enough cholesterol - allows LDL from blood to be cleared into liver cell (clearance increases)

• they also do more than just lower cholesterol = they can inhibit and stop lots of other things that cause atherosclerosis