Lipids and Metabolism

Question 1

Lipids

Answer 1

Most lipids contain or are derived from fatty acids and they perform many important biological functions :

• triglycerides = a fuel store of the body
• phospholipids = crucial constituents of biological membranes
• orlistat = weight loss med

Question 2

Adipose Cells

Answer 2

Also known as fat cells

Adipose cells contain large lipid droplets and a flattened squashed nucleus

Adipose cells can quadruple in size when we put on weight

Question 3

Lipid metabolism

Answer 3

In order to begin the process of fat metabolism , triglycerides must be broken down into their component fatty acids and glycerol. This occurs primarily in the duodenum during digestion and liberates fatty acids from adipose cells.

Pancreatic lipases are responsible for the release of fatty acids from triglycerides by hydrolysis.

Question 4

Lipids in the aqueous environment

Answer 4

Bile acids are synthesized from cholesterol in the liver.

Question 5

Fat burners

Answer 5

Senna - a natural senna stimulant.

Orlistat - lipase inhibitor, reduces the absorption of dietary fat.

Question 6

Utilisation of fatty acids as fuels

Answer 6

Three Stages :

• mobilisation
• activated and transportation
• breakdown to acetyl CoA which is then processed in the citric acid cycle

Question 7

Mobilisation

Answer 7

Triglycerides must be hydrolysed before they can be utilised as fuels.

Hormonally controlled lipases and phosphorylation of two key proteins:

• Perilipin A = phosphorylation restructures fat droplets so that triglycerides are more accessible to the hormone sensitive lipase .
• Hormone sensitive lipase = this phosphorylated lipase hydrolyses triglycerides to free fatty acids

Question 8

Activation and Transportation

Answer 8

• fatty acids are oxidised in the mitochondria
• they are first activated through the formation of thioester linkage to coenzyme A before mitochondrial entry.
• fatty acids are activated on the outer mitochondrial membrane but oxidisation takes place in the mitochondrial matrix. Fatty acids are conjugated to cartinine for transport across the inner mitochondrial membrane into the matrix

Question 9

Fatty acid summary

Answer 9

• triglycerides as energy stores of fatty acids
• triglycerides breakdown in intestine
• utilisation of fatty acids as fuels - three stages