Lipids 1

Question 1

What is the structure of a fatty acid?

Answer 1

Polar (soluble) carboxylic acid ‘head’.

Non-polar (insoluble) hydrocarbon chain ‘tail’.

Question 2

What are the two types of unsaturated fatty acids?

Answer 2

Monounsaturated (MUFAs) - only one double bond in chain.

Polyunsaturated (PUFAs) - multiple double bonds in chain.

Question 3

What does the stability of a fatty acid depend on?

Answer 3

Length, degree of saturation.

Question 4

What is the difference between cis and trans double bonds?

Answer 4

Cis = two hydrogen atoms on the same plane.

Trans = two hydrogen atoms in opposite planes.

Question 5

Describe the storage lipid triacylglycerol (TAG).

Answer 5

Formed of three fatty acid chains joined in a glycerol backbone by ester bonds.

Neutral - do not carry charge, are not soluble in water.

Question 6

How are membrane lipids categorised?

Answer 6

Initially into phospholipids and glycolipids.

Then by backbone group - glycerol or sphingosine.

Question 7

Describe the structure of the phospholipid bilayer.

Answer 7

Hydrophilic heads on the outside, facing water. Hydrophobic tails on the inside.

This dual nature of the same molecule means they are classed as amphipathic.

Question 8

What are the 2 main categories of hormone?

Answer 8

Eicosanoids and steroids.

Question 9

What molecule are steroid hormones formed from?

Answer 9

Cholesterol.

Question 10

What are the classifications of steroid hormones?

Answer 10

Sex hormones, glucocorticoids, mineralocorticoids, synthetic steroids.

Question 11

How are fatty acids produced?

Answer 11

Acetyl CoA + CO2 + ATP + biotin -> Malonyl CoA (by acetyl-CoA carboxylase)

Fatty acid synthase donates 2 carbons from malonyl CoA to acetyl CoA, with addition of 4 hydrogens and 2 electrons.

Continues until palmitate (16 carbons) is formed.

Question 12

Where does the process of lengthening fatty acid chains take place?

Answer 12

Smooth endoplasmic reticulum / mitochondria.

Question 13

Describe the process of desaturation of fatty acids.

Answer 13

Fatty acid desaturated by fatty acyl-CoA desaturase, NADPH molecule oxidised to produce 2H2O molecules.

Question 14

Describe the formation of eicosanoids.

Answer 14

Phospholipids + phospholipase A2 -> Arachindonate

Arachidonate + cyclooxygenase -> prostaglandin G2 -> prostaglandin H2

Question 15

What are the precursors of TAGs?

Answer 15

Fatty acyl-CoA, glycerol 3-phosphate.

Question 16

What does insulin promote the conversion of into TAGs?

Answer 16

Dietary carbohydrates and proteins.

Question 17

How are TAGs formed?

Answer 17

Phosphatidic acid -> 1,2-diacylglycerol (by phosphatidic acid phosphatase).

Diacylglycerols -> triacylglycerols by transesterification with a third fatty acyl-CoA.

Question 18

How are glycerophospholipids formed?

Answer 18

Phosphatidic acid -> 1,2-diacylglycerol (by phosphatidic acid phosphatase).

Head group attached to phosphate group.

Question 19

Describe the steps of formation of sphingolipids.

Answer 19

1. Synthesis of backbone molecule (glycerol / sphingosine).
2. Attachment of fatty acid(s) to backbone through ester / amide linkage.
3. Addition of hydrophilic head group to backbone through phosphodiester linkage.
4. Alteration / exchange of head group to yield final phospholipid product.

Question 20

How is cholesterol formed?

Answer 20

3 acetate molecules -> mevalonate

-> 2 activated isoprenes

6 activated isoprenes -> squalene

• > four-ring steroid nucleus
• > lanosterol -> cholesterol