Leyland 6 stage 2

Question 1

LIPIDS

Answer 1

• Structurally diverse
• Generally insoluble in water (hydrophobic)
• Most only contain C, H, O
(phospholipids contain P, N)
• More reduced than carbohydrates release more energy when oxidised

Question 2

1. Fatty acid derivatives:

Answer 2

• Fatty acids – fuel molecules.
• Triacylglycerols – fuel storage and insulation
• Phospholipids – components of membranes and plasma lipoproteins
• Eicosanoids – local mediators

Question 3

2. Hydroxy-methyl-glutaric acid derivatives (C6 compound):

Answer 3

• Ketone bodies (C4) – water soluble fuel molecules
• Cholesterol (C27) – membranes and steroid hormone synthesis
• Cholesterol esters – cholesterol storage
• Bile acids and salts (C24) – lipid digestion

Question 4

3. Vitamins

Answer 4

• A, D, E and K.

Question 5

What are triacylglycerols?

Answer 5

(triglycerides, TAG)
• major dietary and storage lipid
• consist of 3 fatty acids esterified to glycerol
• hydrophobic

Question 6

Fatty Acids

Answer 6

CH3(CH2)nCOOH
where n = 14 - 18 (ie 16 - 20 C in total)
• saturated or unsaturated ( ie one or more double bonds C=C)
• amphipathic (contain hydrophilic & hydrophobic groups)
• certain polyunsaturated FA are essential (ie cannot be synthesized) (because mammals cannot introduce a double bond beyond C9) eg linolenic acid 18 : 3 (9,12,15)

Question 7

Dietary lipids

1. Lipids are emulsified in the small intestine

Answer 7

• bile salts

Question 8

2. Digestion of lipids by lipases

Answer 8

• TAGs - digested by pancreatic lipase
• cholesterol esters - digested by cholesterol esterase
• phospholipids - digested by phospholipases

Question 9

3. Absorption by intestinal mucosal cells

Answer 9

lumen: triacyglycerides + lipases -> fatty acids & monoacylglycerols

to

Mucosal cell

-> tiracyglycerides

Question 10

4. Transportation to tissues

Answer 10

• consumer tissues - fatty acid oxidation
  
  • adipose tissue - storage
• consumer tissues
  TAG broken down by lipases to release free FA and glycerol
• fatty acid oxidation
• adipose tissue
• storage

Question 11

Fatty acid catabolism (b-oxidation)

Answer 11

• occurs in mitochondria
• FA cycles through sequence of reactions
• C2 removed at each cycle
• 1 NADH, 1 FADH2 produced in each cycle
• all intermediates linked to coenzymeA (FA activation)

Question 12

Fatty acid catabolism (b-oxidation)

1. Activation of fatty acids

Answer 12

• Occurs in the cytoplasm
• FA activated by linkage to coenzyme A
• Catalysed by acyl CoA synthetase

fatty acid + coenzyme A -> fatty acyl CoA

Question 13

Fatty acid catabolism (b-oxidation)

2. Transport of fatty acyl CoA into mitochondria

Answer 13

• fatty acyl group linked to carnitine
• transported across the membrane by a translocase protein
• fatty acyl CoA reformed in the matrix
• Rate limiting step for fatty acid oxidation

Carnitine (carnitine acyltransferase I) -> acyl carnitine

across to matrix side
(carnitine acyltransferace II) -> carnitine

back to cytoplasmic side

Question 14

Fatty acid catabolism (b-oxidation)

3. Oxidation of fatty acyl CoA

Answer 14

• a series of 4 reactions
• 1 NADH, 1 FADH2 and 1 acetyl CoA are generated in each round
• each round shortens the chain by 2 carbon atoms
• cycle continues until only acetyl CoA remains

Question 15

Summary

Fatty acid catabolism (b-oxidation)

Answer 15

• Oxidative process that release a large amount of energy
e.g. palmitate C16
8 acetyl CoA, 7FADH2, 7NADH

106 molecules of ATP
• unsaturated FAs need additional steps for degradation
isomerase / reductase

Question 16

Glycerol metabolism

Answer 16

• transported to the liver

* used for glycolysis / gluconeogenesis

Question 17

Protein catabolism (Stages I & II)

Answer 17

• dietary proteins are a source of amino acids
• 9 essential amino acids – those that cannot be synthesised; histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine

Question 18

Digestion and absorption of proteins

Answer 18

• Dietary protein digestion begins in the stomach
- denaturation
- pepsin
• Further digestion in the lumen of the intestine
- chymotrypsin, trypsin, carboxypeptidase – pancreas aminopeptidase
• Transport into intestinal cells and into blood

Question 19

Degradation of amino acids:

Answer 19

• Excess amino acids cannot be stored so have to be degraded

Question 20

Degradation of amino acids

1Transfer of amino group to a-ketoglutarate

Answer 20

aminotransferases

aspartate + a-ketoglutarate produces oxaloacetate + glutamate
alanine + a-ketoglutarate produces pyruvate + glutamate

Question 21

Degradation of amino acids

2. Dehydrogenation to produce ammonium ion
   - glutamate dehydrogenase

Answer 21

• glutamate dehydrogenase

e.g.
aspartate + a-ketoglutarate produces oxaloacetate + glutamate
alanine + a-ketoglutarate produces pyruvate + glutamate

Question 22

Degradation of amino acids

Overall

equation

Answer 22

Amino acid + NAD(P)+ +H2O a-ketoacid + NH4+ + NAD(P)H

Question 23

Removal of ammonium ion - the urea cycle

Answer 23

Toxic NH4+ is converted to urea and excreted

Question 24

Carbon skeletons of amino acids

Answer 24

• Deamination of amino acids produces carbon skeletons that are used in many other pathways

Question 25

Protein Metabolism

Answer 25

• Proteins contain > 90% of the nitrogen in the body
• Proteins are produced for a specific function NOT synthesised as a store of excess amino acids
• Muscle protein can be broken down to provide energy during starvation
• Proteins are continuously being broken down and resynthesised

Question 26

Nitrogen balance

Answer 26

Positive nitrogen balance (intake of nitrogen (protein) > loss)
- during active growth, pregnancy, tissue repair
Negative nitrogen balance (intake of nitrogen (protein) < loss)
- during starvation