lecture 26

Question 1

dietary intake per day of the 3 important food nutrients

Answer 1

250-800gm of carbohydrate
70-100gm of protein
100-150g lipids

Question 2

why is it called alpha amylase

Answer 2

alpha amylase as it breaks the alpha 1-4 glycosidic bonds of glucose polymers

Question 3

proteins aren’t necessarily a source of energy, so why are they essential in the diet

Answer 3

there are 20 amino acids, 8 of which we cant make in our body, so they must come from an external source

Question 4

what are our sources of protein

Answer 4

50% is dietary, 50% is endogenous so enzymes and immunoglobulins

Question 5

what good do lipids do

Answer 5

energy storage, they provide fat soluble vitamins ADEK, they slow gastric emptying

Question 6

what are the lengths of the short medium and long chain fatty acids

Answer 6

short chain are less than 6, medium are 6 to 12 and long chain are 12-24

Question 7

what are the two stages of digestion and describe them

Answer 7

luminal digestion, digestion which intitially involves enzymes secreted into lumen. and mechanical digestion which happens in the small intestine before things are absorbed

Question 8

describe lumenal digestion of carbohydrates

Answer 8

salivary and pancreatic amylases convert the polysaccharide chains into di and oligosaccharides

Question 9

describe contact digestion of carbohydrates

Answer 9

digestion at the brush boarder. turns disaccharides into monomers. involves enzymes bound to brush boarder. enzymes here at specific to the given disaccharides, so maltase does maltose, lactase does lactose

Question 10

describe luminal digestion of proteins

Answer 10

enzymes in the lumen convert proteins into polypeptides.
pepsin in the stomach
trypsin and chymotrypsin in the small intestine
carboxypeptidase in SI, secreted by pancreas

Question 11

describe contact digestion of proteins

Answer 11

involves peptidases which are attached to the brush boarder, these convert polypeptides into individual amino acids for absorption

Question 12

describe contact digestion of lipids

Answer 12

does not happen, lipids are insoluble in water and enzymes are dissolved in aqueous environment so this wont work.

Question 13

what are the 4 stages of fat digestion

Answer 13

emulsification, stabilisation, digestion, formation of micelles

Question 14

describe emulsification

Answer 14

the motility of the stomach- retropulsion- and small intestine- segmentation, break lipid droplets into smaller droplets.
this occurs to increase Surface area for fat digestion

Question 15

describe stabilisation

Answer 15

occurs in the small intestine, bile salts suspend the emulsion droplet in solution as they have hydrophobic side and hydrophilic side.

Question 16

describe digestion/hydrolysis of fats

Answer 16

occurs in the small intestine at the surface of the emulsion droplets. the lipase is helped to bind to the emulsion by colipases. the lipases then break down tricylglycerides into monoglycerides and free fatty acids

Question 17

describe formation of micelles in fat digestion process

Answer 17

fat digestion products are highly insoluble,. these insoluble units are kept in solution by micelle formation.
micelles are small droplets containing around 30 molecules, molecules being bile salts, fatty acids and monoglycerides. this is done as the bile salts are amphiphatic