lecture 23 - digestion of food molecules

Question 1

what are the two main phases of digestion

Answer 1

1. hydrolysis of bonds connecting monomer units in food macromolecules
2. absorption of hydrolysis products from gastrointestinal tract

Question 2

what % of energy intake do carbohydrates provide

Answer 2

40-50%

Question 3

what is an example of fibre and why can we not digest it

Answer 3

cellulose = do not have the enzyme that can hydrolyse the B(1,4) glycosidic bond in cellulose

Question 4

what is the repeating disaccharide unit that is in cellulose

Answer 4

cellobiose

Question 5

what is glycogen synthesised from and where is it stored + what happens when it is needed

Answer 5

glycogen is synthesised from glucose and stored in liver and muscle,

and then broken down to glucose when required by the body

Question 6

how does amylase break down starch

Answer 6

hydrolysis a(1,4) glycosidic bonds creating smaller and smaller oligosaccharides to produce maltose / isomaltose

Question 7

what breaks down maltose and isomaltose

Answer 7

maltase and isomaltase (same for sucrose and lactose = sucrase and lactase)

Question 8

what does protein digestion involve

Answer 8

hydrolysis of specific peptide bonds

• performed by several different proteases

Question 9

what is the specificity of proteases

Answer 9

pepsin = aromatic

trypsin = positively charged

chymotrypsin = aromatic

Question 10

what are the two stages of protein digestion and what happens

Answer 10

endopeptidases = attack peptide bonds within the protein (peptide) polymer - pepsin, trypsin, chymotrypsin

exopeptidases = attack peptide bonds at the end of the protein (peptide) polymer (aminopeptidase and carboxypeptidase)

Question 11

what is the protein digestion in the small intestine

Answer 11

trypsin and chymotrypsin = break the peptide bonds within the protein

carboxypeptidases and aminopeptidases = break peptide bonds at end of the peptide fragments