chapter 16 - metabolism

Question 1

metabolism

Answer 1

refers to chemical processes within a cell or organism
starts with digestion

Question 2

nutrients

Answer 2

biomolecules which provide energy
(proteins, triglycerides, carbohydrates, minerals, vitamins, water)
macronutrients/ micronutrients

Question 3

hydrolysis of carbohydrates

Answer 3

amylase in saliva
- starch molecules - disaccharides in mouth (maltose)
- disaccharides - monosaccharides in small intestine (glucose)
require 2 different enzymes

Question 4

hydrolysis of proteins

Answer 4

pepsin (stomach) commences process
protease is general term
- protein - polypeptides in stomach
- polypeptides - dipeptides in small intestine
- dipeptides - amino acids in intestines

Question 5

hydrolysis of triglycerides

Answer 5

catalysed by lipase
triglycerides - diglycerides + fatty acid - monoglycerides + 2 fatty acids - glycerol + 3 fatty acids
in small intestine

Question 6

hydrolysis of cellulose

Answer 6

cellulase
- human do not have cellulase
- pass as dietary fibre
- small amount can be hydrolysed by bacteria in gut
- cows have sufficient bacteria to synthesise cellulase

Question 7

enzymes

Answer 7

• proteins that act as biological catalysts
• only act in narrow pH and temp ranges
  tertiary structure
• active site
• substrate
• bind through intermolecular forces

Question 8

lock and key model

Answer 8

active site fits substrate perfectly, forming enzyme - substrate complex

Question 9

optical isomer and enzymes

Answer 9

• amino acids are chiral
• only one enantiomer of each amino acid is used to build proteins
• enzymes must distinguish between enantiomers, by being chiral
• only one enantiomer will fit in active site
• intermolecular forces are formed between substrate and groups on enzyme surface (all - except covalent)
• weaken peptide link and make it easier to break

Question 10

induced fit

Answer 10

slightly flexible active site (mold around substrate)

Question 11

coenzymes

Answer 11

• many can’t function without cofactor
• metal ion or non-protein organic compound (coenzyme)
  change shape of enzyme, changing binding properties of active site, allowing substrate to bind

Question 12

enzyme activity

Answer 12

rate of reaction
substrate turned into product per unit of time

Question 13

enzymes and pH

Answer 13

operate best at optimum pH
denature
TS depends on bonds between side chains
ionic bonds between NH3+ and COO- in side chains
pH change can cause NH3+ to lose an H+ and COO- to gain an H+, removing the ionic bond
Arg + Lys positive
Asp + Glu negative

Question 14

enzymes and temp

Answer 14

operate best at optimum temp (37˚C)
intermolecular bonds broken
denatured

Question 15

coagulation

Answer 15

after denaturation
proteins clump together again but working shape is lost

Question 16

difference between hydrolysis and denaturation

Answer 16

hydrolysis breaks the peptide bonds, changing the primary structure but denaturation is a change to the tertiary structure, leaving the primary structure intact

Question 17

glycaemic index

Answer 17

a scale that compares the rates at which different foods release energy and effect blood sugar levels
pure glucose = GI score of 100, other foods compared to this
- food with high GI release energy quickly (>70)
- food with low GI release energy slowly (<55)

Question 18

hydrolysis of triglycerides

Answer 18

insoluble
intact until small intestine
bile as an emulsifying agent
breaks them down and disperses them
once emulsified lipase can hydrolyse

Question 19

rancidity

Answer 19

triglycerides go off (unsaturated)
c=c are more reactive
cause odours

Question 20

oxidative rancidity

Answer 20

forms aldehydes or ketones by oxidation
c=c reacts with O
more unsaturated, more reactive, more susceptible to OR

Question 21

antioxidants

Answer 21

help slow the deterioration of food
prevent oxidation as they are oxidants themselves