2.4.1 enzymes as biological catalysts

Question 1

active site

Answer 1

indented area on the surface of an ezyme molecule, with a shape that’s complementary to the shape of the substrate molecule

Question 2

catalyst

Answer 2

chemical that speeds up the rate of reaction & remains unchanged/reusable at the end of the reaction

Question 3

extracellular

Answer 3

outside the cell

Question 4

intracellular

Answer 4

inside the cell

Question 5

metabolic/metabolism

Answer 5

the chemical reactions that take place inside living cells/organisms

Question 6

substrate

Answer 6

molecule that’s altered by an enzyme-catalysed reaction

Question 7

why are enzymes called biological catalysts

Answer 7

speed up metabolic reactions in living organisms & their actions affect both structure/function within cells/tissues/organs

Question 8

turnover number

Answer 8

the number of reactions an enzyme molecule can catalyse per second

Question 9

how enzyme structure determines function

Answer 9

• for catalysing some reactions, may need help of cofactors
• if the gene has a mutation which alters the amino acid sequence in the protein, this may alter the enzymes tertiary structure & prevent it from functioning
• if an enzyme that catalyses a metabolic reaction is deficient then a metabolic disorder results
• catalyse formation of organisms structural components (eg. collagen in bone, cartilage)

Question 10

why is the tertiary structure of the active site crucial

Answer 10

it’s shape is complementary to the shape of the substrate molecule

Question 11

each type of enzyme is highly specific in it’s function - how does this impact the active site?

Answer 11

the enzyme can only catalyse a reaction involving the particular substrate molecule that fits into it’s active site

Question 12

how can the shape of the active site be altered

Answer 12

by changes in temperature & pH which affect the bonds that hold the proteins in their tertiary structure

Question 13

what do enzymes catalyse

Answer 13

wide range of intracellular & extracellular reactions

Question 14

properties of intracellular enzymes

Answer 14

• each metabolic pathway in a living cell is 1 of a series if consecutive reactions & every steps catalysed by a specific enzyme that produces a specific product
• various reactants & intermediates act as substrates for specific enzymes
• respiration & photosynthesis are examples of complex metabolic pathways, with many enzymes involved

Question 15

what are the reactions, intermediates & products known as (intracellular)

Answer 15

metabolites

Question 16

what are described as catabolic (intracellular)

Answer 16

some metabolic pathways where metabolites are broken down to smaller molecules & release energy

Question 17

what are described as anabolic (intracellular)

Answer 17

other metabolic pathways where energy is used to synthesise larger molecules from smaller ones

Question 18

what’s catalase

Answer 18

• found in nearly all living organisms that are exposed to oxygen
• very important enzyme
  —> protects cells from damage by reactive oxygen by quickly breaking down hydrogen peroxide to water and oxygen

Question 19

what’s hydrogen peroxide

Answer 19

a potentially harmful by-product of many metabolic reactions

Question 20

what does catalase consist of

Answer 20

4 polypeptide chains & contains a haem group with iron

Question 21

is it a fast acting enzyme - whats its turnover number

Answer 21

• fastest-acting enzyme
• highest turnover number known of about 6 million per second

Question 22

where is catalase found in eukaryotic cells

Answer 22

found inside small vesicles called peroxisomes

Question 23

how do white blood cells use catalse

Answer 23

when they ingest pathogens they use it to help kill the invading microbe

Question 24

what’s the optimum pH/temp for catalase in different environments

Answer 24

• human catalse: around pH 7 & 45 degrees
• other species it varies between pH 4 & 11
• for some thermophilic archaea it’s 90 degrees

Question 25

describe extracellular enzymes - use example of fungi

Answer 25

- some enzymes are secreted from the cells once made & act on their substrates outside - fungi (eg. bread mould ‘mucor’) release hydrolytic enzymes from their thread-like hyphae —> enzymes digest carbohydrates, proteins & lipids in the bread & the products of digestion - glucose, amino acids, glycerol & fatty acids - are absorbed into the fungal hyphae for use in respiration & growth

Question 26

how do extracellular enzymes work in our digestive system

Answer 26

- many are secreted from cells lining the alimentary canal, into the gut lumen - they extracellulay digest large molecules (eg. proteins, lipids, carbohydrates & nucleic acids) found in food - products of digestion are absorbed (via epithelial cells of the gut wall) into the bloodstream to be used for respiration, growth & tissue repair

Question 27

where is amylase produced & what does it do

Answer 27

- salivary glands in the mouth & in pancreas - mouth: digests polysaccharide starch into disaccharide maltose - pancreas: catalyses same reaction^ in lumen of small intestine

Question 28

where is trypsin made & what does it do - what's its optimum pH

Answer 28

- pancreas - acts in lumen of small intestine to digest smaller peptides by hydrolysing peptide bonds - optimum pH = between 7.5 & 8.5