chapter 4 - enzymes

Question 1

catalyst

Answer 1

substance that speeds up the rate of chemical reactions, without itself being chemically changed at the end of the reaction, by lowering the activation energy required to start the reaction

Question 2

enzymes

Answer 2

proteins that function as biological catalysts that catalyse or speeds up the rate of chemical reactions (aerobic respiration / digestion). they remain chemically unchanged at the end of the reaction

Question 3

name some digestive enzymes and what reactions they catalyse

Answer 3

• amylase : starch into maltose
• maltase : maltose into glucose
• pepsin and trypsin : proteins into polypeptides
• peptidase : polypeptides into amino acids
• lipase : fats into glycerol and fatty acids

Question 4

describe the lock and key hypothesis

Answer 4

enzyme is the lock and substrate is the key. the three dimensional shape of the substrate is complementary to the active site of the enzyme. thus, it fits and binds to the enzyme to form the enzyme substrate complex. a chemical reaction takes place and the substrate forms products. the enzymes remain chemically unchanged at the end of the reaction.

Question 5

describe the temeprature graph for enzymes

Answer 5

at low temperatures, the rate of enzyme activity is low as the enzymes are inactive as the temperature increases, the enzyme and substrate have higher kinetic energy, increasing the chances of effective collisions between the substrate and enzyme collision between substrate and the enzyme molecules, therefore having a higher rate of enzyme-substrate complex formation. at the optimum temperature, the rate of enzyme activity is the highest as the enzymes are most active. beyond the enzyme’s optimum temperature, the rate of enzyme activity decreases rapidly and reaches zero as the enzymes are denatured. the weak hydrogen bonds are broken and the enzyme loses its original three-dimensional shape and the shape of its active site. the substrate cannot fit and bind onto its active site and there is a large decrease in the formation of the enzyme-substrate complex.

Question 6

describe the pH graph for enzymes

Answer 6

at the optimum pH level, the rate of enzyme activity is the highest as the enzyme retains its three-dimensional shape and the shape of its active site, therefore having the highest rate of formation of enzyme-substrate complexes. beyond the optimum pH, the rate of enzyme activity decreases rapidly and reaches zero, as the enzymes have denatured. the weak hydrogen bonds are broken and the enzyme loses its original three-dimensional shape and the shape of its active site. the substrate cannot fit and bind with the active site, and the formation of enzyme-substrate complex decreases.