Enzymes

Question 1

Enzymes affect structure and function.

Answer 1

Structure: involved in production of collagen which is a protein present in connective tissue.
Function: respiration and digestion

Question 2

Intracellular enzymes

Answer 2

Enzymes in cells - Catalase

• catalyses breakdown of Hydrogen Peroxide into water and oxygen.
• It is a harmful by-product of metabolic reactions.

Question 3

Extracellular enzymes

Answer 3

Work outside cell - amylase and trypsin
Amylase
- in saliva, secreted by salivary glands.
-catalyses hydrolysis of starch into maltose.
Trypsin
-catalyses hydrolysis of peptide bonds - larger to smaller ones.
-produced in pancreas secreted in small intestine.

Question 4

Lock and key hypothesis

Answer 4

• substrates and enzyme shave kinetic energy so move randomly.
• if successfully collide, enzyme-substrate complex forms by a substrate molecule binding to the complementary shaped active site of the enzyme.
• substrate is either broken down or built up forming an enzyme-product complex.
• products molecules released from active site of enzyme and enzyme is unchanged.

Question 5

Induced fit hypothesis

Answer 5

• active site still has a complementary shape to the substrate.
• but when they bind, the active site changes shape slightly to fit the substrate more closely.
• an enzyme-substrate complex is forms.
• substrate is converted into the product so an enzyme-product complex is formed.
• products detach from active site of the enzyme.

Question 6

What is activation energy?

Answer 6

• A certain amount of energy that needs to be supplied to the reactants for the reaction to start.
• enzymes reduce the activation energy so reaction can occur at lower temperatures so speeds up the reaction.

Question 7

What lowers the activation energy?

Answer 7

• the formation of enzyme-substrate complex lowers activation energy
• > substrate molecules that need to join attach to an enzyme that holds them close together for the repulsion to reduce so they can bond easily.
• > if enzyme is catalysing breakdown reaction, fitting substrate into the active site puts strain onto the substrates bonds so that it breaks easily.

Question 8

Effect of temperature

Answer 8

• as temperature increases, rate of reaction also increases.
• more kinetic energy so molecules move faster.
• more likelihood of successful collisions so more chance of a reaction.
• temp is too high, molecules vibrate more, vibration breaks bonds that hold enzymes shape, active site changes shape.
• enzyme denatures.

Question 9

Effect of pH

Answer 9

• each enzyme and an optimum pH
• pepsin works best at acidic pH 2 since in stomach
• if pH is too high or low, H+ and OH- ions in acids/alkalis can break ionic bonds and hydrogen bonds.
• this changes tertiary structure so active site changes shape
• enzyme is denatured.

Question 10

Effect of enzyme concentration

Answer 10

• increase in enzyme conc increase rate of reaction.
• higher the enzyme conc, more chances of collisions, so more enzyme-substrate complexes form.
• if substrate is limited, increase in enzyme conc will have no further effect.

Question 11

Effect of substrate concentration

Answer 11

• higher substrate conc, higher the rate of reaction.
• more chances of collisions so more active sites will be occupied.
• until saturation point where they are too many substrates so adding more has no further effect.
• substrate conc decreases with time.
• if no variables change, rate of reaction will decrease over time.
• initial rate of reaction will be the highest throughout reaction process.

Question 12

What are enzymes?

Answer 12

• Enzymes are biological catalysts which speed up chemical reactions.
• they catalyse metabolic reactions.
• cellular (respiration)
• organism (digestion)