1.15 to 1.17 enzymes

Question 1

state how a catalyst affects the rate of a reaction (1)

Answer 1

a catalyst increases the rate of a reaction (1)

Question 2

name the part of an enzyme where substrate molecules bind (1)

Answer 2

active site (1)

Question 3

enzymes have a ‘high specificity’ for their substrates. describe what this means. (1)

Answer 3

it means usually only one type of substrate will fit into the active site of a specific enzyme (1)

Question 4

explain why increasing the substrate concentration fails to affect the rate of an enzyme-controlled reaction after a certain point. (2)

Answer 4

after a certain point, all of the active sites on the enzymes are full (1) and increasing the substrate concentration does not result in more substrate molecules entering the active sites of enzymes, so the rate of the reaction is not affected (1).

Question 5

enzyme A’s activity will be different at 38°C and 60°C. explain why (3)

Answer 5

At 38°C enzyme A will most active as this is its optimum temperature (1). at 60°C, enzyme A is denatured and will not be active (1) because the shape of the active site has changed (1)

Question 6

describe and explain the effect on enzyme activity of increasing the pH above the optimum level. (3)

Answer 6

the enzyme activity decreases (1) because the pH affects the bonds in the enzyme, causing the active site to change shape (1) and denaturing he enzyme (1)

Question 7

explain why the breakdown of large molecules into smaller components is necessary for organisms (2)

Answer 7

organisms need to be able to break down large molecules into smaller components so that they can be absorbed into the bloodstream and into cells (1) to be used for growth and other life processes (1)

Question 8

[orlistat is a drug that is used to help lower obesity rates. it works by preventing lipase from working in the digestive system.]
explain why patients taking orlistat may have oily faces. (3)

Answer 8

orlistat prevents lipase from working so lipids are not broken down (1) into fatty acids and glycerol (1). this means lipids are not absorbed into the blood and instead pass through the digestive system and into the faeces. (1)

Question 9

What are enzymes?

Answer 9

Biological catalysts that increase the rate of a chemical reaction without being permanently altered themselves

Question 10

What is an advantage of enzymes in the body?

Answer 10

They enable cellular reactions to take place at lower temperatures

Question 11

What is the active site of an enzyme?

Answer 11

The region of an enzyme to which a substrate molecule binds and the reaction takes place

Question 12

Describe the ‘lock and key’ model

Answer 12

1. Substrate collides with the active site of an enzyme
2. Substrate binds, enzyme-substrate complex forms
3. Substrate converted to products
4. Products released from the active site which is now free to bind to another substrate

Question 13

What factors affect the rate of an enzyme-controlled reaction?

Answer 13

● Temperature
● pH
● Substrate concentration

Question 14

Explain how increasing temperature initially affects the rate of an enzyme-controlled reaction

Answer 14

● As temperature increases molecules have more KE
● Movement of molecules increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases

Question 15

Explain how pH affects the rate of an enzyme-controlled reaction

Answer 15

● Enzymes have an optimum pH
● pH shifts from the optimum
● Bonds in the enzyme’s structure are altered
● Active site changes shape, enzyme is denatured
● Rate of reaction decreases

Question 16

Explain how the substrate concentration affects the rate of an enzyme-controlled reaction

Answer 16

● Substrate concentration increases
● Number of substrate molecules in the same volume increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases
● Once all active sites become full, the rate of reaction plateaus

Question 17

How can the rate of an enzyme-controlled reaction be calculated when given a value for time?

Answer 17

rate = 1/time

Question 18

What are the units for rate?

Answer 18

s^-1

Question 19

Why must large organic molecules be broken down into smaller, simpler molecules in the body?

Answer 19

● Large molecules are too big to be absorbed across the surface of the gut wall
●∴ large molecules are broken down into smaller molecules for absorption into the bloodstream

Question 20

Give an example of the breakdown of large molecules into smaller molecules in plants

Answer 20

Starch is broken down by enzymes into simpler sugars which are respired to release energy.

Question 21

What type of molecules are proteins and carbohydrates?

Answer 21

Polymers

Question 22

What are the monomers of carbohydrates?

Answer 22

Simple sugars

Question 23

Which group of enzymes catalyses the breakdown of carbohydrates?

Answer 23

Carbohydrases

Question 24

Which type of carbohydrase catalyses the breakdown of starch?

Answer 24

Amylase

Question 25

What are the monomers of proteins?

Answer 25

Amino acids

Question 26

Which type of enzyme catalyses the breakdown of proteins?

Answer 26

Proteases

Question 27

What is the function of lipases?

Answer 27

Enzymes which catalyse the breakdown of lipids into fatty acids and glycerol

Question 28

Why are small molecules synthesised into larger organic molecules in the body?

Answer 28

Large molecules are used for storage (e.g. glycogen) or are used to build structures(e.g. organelles).

Question 29

Which enzyme catalyses the formation of glycogen from glucose?

Answer 29

Glycogen synthase

Question 30

How can the amount of energy contained in food be measured?

Answer 30

Measured using calorimetry

Question 31

What is calorimetry?

Answer 31

A method of measuring the heat transfer during a chemical reaction

Question 32

Describe the method used to measure the amount of energy in a sample of food

Answer 32

1. Add a set volume of water to a boiling tube, record initial temperature
2. Record the mass of a small sample of food (e.g. bean)
3. Stick the sample onto a mounted needle
4. Using a Bunsen burner light the food sample
5. Hold the sample under the boiling tube until it burns up
6. Record the maximum temperature reached by the water
7. Record the final mass of the food sample

Question 33

How can the amount of energy in the food sample be calculated?

Answer 33

energy in food (J) = mass of water (g) x temperature change of water (°C) x 4.2
energy (J/g) = energy in food (J) / mass of food burnt (g)

Question 34

Digestion?

Answer 34

A process that breaks down large insoluble molecules into smaller useful soluble molecules via enzymes, chemicals and mechanical action

Question 35

Large insoluble molecules?

Answer 35

Such as carbohydrates, proteins and lipids, need to be broken down during digestion into dissolvable products that can be absorbed by the body

Question 36

Small soluble molecules?

Answer 36

Products of digestion such as glucose, amino acids, glycerol and fatty acids, these molecules are small enough to be absorbed by the body for specific uses

Question 37

Absorption?

Answer 37

Small soluble molecules can be absorbed in the small intestine following digestion, they diffuse into the blood and are then transported around the body for specific purposes

Question 38

Carbohydrates

Answer 38

Provide energy for chemical reactions and can break down into sugars

Question 39

Proteins

Answer 39

The building blocks of cells and tissues that can break down into amino acids

Question 40

Lipids

Answer 40

An energy store of fats and oils that can break down into glycerol and fatty acids

Question 41

Conversion of glucose to complex carbohydrates

Answer 41

Glucose, a product of digestion, can be converted into new complex carbohydrates such as glycogen

Question 42

Glucose

Answer 42

A soluble product of digestion, essential for respiration to release energy and is also needed to synthesise new molecules

Question 43

Formation of lipid molecules

Answer 43

Glycerol and fatty acids, products of digestion, join together to form new lipids

Question 44

Protein synthesis

Answer 44

Amino acids, products of digestion, join together in specific arrangements to form new proteins for growth and repair

Question 45

Enzymes

Answer 45

Biological catalysts which speed up reactions without being used up, essential for the digestion of large insoluble molecules

Question 46

Amylase

Answer 46

A carbohydrase enzyme found in saliva and the small intestine that breaks the chemical bonds in starches

Question 47

Carbohydrases

Answer 47

Enzymes that speed up the breakdown of carbohydrates into simple sugars

Question 48

Lipase

Answer 48

Enzyme found in the small intestine that breaks down lipids into glycerol and fatty acids

Question 49

Protease

Answer 49

Enzyme found in the stomach and small intestine that breaks down proteins into amino acids

Question 50

Metabolic reactions

Answer 50

Enzymes are involved in many important reactions in the body, building large molecules from small ones as well as breaking down large molecules into small ones

Question 51

Metabolism

Answer 51

the sum of all the reactions in a cell or the body including reactions such as respiration or the synthesis of new molecules

Question 52

Enzymes as proteins

Answer 52

Enzymes are made up of specific sequences of amino acids, which are linked to form chains that fold up into the specific shape of the overall enzyme protein

Question 53

Importance of amino acid sequence

Answer 53

The sequence of amino acids determines the overall structure and function of a protein such as an enzyme, different amino acids could lead to proteins with altered structures or functions