Enzymes

Question 1

Enzymes

Answer 1

Enzymes
Enzymes increase the speed of reactions. They are often called biological catalysts. The active site of an enzyme is very important:

Question 2

Active site activity

Answer 2

To catalyse (speed up) a reaction, the reacting chemical (substrate) must bind to the enzyme’s active site.
The active site will only fit specific substrates.

Question 3

Lock and key

Answer 3

Lock and key
The active site is like a lock and the substrate is like a key.
In the same way, there is usually only one enzyme for every substrate (or one key for each lock).

Question 4

Enzyme activity

Answer 4

The substrate binds to the active site of an enzyme, which has a matching shape. Here, it’s reaction is sped up. In this case, the molecule is broken down.

Question 5

Why are enzymes called biological catalysts

Answer 5

Enzymes increase the speed of reactions, so are often called biological catalysts.

Question 6

Substrate Concentration

Answer 6

Increasing the substrate concentration will increase the rate of activity to a certain point until it levels off.
This is because if there are more substrate molecules available for the enzyme to bind to, the rate increases.
But once there are enough substrate molecules for all the enzymes to bind to, increasing the substrate concentration any more will have no effect on the rate of activity.

Question 7

What happens to an enzyme’s pH is very high?

Answer 7

Denature

Question 8

Enzyme Activity and pH

Answer 8

Enzymes have an optimum pH (measure of acidity). If the pH changes away from the optimum, then the enzyme activity decreases. If the pH is too low or too high, then the enzyme is denatured and will not function.

Question 9

Calculating Rate of Reaction

Answer 9

The rate of reaction is equal to the gradient of the graph, which shows mass of the product plotted against the reaction time.
The gradient is calculated by picking two points on the graph, then dividing the change in the value on the y axis (mass) by the change in the x axis value (time), between those two points.
In the example above, the rate of reaction = 10g ÷ 60s = 0.17 g/s.

Question 10

In a reaction involving enzymes, the change in mass is 10g and the change in time is 60 seconds. What is the rate of reaction?

Answer 10

0.17 g/s

Question 11

Factors Affecting the Rate of Enzyme Action
The factors that affect the rate (speed) of enzyme action are: Temperature

Answer 11

Increasing the temperature of a working enzyme initially increases the reacting activity.
Enzymes have an optimum temperature. Once this temperature is reached, the activity decreases.
Past a certain temperature, the active site changes shape, and the enzyme is denatured (loses its catalytic activity).

Question 12

Factors Affecting the Rate of Enzyme Action
The factors that affect the rate (speed) of enzyme action are: pH

Answer 12

pH (measure of acidity)
Enzymes have an optimum pH (measure of acidity).
If the pH changes away from the optimum pH, then the enzyme activity decreases.
If the pH is too low or too high, then the enzyme is denatured and will not function.

Question 13

Factors Affecting the Rate of Enzyme Action
The factors that affect the rate (speed) of enzyme action are: Substrate concentration

Answer 13

Substrate concentration
Increasing the substrate concentration will increase the rate of activity to a certain point until it levels off.
This is because if there are more substrate molecules available for the enzyme to bind to, the rate increases. But once there are enough substrate molecules for all the enzymes to bind to, increasing the substrate concentration any more will have no effect on the rate of activity.

Question 14

Calculating Rate of Reaction

Answer 14

The rate of reaction is equal to the gradient of the graph, which shows mass of the product plotted against the reaction time.
The gradient is calculated by picking two points on the graph, then dividing the change in the value on the y axis (mass) by the change in the x axis value (time), between those two points. In the example above, the rate of reaction = 10g ÷ 60s = 0.17 g/s.

Question 15

Investigating the Effect of pH on Amylase: What do amylase break down?

Answer 15

Amylase breaks down starch, which can be detected using iodine solution.

Question 16

Measuring reaction time

Answer 16

-Add amylase to starch solution.
-Every 30 seconds, take a drop of the mixture and add a drop of iodine solution.
-Record the total time taken for the iodine solution to stop turning blue when added (which indicates that all the starch has been broken down).

Question 17

Finding amylase’s optimal pH

Answer 17

Repeat this experiment using starch solutions with different pHs.
The shorter the time taken for the iodine to stop changing colour, the faster the amylase has broken down the starch and the closer this pH is to amylase’s optimal pH.

Question 18

What are the dependent and independent variables in the experiment investigating the effect of pH on amylase?

Answer 18

The independent variable is pH. the dependent variable is the time taken for the starch to be broken down.

Question 19

Iodine

Answer 19

Iodine is a test for starch; when iodine is added to a solution that contains starch, it turns blue.

Question 20

A graph, with enzyme activity on the y axis, has a steep curve. This reflects:

Answer 20

Fast rate of reaction

Question 21

Equation for reaction rate
reaction rate= change in mass/change in time

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Answer 21

reaction rate is equal to the change in mass divided by the change in time.

Question 22

Enzymes in Digestion

Answer 22

Digestive enzymes are produced by specialised cells (perform a specific function) in the glands and the lining of the gut. They are then secreted (released) out of the body cells and into the cavity of the digestive system.

Question 23

Digestive enzymes are used to: Breakdown large food molecules

Answer 23

The digestive enzymes catalyse (speed up) the breakdown of large, insoluble food molecules into smaller, soluble (can be dissolved) molecules that are then small enough to be absorbed into the bloodstream.
Digested molecules can be used to construct new carbohydrates, proteins and lipids in the body.
Some glucose produced by digestion is used for respiration.

Question 24

Enzymes in digestion

Answer 24

The 3 main digestive enzymes are:
Amylase
Protease
Lipase

Question 25

Digestive enzymes

Answer 25

Digestive enzymes are produced by specialised cells in the glands and the lining of the gut.

Question 26

Enzymes in Digestion

Answer 26

Digestive enzymes are produced by specialised cells in the glands and the lining of the gut. They are then secreted (released) out of the body cells and into the cavity of the digestive system.

Question 27

Breakdown large food molecules

Answer 27

Catalyse the breakdown of large, insoluble food molecules into smaller, soluble molecules.

Question 28

Why is it necessary to breakdown large, insoluble food molecules into smaller, soluble molecules?

Answer 28

Large, insoluble food molecules can't be absorbed into the bloodstream. Small, soluble molecules can be absorbed into the bloodstream and used to construct new carbohydrates, proteins and lipids in the body. Some glucose produced by digestion is used for respiration.

Question 29

Digestive enzymes catalyse

Answer 29

Digestive enzymes catalyse (speed up) the breakdown of large, insoluble food molecules into smaller, soluble molecules.

Question 30

Amylase

Answer 30

Carbohydrases break carbohydrates down into sugars. Amylase is a type of carbohydrase that breaks down starch in our bodies.

Question 31

Action sites The sites of action of amylase are:

Answer 31

The small intestine The mouth

Question 32

Purpose

Answer 32

Amylase breaks down starch into its constituent simple sugars (predominantly maltose). Starch → Maltose (+ other sugars).

Question 33

Proteases

Answer 33

Proteases are digestive enzymes that break down proteins into amino acids.

Question 34

Action sites The sites of action of proteases are the:

Answer 34

small intestine stomach

Question 35

Production Proteases are produced in the:

Answer 35

Proteases are produced in the: small intestine pancreas stomach

Question 36

Purpose

Answer 36

Proteases break down proteins into amino acids. Protein → Amino acids.

Question 37

Digestive enzymes break proteins into

Answer 37

Amino acids

Question 38

Lipase

Answer 38

Lipase is a type of digestive enzyme that breaks down lipids into glycerol and fatty acids.

Question 39

Production Lipase is produced in the:

Answer 39

Small intestine Pancreas

Question 40

Purpose

Answer 40

Lipase breaks down lipids into a molecule called glycerol and fatty acids. Lipid → Glycerol + Fatty Acids.

Question 41

Write the correct digestive enzyme next to its function:

Answer 41

Lipase Breaks down lipids into a molecule called glycerol and fatty acids. Proteases Break down proteins into their constituent amino acids. Amylase Breaks down starch into its constituent simple sugars (predominantly maltose).

Question 42

Lipase catalyses the break down of lipids:

Answer 42

Lipid → Glycerol + Fatty acids.

Question 43

Testing For Carbohydrates, Lipids & Proteins

Answer 43

Reagents can be used to test for the presence of various food substances. first step is to grind up the food and add distilled water to dissolve some of the food. You can then test for the food substances

Question 44

Proteins

Answer 44

To test for proteins, add Biuret solution. It will turn mauve or purple if proteins are present.

Question 45

Lipids

Answer 45

To test for lipids, add ethanol and water and shake. If lipids are present, a white emulsion (cloudy liquid) will form.

Question 46

Calorimetry

Answer 46

We can also test the calorie content of foods: Burn a known mass of the food under a boiling tube filled with a known volume of water. Calculate the change in temperature of the water.

Question 47

Sugar

Answer 47

To test for sugar, add Benedict’s reagent and heat for about two minutes. It will turn any of green, yellow or red if sugar is present. The colour depends on the concentration.

Question 48

Starch

Answer 48

To test for starch, add iodine solution. It will turn blue-black if starch is present.

Question 49

Tests for various food substances:

Answer 49

Proteins Add Biuret solution. It will turn mauve or purple if present. Starch Add iodine solution. It will turn blue-black if present. Sugar Add Benedict’s reagent and heat for about two minutes. It will turn any of green, yellow or red if this food substance is present. Lipids Add ethanol and water and shake. A white emulsion (cloudy liquid) will form if present. Calorie content Burn a known mass of a food under a boiling tube of water. Calculate change in water temperature.

Question 50

If we add iodine to starch then it will turn.

Answer 50

Blue-black

Question 51

What are proteins broken down into during digestion?

Answer 51

Amino acids

Question 52

What does the small intestine do?

Answer 52

Absorbs soluble food molecules, digests foods

Question 53

Where is amylase produced?

Answer 53

Smaller intestines, pancreas

Question 54

Name one different digestive enzyme

Answer 54

Pepsin

Question 55

The ‘lock and key theory’ is a model used to explain enzyme action

Answer 55

The key is the substrate. The lock is the active site of an enzyme. The substrate fits into the active site. There is usually only one enzyme for every substrate.