Enzymes

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Notas de aula

What Are Enzymes?

Enzymes are biological catalysts that speed up chemical reactions without being changed or used up.
They are proteins made in living cells.
Enzymes maintain metabolic reaction speeds at a rate that can sustain life.
Without enzymes, digestion would take 2–3 weeks per meal; with enzymes it takes ~4 hours.

Enzyme Action & Specificity (Extended)

Each enzyme has a specific active site with a shape complementary to its substrate (lock and key hypothesis).
When substrate binds to the active site, an enzyme-substrate complex forms.
After the reaction, products leave the active site; the enzyme is unchanged and can catalyse further reactions.
Enzymes and substrates move randomly in solution; collisions lead to reaction when shapes match.

How enzymes work

Effect of Temperature (Extended)

Enzymes have an optimum temperature (e.g., 37 °C in the human body) where activity is fastest.
Increasing temperature from 0 °C to optimum increases kinetic energy, more collisions, faster rate.
Above optimum, bonds holding the enzyme's shape break → denaturation (active site changes shape irreversibly).
Low temperatures slow activity but do not denature enzymes.

Graph showing the effect of temperature on the rate of enzyme activity

Effect of pH (Extended)

Most enzymes have an optimum pH near 7; some (e.g., in stomach) work best at pH 2; others (e.g., in duodenum) at pH 8–9.
Extreme pH disrupts bonds in the protein, altering the active site shape → denaturation.
Moving away from optimum pH reduces activity; too far causes irreversible denaturation.

Graph showing the effect of pH on rate of activity for an enzyme from the duodenum

Investigating Enzyme Activity

Temperature investigation: Heat starch and amylase at set temperatures; test with iodine every minute until no blue-black colour (starch digested).
pH investigation: Mix amylase, buffer, and starch; test with iodine every 10 s until orange-brown (starch digested).
Shorter time to digest starch indicates higher enzyme activity at that temperature/pH.
Always control variables like enzyme concentration, substrate volume, and temperature (except the independent variable).

Investigating the effect of temperature on amylase activity

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Questões de prática

Prévia grátis — 8 de 54 perguntas. Cadastre-se para ver todas.

1.Which of the following best describes what an enzyme is?
Easy
- AA catalyst that speeds up reactions in cells, being used up in the process
- BA protein that speeds up reactions in cells, being used up in the process
- CA carbohydrate that functions as a biological catalyst
- DA protein that functions as a biological catalyst
2.What is a feature of all catalysts?
Easy
- AThey are made from protein
- BThey are not changed by the reaction
- CThey are broken down in the reaction
- DThey are altered by the rate of the reaction
3.What can be said to be true of all enzymes?
Medium
- Atheir optimum pH is 7
- Bthey are made from amino acids
- Cthey move about randomly in a fluid
- Dthey are all proteins
4.Name the group of compounds that ensures metabolic reactions take place in living organisms at a speed necessary to sustain life.
Easy
5.The pH of an enzyme-controlled reaction is decreased by a pH of 2. How does this affect the rate of the reaction?
Medium
- AIt has no effect on the rate.
- BIt always decreases the rate.
- CIt always increases the rate.
- DIt may increase or decrease the rate.
6.A student decided to investigate the effect of pH on the activity of the enzyme lipase. Five different test tubes are set up. Each test tube contains a mixture of the enzyme lipase and its substrate, a lipid. Which condition should not be kept the same in each of the five test tubes?
Medium
- ATemperature
- BConcentration of lipase
- CVolume of lipid solution
- DpH
7.Starch is digested by the enzyme amylase. Four identical mixtures of starch and amylase were kept at different temperatures. The table shows the time taken for the starch to be completely digested at each temperature. | Temperature (°C) | 10 | 20 | 30 | 40 | |---|---|---|---|---| | Time taken (minutes) | 18 | 9 | 4 | 11 | At which temperature is the rate of reaction highest?
Medium
- A10°C
- B20°C
- C30°C
- D40°C
8.Fill in the blank to complete the sentence about enzymes.
Easy
Enzymes are biological ____ that speed up chemical reactions without being changed.

Mais perguntas

9.Increasing the temperature from 0°C to the optimum temperature increases the rate of an enzyme-controlled reaction because the molecules have more kinetic energy and collide more frequently.
Medium
True or false?
10.Match each term related to enzyme action with its correct description.
Medium
- Active site
- Denaturation
- Enzyme-substrate complex
- Region where substrate binds
- Loss of enzyme shape due to high temperature or extreme pH
- Temporary structure formed when substrate binds to enzyme
11.What is the optimum temperature (in °C) for most human enzymes?
Easy
- A41
- B33
- C37
- D45
12.What type of biological molecule are enzymes?
Easy
- ACarbohydrates
- BLipids
- CProteins
- DNucleic acids
13.Enzymes are used up in the reactions they catalyse.
Easy
True or false?
14.Which of the following best describes the lock and key hypothesis?
Medium
- AThe enzyme changes shape to fit the substrate
- BThe substrate changes shape to fit the enzyme
- CThe active site has a fixed shape complementary to the substrate
- DThe enzyme and substrate form a permanent bond
15.Increasing temperature always increases the rate of an enzyme-controlled reaction.
Easy
True or false?
16.What happens to an enzyme when it is heated above its optimum temperature?
Easy
- AIt works faster
- BIt denatures and loses its shape
- CIt becomes more specific
- DIt changes the substrate
17.Which pH is likely to be the optimum for an enzyme found in the stomach?
Easy
- ApH 2
- BpH 7
- CpH 9
- DpH 12
18.Which of the following can cause an enzyme to denature? (Select all that apply)
Medium
- AHigh temperature
- BLow temperature
- CExtreme pH
- DHigh substrate concentration
19.Place the following steps of an enzyme-controlled reaction in the correct order.
Medium
- Products leave the active site
- Enzyme and substrate collide
- Enzyme-substrate complex forms
- Substrate binds to active site
20.Match each term with its correct description.
Easy
- Enzyme
- Substrate
- Active site
- Product
- The molecule that binds to the enzyme
- The biological catalyst that speeds up reactions
- The region on the enzyme where the substrate binds
- The molecule formed at the end of the reaction
21.Which of the following can affect the rate of an enzyme-controlled reaction? (Select all that apply)
Medium
- ATemperature
- BpH
- CConcentration of enzyme
- DColour of the enzyme
- EConcentration of substrate
22.Enzymes are used up during the reactions they catalyse.
Easy
True or false?
23.The graph shows the effect of temperature on the rate of an enzyme-controlled reaction. At point X on the graph, the rate is increasing. What is happening to the enzyme molecules at point X?
Medium
- AThey are denaturing
- BThey have more kinetic energy
- CThey are being used up
- DThey have a changed active site
24.Which of the following statements about the lock and key hypothesis are correct? (Select all that apply)
Hard
- AThe active site is flexible and changes shape to fit the substrate
- BThe enzyme and substrate have complementary shapes
- CThe substrate fits into the active site like a key into a lock
- DThe enzyme is permanently altered after the reaction
- EThe enzyme-substrate complex is formed during the reaction
25.Which graph shows the correct effect of temperature on the activity of an enzyme?
Medium
- AA curve that increases steadily then drops sharply after the optimum
- BA straight line increasing with temperature
- CA curve that decreases steadily then increases
- DA curve that increases then plateaus
26.Match each part of the diagram of an enzyme-catalysed reaction with its label.
Easy
- E
- F
- G
- H
- Enzyme
- Product
- Enzyme-substrate complex
- Substrate
27.A student investigates the effect of temperature on the enzyme catalase. The number of oxygen bubbles produced per minute at 30°C is 68. At 40°C, the number is 79. At 50°C, the number is 5. What is the most likely reason for the low number of bubbles at 50°C?
Medium
- AThe enzyme has denatured
- BThe substrate has been used up
- CThe temperature is too low for the reaction
- DThe enzyme is working more slowly due to low kinetic energy
28.Which of the following factors can affect the rate of an enzyme-controlled reaction? (Select all that apply)
Medium
- ATemperature
- BpH
- CColour of the enzyme
- DConcentration of substrate
- EConcentration of enzyme
29.A student investigates the effect of pH on the activity of the enzyme lipase. Five test tubes are set up, each containing lipase and lipid. Which condition should NOT be kept the same in each test tube?
Medium
- ATemperature
- BConcentration of lipase
- CVolume of lipid solution
- DpH
30.A student investigates the effect of temperature on the enzyme catalase. Cubes of liver are incubated with hydrogen peroxide at different temperatures and the number of oxygen bubbles per minute is counted. The results are shown in the table: temperature / °C: 10, 20, 30, 40, 50 bubbles per minute: 35, 68, 79, 63, 5 Which conclusion can be drawn from these results?
Medium
- AThe optimum temperature for catalase is 30°C.
- BCatalase is denatured at 50°C.
- CThe rate of reaction increases continuously from 10°C to 50°C.
- DCatalase works best at 10°C.
31.The diagram shows an enzyme-catalysed reaction. Which row correctly identifies the labelled parts?
Medium
- AX = enzyme, Y = substrate, Z = enzyme-substrate complex, W = product
- BX = substrate, Y = enzyme, Z = product, W = enzyme-substrate complex
- CX = enzyme, Y = product, Z = substrate, W = enzyme-substrate complex
- DX = product, Y = enzyme, Z = enzyme-substrate complex, W = substrate
32.Which of the following are correct statements about the lock and key hypothesis? (Select all that apply)
Medium
- AThe enzyme's active site has a rigid shape complementary to the substrate.
- BThe substrate changes shape to fit into the active site.
- CThe enzyme-substrate complex is formed during the reaction.
- DThe product is released from the active site after the reaction.
- EThe enzyme is permanently altered after the reaction.
33.What is the optimum temperature for most human enzymes?
Easy
- A25°C
- B37°C
- C40°C
- D50°C
34.The diagram shows an enzyme-catalysed reaction. Which row correctly identifies the labelled parts?
Medium
- AE: enzyme, S: substrate, F: enzyme-substrate complex, G: product
- BE: enzyme, S: product, F: enzyme-substrate complex, G: substrate
- CE: substrate, S: enzyme, F: product, G: enzyme-substrate complex
- DE: product, S: enzyme, F: enzyme-substrate complex, G: substrate
35.A student investigates the effect of pH on the activity of the enzyme amylase. At pH 7, the starch is completely digested in 120 seconds. At pH 5, it takes 300 seconds. What does this indicate about the optimum pH of amylase?
Medium
- ApH 5 is the optimum
- BpH 7 is closer to the optimum than pH 5
- CpH 7 is the optimum
- DThe optimum is below pH 5
36.Liver cells produce an enzyme called catalase which breaks down toxic hydrogen peroxide into water and oxygen. A student set up an experiment where cubes of cows' liver in a test tube were incubated with hydrogen peroxide at different temperatures. The student counted the number of bubbles of oxygen released per minute at each temperature. Their results are shown in the table below: | temperature / °C | 10 | 20 | 30 | 40 | 50 | |---|---|---|---|---|---| | number of bubbles / minute | 35 | 68 | 79 | 63 | 5 | The results suggest that the optimum temperature for catalase is between which two values?
Medium
- A10°C and 40°C
- B20°C and 30°C
- C30°C and 40°C
- D20°C and 40°C
37.A student investigates the effect of temperature on the activity of amylase. They add amylase to starch solution at different temperatures and test samples with iodine every minute. The time taken for the iodine to remain orange-brown is recorded. Which of the following is the independent variable in this experiment?
Medium
- ATime taken for starch to be digested
- BTemperature
- CConcentration of amylase
- DVolume of starch solution
38.In an investigation of the effect of pH on amylase activity, a student uses buffer solutions to maintain different pH values. Which of the following should be kept constant in all test tubes?
Medium
- ApH
- BTemperature
- CType of buffer
- DVolume of iodine
39.The graph shows the effect of pH on the rate of reaction of three different enzymes. What does the graph show?
Medium
- AEach enzyme works best over a narrow temperature range.
- BMost enzymes work best around a neutral pH.
- CEnzymes work better in acidic conditions.
- DEach enzyme works best at a different pH.
40.Complete the sentence.
Easy
The part of an enzyme where the substrate binds is called the ____.
41.Name the substance used to test for the presence of starch in an enzyme investigation.
Easy
42.A student investigates the effect of temperature on the enzyme catalase. The number of oxygen bubbles produced per minute at 30°C is 68. At 40°C, the number is 63. What is the percentage decrease in the number of bubbles from 30°C to 40°C? Give your answer to the nearest whole number.
Medium
43.A student investigates the effect of pH on the activity of the enzyme amylase. At pH 7, the starch is completely digested in 120 seconds. At pH 5, it takes 300 seconds. How many times faster is the reaction at pH 7 compared to pH 5? Give your answer to 2 significant figures.
Medium
44.What is the name of the hypothesis that describes how the shape of an enzyme's active site is complementary to its substrate?
Easy
45.A student investigates the effect of temperature on the enzyme catalase. The number of oxygen bubbles produced per minute at 30°C is 68. At 40°C, the number is 79. At 50°C, the number is 5. What is the optimum temperature (in °C) for catalase based on these results?
Easy
46.Complete the sentence about enzymes.
Easy
Enzymes are ____ that speed up chemical reactions in living organisms.
47.Complete the sentence about enzyme action.
Easy
The hypothesis that describes how the shape of an enzyme's active site is complementary to its substrate is called the ____ and ____ hypothesis.
48.What is the name of the substance used to test for the presence of starch in an enzyme investigation?
Easy
49.State the optimum pH for most human enzymes.
Easy
50.Explain why the rate of an enzyme-controlled reaction decreases when the pH is moved far from the optimum.
Medium
51.Describe how you would investigate the effect of pH on the activity of amylase.
Hard
52.A student investigates the effect of temperature on the enzyme catalase. The number of oxygen bubbles produced per minute at 30°C is 68. At 40°C, the number is 63. What is the percentage decrease in the number of bubbles from 30°C to 40°C? Give your answer to the nearest whole number.
Medium
- A8 %
- B9 %
- C6 %
- D7 %
53.A student investigates the effect of pH on the activity of the enzyme amylase. At pH 7, the starch is completely digested in 120 seconds. At pH 5, it takes 300 seconds. How many times faster is the reaction at pH 7 compared to pH 5? Give your answer to 2 significant figures.
Medium
- A2.5
- B3.5
- C1.5
- D4.5
54.A student investigates the effect of temperature on the enzyme catalase. The number of oxygen bubbles produced per minute at 30°C is 68. At 40°C, the number is 79. At 50°C, the number is 5. What is the optimum temperature (in °C) for catalase based on these results?
Medium
- A40 °C
- B48 °C
- C36 °C
- D44 °C

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