2.4 Enzymes

Question 1

How would you speed up a chemical reaction in a laboratory setting and why isn’t this possible in the human body?

Answer 1

-Increase pressure
-Increase temperature because thermal energy gives particles kinetic energy to collide
-Enzymes would denature and cause death

Question 2

What are enzymes and what is a turnover number?

Answer 2

-Biological catalysts that speed up chemical reactions in living organisms, they are globular proteins
-They help sustain life by speeding up chemical reactions needed to sustain life that would happen too slowly
-The turnover number is the number of reactions an enzyme can catalyse per second

Question 3

What is an anabolic and catabolic reaction?

Answer 3

-Anabolic: builds up and synthesise large polymers
-Catabolic: break down large organic molecules

Question 4

Where does enzyme action occur?

Answer 4

-Both intracellularly and extracellularly

Question 5

What do the enzymes Protease, Carbohydrase, Lipase and Cellulase catalyse?

Answer 5

-Protease: Proteins-peptides
-Carbohydrase: monosacharides- carbohydrates
-Lipase: Lipids- glycerol and fatty acids
-Cellulase- Cellulose- β glucose

Question 6

What is catalase?

Answer 6

-Intracellular enzyme
-Protects cell by breaking down hydrogen peroxide into water and oxygen
-Highest turnover number

Question 7

What is a metabolic pathway?

Answer 7

-A series of consecutive chemical reactions with each step being catalysed by a different specific enzyme.
-If one enzyme can’t function the pathway can’t run
-Can be both catabolic and anabolic e.g photosynthesis

Question 8

What is the equation for an enzyme controlled reaction?

Answer 8

-Enzyme + substrate -> Enzyme-substrate complex -> Enzyme-Product complex -> Enzyme + Product

Question 9

How do enzymes increase rate of reaction?

Answer 9

-Enzymes lower the activation energy by creating an enzyme-substrate complex so the two substrates are held close to bond in an anabolic reaction or it puts strain on the complex in a catabolic reaction so it breaks down.

Question 10

How are enzymes highly specific and how will temperature and PH affect it?

Answer 10

-The tertiary structure of the active site is complementary to the shape of the substrate which makes the enzymes function specific
-Changes in temperature and PH will affect its ability to function because the bonds holding the tertiary structure will be affected

Question 11

What is the lock and key hypothesis?

Answer 11

-The hypothesis states that the substrate molecule fits into the active site like a key into a lock
-Various bonds hold it to form an enzyme-substrate complex
-A substrate molecule is split into two or two or more are joined together as strain is put on bonds to break them or the substrates are brought closer together to join
-The enzyme-product complex forms for a second and the products then leave the site

Question 12

What is the induced fit hypothesis?

Answer 12

-this proposes that the active site initially isn’t an exact fit for the substrate molecule
-As the substrate moves into the enzyme it distorts the enzyme and its active site so that it tightly envelopes the substrate

Question 13

What is a cofactor and the two types?

Answer 13

-A small protein that attaches to a molecule so that it can work
-Two types: activators (permanently bound to the enzyme so therefore a prosthetic group) and Coenzymes (large molecules that temporarily bind to the enzyme transferring a chemical group that is necessary e.g. ATP

Question 14

Why is the initial rate of reaction the fastest?

Answer 14

-The chance of collision is at the highest because there is plenty of substrate and enzymes free

Question 15

What is temperature coefficient?

Answer 15

-The change in rate of reaction for every 10 degrees Celsius rise.
Temperature coefficient= rate of reaction +10 degrees/rate of reaction

Question 16

What happens when you change the temperature of an enzyme-controlled reaction?

Answer 16

-Initially increasing the temperature will increase rate as more enzyme-substrate complexes form as both the enzyme and substrate will have more kinetic energy
-When the temperature is too high however bonds that hold the tertiary structure break so the active site changes and the substrate won’t fit so the rate will decrease
-Way too much heat will cause irreversible change in the shape of the active site and the enzyme will become denatured

Question 17

How does changes in PH affect enzymes?

Answer 17

-Hydrogen+ ions interfere with the hydrogen bonds that hold the tertiary structure together, when too acidic and when too alkaline OH- ions also affect hydrogen bonds and change the shape of the active site and the rate will decrease
-If normal PH is restored hydrogen bonds will be restored but at high levels of acidity and alkaline the active site can be permanently changed

Question 18

What is a buffer?

Answer 18

-Something that resists change to PH e.g. Blood keeps PH at 7.4

Question 19

What are two limiting factors of enzyme controlled reactions and Vmax

Answer 19

-Enzyme and substrate concentration
-Vmax is the maximum value the rate of reaction will increase up to if more substrate is added it will have a negligible effect as all active sites are used up

Question 20

What are enzyme inhibitors?

Answer 20

-Inhibitors are molecules that prevent enzymes from carrying out their function or slow them down
-Two types: competitive and non-competitive

Question 21

How do competitive inhibitors work?

Answer 21

-They have a similar shape to the substrate and compete with the substrate to bind
-They form an enzyme inhibitor complex physically preventing entry of the substrate
-However they bind to the active site with weak bonds so can be removed.

Question 22

How do non-competitive inhibitors work?

Answer 22

-They bind to the allosteric site causing a conformational change in the active site so the substrate can’t bind

Question 23

What determines wether the inhibitor is reversible or non-reversible

Answer 23

-Both competitive and non-competitive inhibitors can be reversible and non-reversible
-It depends on the strength of the bonds hydrogen bonds or ionic bonds are weak so can break easily but if the inhibitor forms covalent bonds it cannot be removed

Question 24

What is inside poisons?

Answer 24

-Poison contains inhibitors which irreversibly block enzymes like enzymes important for neuromuscular synapses causing paralysis and death