Enzymes 1

Question 1

what do enzymes do?

Answer 1

enzymes speed up chemical reactions by acting as biological catalysts

Question 2

what is a catalyst?

Answer 2

a catalyst is substance that speeds up a chemical reaction without being used up in the reaction itself

Question 3

what are biological catalysts?

Answer 3

those found in living organisms

Question 4

what 2 levels do enzymes catalyse reactions on?

Answer 4

both on a cellular level (e.g. respiration) and for the organism as a whole (e.g. digestion in mammals)

Question 5

how can enzymes affect the structure of an organisms?

Answer 5

-e.g. enzymes are involved in the production of collagen, an important proteins in the connective tissues of animals, as well as functions (respiration)

Question 6

what are the 2 types of enzyme action?

Answer 6

intracellular- within cells

-extracellular- outside cells

Question 7

give an example of intracellular enzymes and how they work?

Answer 7

• CATALASE is an enzyme that works inside cells to catalyse the breakdown of hydrogen peroxide to harmless oxygen (O2) and water (H2O).
• HYDROGEN PEROXIDE (H2O2) is the toxic by-product of several cellular reaction. If left to build up, it can kill cells.

Question 8

give an example of extracellular enzymes and how they work

Answer 8

amylase and trypsin both work outside cells in the human digestive system.

• amylase is found in saliva. It’s secreted into the mouth by cells in the salivary glands. It catalyses the hydrolysis of starch into maltose (a sugar) in the mouth.
• Trypsin catalyses the hydrolysis of peptide bonds- turning big polypeptides into small ones (which then get broken down into amino acids by other enzymes). Trypsin is produced by cells in the pancreas and secreted into the small intestine.

Question 9

what type of protein are enzymes?

Answer 9

globular proteins

Question 10

describe the structure of enzymes?

Answer 10

• they’re globular proteins
• they have an active site.
• the active site is the part of the enzyme where the substrate molecules (the substance that the enzyme interacts with) binds to.
• the active site has a specific shape, which is determined by the enzyme’s tertiary structure.

Question 11

what needs to occur for enzymes to work?

Answer 11

• for enzymes to work, the substrate has to fit into the active site (its shape has to be complementary).
• if the substrate shape doesn’t match the active site, the reaction won’t be catalysed.
• This means that enzymes are very specific and work with very few substrates- usually only one.
• when a substrate binds to an enzyme’s active sit, an enzyme- substrate complex is formed

Question 12

what is activation energy?

Answer 12

the minimum amount of energy that needs to be supplied for a reaction to be able to start

Question 13

how do enzymes work?

Answer 13

enzymes reduce the amount of activation energy that’s needed, often making reactions happen at a lower temperature than they could without an enzyme.
-this speeds up the rate of a reaction.

Question 14

draw and label a graph to show the activation energy needed for a reaction with and without an enzyme

Answer 14

insert pic, page 106 CGP

Question 15

what lowers the activation energy for a reaction?

Answer 15

when a substance binds to an enzyme’s active site, an enzyme- substrate complex is formed, which lowers the activation energy

Question 16

how does the formation of enzyme-substrate complex’s lower the activation energy?

Answer 16

• if 2 substrate molecules need to be joined, attaching to the enzyme holds them together, reducing any repulsion any repulsion between the molecules so they can bond more easily
• if the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate. This strain means the substrate molecule breaks up more easily

Question 17

describe the lock and key model

Answer 17

This is where the substrate fits into the enzyme in the same way that a key fits into a lock- the active site and substrate have a complementary shape.

Question 18

describe the problems with the lock and key model

Answer 18

scientists soon realise that the lock and key model didn’t give the full story. The enzyme and substrate do not have to fit together in the first place, but new evidence showed that the enzyme- substrate complex changed shape slightly to complete the fit.

• this locks the substrate even more tightly to the enzyme.
• Scientists modified the lock and key model and came up with the ‘induced fit’ model.

Question 19

draw and label a diagram for the lock and key model

Answer 19

insert pic page 106 CGP

Question 20

describe the ‘induced fit’ model and why it’s widely accepted

Answer 20

• the ‘induced fit’ model helps to explain why enzymes are so specific and only bond to one particular substrate.
• the substrate doesn’t only have to be the right shape to fit the active site, it has to make the active site change shape in the right way as well.
• this is a prime example of how a widely accepted theory can change when new evidence come along.
• the ‘induced fit’ model is still widely accepted.

Question 21

draw and label a diagram for the ‘induced fit’ model

Answer 21

insert pic page 106 CGP

Question 22

what happens to an enzyme as you increase the temperature?

Answer 22

• the rate of an enzyme- controlled reaction increases when the temp’s increased.
• more heat= more kinetic energy, so molecules move faster.
• this makes the substrate molecules more likely to collide with the enzyme’s active sites.
• the energy of these collisions also increases, which means each collision is more likely to result in a reaction.
• the rate of reaction continues to increase until the enzyme reaches its optimum temperature.

Question 23

what’s meant by the optimum temperature?

Answer 23

this is the temp at which the rate of an enzyme- controlled reaction is at its fastest.

Question 24

what happens to an enzyme- controlled reaction beyond the optimum temperature?

Answer 24

• if the temp gets too high, the reaction stops.
• the rise in temp makes the enzyme’s molecules vibrate more.
• if the temp goes above a certain level, this vibration breaks some of the bonds that hold the enzyme in shape.
• the active site changes shape and the enzyme and substrate no longer fit together.
• at this point, the enzyme is denatured- it o longer functions as a catalyst.