chapter 4 - enzymes

Question 1

define a catalyst.

Answer 1

a catalyst is a substance that can speed up a chemical reaction, without itself being chemically changed at the end of a reaction.

Question 2

what is an enzyme?

Answer 2

enzymes are PROTEINS that function as biological catalysts

Question 3

what is activation energy?

Answer 3

the energy needed to start a chemical reaction.

Question 4

how do enzymes speed up the rate of chemical reaction?

Answer 4

by lowering activation energy

Question 5

what is an anabolic reaction?

Answer 5

a reaction that BUILDS up/synthesis complex substances from simpler ones

Question 6

what is a catabolic reaction?

Answer 6

a reaction that BREAKS down complex substances to simpler substances

Question 7

example of an anabolic reaction

Answer 7

amino acids —> polypeptides —-> proteins

OR (protein synthesis, DNA replication, photosynthesis)

Question 8

examples of catabolic reactions

Answer 8

digestion, respiration, decomposition,
&
breakdown of hydrogen peroxide by catalase to water and oxygen

Question 9

what are the characteristics of an enzyme? (5)

Answer 9

1. speed up chemical reactions (by lowering activation energy)
2. remain unchanged at the end of the reaction
3. highly specific in action (substrate complementary to active site of enzyme)
4. affected by temperature
5. affected by pH

Question 10

explain the mode of action of an enzyme using the lock-and-key hypothesis.

Answer 10

1. an enzyme has an active site with a specific 3-D shape
2. only the substrate with a shape complementary to that of the active site can fit into the enzyme
3. this results in the formation of an enzyme-substrate complex
4. chemical reaction occurs. at the end of the chemical reaction, products leave the active site
5. enzyme remains chemically unchanged

Question 11

explain the effects of temperature on the rate of enzyme catalysed reactions

Answer 11

(refer to temp. graph - tb pg 67/ slides pg 22)
1. low temperature: enzymes are less reactive. rate of reaction is slow.
2. temp. increases (before optimum temp.) KE pf substrate molecules increases. higher rate of effective collision btw. enzyme and substrate molecules, increasing rate of formation of enzyme-substrate complexes.
3. at optimum temp: rate of reaction is highest as most enzyme-substrate complexes formed
4. beyond optimum temp. enzyme becomes progressively denatured. rate of enzyme activity decreases as active site is no longer complementary to shape of substrate
5. ALL enzymes are COMPLETELY denatured

Question 12

what is denaturation?

Answer 12

denaturation is he change in the 3-D structure of an enzyme, perhaps caused by heat or chemicals

Question 13

when an enzyme is denatured, it can no longer act as a _________.

Answer 13

catalyst

Question 14

when enzymes are placed in pH conditions that vary from the optimum, they start to ___________.

Answer 14

denature