Enzymes

Question 1

define an enzyme

Answer 1

Enzymes are globular proteins that act as catalysts.

they alter the rate of a chemical reaction without undergoing permanent changes themseves.

Question 2

what is required for reactions like sucrose + water= glucose to take place naturally

Answer 2

the sucrose water molecules must collide with sufficient energy to alter the arrangement of their atoms to form glucose and fructose

the free energy of the products must be less than that of the substrates sucrose and water

many reactions require an activation energy

Question 3

what must happen before a reaction can proceed

Answer 3

there is an activaion energy level, like an energy barrier which must initially be overcome before the reaction can proceed

Question 4

explain how enzymes help reactions proceed

Answer 4

enzymes work by lowering this activation energy level

in this way enzymes allow reactions to take place at lower temperature than normal

this enables some metabolic processes to occur rapidly at the human body temperature of 37 degrees Celsius

Question 5

what would happen without enzymes

Answer 5

these reactions would proceed too slowly to sustain life as we know it

Question 6

what region of the enzyme is functional

Answer 6

active site

Question 7

describe the active site

Answer 7

the active site is made up of a relatively small number of amino acids

he active site forms a small depression within the much larger enzyme molecule

Question 8

what is the molecule on which the enzyme acts called

Answer 8

the substrate

Question 9

explain the role of a substrate

Answer 9

fits neatly into this depression and forms an enzyme-substrate complex.

the substrate molecule is held within the active site by bonds that temporarily form between certain amino acids of the active site and group of the substrate molecule

Question 10

describe the induced fit model of enzyme action

Answer 10

the induced fit model of enzyme action proposes that the active site forms as the enzyme and substrate interact

the enzyme is flexible and can mould itself around the substrate

the enzyme has a certain general shape but this alters in the presence of a substrate

As it changes shape, the enzyme puts a strain on the substrate molecule.

the strain distorts particular bonds in the substrate and consequently lowers the activation energy needed to break the bond

Question 11

explain the induced fit concept

Answer 11

any change in an enzymes environment is likely to change its shape.

the very act of colliding with its substrate is a change in its environment and so its shape changes- induced fit

Question 12

explain the mechanism of enzyme action

Answer 12

Substrates collide with the enzyme’s active site and this must happen at the correct orientation and speed in order for a reaction to occur

An enzyme-substrate complex forms when an enzyme and its substrate join together

The enzyme-substrate complex is only formed temporarily before the enzyme catalyzes the reaction and the product(s) are released

Question 13

explain the specificity of an enzyme

Answer 13

The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s)

Question 14

what determines the shape of the active site

Answer 14

The shape of the active site (and therefore the specificity of the enzyme) is determined by the complex tertiary structure of the protein that makes up the enzyme

Question 15

what forms when an enzyme and substrate join together

Answer 15

an enzyme-substrate complex

Question 16

what are the two types of enzyme reactions

Answer 16

Enzyme reactions can either be catabolic or anabolic

Question 17

explain catabolic reactions

Answer 17

Catabolic reactions involve the breakdown of complex molecules into simpler products, which happens when a single substrate is drawn into the active site and broken apart into two or more distinct molecules (products)

Question 18

give two examples of catabolic reactions

Answer 18

cellular respiration and hydrolysis

Question 19

explain anabolic reactions

Answer 19

Anabolic reactions involve the building of more complex molecules from simpler ones by drawing two or more substrates into the active site, forming bonds between them and releasing a single product

Question 20

give two examples of anabolic reactions

Answer 20

protein synthesis

photosynthesis

Question 21

what type of protein are enzymes

Answer 21

globular proteins

Question 22

what can enzymes be

Answer 22

Enzymes can be intracellular or extracellular referring to whether they are active inside or outside the cell respectively

Question 23

define intracellular enzymes

Answer 23

Intracellular enzymes are produced and function inside the cell

Question 24

define extracellular enzymes

Answer 24

Extracellular enzymes are secreted by cells and catalyse reactions outside cells (eg. digestive enzymes in the gut)

Question 25

explain the effect of a rise in temperature on enzyme action

Answer 25

a rise in temperature increases the kinetic energy of molecules.

as a result, the molecules move around more rapidly and collide with each other more often

in an enzyme catalysed reaction, this means that the enzyme and substrate molecules come together more often in a given time

there are more effective collisions resulting in more enzyme-substrate complexes being formed and so the rate of reaction increases

Question 26

what happens when the temperature exceeds 37 degrees celsius

Answer 26

it causes the hydrogen and other bonds in the enzyme molecule to break

this results in the enzyme, including its active site changing shape, slowing the rate of reaction

Question 27

explain when denaturation occurs and define it

Answer 27

usually, around 60 degrees the enzyme is so disrupted that it stops working altogether. it is said to be denatured

denaturation is a permanent change and once it has occurred, the enzyme does not function again

Question 28

why have our bodies evolved to be 37 degrees celsius

Answer 28

althougher higher body temperatures would increase te metabolic rate slightly, the advantages are offset by the additional energy that would be needed to maintain the higher temperature

other proteins, apart from enzymes, may be denatured at higher temperatures

at higher temperatures any further rise in temperature, for example, during illness, might denature the enzymes