Biological Molecules: proteins: enzymes

Question 1

what is the name of the structure of enzymes

Answer 1

globular proteins

Question 2

what type of reactions do enzymes catalyse

Answer 2

reversible reactions

Question 3

what are the two categories of enzymes

Answer 3

intracellular - produced and function inside the cell
extracellular - secreted by cells and function outside cells

Question 4

function of catalase

Answer 4

to convert hydrogen peroxide into water and oxygen to prevent damage to tissues and cells
- intracellular enzyme -

(hydrogen peroxide is a product of many metabolic reactions and is harmful to cells)

Question 5

function of amylase

Answer 5

to hydrolyse starch into simple sugars (carbohydrate digestion)

Question 6

where is amylase secreted from and where does it act

Answer 6

• secreted from salivary glands and the pancreas
• acts in the mouth and small intestine respectively

Question 7

how is the shape of the active site determined

Answer 7

by the complex tertiary structure of the protein

Question 8

what is a catabolic reaction

Answer 8

involves the breakdown of complex molecules into simpler products —- happens when a single substrate is drawn into the active site and broken apart into two distinct molecules

Question 9

what are the two types of enzyme reaction

Answer 9

• catabolic
• anabolic

Question 10

what is a anabolic reaction

Answer 10

involves the building of more complex molecules from simpler ones by drawing two or more substrates into the active site and forming bonds between them

Question 11

what are examples of catabolic reactions

Answer 11

• cellular respiration
• hydrolysis

Question 12

what are some examples of anabolic reactions

Answer 12

• protein synthesis
• photosynthesis

Question 13

what is the activation energy

Answer 13

the amount of energy needed by the substrate to become just stable enough for a reaction to occur and products to be formed

Question 14

how do enzymes lower the activation energy of a reaction

Answer 14

they influence the stability of bonds in the reactants. the destabilisation of bonds in the substrate makes it more reactive

Question 15

what are the two hypotheses on how enzymes work

Answer 15

• the lock and key hypothesis
• the induced fit hypothesis

Question 16

what type of proteins are enzymes and why is this significant

Answer 16

globular proteins

this means their shape is determined by the complex tertiary stricture of the protein and is therefore highly specific

Question 17

what is the lock and key hypothesis

Answer 17

it suggests that both enzymes and substrates were rigid structures that locked into each other very precisely

Question 18

what is the induced fit hypothesis

Answer 18

• the induced fit states that the active site changes shape to fit the substrate when it comes into contact with the active site (these changes of shape are known as conformational changes)
• this ensures an ideal binding arrangement between the enzyme and substrate is achieved —-this maximises the ability of the enzyme to catalyse the reaction

Question 19

what is the main difference between the induced fit and the lock and key

Answer 19

• the lock and key model states that the enzyme and substrate fit perfectly together
• the induced fit states that the active site changes shape to fit the substrate when it comes into contact with the active site

Question 20

required practical: measuring enzyme activity

Question 21

maths skill: drawing a graph for enzyme rate experiments

Question 22

maths skill: using a tangent to find initial rate of reaction

Question 23

what is the specific optimum temperature of an enzyme

Answer 23

the temp at which they catalyse a reaction at the maximum rate

Question 24

how do low temperatures prevent/slow down reactions

Answer 24

• molecules have low kinetic energy so move slow
• lower frequency of successful collisions between substrate molecules and active site of enzymes
• enzyme-substrate complexes form less frequently
• substrate and enzyme collide with less energy making it less likely for bonds to be formed or broken

Question 25

how can high temperatures prevent reactions from occuring

Answer 25

• hydrogen bonds between amino acids (holding it in its precise shape) start to break
• tertiary structure changes
• permanently damages active site
• prevents substrate from binding
  —denaturation

Question 26

what are the critical body temperatures for humans (enzymes)

Answer 26

• body temp of 37*C
• denaturation of enzymes above 40*C
• very few human enzymes can function above 50*C

Question 26

what bonds within enzymes are affected by high temperatures

Answer 26

the hydrogen bonds between amino acids

Question 27

what is the optimum pH of pepsin and why

Answer 27

pH 2 because it functions in the stomach which is a highly acidic environment due to the presence of hydrochloric acid

Question 27

what bonds within enzymes are affected by extreme pH

Answer 27

hydrogen and ionic bonds which hold together the tertiary structure of the protein

due to the excess of H+ ions in acidic solutions and OH- ions in alkaline solutions

Question 27

what do buffer solutions do

Answer 27

• they each have a specific pH and maintain this pH even if the reaction

Question 27

how do we use buffer solutions

Answer 27

• a measured volume of the buffer solution is added to the reaction mixture
• the same volume should be added for each different pH value being tested

Question 27

what equation can be used to find the pH of a solution and what information do you need to know

Answer 27

pH = -log10[H+]
‘log’ is the same as ‘log10’ on the calculator

if the hydrogen ion (H+) concentration of the solution is known —in mol/dm3

Question 27

how does enzyme concentration affect rate of reaction

Answer 27

• high enzyme conc
• greater number of active sites available
• greater likelihood of enzyme-substrate complex formation

(as long as there is sufficient substrate available, the initial rate will increase linearly)

Question 28

factors affecting enzymes

Answer 28

• temperature
• pH
• enzyme concentration
• substrate concentration
• presence of inhibitors

Question 29

what are the two types of inhibitors

Answer 29

• competitive
• non-competitive

Question 30

what is a competitive inhibitor

Answer 30

• has a similar shape to the substrate molecules and therefore compete for access to the active site

Question 31

what is a non-competitive inhibitor

Answer 31

• binds to the enzyme away from the active site, altering the shape of the active site and therefore preventing the substrate from binding

Question 32

how can we regulate metabolic pathways

Answer 32

inhibitors

Question 33

why must metabolic reactions be controlled

Answer 33

so that not all enzymes are working at maximum capacity at all times which would result in build ups of one product and a deficit of others