Chapter 1 Biological molecules - Enzymes (1.7-1.9)

Question 1

What are enzymes

Answer 1

Enzymes are tertiary structure proteins which catalyse and control chemical reactions in the body without being changed by the reaction

Question 2

What is the active site

Answer 2

It’s a specific and unique shape due to the specific folding and bonding in the tertiary structure of the protein

Question 3

How do enzymes speed up the reaction

Answer 3

When the enzymes attach to the substrate they lower the activation energy needed for the reaction to occur by providing an alternative reaction pathway with a lower activation energy and allow the reaction to proceed at body temperature and therefore speed up the reaction

Question 4

What two models explain how enzymes react with substrates

Answer 4

Lock and key theory
Induced fit model

Question 5

Explain the lock and key theory

Answer 5

The enzyme is the lock and the substrate is the key that fits into it due to their complimentary shape
This model suggests that the enzymes active site is a fixed shape and that due to the random collisions the substrate can collide and attach to the enzyme forming an enzyme substrate complex. And once the enzyme substrate complex has formed the charged groups within the active site will cause the substrate to distort in shape and lower the activation energy. The products are then released and the enzymes active site is empty and ready to be reused

Question 6

Explain the induced fit model

Answer 6

• suggests that the enzyme active site is slightly different from the shape of the substrate at first
  1) Substrate binds to the active site forming Enzyme-substrate complex
  2) Active site changes shape so it is complementary to substrate putting strain and breaking bonds in the substrate
  3) therefore lowers the activation energy as less energy is needed for the reaction to occur
  4) The product are then removed and the enzyme active site returns to its original shape

Question 7

Factors that affect enzyme action

Answer 7

• temperature
• pH
• substrate concentration
• enzyme concentration
• inhibitors

Question 8

How does temperature affect enzymes

Answer 8

• if the temperature is too low there is not enough kinetic energy for successful collisions between the enzyme and substrate so fewer E-S complexes can form
• if the temperature is too high enzymes denature and enzyme substrate complexes cannot form as the hydrogen/ionic bonds are broken changing the shape of the teritiary structure and altering the specific shape of the active site, so it may no longer be complementary to the substrate so the enzymes cannot bind with the substrateso fewer E-S complexes can form

Question 9

Explain the temperature graph on enzyme activity

Answer 9

1) the enzyme activity increases as the enzymes are gaining kinetic energy so there is a higher frequency of successful collisions between enzyme and substrate
2) the enzymes have reached their optimum temperature so enzyme activity has reached its maximum
3) the enzymes have denatured as its gone beyond its optimum temperature so enzyme activity decreases as the enzymes cannot bind to substrate and form enzyme substrate complex

Question 10

How does pH affect enzyme activity

Answer 10

• as pH increases or decreases this causes the hydrogen/ionic bonds to break, causing the enzyme tertiary structure and active site to change shape
• so the active site is no longer complemenry to the substrate so fewer enzyme substrate complexes can form

Question 11

How does substrate and enzyme concentration affect enzyme activity

Answer 11

• as substrate concentration increases the rate of reaction increases as at this point the substrate is limiting so more E-S complexes can form until the enzymes become saturated making the enzymes the limiting factor causing the rate of reaction to plateau
• as the enzyme concentration increase the rate of reaction increases as the increase in enzymes results in more active sites to become available until at a certain point the rate if reaction plateaus as the substrate becomes limiting as they all binded to the enzymes

Question 12

How does substrate conc. affect inhibitorsand enzyme activity

Answer 12

Competitive inhibitors - adding more substrate will out compete the inhibitors, knocking them out of the active site increasing the rate of reaction (vice versa)
Non competitive inhibitors - substrate concentration has no affect on the enzyme activity as the inhibitors change the shape of the active site and enzyme

Question 13

What are competitive inhibitions

Answer 13

This is when the inhibitor is a SIMULAR shape as the substrate and can bind to the active site. This prevents the substrate from binding and REDUCES THE AMOUNT OF ENZYME COMPLEXES from forming

Question 14

What is non competitive inhibition

Answer 14

This is when the inhibitor binds to the enzyme away from the active site, the allosteric site, changing the tertiary structure of the enzyme this causes the active site to change shape so the substrate is no longer complimentary to the enzyme

Question 15

Why is the Vmax the same as the Vmax without an inhibitor in competitive inhibitions

Answer 15

As when there is a high amount of substrate concentration the substrates out compete the inhibitors, knocking them off the active site so the substrate can bind with the enzyme returning the rate of reaction to normal

Question 16

Why is the Vmax low in non competitive inhibitions

Answer 16

As even if you add more substrate the substrate cannot out compete the inhibitors as the active site is a different shape so the enzyme cannot catalyse the reaction

Question 17

formation of enzyme substrate complex increases rate of reaction explain why

Answer 17

• reduces the activation energy
• ## due to pressure put on bonds

Question 18

How to calculate pH

Answer 18

pH = -log[H+] - equation
Put in the number of hydrogen atoms in calculator
Press log and enter number of h atoms
Then the answer would be the opposite to the original answer e.g if the original answer was a minus then then the new answer would be a plus (vice versa)

Question 19

how does temperature affect ENZYME ACTIVITY (3 marks)

Answer 19

increase in temperature increases kinetic energy;
increases frequency of successful collisions per unit time (between enzyme/active site and substrate) /
increases formation of enzyme/substrate complexes;
increases rate of breakdown
so increases overall enzyme activity

Question 20

n an investigation the enzyme amylase was mixed in a test tube with a buffer solution and a suspension of starch. The amylase broke down the starch to maltose. When all the starch had been broken down, a sample was removed from the test tube and tested with biuret reagent.
i)Explain why a buffer solution was added to the amylase starch mixture.
ii)What colour would you expect the reagent to go when tested with biuret reagent
iii)Give an explanation for your answer to part ii)

Answer 20

i) Keeps pH constant so enzymes dont denature

ii) purple

iii) proteins are present as amylase is a protein

Question 21

describe how temperature can be controlled

Answer 21

• using a thermostatically controlled water bath
• monitor using a thermometer at regular intervals and add hot/cold water if temp fluctuates

Question 22

describe how pH can be controlled

Answer 22

• use a buffer solution
• monitor using a pH meter at regular intervals

Question 23

why were the enzyme and substrate solutions left in the water bath for 10 mins before mixing

Answer 23

so solutions equilibrate so can reach the temp of the water bath

Question 24

describe how the rate of an enzyme controlled reaction can be measured

Answer 24

• measure the time take for the reaction to reach a set point (conc/volume/mass/colour change)
• measure (conc/volume/mass/colour change) at regular intervals throughout the reaction
• plot a graph with time being on the x axis and what is being measured on the y
• draw a tangent
• initial rate of reaction = change in y/ change in x

Question 25

suggest a safety risk and explain how to reduce the risk (core pract 1:enzyme pract)

Answer 25

• handling enzymes may cause allergic reaction
• avoid contact with skin by wearing gloves and eye protection

Question 26

explain why using colourimeters to measure colour change is better than comparison to colour standards

Answer 26

• not subjective
• more accurate

Question 27

explain a procedure that could be used to stop each reaction (core pract 1:enzyme pract)

Answer 27

• boil to denature enzyme
• put in ice to lower kinetic energy so no E-S complexes can form
• add high conc of inhibitor so no E - S complexes can form

Question 28

explain why the rate of reaction decreases over time throughout each experiment

Answer 28

• initial rate is the highest as substrate conc is not limiting so many E-S complexes will form
• reaction slows as substrate is used up and often stops as there is no substrate left