2.1.4 - Enzymes

Question 1

What does a substrate need to have in order to bind with an active site

Answer 1

Complementary shape

Opposite charges to the active site

Question 2

How does change in pH alter the rate of the reaction

Answer 2

Electric charges of both the enzyme and substrate are neutralised by the presence of either positive or negative ions so no enzyme-substrate complex is formed

Question 3

Allosteric enzyme regulation

Answer 3

An inhibitor can bind to the allosteric site and usually inhibits the activity
However Cyclic AMP can bind to the inhibitor and remove it so the enzyme can be active again

Question 4

Competitive inhibition

Answer 4

Competitive inhibitors compete with the substrate to bind with the active site
Has sim shape to part of/all of substrate
A competitive inhibitor occupies the active site only temporarily and so the reaction is reversible
Doe not change Vmax

Question 5

Non-competitive inhibition

Answer 5

Non competitive inhibitors binds with the enzyme at allosteric site. Inactivates the enzyme by altering shape (changes 3’ structure)
Can be irreversible

Question 6

Why are heavy metals (e.g. lead and arsenic) poisonous

Answer 6

They have such strong affinities for - SH (sulfhydryl) groups and destroy catalytic activity

Question 7

How is enzyme inhibition exploited to control disease

Answer 7

Penicillin and other drugs inhibit enzymes that certain diseases use in order to survive

Question 8

2 types of enzymes

Answer 8

Intracellular (catalase, converts H2O2 into O2 and H2O)

Extracellular (digestive enzymes)

Question 9

Properties of enzymes

Answer 9

Complementary active site to shape of substrate
High turnover no.
Ability to reduce activation energy
Left unchanged after reaction

Question 10

What are enzymes affected by

Answer 10

Temperature
pH
Enzyme conc.
Substrate conc.

Question 11

Lock and key hypothesis

Answer 11

Shape of active site caused by sequence of amino acids (specific tertiary structure - 3D)

Question 12

Induced fit hypothesis

Answer 12

Explains how activation energy is reduced
Active site is not perfectly complementary but when substrate moves into active site, interferes with the bonds holding active site together
Induces changes in 3’ structure to strengthen binding and weaken bonds in substrate
Active site alters to give perfect fit. Changed shape of active site —> bonds in substrate easier to make or break (reduces activation energy)

Question 13

Enzyme controlled reaction

Answer 13

Enzyme + substrate (E + S) —> enzyme substrate complex (ESC) —> enzyme product complex (EPC) —> Enzyme and product (E + P)

Question 14

Effects of pH on enzymes

Answer 14

Enzymes fully denatures before pH 3 and after pH 11
Enzymes start to denature after pH 7
Hydrogen ions that cause acidity affect interaction between polar and charged R groups and alter tertiary structure

Question 15

Co-enzymes

Answer 15

Small, organic, non protein molecules that bind to active site for short time
Take part in reaction and is recycled
Can carry chemical groups

Question 16

Example of co-enzymes

Answer 16

FAD
NAD
Co-enzyme A
Vitamin B3 - helps break down carbs and fat

Question 17

Prosthetic groups

Answer 17

Co-enzyme that is a permanent part of an enzyme molecule (inorganic ion)
Found in conjugated protein molecules e.g. haemoglobin (Fe^2+)
Contribute to final 3D shape and charge

Question 18

Example of prosthetic groups

Answer 18

Carbonic anhydrase contains a zinc based prosthetic group, helps catalyse CO2 and H2O to make carbonic acids (found in rbc)

Question 19

Co-factors

Answer 19

Presence of certain ions increase reaction rate
Ions combined with an enzyme or substrate
Binding helps form an ESC more easily, affects shape and charge
e.g. Cl- helps form active site to amylase

Question 20

How are hydrogen bonds formed

Answer 20

The slight -ve charge on the oxygen atom attracts the slight +ve charge on a hydrogen atom forming a strong bond

Question 21

Which enzyme group can catalyse oxidation reactions

Answer 21

Dehydrogenases

Question 22

What is the approximate temperature coefficient (Q10) of an enzyme controlled reaction

Answer 22

2
The rate of reaction typically doubles w/ a 10 degrees C increase
Does not apply to denatured enzymes

Question 23

Which enzyme catalyses the breakdown of triglycerides into glycerol and 3 fatty acids

Answer 23

Hydrolase

Question 24

Which type of enzyme catalysed the conversion of a dipeptide into two separate amino acids

Answer 24

Hydrolase

Question 25

End product inhibition

Answer 25

Where the product made stops the enzyme from making further products and binding to more substrates

Question 26

Measuring the rate of an enzyme-controlled reaction

Answer 26

Measure how fast the product appears and use this for comparison
Catalase catalyses H2O2 –> H2 + O2

Question 27

Variables for reaction of breakdown of H2O2

Answer 27

IV -Temp (use water baths)
DV - vol of O2. produced
CV - pH (use same type of buffer), vol and conc of H2O2 and catalase (from celery)

Question 28

Precursors (apoenzymes)

Answer 28

Enzymes that are inactive because we don’t want the metabolic process to occur
Requires cofactors to be activated (holoenzyme)

Question 29

Vmax

Answer 29

Maximum initial velocity/ rate of enzyme controlled reaction

Question 30

Digestion of starch

Answer 30

Starch + amylose –> maltose
Occurs in mouth (saliva) and small intestine (pancreatic juice)
Maltose + maltase –> glucose (absorbed directly into bloodstream)
Occurs in small intestine

Question 31

Digestion of proteins

Answer 31

Trypsin catalyses breakdown of proteins into smaller peptides in small intestine - release w/ pancreatic juices
AA absorbed by cells lining digestive system and then absorbed into the bloodstream

Question 32

pH of enzymes in small intestine

Answer 32

8
Trypsin
Lipase
Amylase
Maltase

Question 33

How to increase Vmax

Answer 33

Add more enzyme

Increase temp

Question 34

End product inhibition

Answer 34

Example of -ve feedback
Prevents waste of resources to make excess products
Example of non competitive reversible inhibition

Question 35

Precursors (Zymogens)

Answer 35

Require action of another enzyme to bring about change in 3’ structure