3.1.4.2 Many proteins are enzymes

Question 1

Enzymes as a catalyst

Answer 1

• enzymes decrease activation energy (minimum energy to start the reaction)
• to increase the rate of reaction

Question 2

Specificity of proteins (enzymes/antibodies)

Answer 2

• tertiary structure of the
• active site/ variable region is
• complimentary to the shape of the substrate and forms an
• enzyme-substrate complex/ antibody-antigen complex

Question 3

Non-functional proteins

Answer 3

e.g. mutation changes 1ᵒ structure
e.g. denaturation changes ionic bonds
-→changes 3ᵒ structure
-changes shape of active site
-substrate not complimentary
=no e-s complex

Question 4

Induced fit model of enzyme action

Answer 4

-enzyme and substrate are not exactly complimentary
-so enzyme changes shape slightly so substrates fit
-substrate changes shape slightly
└=bonds break more easily
└=lower activation energy

Question 5

Lock and key model of enzyme action

Answer 5

-enzyme and substrate are exactly complimentary

=enzyme substrate complex →enzyme product complex

Question 6

Factors effecting enzyme activity

pH

Answer 6

-pH is altered
=denature enzyme 
=change in 3D/ 3ᵒ structure
└due change in charge distribution / hydrogen and ionic bonds affected 
-changes specific shape of active site 
=substrate not complimentary to enzyme 
=substrate cannot fit and bind to the active site 
=e-s complexes not formed
-this decreases enzyme activity 
=decrease rate of reaction

Question 7

Factors effecting enzyme activity

Temperature

Answer 7

Optimum temperature 
-increase kinetic energy
=increase frequency and energy of collisions
=increase E-S complexes
=max rate of reaction achieved 

Higher than optimum temperature 
-increase kinetic energy 
=increase frequency and energy of collisions
=enzyme vibrates too much 
=breaks hydrogen binds 
=change in 3D/ 3ᵒ structure 
=substrate not complimentary to enzyme 
=substrate cannot fit and bind to the active site 
=e-s complexes not formed
-this decreases enzyme activity 
=decrease rate of reaction

Question 8

Factors effecting enzyme activity

Enzyme concentration

Answer 8

-increase enzyme concentration
-increase number of active sites available
└as long as there are enough substrates to fill them
-this increases enzyme activity / e-s complexes
=increase rate of reaction
└until substrate is used up (becomes a limiting factor)

Question 9

Factors effecting enzyme activity

Substrate concentration

Answer 9

-increase substrate concentration
-increase number of substrates available to fill active sites
└as long as there are enough active sites for them to fill
-this increases enzyme activity/ e-s complexes
=increase rate of reaction
└until there are no more active sites available (becomes a limiting factor)

Question 10

Factors effecting enzyme activity

Competitive inhibitor

Answer 10

-inhibitor has a similar shape to the substrate
└= complimentary/ can fit in active site for a short time
=prevents the substrate from entering the active site.

-less effect if more substrate is added

Question 11

Factors effecting enzyme activity

Non-competitive inhibitor

Answer 11

-inhibitor fits into a site other than the active sit (allosteric site) 
=alters shape/charge of active site 
=change in 3D/ 3ᵒ structure 
=substrate not complimentary to enzyme 
=substrate cannot fit and bind to the active site 
=e-s complexes not formed
-this decreases enzyme activity 
=decrease rate of reaction
-reaction won’t reach maximum

-increasing substrate concentration has no effect