| P72/Q1 |
a) |
Activation energy = energy needed to bring molecules
together so that they will react with each other.
|
| |
b) |
(i) The Lock & Key hypothesis. An enzyme described
as a rigid structure. The enzyme active site is a
negative impression of the molecule of the
substrate. Substrate arrives at the active site of
the enzyme →
thanks to intermolecular forces of
attraction/hydrogen bonds, the molecule of the
substrate fits into the active site
→ the molecules
are rearranged there to form products
→ products leave
active site. (ii) The Induced Fit hypothesis: an
enzyme is described as a flexible, elastic, "wobbly"
structure. Substrate arrives at the active site.
Thanks to some intermolecular forces of
attraction/hydrogen bonds, the molecule of the
substrate fits into the active site of the enzyme.
The active site of the enzyme is not a negative
impression of the molecule of the substrate
→ the shape of
the molecule of the enzyme is altered by a slightly
different shape of the molecule of the substrate.
The distorted molecule of the enzyme in turn
distorts the substrate in the resulting
enzyme-substrate complex. Strains/tensions created
within the molecule of the substrate lower the
activation energy needed for the chemical change
(reaction) to occur.
|
| |
c) |
2H2O2 → 2H2O +
O2 (gas) by catalase As O2 (gas) evolves and
escapes to the atmosphere, the mass of the contents
of the beaker drops.
|
| |
d) |
The concentration of the enzyme remained the same,
yet the concentration of the substrate dropped
→ lower ratio of
substrate molecules: enzyme molecules
→ fewer
collisions →
lower rate of reaction.
|
| P72/Q2 |
a) |
A molecule of the competitive inhibitor (CI) has a
similar shape to the molecule of the true substrate
→ CI takes the
substrate's place at the enzyme's active site
→ fewer active
sites available for the molecules of the true
substrate →
lower enzyme concentration
→ lower rate of
reaction.
|
| |
b) |
The limiting factor is the concentration of the
enzyme. Until its concentration is higher, the rate
of reaction will not increase because the turnover
rate of an enzyme is a fixed value.
|
| |
c) |
The ratio "substrate : enzyme" will increase, while
the ratio "CI : enzyme" will stay the same. Hence
more collisions between enzyme and substrate
→ higher rate of
reaction.
|
