1. Chapter 10 Higher Level Enzymes and Energy Carriers
The active site is the part of an enzyme that combines with the substrate
The active site is a depression on pocket on the surface of an enzyme. It does not have a rigid shape. Every active site is specific to substrate that it acts on.
The substrate causes (induces) the active site to change shape slightly when they come in contact and the active site then fits more precisely around the substrate. This is called the induced fit model. E.g. bean bag moulding around your body when you sit on it.
Mechanism of Enzyme Action – The induced fit model

2. Enzyme specificity means that each enzyme will react with only one particular substrate.
Most enzymes are specific to a single substrate i.e. they will only react with one substrate. Anything that changes the shape of an active site will reduce the ability of the enzyme to work.
Optimum pH – shape of enzyme is
very sensitive to pH e.g. pH 2 is optimum
pH for pepsin

3. 2. Temperature Enzymes are less sensitive to temperature than pH.
At higher temperatures substrate molecules move more
quickly and collide more frequently with enzymes therefore
the rate of reaction increases.
An enzymes optimum pH means the pH value at which the enzyme works best.
20 – 30C is the optimum pH for most plant enzymes and 37C is the optimum temperature for human enzymes.
Denaturation
A denatured enzyme has lost its shape and can no longer carry out its function.
Explanation
When most proteins are heated above 40C
they gradually lose their 3D shape i.e. become denatured.

4. ADP = Adenosine diphosphate ADP is a low energy molecule
Energy Carriers
Energy is necessary for both photosynthesis and respiration.
ADP & ATP
ADP = Adenosine diphosphate
ADP is a low energy molecule
ATP = Adenosine triphosphate
ATP is a high energy molecule
The process of adding a phosphate group
is called phosphorylation.

5. ATP can be moved around inside a cell i.e. it is an energy carrier.
When ATP breaks down it releases energy and a phosphate and forms ADP.
In respiration glucose breaks down to form ATP. This ATP is used to provide energy in a human cell for e.g. muscle movement, urine formation etc.
NADP+ and NADPH
NADP+ = Nicotinamide Adenosine Dinucleotide Phosphate
NADP+ = a low energy molecule involved in photosynthesis.
The addition of electrons to a molecule is called reduction
NADPH
NADPH = an electron and hydrogen carrier. The energy and hydrogen it contains is used in photosynthesis to form glucose.
NADPH releases two high energy electrons and a hydrogen ion or proton when it breaks down.

6. NAD+ and NADH
NAD+ is used in respiration as an equivalent low energy molecule to NADP+.