1. Regulator gene
Produces a protein called the repressor molecule
Operator gene
Switches on the structural gene to make the enzyme (lactase)
Structural gene
Has the DNA code to make the enzyme b galactosidase (lactase)
Repressor molecule
Attaches to the operator gene and switches it off
Inducer
This is the lactose sugar that attaches to the repressor molecule and prevents it from attaching to the operator gene.

2. If lactose is present explain how gene action switches the synthesis of b galactosidase.
Lactose is the inducer as it binds to the repressor molecule so it cannot bind to the operator gene
The operator gene is now free to switch on the structural gene
The structural gene makes the b galactosidase
If no lactose present
The repressor molecule is free to bind to the operator gene which will then be switched off
The structural gene will not be switched on by the operator gene and no enzyme made.

3. What is beneficial, to the bacteria, by using this mechanism of switching on and off genes?
Only makes the protein when needed so does not waste energy and reources
List the two ways the body can obtain a supply of the amino acid tyrosisn.
From the protein in the food eaten
By changing the amino acid phenylalanine into tyrosine.
Explain the part played by genes in the case of the hereditary disorder called Phenylketonuria (PKU)
The amino acid phenylalanine is not changed into tyrosine as the enzyme is not made due to a gene mutation.

4. Explain how gene activity is involved in cell differentiation.
As some genes are switched on and other switched off.
What is the meaning of undifferentiated cells?
The cell has no particular shape or function.
Remember
All cells in an organisms have the same genes but they switch on only the ones that will make protein they need.
Stomach wall cells are the only cells in your body that switch on the pepsin gene.