8.1 Mutation

• Addition • Deletion • Substitution • Inversion • Duplication • Translocation

Addition mutations are where one or more bases are added to the DNA sequence.

Deletion mutations are where one or more bases are removed from the DNA sequence.

Substitution mutations are where bases are removed and then replaced in the DNA sequence.

Inversion mutations are where the order of bases in the DNA sequence are reversed.

Duplication mutations are where bases are repeated in the DNA sequence.

Translocation mutations are where a section of the DNA sequence is moved to another section of the DNA sequence. Translocation can be within and across chromosomes.

Mutations give rise to a change in the base sequence in DNA. This could alter the amino acids that the DNA encodes. If the amino acids in a protein are changed, the 3D structure of the protein may break down as bonds between R groups of amino acids can differ.

Some amino acids are encoded by more than one codon. The fact that DNA is degenerate means that a mutation in the base sequence does not necessarily affect the protein. If one base is substituted for another base, (e.g. CAA → CAG), the mutated codon may still encode the same amino acid (e.g. both encode glutamine).

• Addition • Deletion • Duplication

-DNA replication - There can be be errors in the replication process causing mutations. -Mutagenic agents - Can increase the rate at which mutations occur e.g. UV radiation, smoking etc.

When a gamete containing a mutation for a genetic disorder or type of cancer is fertilised. The mutation is present in the new fetus formed.

A gene that controls cell division

A mass of abnormal cells caused by uncontrolled cell division

• Tumour suppressor genes (TSG) • Proto-oncogenes

Slow cell division by producing proteins that stop cells dividing or cause them to die (apoptosis)

Cannot produce protein which slows cells dividing division so cells will divide uncontrollably

Stimulate cell division by producing proteins that make cells divide

The gene becomes overactive which stimulates cell division uncontrollably resulting in a tumour.

Oncogene

• Malignant - cancerous • Benign - not cancerous

• Benign - Grow slower and covered in fibrous tissue that stops cells invading other tissues • Malignant - Grow rapidly and invade and destroy surrounding tissues. Cells can break off tumours and spread to other parts of the body in the blood stream or lymphatic system

When genes that control cell division are abnormally methylated, tumours can grow. When TSG are methylated too much (hypermethylation), the genes are not transcribed. This means cells can grow uncontrollably. When proto-oncogenes are not methylated enough (hypomethylation), they produce too much protein that encourages cell division.

• Oestrogen can stimulate certain breast cells to divide which can cause an increased risk of mutation in the DNA replication process. • Since oestrogen can stimulate cell division, it is thought that if cells do become cancerous, oestrogen can aid rapid replication further.