Transcript Mutations - KingsfieldBiology

So Mutations!
 Any change to the quantity or structure of
DNA of an organism is known as a mutation.
 Mutations can occur in either somatic cells
(body cell) and germ cells (those that produce
the gametes (these can be passed on!)).
 Changes in the structure or number of a whole
chromosome is know as a chromosome
mutation
 Changes which affect a single locus and
therefore produce a different allele are know
as gene mutations.
 They are the basis of discontinuous variation
Gene Mutations
 There are three main types of gene mutation
which you have to know about:
1.Base substitution Base additions and deletions tend to have the
most significant effect on the polypeptide
2.Base addition
produced as they cause frame shifts, in the
3.Base deletion
code. More of a problem at the start of the
sequence compared to the end.
Base substitutions often = silent mutations.
However sometimes they can have a very large
effect e.g. ATG tyrosine to ATT = stop
Changes to a single base
could result in
 A nonsense mutation – when a change causes
on of the three stops to be coded.
 A mis-sense mutation – where a change in a
base results in the coding of a different
amino acid – the significance of this depends
of the role of the original amino acid e.g. If
it had a role in forming a bond.
 A silent mutation – where the change still
results in the same amino acid being coded
for – has no effect
Sickle Cell Anaemia
 First human disease
understood on the
molecular level (1949 Linus
Pauling).
 All related to the DNA
that codes for the β –
amino acid chain within
haemoglobin.
 Caused by a single
substitution the base
thymine to adenine (CTT
to CAT) causing glutamic
acid rather than valine.
 This produces
haemoglobin with a sticky
patch.
•The molecules tend to stick to each other
forming long fibres inside the red blood cell.
The fibres distort the red blood cell making
them inflexible and sickle shaped.
•The red blood cells are then unable to carry
oxygen and block small capillaries.
•Sufferers become tired, listless, and have a
shortened life span.
Phenylketonuria or PKU
 Caused by an abnormal base sequence
in part of the DNA molecule.
 Codes for an enzyme
 Phenylalanine is found in many foods
 Tyrosine is converted to melanin.
 So people with PKU have lighter skin
and hair than normal.
 Without the enzyme phenylalanine
accumulates in the blood and tissues
and can cause severe brain damage in
young children even mental
retardation.
 However it can be treated by diet
and the HUMAN GENOME PROJECT
IS HELPING.
Mutagens or mutagenic
agents
 Agents that increase
the rate of mutation
(usually 1 – 2
mutations per 100 000
genes) the main two
are:
1. Chemicals
2.High energy radiation
Mutations –
costs and benefits
 Benefit
 Can increase variation and genetic
diversity
 Cost
 Tend to produce organisms which are less
well suited to the environment.
 Mutations that occur in body cells rather
than gametes can disrupt normal cellular
activities such as cell division
Genetic control of Cell
division
 Controlled by two genes:
 Proto-oncogenes which stimulate cell
division
 Tumour suppressor genes – which slow
cell division.
 Use page 232 to write a job
advertisement for each of the genes
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