Cellular control
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The Genetic Code
The base sequence that codes for proteins * Universal * Non-overlapping * Degenerate
DNA Gene mutation
A change to one or more DNA bases that may or may not an effect on the final polypeptide product
A substitution mutation Point mutation
A type of mutation in DNA or RNA wher ONE single nucleotide is affected
type of point mutation Silent mutations
When there is a change to the base triplet but that triplet still codes for the same amino acid / nothing changes and polypeptide isn’t altered (due to the degenerative nature of the genetic code) this is most mutations
type of point mutation Missense mutations
Change in base triplet leads to a different amino acid being coded for. This alters the polypeptide. Example: sickle cell anaemia
type of point mutation Nonsense mutations
Change in base triplet leads to the triplet becoming a termination (stop) triplet. This changes the polypeptide structure and the protein can’t complete it’s function. Example: Duchenne muscular dystrophy
Indel mutations
Causes a frameshift. Code is non-overlapping and read in 3s. So any insertion (addidng of bases) or deletion (removing of bases) causes all subsequent base triplets to be altered. Example: (deletion) Tay-sachs
Degenerate code
(Apart from Try and Met) All other amino acid has more than one code (called redundancy/ degernerate in the genetic code)
Chromosome mutation
Changes in whole sets of chromosomes
Beneficial mutation
These mutations provide a selective advantage to an individual. well-adapted individuals can out compete those w/o those advantages. This is the driving force behind natural selection. Example: melanin
Neutral Mutations
If the mutation occurs in the non-coding part of DNA. Silent mutations.
Harmful Mutations
• Usually deletion mutations (i.e. cystic fibrosis) • Point mutations (i.e. proto-oncogenes being changed to oncogenes which promote uncontrolled cell division) • Repeated sections of gene (i.e. huntington disease) Example: Sickle cell anaemia
Causes of mutations
• A mistake occuring during DNA replication • Can occur spontaneously • When DNA polymerase makes a mistake
Selective pressures
if a mutation changes a characteristic there can be positives and negatives to the new feature. The environment plays a role in determining the likelihood of this feature remaining through natural selection.
Transcription Factors
What is Mitosis?
A type of cell divison that creates 2 identical daughter cells * used for growth and repair of tissues and replacement of cells
What is apoptosis?
controlled cell death - ensures that older cells reaching the max no. of cell divisions are removed
What is the process of apoptosis?
What are the roles of apoptosis?
• Destroy harmful T-lymphocytes (that could attack the body) • Orchestrate development in an organism (webbed toes destroyed) • Destroys cell that are damaged that could give rise to cancer
How is apoptosis controlled?
Controlled by 2 sets of genes: * Proto-oncogenes * Tumour suppressor genes
What are proto-oncogenes?
Genes that stimulate cell division
What are tumour suppressor genes?
Genes that inhibit cell division