Genetics

Translation

Process of translating the RNA sequence -> amino acid sequence (protein)

tRNA functions by transporting anticodon sequence complementary to mRNA sequence

Transcription

Derived from DNA into single strand -> mRNA strand (singular)

Like a "recipe card" to produce many proteins

E.g. In immunology, B-cells are required to multiply and produce many specific proteins (antibodies)

Requires RNA polymerase to further replicate the RNA strand following transcription (in the direction guided by the PROMOTOR)

Regulation of transcription is important during infection, as gene activity can require a high energy yield, minimising activity will be most efficient during this process

Gene expression is controlled by many different transcription factors

Termination of transcription; hairpin loop (prokaryotes) & termination site '250 A nucleotides' (in eukaryotes)

Introns function to interrupt the RNA sequence

Spontaneous Genetic Mutations

1. Silent-mutation; when a single DNA base mutation occurs but doesn't alter the protein produced (I.e. due to degeneracy)

- A single base deletion is more detrimental than a base substitution

2. Missense mutation

3. Nonsense mutation

Uncontrolled Cell Growth

DNA Repair Mechanisms

1. Base excision repair (BER); mutated single base removed & repaired

2. Light & dark repair; enzyme uses visible light to break thymidine dimer (light) & nucleotide exicision repair of thymidine dimer (dark)

- Defective NER enzymes - e.g. skin cancer

3. N.E.R; enzymes remove several nucleotides > dependant on several enzymes > defective enzyme > becomes problematic

4. SOS Repair; replicates DNA past thymidine dimer WITHOUT PROOFREADING = increased risk of mutations

5. Apoptosis; aka Programmed cell death, p53 enzyme pathway

Genetic Coding & Expression

Induced Genetic Mutations

1. X-ray induced;

2. UV induced;

Differentiating Eukaryotic to Prokaryotic cells

Prokaryotic (pre-nucleus)

Single cell type found in bacteria & archaea

Presents as small circular genome with one circular chromosome per copy of gene

Eukaryotic (true nucleus)

Found in multi-cellular organisms (including algae, yeast)

Cell appears larger, genome is non-circular, arranged in separate chromosomes & has multiple copies of each chromosome/gene

Junk DNA; involved in cell communication, regulation & other diverse functions

DNA Degeneracy

More than one codon can code for the same protein = Degenerate

This is beneficial when a mutation occurs -> base change doesn't alter protein produced

Gene Expression

Knock-out disruption of genes by homolygous recombination of a single strand > alterations in phenotype

Small interfering RNA (siRNA); binds to new transcribed mRNA & prevents further translation into protein sequences

Disorders of Gene Expression

1. Duchenne Muscular Dystrophy; Dystrophin gene mutated > no functional protein present > cell mass lost

- Presents with pseudohypertrophic calf muscles

2. Bubble boy disease; defective adenosine deaminase > loss of entire immune system

3. Congenital hypothyroidism; mutated thyroid stimulating hormone beta > mental retardation/abnormal growth if untreated

4. Congenital hypothyroidism; defective thyroid stimulating hormone receptor/defective hormone

5. Sickle cell anaemia; causes membrane rigidity > pain & tissue damage

6. Hypertrophic cardiomyopathy (HCM); heart muscle abnormally thick/abnormal arrangement