Week 12 Gene Expression and Regulation
4. Outline briefly the steps in transcription, RNA processing and translation
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RNA is transcribed from a DNA template
In Eukaryotes the RNA transcript is spliced and modified to produce mRNA
which moves from the nucleus to the cytoplasm.
The mRNA leaves the nucleus and attaches to a ribosome.
Each amino acid attaches to its proper tRNA with the help of a specific enzyme
and ATP
A sucession of tRNAs add their amino acids to the polypeptide chain as the
mRNA is moved through the ribosome.
5. Describe common types of mutations
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Mutations may occur at a single base or involve large scale rearrangement of
chromosomes.
Nucleotide substitutions, insertions, deletions or amino acid substitutions.
Result in either incorrect amino acid due to redundancy of the code. Or, a frame
shift that may render the protein un functional.
Germ line mutations occur in the cells that give rise to gametes. Gametes will
carry mutation to next generation (heritable).
Somatic mutations, happen in non-germ cell line, organism becomes a mosaic.
(most common cause of cancers).
MOST mutations occur in non coding regions, only important when they affect
the gene or its expression.
“gain of function mutations (up regulation of a gene)” vs “loss of function
mutations (most metabolism mutations)”.
6. Indicate how point mutations may alter function: regulation, sequence, premature
termination, post-translational modification, trafficking.
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If a point mutation converts a codon to a stop codon, the protein (polypeptide
sequence) will be terminated . This may prevent post transcriptional processing
and incur in incorrect folding of the protein.
Point mutation (deletion and insertion) result in a frame shift mutation.
Normally fatal to gene.
Substitution point mutations often result in no phenotypic change in protein
expression. (due to redundancy of the code with more than one codon coding for
a specific amino acid (tRNA). Or, a single incorrect amino acid in the sequence.
(could not affect the protein folding, or, if the amino acid is involved in a folding
(binding) site on the polypeptide, may render protein unstable (sickle cell
anaemia).