BGM1004/L03 Bacterial Genetics II Flashcards
What is the Central Dogma of Biology?
DNA-RNA-Protein
What is different about transcription and translation in bacteria?
They are coupled
Describe what coupled transcription and translation means in bacteria.
Ribosomes bind to RNA as it is transcribed
Why can’t transcription and translation be coupled in higher organisms?
Transcription and translation occur in different cellular compartments
Approximately how proportion of base pairs are organised into genes that code for proteins or (less often) RNA in bacteria?
95%
Approximately what proportion of DNA is involved in gene expression and structural organisation in bacteria?
5%
Give the 3 phases of transcription.
Initiation
Elongation
Termination
Describe initiation.
RNA polymerase binds to promoter sequence and starts transcription
Describe elongation.
RNA polymerase uses DNA as a template to synthesise RNA from ribonucleotide triphosphates
Describe termination.
RNA polymerase recognises sequences in RNA that stops RNA synthesis
Give the 3 most common types of RNA.
Messenger RNA
Ribosomal RNA
Transfer RNA
What base differs between DNA and RNA?
Thymine - Uracil
How many bases make a codon?
3
How many stop codons are there?
3
How many reading frames does each piece of duplex DNA have?
6
Where does mRNA bind on the ribosome to begin transcription?
End of 16S ribosomal RNA
What form does most bacterial DNA take?
Circular chromosome (plasmid)
What enzymes are responsible for DNA synthesis?
DNA-dependent DNA polymerases
Why is DNA replication described at semi-conservative? (2)
One strand consists of original DNA and one newly synthesised DNA
Old strand used to correct errors in new strand
What is required to initiate DNA synthesis?
Pre-existing RNA or DNA primer
What bonds do DNA polymerases form and where?
Phosphodiester bonds
Between 3’OH of DNA and 5’PO4 on incoming dNTP
What is the unique site of bacterial replication called?
Origin of replication (OriC)
How does plasmid replication proceed?
Bi-directionally from origin to terminus (terC)
What are the 2 sites of RNA synthesis called?
Replication forks
How are mutations detectable? (2)
Sequence analysis or change in phenotype
Give 4 examples of types of mutations.
Base-pair changes
Frameshifts
Deletions
Insertions
Inversions
Duplications
What is a transition mutation?
A swap between two purines OR two pyramidines
What is a transversion mutation?
A swap between a purine and a pyramidine
Give 3 potential consequences of base-change mutations.
No change
One amino acid change
Premature stop codon
What is a silent mutation?
A mutation having no change on amino acid sequence
What is a nonsense mutation?
A mutation resulting in a premature stop codon
What is a missense mutation?
A mutation having an impact on one amino acid in sequence
What is a frameshift mutation?
A mutation resulting in a shift in the reading frame
What types of mutation can cause a frameshift?
Insertion or deletion of several bases not divisible by 3
What is the probability that a randomly generated codon will be a stop codon?
1/20
What is the equation for mutation frequency?
MF = m/N
Where m= no. mutants
N = total no. bacteria
Why do mutations occur spontaneously at low frequencies?
Powerful repair mechanisms
What needs to occur to increase mutation frequency?
Overloading of repair systems
How can bacterial repair systems be overloaded?
Treatment with chemicals/radiation to damage DNA
Describe general selection of mutants.
Isolate randomly distributed mutants
Screen for desired mutant
Describe specific selection of mutants.
Every mutant isolated is of interest
Requires knowledge of system
Describe negative selection of mutants.
Select against mutant growing
Describe enrichment selection of mutants.
Inhibit growth of mutants and kill wildtype using antibiotics
Describe positive selection of mutants.
Selective conditions where only mutants grow
