Bacterial Genetics Flashcards
Why is bacterial genetics relevant to medical microbiology
Emergence of antibiotic resistant pathogens and pathogens with enhanced virulence are driven by genetic variation processes
Some antibiotics target genetic processes e.g. DNA gyrase targets
Genetic methods have been developed that facilitate early detection of pathogens allowing more timely treatment
What is meant by the bacterial genome
The total collection of genes carried by a bacterium both on its chromosome and on plasmids or in the form of bacteriophages
It contains genetic information required for all cellular processes
It contains approximatelt 4000 genes, 5 million DNA base pairs
What is the plasmid?
A circular molecule of double stranded DNA (helix)
What are the two ways alterations in genotypes can occur?
Mutations through vertical gene transfer
Transfer of DNA by horizontal gene transfer (HGT)
What is vertical gene transfer?
Whereby an organism receives genetic material from a parent cell
Down from a parent cell to a daughter cell
What is horizontal gene transfer?
Whereby an organism incorporates genetic material from another organism without being the offspring of that organism
It can be from one species to another
How does vertical gene tranfer occur
Changes in the genetic material that occurs as DNA is passed from a parent bacterial cell to its daughter cell during reproduction
It occurs through processes like binary fission, the primary method of bacterial reproduction
DNA replication is an efficient process with each daughter cell acquiring an exact copy of the parental genome
Mutations during VGT can result in genetic variation which is critical for adaption and evolution
How frequent are mutations in binary fission?
Frequency of error is about 1 in 10^5 -> 1 in 10^10 per cell division
What are the four types of mutations?
Point mutations
Frame shift mutations
Large scale mutations
Spontaneous mutations
What are point mutations?
A single nucleotide change (substiutions, insertions or deletions)
They may result in silent, missense or nonsense mutations depending on the impact of the encoded proteins
What are frame shift mutations?
Addition or loss of DNA bases
Can cause frameshift mutations if they disrupt the reading frame of a gene
What are large-scale mutations?
These involve rearrangements, duplications or deletions of large DNA segments
What are spontaneous mutations?
These occur due to errors in DNA replication or repair mechanisms
They typically happen at a low but signficant rate
When do point mutations occur?
They occur after DNA replication when a single nucleotide is replaced by a different nucleotide leading to a base pair substitution
A single nucleotide replacing what was in the parent cell
What are the three types of point mutations?
Samesense/silent mutations
Missense mutations
Nonsense mutations
What is a samesense/silent mutation?
This is where the new codon encodes the same amino acid as the original codon resulting in no change to the protein
What is a missense mutation
This is where the new codon specified a different amino acid, potentially alterin the proteins structure and function
What is a nonsense mutation?
This is where a new codon becomes a stop signal causing premature termination of translation and likely producing a truncated, nonfunctional protein
How do point mutations affect bacterial proteins
The effects of base subsitutions in protein-coding regions depend on the type of mutation and its specific location within the gene, these mutations can range from having no impact to causing significant changes in the protein function
How do frameshift mutations occur
Thes occur due to the insertion or deletion of a nucleotide
This disrupts the grouping of nucleotides into a codon causing a shift in the reading frame which leads to improper grouping of all downstream nucleotides
How do frameshift mutations affect proteins
The resulting protein typically undergoes significant changes in its amino acid sequence and is often truncated due to the generation of a premature stop codon
Depending on the affected region, the altered protein may retain some biological activity or in rare cases function normally
Define horizontal gene transfer
The process by which genetic material is transferred between organisms that are not parent and offspring
HGT allows bacteria and other organisms to acquire and exchange genes across species -> physical exchange of genetic material
Contributs to genetic diversity, adaptation and evolution
How does horizontal gene transfer contribute to genetic diversity adaptation and evolution?
It typically involves functional genes that are likely to be expressed phenotypically such as those responsible for antibiotic resistance or virulence
What are the two forms of HGT
Integration into the host genome
Retention on a plasmid