Bacterial Genetics Flashcards
1
Q
Genetic material of bacteria
A
- chromosomal DNA- a large circle of DNA containing almost the entire genome of the bacterium (typically 2,000-5,000 genes)
- plasmids- circles of DNA containing small number of genes, (typically 3 or 4) that are not essential to the bacterium. They are extrachromosomal
- bacteriophages- viruses that infect bacteria and carry a small number of genes (typically 3-4) that are not essential to the bacterium. They may be extrachromosomal or integrated
2
Q
Bacterial vs Human Genetics
A
Nucleus: Bacterial-No; Human-Yes
Number of genes: B- 4,000; H- 25,000
Ploidy: B- Haploid; H-Diploid
Chromosomes: B-One, Circular; H-Many,Linear
Extra-chromosomal: B-plasmids/phage; H-mtDNA
3
Q
Expression of bacterial genes
A
- similarly to eukaryotic cells, genes consist of specific DNA sequences which can be transcribed into RNA, which can be translated into protein
- in eukaryotic DNA each gene has its own regulatory elements. In bacteria, genes with related functions all share the same regulatory elements and are known as an operon
- transcriptional regulation. In eukaryotic cells the expression of gene is regulated by proteins that interact with the gene promoter. In bacteria expression is often regulated by metabolic products or deficiencies directly. This can be by positive or negative regulatoion
- post translational regulation
4
Q
Phage and plasmids can encode virulence factors
A
- enterotoxin (E. colim V. Cholerae)
- exfoliatin (S. aureus)
- erythrogenic toxin (S. pyogenes)
- neurotoxin (C. tetani)
5
Q
16sRNA
A
- unique for each bacterial species, but is flanked by conserved sequences
- universal regions can be used as primer binding sites for PCR or sequencing
- intervening regions can be used to identify bacteria at genus or species level
- this allows microbiome-wide identification of bacteria
6
Q
Different features of expression of Human and Bacterial genes
A
Human- individual genes, multiple transcription factors, enhancers, RNA is spliced, post-translational control (proteins modified)
Bacteria- operons, operator/repressors, none, not, none
7
Q
Bacterial genotypes
A
Biosynthetic genes- ala means organism synthesizes alanine
Catabolic genes- lac meansit can digest lactose
Drug resistance genes- cat means it resists chloramphenicol
8
Q
Regulation of gene expression in bacteria
A
- nutritional status
- cell-surface sensing
- quorum sensing
9
Q
Operon
A
- the promoter is separated from the genes by an opertator-which regulates expression of the operons
- the expression of the lac operon genes is normally prevented by a repressor protein
- “inducible expression”- when lactose is present the genes to metabolize it are induced by the lactose
10
Q
Mutations in bacteria
A
- chemical modifying agents (base-modifying agents, base analogs, intercalating agents)
- physical agents (X rays, UV light)
- often carcinogenic to eukaryotic cells- basis of the Ames test- test it with Salmonella his- , negative some spontaneous revertants, positive result- increased revertants near test chemical
-can lead to resistance to antibiotics- very rare
11
Q
Genetic exchange of bacteria experiment
A
- SII- capsule, lethal to mice
- SI- no capsule, mice live
- heat killed SII- mice live
- combined SI and heat killed SII- lethal
12
Q
Transformation
A
- DNA released from dead bacteria may be taken up non-specifcally by live bacteria
- if it is not digested by restriction enzymes it may be incorporated into the recipient genome by homologous recombination
- this is the mechanism that allows the capsule gene of S. pneumonii to be transferred, the DNA might be chromosomal DNA or plasmid DNA
13
Q
Conjugation
A
- some bacteria carry a large plasmid- the F factor- which can exist as an extrachromosomal element or can be integrated into the chromosome
- the F factor also encodes sex pili and the genes for the process of conjugation
- during conjugation the F plasmid, plus bacterial DNA from the integration site, is transferred from the donor bacterium (male) through the sex pilus into the recipient bacterium (female)
- bacteria can be F- (female), F+ (male), Hfr (Male with integrated plasmid)
- transfers many antibiotic resistant genes in intestinal bacteria
14
Q
Prevention of recombination
A
-resistriction modification system
Bacterial enzymes:
- modify their own DNA by methylation
- digest DNA from other sources (non-methylated)
- repair damaged DNA and splice in DNA that is modified (methylated)
15
Q
Transduction
A
- transmission of DNA between bacteria by bacteriphage
- lytic phage can infect bacteria and can cause lysis- this can release DNA which can be taken up by the bacteriophage and be carried into another bacterium- this is known as generalized transduction
- lysogenic phage can insert themselves into the bacterial chromosome (lysogeny, producing a prophage in the chromosome) and later can excise themselves with some adjacent bacterial DNA which can be carried into another bacterium- this is known as specialized transduction. This mechanism transfers toxins of of diphtheria, botulism, cholera, scarlet fever
- Segments of non-chromosomal DNA that carry genes for antibiotic resistance are called R-factors, larger ones are called F factors
