Bacteria and viral genetics Flashcards
Bacteria and viral genetics
Where is the bacterias genes found?
It’s circular bacterial chromosome
Bacteria and viral genetics
Where do you find a bacteria’s chromosome?
In the nucleoid
Bacteria and viral genetics
How does a bacterial chromosome fit inside the bacteria
Compacted by supercoiling
Bacteria and viral genetics
Supercoiling (picture)

Bacteria and viral genetics
what controls the DNA twisting in supercoiling of bacterial chromosome?
Topoisomerase enzymes
Bacteria and viral genetics
Antibiotics can be used to target what part of the supercoiling process of compacting bacterial chromosomes?
Topoisomerase enzymes
Bacteria and viral genetics
At what point of the chromosome does DNA synthesis occur in bacteria?
The origin of replication
Bacteria and viral genetics
What term describes the DNA replication in bacteria
- Meaning
Bidirectional
- Goes both ways from the origin of replication
Bacteria and viral genetics
Bacterial DNA replication (picture)

Bacteria and viral genetics
Plasmids
Small cicrular pieces of DNA
Can replicate independantly of the bacterial chromosome
Not usually necessary for survival but can provide growth advantages
Bacteria and viral genetics
5 types of plasmid
- Resistance plasmids (R factors)
- Degradative plasmids
- Col-plasmids
- Virulence plasmids
- Fertility plasmids (F factor)
Bacteria and viral genetics
Resistance plasmids
Contain genes confer resistance against antibiotics and other types of toxins
Bacteria and viral genetics
Degradative plasmids
Carry genes that eneable the bacterium to digest and utilise an unusual substance
Bacteria and viral genetics
Virulence plasmids
Carry genes that turn a bacterium into a pathogenic strain
Maybe carrying a capsule protein
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Fertility plasmids
Allow bacteria to mate with each other
Bacteria and viral genetics
Conjugation
Direct physical interaction transfers genetic material from donor to recipient cell
Bacteria and viral genetics
How do bacteria maintain diversity?
Mutations that may occur
Genetic transfer between bacteral cells
Bacteria and viral genetics
Induced mutations
Mutagens can increase the mutation rate
Bacteria and viral genetics
Mutagens
Chemical, biological and physical agents that may increase muation rate
Bacteria and viral genetics
Possible causes of spontaneous mutation
Natural radiation
Free radicals from cellular oxidation
Errors during replication
Bacteria and viral genetics
Point mutations
Alteration of a base pair of DNA
Bacteria and viral genetics
Frame shift mutations
Deletion or insertion of DNA
Bacteria and viral genetics
What is the potential consequences of a mutation?
New proteins could be produced
Proteins that don’t function properly are produced
Bacteria and viral genetics
Forms of genetic transfer between bacteria
Conjugation
Transformation
Transduction
Bacteria and viral genetics
Transformation
When DNA released from dead bacterium into the environment is taken up by another bacteria
Bacteria and viral genetics
Transduction
Bacterial DNA is transferred between bacteria by bacteriophage virus
Bacteria and viral genetics
Selective advantages that may be gained by the transfer of plasmids between bacteria
Antibiotic resistance
Synthesis of the pilus
Utilisation of unusal nutrients
Increased virulence
Toxin production
Bacteria and viral genetics
What ensures cell-to-cell contact occurs in conjuction and how?
Pilus
The pilus of the donor cell recognised receptors on the recipient cell wall
Contracts to create cell-to-cell contact
Bacteria and viral genetics
In conjugation does the donor simply give away one of it’s plasmids?
No
Replicates the plasmid and transfers the copy
Bacteria and viral genetics
Avery, Macleod and McCarty
Found that type-R Salmonella doesn’t affect mice, but would infect and kill the mice if left in solution with dead type-S of Salmonella that does affect mice
Concluded that the DNA from type-S was taken up by type-R by transformation
Bacteria and viral genetics
Can any bacterial cell acquire genetic material by transformation?
No
Only those that have competence factors
Bacteria and viral genetics
Steps of transformation
Bacterial cell with competence factors encounters DNA from dead cell
DNA fragments bind to bacterial cell surface
DNA taken into the cytoplasm
Imported DNA incorporated into bacterial chromosome
Bacteria and viral genetics
Horizontal gene transfer
Movement of one or more genes from one species to another
Bacteria and viral genetics
Vertical gene transfer
From mother to daughter cell
Bacteria and viral genetics
Major differences between viruses and cells
No mitochondria so no biochemical enegry machinery
No ribosomes so no protein synthesis machinery
Bacteria and viral genetics
What does HIV target?
T helper cells
Bacteria and viral genetics
What does the destruction of larger numbers of T helper cells cause?
The immune system is seriously comprimised
Become highly susceptible to infections
Bacteria and viral genetics
When outside a host a virus is called?
A virion
Bacteria and viral genetics
When is a virus called a virus?
When it is inside a host
Bacteria and viral genetics
Basic compostition of a virus
Tiny non-living particle
Contains nucleic acid (DNA or RNA) surrounded by a protein coat called a capsid
Bacteria and viral genetics
How are viruses classified
By their genome, then by the host they infect
Bacteria and viral genetics
How are viruses classified by their genome?
DNA virus
- Single stranded (ss)
- Double stranded (ds)
RNA virus
- ssRNA
- dsRNA
Bacteria and viral genetics
What classification of virus is HIV (genome)
ssRNA
Bacteria and viral genetics
Viruses capsid
Protective coat
Built of indentical protein subunits called capsomeres
Bacteria and viral genetics
Capsomeres
Identical protein subunits that build up the capsid in viruses
Bacteria and viral genetics
Enveloped virus
Has a viral envelope that surrounds the capsid
Envelope made up of the lipid bilayer of the host cell
This envelope fuses with existing host cell membrane when virsus enters host cell
Bacteria and viral genetics
Basic steps of virus division
- Attachment to host cell
- Entry
- Intergration into host DNA
- Synthesis of viral components
- Viral assembly
- Release
Bacteria and viral genetics
Retrovirus
Virus that has RNA
Must transcribe RNA to DNA by reverse transcriptase enzyme
Bacteria and viral genetics
Where does a retrovirus get the reverse transcriptase enzyme from?
It is carried inside the capsid
Bacteria and viral genetics
Why do retroviruses need to convert their RNA into DNA?
Only DNA can be intergrated into the host DNA
Only DNA can be copied by the host DNA polymerase
Bacteria and viral genetics
Why is it difficult to create a vaccine for HIV
Reverse transcriptase used to convert ssRNA to DNA lacks a proof reading function
This leads to more errors and mutant strains of HIV
Bacteria and viral genetics
When does the viruses DNA move into the nucleus
When mitosis occurs
Bacteria and viral genetics
How is the viruses DNA intergrated into the host DNA
Viral enzyme integrase cuts the host DNA
Bacteria and viral genetics
Provirus
Virus that has been integrated into the host chromosome
Is responsible for synthesis of viral componenets
Bacteria and viral genetics
Once the provirus has synthesised new viral components, what happens?
Capsid proteins enclose 2 molecules of viral DNA and 2 molecules of reverse transcriptase
Virus buds from plasma membrane of host cell and is released
Bacteria and viral genetics
Transduction
Method of introducing genetic diversity into bacteria
Viruses that infect bacteria can transfer bacterial genes from one bacterium to another
Bacteria and viral genetics
Two types of virus replication
Lysogenic cycle
Lytic infection cycle
Bacteria and viral genetics
Lysogenic cycle
Type of virus replication
Intergrate into host DNA
Viral DNA is replicated when host divides
Little or no affect to host
Bacteria and viral genetics
Lytic infection cycle
Type of virus replication
Replicates virus particles within the host cell
Released to infect more host cells
Damages host
Bacteria and viral genetics
Viriod
Infects plant cells
Circular ssRNA molecule a few hundred nucleotides in length present in the host cells nucleus
Genome does not code for proteins
Bacteria and viral genetics
Prions
Non-living infectious particle
Does not contain any nucleic acid (genetic material)
Causes neurodegenerate diseases
Form aggregates in the brain
Bacteria and viral genetics
Who carried out the experiment that found bacteria could gain genetic material by transformation
Avery, Macleod and McCarty