Bacterial Genetics 8 Flashcards
What is the role of antibiotics
What are the modes of action of antibiotics
Give one mechanism of antibiotic resistance
Give another mechanism of antibiotic resistance
Give another two mechanisms of antibiotic resistance
What is one way antibiotic resistance is transmitted
Give a second and third way that antibiotic resistance is transmitted
What does vertical gene transfer lead to
Give an outline of mechanisms of horizontal gene transfer
What key factors drive the spread of antibiotic resistance
How can antibiotics be over prescribed?
What is bacterial transformation
What experiment did Frederic Griffith carry out on bacterial transformation
Describe the Avery-MacLeod-McCarty Experiment
are all bacteria naturally transformable? Give some examples
Why do bacteria undergo transformation
Genome diversification:
Uptake of exogenous DNA increase diversity
Could this cause loss of beneficial alleles/replace deleterious alleles? Increase survival in future stress. Darwinism? Evade antibiotics?
What are some disadvantages of transformation
List the common steps of transformation
When would bacteria develop competence
How does Binding of extracellular dsDNA for transformation occur in gram positive bacteria
How does Binding of extracellular dsDNA for transformation occur in gram negative bacteria
Translocase is a protein which aids transport across membrane
What are the differences between DNA uptake and membrane structure in gram negative and gram positive bacteria
What happens in the Homologous recombination step
Of transformation
What is artificial transformation
Explain 2 methods of artificial transformation
What is the difference between chemical vs electroporation artificial transformation
What determinants are there of the efficiency of transformation
How is transformation used in gene cloning
What are the uses of artificial transformation
What is bacterial conjugation
What experiment did lederberg and Tatum Carry out
Prototrophic microorganisms can synthesize all the nutrients that are required for their growth from minimal medium without the addition of supplements. However, many microorganisms in nature (and in culture collections) are auxotrophic; that is, they are unable to synthesize all of the vital nutrients.
How is the idea that physical contact required for genetic recombination demonstrated during transformation
That is a fertility (F) factor in bactena
What are the F pilus
What is the F plasmid and what does it do
What is the first step of conjugation in bacteria
What is the second step of conjugation in bacteria
What is the third step of conjugation in bacteria
What is the fourth step of conjugation in bacteria
What is the fifth step of conjugation in bacteria
What is the host range and what factors is it defined by
the term “host range” refers to the range of bacterial species or strains that a particular conjugative plasmid (a small, circular DNA molecule) can transfer its genetic material to. Conjugative plasmids carry genes that facilitate their own transfer from one bacterial cell to another during conjugation.
Some conjugative plasmids have a narrow host range, meaning they can only transfer between closely related bacterial species or strains. Others have a broad host range and can transfer between more distantly related bacteria.
What is a resistance (R) factor
What differences are there in conjugation in gram positive bacteria
In the absence of a recipient, the transfer genes are switched off by TraA. The recipient produces a peptide, cAD1, which inactivates TraA, allowing conjugation to proceed.
One of the products, aggregation substance (Asa) coats the outside of the donor cell, resulting in the formation of a mating aggregate with donor and recipient cells bound together.
Plasmid transfer then ensues, by a mechanism similar to that described previously.
Summarise bacterial conjugation
What are High frequency recombinant (Hrf) strains and how do they arise
the DNA strand transferred is very long and often breaks;
-the F plasmid would be the last piece transferred, therefore recipients do not become F+
How is Hfr DNA transferred
What are F’ (F prime) plasmids
How are bacterial chromosomes mapped
What is phage transduction
What is a bacteriophage
How was phage-mediated transfer of genetic material discovered
Describe the lytic cycle of bacteriophages
Describe the lysogenic cycle of bacteriophages
A lysogen or lysogenic bacterium is a bacterial cell which can produce and transfer the ability to produce a phage. A prophage is either integrated into the host bacteria’s chromosome or more rarely exists as a stable plasmid within the host cell.
What are the differences between the lytic vs lysogenic cycle
What are the 2 types of phage transduction
Describe generalised transduction
Phage Infection: The process begins when a bacteriophage infects a bacterial cell. The phage attaches to specific receptors on the bacterial cell surface and injects its DNA into the cell.
Replication of Phage DNA and Degradation of Bacterial DNA: Once inside the bacterial cell, the phage DNA hijacks the bacterial cell’s machinery to replicate its own genome. During this process, the bacterial DNA is often degraded by nucleases encoded by the phage.
Packaging of Phage DNA: As new phage particles are assembled within the bacterial cell, fragments of bacterial DNA may accidentally be packaged into some of the phage capsids instead of phage DNA. This occurs because the phage DNA packaging machinery may sometimes mistakenly package bacterial DNA instead of phage DNA.
Release of Phage Particles: Eventually, the phage particles mature and lyse the host bacterial cell, releasing numerous phage particles, some of which contain fragments of bacterial DNA.
Infection of New Bacterial Cells: The released phage particles can then infect new bacterial cells. If a phage particle containing bacterial DNA infects a new bacterial cell, the bacterial DNA fragment can be integrated into the recipient bacterial chromosome through homologous recombination, potentially leading to genetic recombination.
Expression of Transferred Genes: Once integrated into the recipient bacterial chromosome, the transferred bacterial genes may be expressed, leading to phenotypic changes in the recipient cell.
What is abortive and complete transduction
Abortive Transduction:
Abortive transduction occurs when the transferred DNA fragment fails to integrate into the recipient bacterium’s chromosome. This can happen for various reasons, including the degradation of the transferred DNA fragment or failure of the recipient cell to successfully recombine the transferred DNA into its genome.
In abortive transduction, the DNA fragment may not confer any phenotypic change or genetic alteration in the recipient cell because it does not become stably integrated into the bacterial chromosome.
Complete Transduction:
Complete transduction occurs when the transferred DNA fragment successfully integrates into the recipient bacterium’s chromosome through homologous recombination. This results in the stable incorporation of the transferred genetic material into the recipient cell’s genome.
Complete transduction can lead to phenotypic changes in the recipient cell, as the transferred DNA may contain genes encoding new traits, such as antibiotic resistance, virulence factors, or metabolic enzymes
How can Generalised transduction be used for gene mapping
met+” typically refers to a bacterial strain that is capable of synthesizing the amino acid methionine. In bacterial genetics, “+” is often used to denote the presence or ability to perform a certain function, while “-“ denotes the absence or inability to perform that function
What is Specialised (restrictive) transduction
Specialized transduction is a process in which specific bacterial genes located near the prophage integration site are transferred from one bacterium to another via a temperate bacteriophage during the lysogenic cycle. Here are the steps involved in specialized transduction:
Prophage Integration: The temperate bacteriophage infects a bacterial cell and integrates its DNA into the bacterial chromosome as a prophage. The integration site is usually specific and can vary depending on the bacteriophage and bacterial species.
Prophage Excision: Under certain conditions, such as exposure to UV light or other DNA-damaging agents, the prophage can excise itself from the bacterial chromosome. This excision is mediated by specific enzymes encoded by the phage.
Incorrect Excision: Occasionally, during the excision process, the prophage may mistakenly excise adjacent bacterial DNA along with its own DNA. This occurs due to imprecise recombination events at the prophage attachment sites (attP and attB).
Packaging of Phage DNA: The excised phage DNA, along with the adjacent bacterial DNA fragment, is packaged into newly assembled phage particles during the phage replication process. This results in phage particles containing both phage DNA and bacterial DNA.
Infection of New Bacterial Cells: The phage particles containing the hybrid DNA (phage DNA plus bacterial DNA) infect new bacterial cells. Upon infection, the hybrid DNA is injected into the host bacterial cell.
Integration of Bacterial DNA: The bacterial DNA fragment carried by the phage is integrated into the recipient bacterial chromosome via homologous recombination. The bacterial genes carried by the transducing phage can now become a part of the recipient cell’s genome.
Expression of Transferred Genes: The transferred bacterial genes can be expressed in the recipient bacterial cell, leading to phenotypic changes. These changes can include the acquisition of new metabolic capabilities, antibiotic resistance, or other traits encoded by the transferred genes.
Specialized transduction allows for the transfer of specific bacterial genes between bacterial cells, contributing to genetic diversity and the spread of advantageous traits within bacterial populations.
Summarise transduction
Describe the process of conjugation
