DNA Transfer in Bacteria Flashcards
How are bases bonded in bacterial genomes?
Hydrogen bonded
Does bacterial genome contain a double helix?
Yes
Is bacterial genome the same size in all organisms?
No, it varies
Is the bacterial genome larger or smaller that eukaryotic genomes?
Smaller
Why is bacterial genomes small compared to eukaryotes?
- Genes densely packed
- No introns
- Genes with related functions grouped together
- Coupled transcription and translation
What is the average size of a bacterial genome?
1kb
What is the typical size of a chromosome some in bacterial genome?
2000-8000kbp
How many chromosomes are usually present in bacteria?
1
Can you occasionally have 2 chromosomes per cell in bacteria?
Yes
Does plasmids replicate independently?
Yes
What is the typical size of a plasmid?
10-200 kbp
What can some plasmids do in relation to chromosomes?
integrate themselves into chromosomes
What do you call it when plasmids integrate themselves into chromosomes?
Episomes
What are plasmids classed into?
Incompatibility groups
What are incompatibility groups based on?
Replication control or partition functions
What are the different types of plasmids?
- Antibiotic production
- Metabolic function
- Resistance
- Virulence
What are the two forms of bacterial DNA replication?
- Bi-directional replication
- Rolling circle replication
When does bi-directional replication occur?
During cell division and replication of some plasmids
When does rolling circle replication occur?
During replication of some plasmids and during conjugation
How fast does DNA polymerase copy the DNA of nucleotides?
1000 nucleotides per second
In what direction can DNA polymerase copy in?
5’ to 3’ direction
How long does it take to completely replicate an E. coli genome?
40 minutes
Steps for lagging strand synthesis: 1) 2) 3) 4) 5)
- Primase creates RNA primer
- 5’>3’ extension of RNA primer and dissociation of primase
- DNA polymerase III does 5’>3’ synthesis of DNA initiated at free 3’OH end of primers
- Simultaneous removal of RNA primers by 5’>3’ exonuclease of Polymerase I and 5’>3’ synthesis by Polymerase I
- Covalent closure of gaps by DNA ligase
Summarize the similarities and differences in rolling-circle replication, theta replication, and linear eukaryotic replication.
(1) Rolling-circle replication
• Initiated by cleavage in a single DNA strand
• Uncleaved strand used as template
• New nucleotides added to 3′ end of cleaved strand
• Linear single-strand DNA produced; subsequently circularized
(2) Theta replication
• Two replication forks
• Initiated by DNA denaturation at single origin
• Single, expanding replication bubble
• Bidirectional replication
• Circular DNA molecule produced
(3) Linear eukaryotic replication
• Two replication forks
• Initiated by DNA denaturation at multiple origins
• Multiple, expanding replication bubbles
• Bidirectional replication
• Linear DNA molecule produced
Leading Strand
In what direction is it synthesized?
Continuous or discontinuous?
Newly synthesized DNA strand formed by 5’ to 3’ polymerization in the direction of the
replication fork movement. DNA synthesis in this strand is continuous.
Lagging Strand
In what direction is it synthesized?
Continuous or discontinuous?
Newly synthesized DNA strand formed by 5’ to 3’ polymerization in the direction opposite
the movement of the replication fork. DNA synthesis in this strand is discontinuous.
What is a Okazaki Fragment?
A small segment of single-stranded DNA synthesized as part of the lagging strand in DNA replication.
What is Origin of Replication?
Site at which DNA replication is initiated.
What is horizontal gene transfer?
Transfer of DNA from one organism to another with the organism having to divide give another generation
What are the different types of horizontal gene transfer?
- Transformation
- Transduction
- Conjugation
What are the steps in natural transformation for horizontal gene transfer?
- Competence = extracellular binding
- Uptake = conversion to single stranded DNA stabilisation
- Integration = homologous recombination
What is competence?
Bacteria dying all the time in environment and releasing DNA
- Bacteria in environment can take up free DNA
- Mediated by competency apparatus
What are competency apparatus?
Series of proteins embedded that are embedded in membrane with facilitated pillus-like structure that can pull DNA in
What is transformation?
Recombinant cell with foreign DNA that occurred through the process of transmission called a transformant
What is transduction?
Process of transferring DNA from one bacterial cell to another bacterial cell via bacteriophage or phage or bacteria virus
What are the steps in transduction for horizontal gene transfer?
- Generalised: donor DNA from any part of donor can be transferred
- Virus injection, chromsome disruption
- Donor DNA-containing virus burst cell
- Donor DNA-containing virus injects donor DNA into recipient cell
What do you call bacteria taken up DNA through transduction?
Tranductants
Where do generalised transactions occur?
In lytic cycle of a virus
What is specialised transduction?
Transfer of bacterial gene during release from lysogenic cycle
Describe specialised transduction in a normal event:
- phage DNA circulates and detaches from host DNA
2. Detached DNA gets replicated
3. Phage synthesis is completed
4. Cell lyses and releases normal phase
Described specialised transduction in rare eventL
- A portion of host DNA is exchanged for phage DNA
- Detached DNA gets replicated
- Phage synthesis is completed
- Cell lyses and releases defective phage that can transduce galactose gene
What is conjugation?
Transfer of DNA directly from one cell to another through cell-cell contact
What is conjugation typically initiated by?
Specialised pilus protruding from the donor cell
What does the presence of F plasma lead to in conjugation?
- Ability to synthesis the F pilus
- Mobilisation of DNA for transfer to another cell
- Alteration of cell surface receptors
What does conjugation required?
DNA synthesis
Describe the process of conjugation:
- Donor cell (F+ cell) connected via pilus to recipient (F-cell)
- Pilus retracts
- Cell pairs stabilised
- F plasmid nicked by Tral enzyme in one strand
- Transfer of one stand from F+ cell to F- cell
- F plasmid simultaneously replicated in F+ cell
- Synthesis of complementary stand begins in recipient cell
- Completion of DNA transfer and synthesis
- Cells separate
- F+ cell and F+ cell (two completely separate cells)
What is integration of F and chromosome mobilisation?
Recombination between similar sequences
Cells with an integrated F plasmid are called Hfr
Describe the conjugation process of between Hfr cell and F-cell:
-F plasmid sucked in one strand
-Transfer of F followed by chromosomal DNA
-Synthesis of second strand in recipient
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