Lecture 11/12/13 Flashcards
Rank eukaryotes, prokaryotes, and viruses in order of largest to the smallest genome.
eukaryotes>prokaryotes>viruses
What is the advantage to having a smallest genome?
smaller genomes are able to replicate faster
Describe the T4 bacteriophage.
- Has a protein head
- 169 000 base pairs and 150 characterized genes
- Goes through the lytic cycle
- Looks like the cookie monster from despicable me
Describe the lambda phage.
- 50 000 base pairs and 50 genes
- Can be lytic or lysogenic
- Looks like a screw with a helical head
What are prototrophs?
bacteria that can grow on minimal media because it can synthesize organic factors
What are auxotrophs?
bacteria that requires an organic factor to grow
What is a retrovirus?
a virus with an RNA genome
How does a retrovirus infect and replicate a host cell?
- Virus enters host cell
- RNA is transcribed into DNA using reverse transcriptase
- Viral DNA enters the nucleus and is integrated into host chromosome forming a provirus
- Proviral DNA is then transcribed into viral RNA
- The viral RNA is then translated to make the virus again and leave through the cell membrane
What are the three genes that retroviruses carry and what are they used for?
Gag - encodes the protein capsid
Pol - encodes reverse transcriptase and integrase
Env - synthesizes glycoproteins for the viral envelope
Briefly describe the lytic cycle.
- Phage injects DNA into cell
- Phage DNA replicates and host cell transcribes the phage DNA producing phage proteins
- A phage-encoded enzyme causes the cell to lyse and the new phages are released
Briefly describe the lysogenic cycle.
- Phage injects DNA into cell
- Phage DNA is integrated into host cell DNA - prophage
- Prophage is replicated as part of the bacterial chromosome
- Eventually to prophage will separate and the viral DNA will be ejected from the host DNA
- Cell can then enter lytic cycle
What are episomes?
large circular DNA that can integrate into the bacterial chromosome for replication or remain separate
What are plasmids?
small circular DNA that can replicate independently of the bacterial chromosome (do not integrate themself into host DNA)
What is replica plate culturing?
it uses a velvet stamp to pick up the cultures from a plate and place them on two different medias
Briefly describe conjugation.
requires physical contact, a cytoplasmic bridge is formed between cells and DNA replicates and transfers from one cell to another
Briefly describe transformation.
when naked DNA is taken up by a cell and integrated into the genome, and when the cell replicates one transformed cell and one non-transformed cell is formed; sensitive to DNase
What does the concept of competent bacteria mean?
it means that they can take up more types of DNA or are just better at taking up DNA
Briefly describe transduction.
- bacteriophage attaches to bacterial cell and injects DNA
- the bacterial DNA is then cut up and taken up by the bacteriophage
- the bacteriophage then lyses the cell and infects a new bacteria still carrying the DNA of the first bacteria
- the 2nd bacteria will then contain a recombinant chromosome when injected by the bacteriophage
Briefly describe the U tube experiment.
- Two auxotrophic strains were separated by a filter that allowed mixing of medium but not bacteria
- No prototrophic bacteria were produced
- Showed that the production of prototrophs was dependant on contact
What is conjugation mediated by?
the fertility factor
What is the different between F+ and HFr factors?
F+ is extra chromosomal
HFr is integrated into genome
What is the function of the F pilus?
to bring the cells together for contact in conjugation
What is the function of the conjugation channel?
a bridge that forms to exchange DNA
What is the result of conjugation between an F+ and F-? Hfr and F-? Fâ and F-?
2 F+ cells, one Hfr and one F- cell, two Fâ cells
What is generalized transduction?
When a random fragment of DNA is packaged in the phage head by mistake
What is specialized transduction?
Occurs when the prophage exercises imprecisely from the chromosome and produces a phage chromosome containing only the viral DNA and adjacent bacterial genes
