Lecture 11/12/13

Question 1

Rank eukaryotes, prokaryotes, and viruses in order of largest to the smallest genome.

Answer 1

eukaryotes>prokaryotes>viruses

Question 2

What is the advantage to having a smallest genome?

Answer 2

smaller genomes are able to replicate faster

Question 3

Describe the T4 bacteriophage.

Answer 3

• 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

Question 4

Describe the lambda phage.

Answer 4

• 50 000 base pairs and 50 genes
• Can be lytic or lysogenic
• Looks like a screw with a helical head

Question 5

What are prototrophs?

Answer 5

bacteria that can grow on minimal media because it can synthesize organic factors

Question 6

What are auxotrophs?

Answer 6

bacteria that requires an organic factor to grow

Question 7

What is a retrovirus?

Answer 7

a virus with an RNA genome

Question 8

How does a retrovirus infect and replicate a host cell?

Answer 8

• 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

Question 9

What are the three genes that retroviruses carry and what are they used for?

Answer 9

Gag - encodes the protein capsid
Pol - encodes reverse transcriptase and integrase
Env - synthesizes glycoproteins for the viral envelope

Question 10

Briefly describe the lytic cycle.

Answer 10

• 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

Question 11

Briefly describe the lysogenic cycle.

Answer 11

• 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

Question 12

What are episomes?

Answer 12

large circular DNA that can integrate into the bacterial chromosome for replication or remain separate

Question 13

What are plasmids?

Answer 13

small circular DNA that can replicate independently of the bacterial chromosome (do not integrate themself into host DNA)

Question 14

What is replica plate culturing?

Answer 14

it uses a velvet stamp to pick up the cultures from a plate and place them on two different medias

Question 15

Briefly describe conjugation.

Answer 15

requires physical contact, a cytoplasmic bridge is formed between cells and DNA replicates and transfers from one cell to another

Question 16

Briefly describe transformation.

Answer 16

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

Question 17

What does the concept of competent bacteria mean?

Answer 17

it means that they can take up more types of DNA or are just better at taking up DNA

Question 18

Briefly describe transduction.

Answer 18

• 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

Question 19

Briefly describe the U tube experiment.

Answer 19

• 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

Question 20

What is conjugation mediated by?

Answer 20

the fertility factor

Question 21

What is the different between F+ and HFr factors?

Answer 21

F+ is extra chromosomal

HFr is integrated into genome

Question 22

What is the function of the F pilus?

Answer 22

to bring the cells together for contact in conjugation

Question 23

What is the function of the conjugation channel?

Answer 23

a bridge that forms to exchange DNA

Question 24

What is the result of conjugation between an F+ and F-? Hfr and F-? F’ and F-?

Answer 24

2 F+ cells, one Hfr and one F- cell, two F’ cells

Question 25

What is generalized transduction?

Answer 25

When a random fragment of DNA is packaged in the phage head by mistake

Question 26

What is specialized transduction?

Answer 26

Occurs when the prophage exercises imprecisely from the chromosome and produces a phage chromosome containing only the viral DNA and adjacent bacterial genes