Chapter 9-10: Bacterial/Viral Genetics

Question 1

what are the advantages of being haploid?

Answer 1

makes it easier to identify loss-of-function mutations than in eukaryotes, recessive mutations are not masked by dominant alleles

Question 2

what are the three mechanisms for the transfer of genetic material from one bacterium to another?

Answer 2

conjugation: direct transfer between cells
transduction: transfer of DNA between bacteria through viruses
transformation: uptake of DNA from the environment

Question 3

how does conjugation work between bacteria?

Answer 3

donor cells contain a small circular DNA called an F factor (fertility factor), the F factor carries genes that allow for the transfer of DNA from F+ to F- cells, the protein complex that mediates this transfer is the relaxosome and the conjugation is directly mediated by a sex pilus

Question 4

how does transduction work between bacteria?

Answer 4

bacteriophage infects the bacterial cell and digests the host DNA into fragments before recombining to include the phage DNA as well, as new phages are produced some may contain pieces of the host cells DNA as well, this new phage will then inject its DNA into another recipient bacteria that does not carry that chromosome, the recipient DNA is recombined to then contain that chromosome

Question 5

how does transformation work between bacteria?

Answer 5

a DNA fragment will bind to the surface of a cell, endonuclease outside the cell will then cut up the DNA, one strand of DNA will enter the cell and the other is degraded, the DNA strand is combined with bacterial chromosome through homologous recombination forming a heteroduplex, DNA repair enzymes then repair the strand

Question 6

horizontal vs vertical gene transfer?

Answer 6

horizontal: transfer of genes between organisms, may occur within or between species, contributes to acquired antibiotic resistance
vertical: transfer of gene from mother to daughter cells or from parents to offspring

Question 7

what are the 6 steps of the viral reproductive cycle?

Answer 7

1. attachment: proteins on virus interact with specific molecules at cell surface
2. entry: viral genome enters cell
3. integration: some integrate into host chromosomes through integrase
4. synthesis: of viral components such as genes or proteins
5. viral assembly: protein and nucleic acid subunits come together to make infectious particles
6. release: phage causes cell to rupture (lysis)

Question 8

what is the latency period?

Answer 8

inactive stage of a virus integrating into host cell genome, called a prophage or provirus

Question 9

temperate vs virulent phages?

Answer 9

temperate: has both latent and lysogenic (latency period) cycles
virulent: has only lytic cycle

Question 10

what causes new strains of viruses to emerge?

Answer 10

reverse transcriptase lacks a proofreading function cause mutant strains to arise frequently

Question 11

what does an envelope protein do?

Answer 11

guides assembly and release of virus

Question 12

what does a nucleocapsid protein do?

Answer 12

protects RNA

Question 13

what is a spike protein (S-protein)?

Answer 13

a glycoprotein homotrimer on the viral envelope

Question 14

what are the two subunits of the S-protien?

Answer 14

S1: has a binding domain to receptors on host cells
S2: modulates membrane fusion