Microbial genetics

Question 2

Horizontal and vertical gene transfer

Answer 2

horizontal: takes up new DNA (becomes transformed–expresses new genes); vertical: passes on to offspring

Question 3

Where do replication, transcription and translation being and end?

Answer 3

Rep: start origin, end at origin or end of linear; transcript: promoter/terminator; translate: AUG start to stop codon

Question 4

Purines vs pyrimidines

Answer 4

Purines: larger, A and G; pyrimidines: smaller, T, C, U

Question 5

Bacterial DNA replication

Answer 5

Gyrase reduces supercoil; helicase unzips DNA, SSB keep it unwound, primase adds primers, DNA polymerase III adds dNTPs and proofreads, ligase joins okazaki fragments, DNA polymerase I replaces primer

Question 6

Define genome

Answer 6

All coding and non-coding DNA of an organism (include plasmids); Viral can be RNA.

Question 7

Codon

Answer 7

three base pairs on mRNA that code for a amino acid

Question 8

How do you know you have a gene?

Answer 8

1. Start/stop codon with open reading frame (long line of codons for amino acids without stop codon). 2. Promoter. 3. Terminator. 4. Shine delgarno sequence (for ribosome binding)

Question 9

Plasmid characteristics

Answer 9

Small piece of DNA that replicates independent of chromosome (has its own origin), not essential for growth or metabolism, sometimes good for survival

Question 10

Types of plasmids

Answer 10

Fertility - F factor required for conjugation; Resistance – antimicrobial resistance genes; Virulence – increases virulence by coding for toxins, structures etc.; Cryptic - ?; bacteriocin - toxins to kill other bacteria

Question 11

Methylation importance

Answer 11

Old strand vs new strand so the new one can be repaired; regulation of unneeded genes; protect against their own restriction enzymes; sometimes help DNA replication initiation, DNA repair

Question 12

Some methylation is reversible. What for?

Answer 12

Gamete formation

Question 13

When would a gene not have a promoter?

Answer 13

In an operon. A bunch of genes just have one promoter at the beginning

Question 14

When are promoters not seen by RNA polymerase?

Answer 14

Repressors bound at operation region, or not exposed

Question 15

Coding vs Template strand ***

Answer 15

Template: read by RNA polymerase; coding: essentially the same as the mRNA (RNA poly travels 5’-3’, but reads the template 3’ to 5’)

Question 16

Types of termination of transcription in bacteria

Answer 16

Rho dependent: Rho protein follows mRNA strand and knocks it off; Rho independent: G-C rich region forms a loop which pulls off the transcript

Question 17

Shine Delgarno sequence

Answer 17

Needed on mRNA for ribosomal binding; need one for each codon

Question 18

How is protein synthesis halted?

Answer 18

Inhibit transcription, regulate enzymes, stoping translation (rare)

Question 19

Inducible and repressible operons

Answer 19

Inducible: always off unless turned on (ex lac operon); Repressible: always on except when turned off (ex trp operon)

Question 20

Describe the lac operon and function

Answer 20

Repressor comes from regulator gene and binds operon; when lactose present, allolactose binds repressor so it can’t bind; single RNA transcript that produces the number of polypeptides in DNA; inducers binding to repressor

Question 21

Describe the trp operon and function

Answer 21

Repressor doesn’t normally recognize operator unless trp is present; save energy by using stuff in the environment

Question 22

What specific effect(s) does the binding of the molecule to a repressor have? What is this form of regulation called?

Answer 22

Confirmation change so it can or cannot bind the operator. This is allosteric regulation.

Question 23

What is required for genetic recombination?

Answer 23

Homologous sequences (and appropriate enzymes)

Question 24

Name of a section of DNA which contains many virulence factors

Answer 24

Pathogenicity island