Chapter 8 Part Two

Question 1

The regulation of bacterial gene expression

Answer 1

• constitutive genes are expressed at a fixed rate
  - housekeeping/ keep cell alive
• other genes are expressed only as needed
  
  • Inducible genes
  • repressive genes
  • catabolism repression

Question 2

Gene organization

Answer 2

Operon-genes encoding for proteins in pathways organized together

Question 3

Pre-transcriptional control -> Repression

Answer 3

• inhibits gene expression no decreases enzyme synthesis
  
  • mediated by depressors, proteins that can block transcription
  • default position of a repressive gene is on —-
• the structural genes are transcribed until they are turned off (or repressed)

Question 4

Induction

Answer 4

• induction turns on gene expression
  - initiated by an inducer
  - default position of an inducible gene is off
• where the structural genes are not transcribed unless an inducer is present
  - inducer = disables repressor

Question 5

The Oberon model of gene expression

Answer 5

• in an inducible operon, structural genes are not transcribed unless an inductor is present
  
  • in the absence of lactose, the repress or binds to the operator, preventing transcription
  • in the presence of lactose, lactose (inducer) binds to the repressor; the repressor cannot bind to the operator and transcription occurs

Question 6

The operon model of gene expression

Answer 6

• in repressive operon s, structural genes are transcribed until they are turned off
  
  • excess tryptophan is a corepressor that binds and activates the repressor to bin to the operator, stopping tryptophan synthesis

Question 7

Genetic diversity

Answer 7

• getting new genetic information to adapt and survive to new environmental conditions
  Genetic recombination: exchange o genes between two DNA molecules; creates genetic diversity
  Crossing over: two chromosomes break and rejoin, resulting in the insertion of foreign DNA into the chromosomes

Question 8

Mutations

Answer 8

Original: THE FAT CAT SAT
Point mutation: THA FAT CAT SAT
Insertion: THE FAT CAT SSAT
Deletion: THE FTC ATS AT

Question 9

Steps of genetic recombination by crossing over

Answer 9

1) DNA from one cell aligns with DNA in the recipient cell. notice that there is a nick in the donor DNA.
2) DNA from the donor aligns with the complementary base pairs in the recipient’s chromosome. This can involve thousands of base pairs
3) RecA proteins catalyzes the joining of the two strands
4) the result is that the recipient’s chromosome contains new DNA. Complementary base pairs between the two strands will be resolved by DNA polymerase and ligaments. The donor DNA will be destroyed. The recipient may now have one or more new genes

Question 10

Transformation

Answer 10

Genes transferred from one bacterium to another as “naked” DNA

Question 11

Transduction in bacteria

Answer 11

• DNA is transferred from a donor cell to a recipient via a bacteriophage
  
  • generalized transduction: random bacterial DNA is packaged inside a phage and transferred to a recipient cell
  • specialized transduction: specific bacterial genes are packaged inside a phage and transferred to a recipient cell

Question 12

Conjugation

Answer 12

• plasmids transferred from one bacterium to another (they form a mating bridge to transfer the plasmids
• requires cell-to-cell contact via sex pili

Question 13

Conjugation in bacteria -> donor cell

Answer 13

• donor cells carry the plasmid (F factor) and are called F^+ cells
  
  • Hfr cells contain the F factor on the chromosome