quiz 4 week 4/5

Question 1

What is the function of sigma factors in prokaryotic transcription?

Answer 1

They recognize promoters and recruit RNA polymerase to initiate transcription

Question 2

What are the two types of transcription termination in prokaryotes?

Answer 2

Rho-dependent protein binds to mRNA and halts transcription.
Rho-independent is a GC-rich hairpin structure that halts transcription.

Question 3

What sequence does the ribosome recognize to initiate translation in prokaryotes?

Answer 3

Shine-Dalgarno sequence at the 5’ end of the mRNA.

Question 4

What are the three ribosomal sites involved in translation, and what happens at each?

Answer 4

A (Aminoacyl) – tRNA enters, P (Peptidyl) – peptide bond forms,
E (Exit) – tRNA exits.

Question 5

What are the three main types of horizontal gene transfer in bacteria?

Answer 5

1. Transformation
2. Transduction
3. Conjugation

Question 6

How does conjugation differ from transduction and transformation?

Answer 6

In conjugation, DNA is transferred directly from one bacterium to another via a pilus. Both cells survive after conjugation.

Question 7

What is a transposon?

Answer 7

A movable DNA sequence that can jump between locations in a genome, sometimes leaving a copy behind.

Question 8

What is the role of activators and repressors in transcription regulation?

Answer 8

Activators recruit RNA polymerase to the promoter, while repressors block RNA polymerase from binding.

Question 9

How does the lactose operon regulate gene expression?

Answer 9

The lactose operon is repressed when glucose is present and activated when glucose is absent and lactose is available.

Question 10

What is transcriptional attenuation in the Trp operon?

Answer 10

High amino acid levels form a 3:4 loop that terminates transcription; low levels allow transcription to continue by forming a 2:3 loop.

Question 11

What is the role of the Shine-Dalgarno sequence in translation?

Answer 11

It helps the ribosome bind to the mRNA to start protein synthesis by aligning it correctly with the start codon.

Question 12

What is the F factor in conjugation, and what are F+ and F- cells?

Answer 12

The F factor is a plasmid that carries genes for conjugation. F+ cells have the F factor, while F- cells do not.

Question 13

What are alternative sigma factors and when are they used?

Answer 13

Alternative sigma factors regulate transcription of specific genes in response to environmental conditions, such as stress.

Question 14

What is the difference between nonreplicative and replicative transposition?

Answer 14

Nonreplicative transposition moves the transposon without leaving a copy behind, while replicative transposition copies the transposon and leaves the original in place.

Question 15

What is electroporation, and when is it used?

Answer 15

Electroporation is a technique to make cells competent by using electric pulses to open pores in the cell membrane, allowing DNA uptake.

Question 16

What is the role of NusA protein in Rho-independent transcription termination?

Answer 16

NusA interacts with the GC-rich hairpin structure in the mRNA, causing RNA polymerase to detach and terminate transcription.

Question 17

What happens during homologous recombination in bacteria?

Answer 17

Homologous recombination involves the exchange of genetic material between similar DNA sequences, often to repair damaged DNA or allow for adaptation.

Question 18

What are outer membrane vesicles, and how do they help bacteria during horizontal gene transfer?

Answer 18

Outer membrane vesicles can act as decoys for bacteriophages or facilitate the transfer of DNA between bacteria, aiding in defense and survival.

Question 19

How do bacteria become “competent” for transformation in a lab setting?

Answer 19

Bacteria are made competent by weakening their cell walls using heat-shock or electroporation, which allows them to uptake DNA from their environment.

Question 20

What is the role of a pilus in bacterial conjugation?

Answer 20

The pilus is an appendage that forms between donor (F+) and recipient (F-) cells, allowing the transfer of DNA during conjugation.

Question 21

What is the difference between a lysogenic and lytic bacteriophage infection during transduction?

Answer 21

In lysogenic infection, the phage DNA integrates into the host genome and is passed on without killing the host, whereas in lytic infection, the phage replicates and lyses the host cell.

Question 22

What is transcriptional regulation through the use of “anti-sigma factors”?

Answer 22

Anti-sigma factors bind to sigma factors and prevent them from activating transcription, providing an additional level of transcriptional control.

Question 23

How do two-component systems work in bacteria to regulate gene expression?

Answer 23

Two-component systems involve a receptor detecting external signals and a responder activating or repressing gene expression, often through phosphorylation.

Question 24

What is the significance of inverted repeats in transposons?

Answer 24

Inverted repeats flank transposons and are recognized by transposase, the enzyme that cuts and inserts the transposon into new genetic locations.