Prokaryotic Gene Expression and Control Part 1 - Transcription

Question 1

Transription

Answer 1

related to
genomics, is the process of making
an RNA copy of a gene’s DNA sequence.

This copy, called messenger RNA
(mRNA), carries the gene’s protein
information encoded in DNA.

mRNA is used for synthesizing the
encoded protein

Question 2

Types of Nucleic Acid

Answer 2

• Deoxyribonucleic acid (DNA)
• store of genetic information (blue print) in all
  cellular forms of life and in some viruses
• Ribonucleic acid (RNA)
• store of genetic information in some viruses
• Intermediary between DNA and protein
  synthesis
• messenger and structural for translation
  RNA Molecules are Single-Stranded

Question 3

RNA Nucleotides

Answer 3

RNA contains the
base uracil, which
differs from thymine, the
equivalent base in
DNA, by the absence of a –CH3 group.

Question 4

RNA polymerase

Answer 4

RNA polymerase (RNAP) is the
multisubunit enzyme that transcribes
template DNA into RNA.
Officially known as DNA-directed RNA
polymerase.
RNA Polymerase
RNAP is found in all living organisms as
well as many viruses.
These RNAP all share similar protein
core structures as well as mechanisms.
Bacteria (prokaryotes) and archaea
contain only one RNAP.
https://www.ncbi.nlm.nih.gov/books/NBK545212/
Alberts, Bruce, et al. Molecular biology of the cell. 6th edition. New York: Garland, 2014.
DNA-Dependent Synthesis of RNA
RNA polymerase and the transcription
bubble move from left to right along
the DNA as shown, facilitating RNA
synthesis.
The DNA is unwound ahead and
rewound behind as RNA is transcribed.
As the DNA is rewound, the RNA-DNA
hybrid is displaced and the RNA strand
is extruded.

Question 5

Template and Notemplate Strands

Answer 5

The RNA transcript is synthesized on
the template strand and is identical in
sequence (with U in place of T) to the
nontemplate strand, or coding strand.
Template and nontemplate (coding) DNA strands.
The two complementary strands of
DNA are defined by their function
in transcription

Question 6

Initiation

Answer 6

Initiation comprises all the steps necessary to begin
RNA synthesis, including:
(1) promoter recognition,
(2) formation of a transcription bubble,
(3) creation of the first bonds between rNTPs, and
(4) escape of the transcription apparatus from the
promoter

Question 7

Promoters

Answer 7

Initiation occurs when RNA polymerase binds at
specific DNA sequences called promoters
Promoters direct the transcription of adjacent
segments of DNA (genes).
In E. coli, RNA polymerase binding occurs within a
region stretching from about 70 bp before the
transcription start site to about 30 bp beyond
it.

Question 8

The Transcription Unit

Answer 8

A transcription unit includes a promoter, an RNA-coding region, and a terminator

Question 9

Promoters

Answer 9

Essential information for the
transcription apparatus—where it
will start transcribing, which
strand is to be read, and in what
direction the RNA polymerase
will move—is embedded in the
nucleotide sequence of the
promoter.

Question 10

Sigma Factor

Answer 10

The sigma (σ) factor controls the
binding of RNA polymerase to the
promoter.
Without sigma, RNA polymerase
initiates transcription at a random
point along the DNA.
After sigma has associated with the
core enzyme (forming a holoenzyme),
RNA polymerase binds stably only to
the promoter and initiates
transcription at the proper start site

Question 11

DNA-Dependent Synthesis of RNA

Answer 11

As it moves downstream along the
template, RNA polymerase progressively
unwinds the DNA at the leading
(downstream) edge of the transcription
bubble, joining nucleotides to the
growing RNA molecule according to the
sequence of the template, and rewinds
the DNA at the trailing (upstream) edge
of the bubble.

Question 12

Termination

Answer 12

RNA polymerase adds nucleotides to the 3 end of the
growing RNA molecule until it transcribes a terminator.
At the terminator, several overlapping events are needed to
bring an end to transcription:
- RNA polymerase must stop synthesizing RNA,
- the newly made RNA molecule must be released from RNA
polymerase,
- the RNA molecule must dissociate fully from the DNA,
- and RNA polymerase must detach from the DNA template

Question 13

Bacterial cells possess two major types of terminators:

Answer 13

• Rho-dependent terminators are able to cause the
  termination of transcription only in the presence of an
  ancillary protein called the rho factor (ρ).
• Rho-independent terminators (also known as intrinsic
  terminators) are able to cause the end of transcription in
  the absence of the rho factor