front 1
What is a “promoter” in bacteria? Is a promoter composed of
DNA, RNA, or protein? What is the relationship between a promoter
and sigma factor? | back 1 -
A promoter is a section of DNA that promotes the
start of transcription.
-
Transcription begins when sigma, as part of the
holoenzyme complex, binds to the promoter
|
front 2
What happens during the “elongation phase” of transcription? | back 2 -
During elongation, the rudder helps steer the
template and non-template strands, the enzyme’s active site
catalyzes the addition of nucleotides to the 3’ end of the growing
RNA molecule and the zipper helps separate the newly synthesized
RNA from the DNA template
|
front 3
How does transcription in bacteria end? | back 3
Transcription stops when RNA polymerase transcribes a
DNA sequence that functions as a transcription termination signal
and as soon as it is synthesized, this portion of RNA folds folds
upon itself to form a short double helix that is held together by
complementary base pairing and this results in the physical
separation of RNA polymerase and the RNA transcript |
front 4
How does transcription in eukaryotes differ from transcription
in prokaryotes? | back 4 - Eukaryotes have three polymerases and RNA polymerase II is the
only polymerase that transcribes protein-coding genes
- Eukaryotes have more diverse promoters
- TATA box is
centered about 30 base pairs upstream of the transcription
site
- Instead of sigma, eukaryotes use basal
transcription factors which assemble at the promoter and RNA
polymerase follows
- Termination of eukaryotic protein-coding
genes involves a short sequence called the poly(A) signal and after
it is transcribed, the RNA is cut by an enzyme downstream of the
poly (A) signal as the polymerase continues to transcribe the DNA
template, RNA polymerase eventually falls off and terminates
transcription
|
front 5
In eukaryotes there are at least three different RNA
polymerase enzymes. Which one is responsible for transcribing
protein-coding genes? | |
front 6
In eukaryotes, how does a mature mRNA differ from a primary
transcript? Draw a schematic of a mature mRNA, and explain the
function of each part of the molecule. | back 6 -
The primary transcript is the result of transcription
using the DNA template and becomes a mature mRNA once the
spliceosome has spliced out introns.
|
front 7
Explain how alternative splicing allows a single gene to code
for more than one protein. | back 7 -
Since the RNA can be spliced in more than one way,
this allows the production of different, related mRNAs and
proteins from one gene.
|
front 8
What are the minimal components required for protein synthesis? | back 8 -
Ribosomes, mRNA, amino acids, tRNA, ATP and
GTP
|
front 9
Where does protein synthesis occur in bacteria? in eukaryotes? | back 9 - In bacteria, protein synthesis occurs concurrently with
transcription because there is no nuclear envelope to separate the
two processes.
- Multiple ribosomes, polyribosome,
attach to each mRNA and many copies of a protein can be produced
from one mRNA.
- In eukaryotes, primary transcripts
are processed in the nucleus to produce a mature mRNA, which is then
exported to the cytoplasm and polyribosomes attach to it and begin
synthesizing proteins.
|
front 10
How does tRNA serve as an “adapter” in protein synthesis?
What is the relationship between a codon and an anticodon? | back 10 -
tRNA serves as an “adapter” by acting as an
interpreter and allowing amino acids to interact with an mRNA
template.
|
front 11
What is the relationship between a codon and an anticodon? How
can 40 tRNAs translate 61 different codons? | back 11 -
The anticodon forms complementary base pairs with an
mRNA codon.
-
According to the wobble hypothesis, particular
non-stranded base pairs, such as G-U, are acceptable in the third
position of a codon and do not change the amino acid that the
codon specifies therefore the wobble in the third position of a
codon allows just 40 or so tRNAs to bind to all 61 mRNA
codons.
|
front 12
What do aminoacyl tRNA synthetases do? | back 12 -
Aminoacyl tRNA synthetases catalyze the addition of
amino acids to tRNAs.
-
There is a different one for each 20 amino acids
and one or more tRNAs, there is a binding site for a particular
amino acid and tRNA
|
front 13
What would be the effect if a mutation in the gene for a
particular aminoacyl tRNA synthetase caused the enzyme to become
completely non-functional? | |
front 14
How do mRNA, tRNA, and ribosome subunits come together to
start the process of translation in bacteria? | back 14 -
The process begins when a section of rRNA in a small
ribosomal subunit binds to complementary sequence on an mRNA, the
mRNA region is called the ribosomal binding site.
-
Initiator aminoacyl tRNA binds to start codon and it
is followed by the binding of the large subunit after which
translation can begin.
|
front 15
Describe the sequence of events that occurs during translation
as a protein elongates by one amino acid and the ribosome moves down
the mRNA. Does protein or RNA catalyze protein synthesis? | back 15 -
The translation of each mRNA codon begins when an
aminoacyl tRNA diffuses into the A site and stays if its anticodon
matches a codon in the mRNA.
-
A peptide bond then forms between the amino acid held
by the aminoacyl tRNA in the A site and the growing polypeptide,
which was held by a tRNA in the P site.
-
The ribosome moves down the mRNA by one codon, and
all three tRNAs move down one position and the tRNA in the E site
exits.
-
Protein synthesis is catalyzed by RNA.
|
front 16
How does protein synthesis conclude when the ribosome reaches
the end of the message? | back 16 -
Release factors recognize stop codon and fill the A
site although they do not carry an amino acid.
-
Then the protein’s active site catalyzes the
hydrolysis of the bond that links tRNA in the P site to the
polypeptide chain.
-
Finally, the polypeptide chain is released from the
ribosome, the ribosome separates from the mRNA and the two
ribosomal subunits dissociate.
|
