In summary, there are several key features that distinguish prokaryotic gene expression from that seen in eukaryotes. These are illustrated in
[link] and listed in
[link] .
Protein targeting, folding, and modification
During and after translation, polypeptides may need to be modified before they are biologically active. Post-translational modifications include:
removal of translated signal sequences—short tails of amino acids that aid in directing a protein to a specific cellular compartment
proper “folding” of the polypeptide and association of multiple polypeptide subunits, often facilitated by chaperone proteins, into a distinct three-dimensional structure
proteolytic processing of an inactive polypeptide to release an active protein component, and
various chemical modifications (e.g., phosphorylation, methylation, or glycosylation) of individual amino acids.
What are the components of the initiation complex for translation in prokaryotes?
What are two differences between initiation of prokaryotic and eukaryotic translation?
What occurs at each of the three active sites of the ribosome?
What causes termination of translation?
Key concepts and summary
In
translation , polypeptides are synthesized using mRNA sequences and cellular machinery, including tRNAs that match mRNA
codons to specific amino acids and ribosomes composed of RNA and proteins that catalyze the reaction.
The
genetic code is
degenerate in that several mRNA codons code for the same amino acids. The genetic code is almost universal among living organisms.
Prokaryotic (70S) and cytoplasmic eukaryotic (80S) ribosomes are each composed of a large subunit and a small subunit of differing sizes between the two groups. Each subunit is composed of rRNA and protein. Organelle ribosomes in eukaryotic cells resemble prokaryotic ribosomes.
Some 60 to 90 species of tRNA exist in bacteria. Each tRNA has a three-nucleotide
anticodon as well as a binding site for a
cognate amino acid . All tRNAs with a specific anticodon will carry the same amino acid.
Initiation of translation occurs when the small ribosomal subunit binds with
initiation factors and an initiator tRNA at the
start codon of an mRNA, followed by the binding to the initiation complex of the large ribosomal subunit.
In prokaryotic cells, the start codon codes for N-formyl-methionine carried by a special initiator tRNA. In eukaryotic cells, the start codon codes for methionine carried by a special initiator tRNA. In addition, whereas ribosomal binding of the mRNA in prokaryotes is facilitated by the Shine-Dalgarno sequence within the mRNA, eukaryotic ribosomes bind to the 5’ cap of the mRNA.
During the
elongation stage of translation, a
charged tRNA binds to mRNA in the
A site of the ribosome; a peptide bond is catalyzed between the two adjacent amino acids, breaking the bond between the first amino acid and its tRNA; the ribosome moves one codon along the mRNA; and the first tRNA is moved from the
P site of the ribosome to the
E site and leaves the ribosomal complex.
Termination of translation occurs when the ribosome encounters a
stop codon , which does not code for a tRNA. Release factors cause the polypeptide to be released, and the ribosomal complex dissociates.
In prokaryotes, transcription and translation may be coupled, with translation of an mRNA molecule beginning as soon as transcription allows enough mRNA exposure for the binding of a ribosome, prior to transcription termination. Transcription and translation are not coupled in eukaryotes because transcription occurs in the nucleus, whereas translation occurs in the cytoplasm or in association with the rough endoplasmic reticulum.
Polypeptides often require one or more
post-translational modifications to become biologically active.
Fill in the blank
The third position within a codon, in which changes often result in the incorporation of the same amino acid into the growing polypeptide, is called the ________.
Below is an antisense DNA sequence. Translate the mRNA molecule synthesized using the genetic code, recording the resulting amino acid sequence, indicating the N and C termini.
Antisense DNA strand: 3’-T A C T G A C T G A C G A T C-5’
is it possible to leave every good at the same level
Joseph
I don't think so. because check it, if the demand for chicken increases, people will no longer consume fish like they used to causing a fall in the demand for fish
Anuolu
is not really possible to let the value of a goods to be same at the same time.....
Salome
Suppose the inflation rate is 6%, does it mean that all the goods you purchase will cost
6% more than previous year? Provide with reasoning.
Not necessarily. To measure the inflation rate economists normally use an averaged price index of a basket of certain goods. So if you purchase goods included in the basket, you will notice that you pay 6% more, otherwise not necessarily.
Good day
How do I calculate this question: C= 100+5yd G= 2000 T= 2000 I(planned)=200.
Suppose the actual output is 3000. What is the level of planned expenditures at this level of output?
I am Camara from Guinea west Africa... happy to meet you guys here
Sekou
ma management ho
Amisha
ahile becheclor ho
Amisha
hjr ktm bta ho
ani k kaam grnu hunxa tw
Amisha
belatari
Amisha
1st year ho
Amisha
nd u
Amisha
ahh
Amisha
kaha biratnagar
Amisha
ys
Amisha
kina k vo
Amisha
money as unit of account means what?
Kalombe
A unit of account is something that can be used to value goods and services and make calculations
Jim
all of you please speak in English I can't understand you're language
Muhammad
I want to know how can we define macroeconomics in one line
Muhammad
it must be .9 or 0.9
no Mpc is greater than 1
Y=100+.9Y+50
Y-.9Y=150
0.1Y/0.1=150/0.1
Y=1500
Kalombe
Mercy is it clear?😋
Kalombe
hi can someone help me on this question
If a negative shocks shifts the IS curve to the left, what type of policy do you suggest so as to stabilize the level of output?
discuss your answer using appropriate graph.