Eukaryotic Translation Flashcards
1
Q
What is translation?
A
Translation (Protein Synthesis) is a process of synthesizing proteins in a chain of amino acids known as polypeptides. It is the second part of the central dogma in genetics.
https://microbenotes.com/translation-protein-synthesis/
2
Q
What is a central dogma?
A
The central dogma of molecular biology is a theory stating that genetic information flows only in one direction, from DNA, to RNA, to protein, or RNA directly to protein.
- Replication: a double-stranded nucleic acid is duplicated to give identical copies. This process perpetuates the genetic information.
- Transcription: a DNA segment that constitutes a gene is read and transcribed into a single-stranded sequence of RNA. The RNA moves from the nucleus into the cytoplasm.
- Translation: the RNA sequence is translated into a sequence of amino acids as the protein is formed. During translation, the ribosome reads three bases (a codon) at a time from the RNA and translates them into one amino acid.
3
Q
Where does translation occur?
A
It takes place in the ribosomes found in the cytosol or those attached to the rough endoplasmic reticulum.
4
Q
What factors aid translation?
A
The translation process is aided by two major factors: A translator – this is the molecule that conducts the translation; substrate – this is where the mRNA is translated into a new protein (translator desk). The translation process is guided by machinery composed of:
- Ribosomes
- Transfer RNA (tRNA)
5
Q
What are the phases/steps in translation?
A
-Initiation
-Elongation
-Termination
6
Q
What is involved in Translation Initiation
A
- Protein synthesis initiation is triggered by the presence of several initiation factors IF1, IF2, and IF3, including mRNA, ribosomes, tRNA.
- The small subunit binds to the upstream on the 5′ end at the start of mRNA. The ribosome scans the mRNA in the 5′ to 3′ direction until it encounters the start codon (AUG or GUG or UUG). When either of these start codons is present, it is recognized by the initiator fMet-tRNA (N-formylMet-tRNA). This initiator factor carries the methionine (Met) which binds to the P site on the ribosome.
- This synthesizes the first amino acid polypeptide known as N-formylmethionine. The initiator fMet-tRNA has a normal methionine anticodon therefore it inserts the N-formylmethionine. This means that methionine is the first amino acid that is added and appears in the chain.
7
Q
What is involved in Translation Elongation
A
- The elongation of protein synthesis is aided by three protein factors i.e EF-Tu, EF-Ts, and EF-G.
- The ribosomal function is known to shift one codon at a time, catalyzing the processes that take place in its three sites.
- For every step, a charged tRNA enters the ribosomal complex and inserts the polypeptides that become one amino acid longer, while an uncharged tRNA departs. In prokaryotes, an amino acid is added at least every 0.05 seconds, which means that about 200 polypeptide amino acids are translated in 10 seconds.
- The bond created between each amino acid is derived from the Guanosine Triphosphate (GTP), which is similar to Adenosine Triphosphate (ATP).
- The three sites (A, P, E) all participate in the translation process, and the ribosome itself interacts with all the RNA types involved in translation.
8
Q
Elongation steps
A
- The mediation of elongation Factor-Tu (EF-Tu) in the entry of amino-acyl-tRNAs to the A site. This entails the binding of EF-Tu to GTP, which activates the EF-Tu-GTP complex to bind to tRNA. The GTP then hydrolyses to GDP releasing an energy-giving phosphate molecule, thus driving the binding of aminoacyl-tRNA to the A site. At this point the EF-Tu is released, leaving the tRNA in the A-site.
- Elongation factor EF-Ts then mediates the releasing of EF-Tu-GDP complex from the ribosomes and the formation of the EF-Tu-GTP.
- During this translocation process, the polypeptide chain on the peptidyl-tRNA is transferred to the aminoacyl-tRNA on the A-site during a reaction that is catalyzed by a peptidyl transferase. The ribosomes then move one codon further along the mRNA in the 5′ to 3′ direction mediated by the elongation factor EF-G. This step draws its energy from the splitting of GTP to GDP. Uncharged tRNA is released from the P-site, transferring newly formed peptidyl-tRNA from the A-site to the P-site.
9
Q
Initiation Steps
A
- Initiation of the binding of mRNA to the small ribosome subunit (the 30S), stimulating the initiator factor IF3. this dissociates the ribosomal subunits into two.
- The initiator factor IF2 then binds to the Guanine-triphosphate (GTP) and to the initiator fMet-tRNA to the P-site of the ribosomes.
- A ribosomal protein splits the GTP that is bound to IF2 thus helping in driving the assembly of the two ribosomal subunits. The IF3 and IF2 are released.
10
Q
What happens in Translation Termination
A
- Termination of the translation process is triggered by an encounter of any of the three stop codons (UAA, UAG, UGA). These triplet-stop codons, however, are not recognized by the tRNA but by protein factors known as the release factors, (RF1 and RF2) found in the ribosomes.
- The RF1 recognizes the triplet UAA and UAG while RF2 recognizes UAA and UGA. A third factor also assists in catalyzing the termination process and it’s known as Release factor 3 (RF3).
- When the peptidyl-tRNA from the elongation step arrives at the P site, the release factor of the stop codon binds to the A site. These releases the polypeptide from the P site allowing the ribosomes to dissociate into two subunits by the energy derived from GTP, leaving the mRNA.
- After many ribosomes have completed the translation process, the mRNA is degraded allowing its nucleotides to be reused in other transcription reactions.
