WEEK 2: DECODING DNA Flashcards
What is translation?
The production of a protein using information that is encoded in an mRNA.
Where does translation occur?
It occurs in the cytoplasm.
State the key components required for translation.
The key components required for translation are mRNA, ribosomes, and transfer RNA (tRNA).
Describe the process of translation
1.tRNA CHARGING:
- Binding of the amino acids to tRNA facilitated by the aminoacyl-tRNA synthase forming an aminoacyl TRN.
2.INITIATION:
- The small ribosomal subunit binds to the initiator tRNA carrying the initiator amino acid methionine. This complex then attaches to the cap structure at the 5’ end of an mRNA and scans for the start codon AUG.
*The process is mediated by several initiation factors.
*At the start codon, the large ribosomal subunit joins the complex and all initiation factors are released.
The ribosome has three sites:
**A-site is the entry site for new tRNA charged with amino-acid or aminoacyl-tRNA
**P-site is occupied by peptidyl-tRNA - the tRNA that carries the growing polypeptide chain
** E-site is the exit site for the tRNA after it’s done delivering the amino acid. The initiator tRNA is positioned in the P-site.
3.ELONGATION
*A new tRNA carrying an amino acid enters the A-site of the ribosome.
*On the ribosome, the anticodon of the incoming tRNA is matched against the mRNA codon positioned in the A-site.
*When the right aminoacyl-tRNA enters the A-site, a peptide bond is made between the two now-adjacent amino-acids.
- As the peptide bond is formed, the tRNA in the P-site releases the amino-acids onto the tRNA in the A-site and becomes empty.
*At the same time, the ribosome moves one triplet forward on the mRNA. As a result, the empty tRNA is now in the E-site and the peptidyl tRNA is in the P-site.
*The A-site is now unoccupied and is ready to accept a new tRNA.
*The cycle is repeated for each codon on the mRNA.
3.TERMINATION
*Termination happens when one of the three stop codons is positioned in the A-site.
*No tRNA can fit in the A-site at that point as there are no tRNA that match the sequence.
- Instead, these codons are recognized by a protein, a release factor.
- Binding of the release factor catalyzes the cleavage of the bond between the polypeptide and the tRNA.
*The polypeptide is released from the ribosome.
*The ribosome is disassociated into subunits and is ready for a new round of translation.
*The newly made polypeptide usually requires additional modifications and folding before it can become an active protein.
State the function of tRNA.
tRNA molecules are therefore responsible for bringing amino acids to the ribosome in the correct order, ready for polypeptide assembly.
State the 2 components which are possessed by the tRNA.
Every tRNA molecule possesses an anticodon that is complementary to the mRNA codon, and at the opposite end lies the attached amino acid.
A single amino acid may be coded for by more than one codon. There are also specific codons that signal the start and the end of translation.
TRUE / FALSE
True
What are enzymes that link amino acids to their corresponding tRNA molecules called?
What is the resulting complex, that is charged referred to as?
*Aminoacyl-tRNA synthetases are enzymes that link amino acids to their corresponding tRNA molecules. *
The resulting complex is charged and is referred to as an aminoacyl-tRNA.
Differentiate between the sense and anti-sense strand.
1.Sense Strand:
*Sense strand is directed in the 3’ to 5’ direction.
*It is involved in coding.
2.Antisense Strand:
*Antisense strand is directed in the 5’ to 3’ direction.
*It is non-coding.
What is meant by pre-mRNA?
The first (primary) transcript from a protein coding gene is often called a pre-mRNA and contains both introns and exons.
How do antibodies work?
By inhibiting protein synthesis.
Explain why some antibodies inhibit protein synthesis in prokaryotes and not eukaryotes?
Give examples of 2 ways in which proteins can become post translationally modified.
*Methylation
*Acetylation
*Lipidation
*Phosphorylation
*Glucosylation
*SUMOylation
*Ubiquitination
*Disulfide bond.
Outline the types of mutation.
1.Point mutations; Change in a single nucleotide bas.
– Missense (change aa): Codon carrying the altered base may be for a different amino acid.
– Nonsense (premature termination): The codon containing an altered base may be a stop codon.
– Silent: Codon carrying the altered base codes for the same amino acid.
- Deletion
– Large variation in size - Insertion
- Duplication
- Splice site
- Regulatory
- Expanded repeat
