case 3 Flashcards
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What are mRNA triplets called and how are they customary written?
the mRNA nucleotide triplets are called codons and they are customary written in the 5’3’direction
In which three stages can we divide translation the synthesis of a polypeptide?
We can divide translation, the synthesis of polypeptide into three stages; initiation, elongation and termination.
Please explain the first stage of translation of the synthesis of a polypetide
The first stage is initiation:
1- A small ribosomal subunit binds to an mRNA. In a bacterial cell, the mRNA binding site on this subunit recognizes a specific nucleotide sequence on the mRNA just upstream of the start codon. An initiator tRNA, with the anticodon UAC, base-pair with the start codon, AUG. this tRNA carries the amino acid met.
2- The arrival of a large ribosomal subunit completes the initiation complex. Proteins called initiation factors. Are required to bring all the translation components together. Hydrolysis of GTP provides the energy for the assembly. The initiator tRNA is in the P site; the A site is available to the tRNA bearing the next amino acid.
Please explain the second stage of translation the synthesis of a polypeptide?
the second part is elongation: amino acids are added one by one to the previous amino acid at the C-terminus of the growing chain. Each addition involves several proteins called elongation factor and occurs in a three-step cycle.
1- Codon recognition; the anticodon of an incoming aminoacyl tRNA base-pairs with the complementary mRNA codon in the a site. Hydrolyse of GTP increases the accuracy and efficiency of this step. Many different aminoacyl tRNA are present, but only the one with the appropriate anticodon will bind and allow the cycle to progress.
2- Peptide bond formation; an rRNA molecule of the large ribosomal subunit catalyse the formation of a peptide bond between the carboxyl end of the growing polypeptide in the p site and the amino acid group of the new amino acid in the A site. This step removes the polypeptide from the tRNA in the P side and attaches it to the amino acid of the tRNA.
3- Translocation; the ribosome translocates the tRNA in the A site to the P site. At the same time, the empty tRNA in the P site is moved to the E site, where it is released. The mRNA moves along with its bound tRNAs, bringing the next codon to be translated into the A site.
Please explain the third stage pf translation the synthesis of a polypeptide?
The third part is termination
1- When a ribosome reaches a stop codon on mRNA, the A site of the ribosome accepts a ‘’release factor’’ –a protein shaped like a tRNA –instead of an aminoacyl tRNA.
2- The release factor promotes hydrolysis of the bond between the tRNA in the P site and the last amino acid of the polypeptide, thus freeing the polypeptide from the ribosome.
3- The two ribosomal subunits and the other components of the assembly dissociate with the hydrolysis of two GPT molecules.
What are the differences between RNA and DNA?
The differences are
- RNA has 1 strand instead of 2 like DNA has.
- RNA is made up of ribose while DNA is made up of deoxyribose.
- RNA has uracil instead of Thymine.
- DNA is read from 3’ 5’ and RNA is made from 5’ to 3’
What is the difference between template strand and codon strand?
For each gene, only one of the two DNA strands is transcribed. This strand is called the template strand. The nontemplate DNA strand is often called the coding strand.
What is a nucleotide-pair substitution?
A nucleotide- pair substitution is the replacement of one nucleotide and its partner with another pair of nucleotides.
Example: 3’CCG’5 on the template strand mutate to 3’CCA’5 (this one has no effect)., the mRNA codon that used
to be GGC would become GGU
What is insertion and what is deletion?
Insertion and deletion are additions or losses of nucleotide pairs in a gene. And also are frameshift mutations. Meaning they alter the reading frame of the triplet grouping of nucleotides on the mRNA that is read during translation.
What are amino acids made of
Made of an nitrogen base, OH at the 3’ and a phosphate group.
What is a missense.
Substitutions that change one amino acid to another one
What is a nonsense mutation?
A point mutation can also change a codon for an amino acid into a stop codon
