Biology Questions and Answers
- Since among the 64
codons of mRNA 61 codify
amino acids that form
polypeptide chains what are
the functions of the three
remaining codons?
Since there are 20 amino acids and 64
possibilitiesexpected som of mRNAe amino codons, it isacids to be
codified by more than one codon. And
that really happens.
Not all 64 acids. Three of them, UAA, codons however codify UGA anaminod
UAG, work on information that the last
amino acid oproductions was already f a polypeptide chain bound, i.e.,under
they signal the end of the polypeptide
synthesis. These codons are calledterminal codons. The codon AUG
codifies the amino acid methionine and
at the same time beginning of the synthit signalsesis of a the (^)
polypeptide chain (it is an initialization
codon).
In prokaryotic cells there is a sequence
called Shine-Dalgargeneral AGGAGG) in the position thatno sequence (in (^)
antecedes the initialization codon AUG.
The function odistinctness between the initializationf this sequence is (^)
AUG and other AUG codons of the RNA.
- What is the cellular
structure to which mRNA
molecules bind to start the
protein synthesis?
To make necessarilyproteins mRNA associate to ribosomes. molecules (^)
Ribosomes have two sites for the
binding of two neighboring mRNA
codons abind by hydrogen bond. Thus ribosomnd where anticodons of tRNA (^) es
are the structure responsible for the
positioning codons to be translated. Iand exposure of mRNAn ribosom (^) es
the peptide bond between two amino
acids boccurs. Trought by tRNAhe peptide bond happens when molecules also (^)
tRNAs carrying amino acids are bound
to exposed mRNA codons.
- How are amino acids
brought to the cellular site
where translation takes place?
What is an anticodon?
Amino acids are brought to ribosomes
by RNA molecules kRNA, or tRNA. One tRNA associated tonown as transfer (^)
its specific amino acid binds by a special
sequence of three nucleotidmRNA codon exposed in the ribosomes to a (^) e.
This sequence in the tRNA is known as
anticodon. Tcomplementary to the mRNAhe tRNA anticodon must be codon to
which it binds, accordinU, CG. The ribosome then slidg to thes alonge rule A-
the mRNA molecule (a process called
translocation) to ecodon to the binding of other tRNA.xpose the following
When amino acids corresponding to
neighboring codons bind by peptidebond the first tRNa is liberated.
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