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Translation PART 1

Protein synthesis occurs in the cytoplasm for prokaryotes and in both the cytoplasm and rough ER for eukaryotes. The genetic code consists of codons, which are groups of three nucleotides in mRNA that correspond to amino acids, with redundancy allowing multiple codons to specify the same amino acid. Transfer RNA (tRNA) and aminoacyl-tRNA synthetases are crucial for translating the genetic code by ensuring the correct amino acids are added to the growing protein chain.

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111 views11 pages

Translation PART 1

Protein synthesis occurs in the cytoplasm for prokaryotes and in both the cytoplasm and rough ER for eukaryotes. The genetic code consists of codons, which are groups of three nucleotides in mRNA that correspond to amino acids, with redundancy allowing multiple codons to specify the same amino acid. Transfer RNA (tRNA) and aminoacyl-tRNA synthetases are crucial for translating the genetic code by ensuring the correct amino acids are added to the growing protein chain.

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Snehasis
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Translation: protein synthesis

Prokaryotes: Protein synthesis happens in cytoplasm


Eukaryotes: Protein synthesis happens in cytoplasm and on rough ER
“Coding problem”
How is the information in a linear sequence of nucleotides
in an RNA molecule translated into the linear sequence of a
chemically quite different set of subunits—the amino acids
in a protein?

Genetic code
The sequence of nucleotides in an mRNA molecule is read
consecutively in groups of three. And because RNA is made
of 4 different nucleotides, there are 4 × 4 × 4 = 64 possible
combinations of three nucleotides: AAA, AUA, AUG, and so
on. However, only 20 different amino acids are commonly
found in proteins. The code is redundant, with some amino
acids being specified by more than one triplet. Each group
of three consecutive nucleotides in RNA is called a codon.
mRNA is red by the ribosome using genetic
code

STOP CODONS
START CODON
Reading frames
ORF : Open reading frame
In‐frame stop codon

Open reading frame (ORF): Long sequence of nucleotides that contains no stop codon;
used to identify potential protein‐coding sequences in DNA. It’s a continuous stretch of
reading frame starts with a START codon and ends with a STOP codon.
Cracking the genetic code

Marshall Nirenberg
performing an experiment,
1962.
National Institutes of Health.

Throughout his career, Har Gobind Khorana was


devoted to working in the lab himself. Khorana is
shown here conducting a DNA polymerase assay at
the University of Wisconsin. Photo: University of
Wisconsin‐Madison Archives (S04437).
Transfer RNA or tRNA
Genetic code is read with the help of tRNA
Transfer RNA or tRNA
The genetic code is translated by the
cooperation of two adaptors: aminoacyl‐tRNA
synthetases and tRNAs.

Each synthetase couples a particular amino acid to its corresponding tRNAs, a process
called charging. The anticodon on the charged tRNA molecule then forms base pairs
with the appropriate codon on the mRNA. An error in either the charging step or the
binding of the charged tRNA to its codon will cause the wrong amino acid to be
incorporated into a protein chain. In the sequence of events shown, the amino acid
tryptophan (Trp) is selected by the codon UGG on the mRNA.
In many codons base pairing at the
3rd position is less stringent

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