BIOL213 Lecture Notes - Lecture 12: Aminoacyl-Trna, Transfer Rna, Ribosomal Rna
Lecture 12 – Introduction to Translation
• For some genes, the RNA transcript is the final product. But for many other genes,
the ultimate product is protein.
• Ribosomes: carry out the process of polypeptide synthesis.
• tRNA molecules align the amino acids in the correct order. Aminoacyl-
tRNA synthesises attach amino acids to their appropriate tRNA molecules.
• mRNA molecules encode amino acid sequence information
• Protein factors facilitate some of the steps of translation.
Ribosomes:
• they supervise the interactions between tRNA and mRNA.
• 65% of ribosomes are rRNA, and 35% are proteins.
• Ribosomes are composed of two subunits (one larger and one smaller with mRNA
running through
them.
• In eukaryotes, ribosomes are larger —> rRNA are larger and there are more RNA
proteins.
• rRNA have complex structures. They are single stranded, but have extensive
intrachain base pairing forming many loops.
• Translation is the synthesis of a polypeptide chain according to the sequence
of mRNA bases. Only RNA from protein-coding genes is translated.
• Each amino acid is encoded for by a triplet of bases called a codon.
tRNA:
• a tRNA molecule is an adaptor that binds both a specific amino acid and the
mRNA sequences that specify the amino acid (codon).
• Each tRNA contains an anticodon and can carry an amino acid at the 3’ end.
• The amino acid attaches to the tRNA at the 3’ end by an ester linkage.
• The anticodon loop recognises the codon on the mRNA sequence.
• tRNAs are named for the amino acids attached to them. ie. tRNA^ala for alanine.
• An amino acyl tRNA is charged with an activated amino acid.
• Each aminoacyl tRNA recognises codons in mRNA because of their
complementarity to the anticodon in the tRNA. Both the anticodon and the 3’ end
of the tRNA are needed to specify the correct amino acid.
• Codon-anticodon pairing is the crucial feature of the reading of the code.
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Lecture 12 – Introduction to Translation
• However, the genetic code is degenerate —> multiple codons code for one protein
in the translation process, as there are 61 codons (and 3 stop codons) but 20 amino
acids. There is redundancy in the genetic code (degeneracy).
Eg. 6 codons code for serine, but only 1 codon codes for methionine and
tryptophan.
• Usually, only the first two amino acids in a codon code for the amino acid, and the
last one varies and is degenerate.
Third base degeneracy and the wobble hypothesis:
• Cricks Wobble hypothesis argues that there must be a lack of specificity at the
third (degenerate) position of the codon and the first base of the anticodon
• mRNA and tRNA line up on the ribosome in a way that permits flexibility or
wobble in the pairing between the third base of the codon and the corresponding
base of the anticodon—> wobble hypothesis which allows for unexpected base
pairing. tRNA are able to pair with more than one codon.
find more resources at oneclass.com
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Document Summary
Lecture 12 introduction to translation: for some genes, the rna transcript is the final product. But for many other genes, the ultimate product is protein: ribosomes: carry out the process of polypeptide synthesis. trna molecules align the amino acids in the correct order. Aminoacyl- trna synthesises attach amino acids to their appropriate trna molecules: mrna molecules encode amino acid sequence information, protein factors facilitate some of the steps of translation. Ribosomes: they supervise the interactions between trna and mrna: 65% of ribosomes are rrna, and 35% are proteins, ribosomes are composed of two subunits (one larger and one smaller with mrna running through them. In eukaryotes, ribosomes are larger > rrna are larger and there are more rna proteins. rrna have complex structures. They are single stranded, but have extensive intrachain base pairing forming many loops: translation is the synthesis of a polypeptide chain according to the sequence of mrna bases.
