01:694:301 Lecture Notes - Lecture 30: Aminoacyl-Trna, Peptide Synthesis, Chain Termination
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14 Nov 2018
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Chapter 30 – ‘Protein Synthesis’
• Genetic info is important because of the proteins it encodes; protein ! functional role in cells
o
Translation
is the process of protein synthesis; it’s dependent on both nucleic acid and
protein factors; it takes place on
ribosomes
o Ribosomes are ‘ribozymes’ and have RNA components that play important role in function
o mRNA and tRNA also have roles in translation
" mRNA sequence dictates sequence of aa that make up proteins
" tRNA carries proper aa to ribosomes to build polypeptide chain
o Amino-acyl tRNA synthetases are enzymes that link aa and nucleic acids
" They translate genetic code by linked tRNA with specific aa
o Protein factors also play role in initiation, elongation, and termination
• The basics of protein synthesis are same for all organisms
o mRNA is decoded (5’ ! 3’ direction) one codon at time
o Proteins corresponding to code is created by adding correct aa to growing peptide chain
o AA added to chain in activated form as amino-acyl tRNAs
" aa-tRNA synthethase catalyzes the joining of –COOH of aa to 3’ end of tRNA molecule
• The process of translation is similar to copying something word-for-word; the process must
both accurate and fast enough to meet cell’s needs
• KNOW the structure of tRNA with specific loops etc (Fig. 30.2-5) and be familiar with the list
of tRNA features on 889-891.
o Accuracy in protein synthesis relies of recognition of 3 base
codons
on mRNA
" AA is attached to tRNA that can recognize said codon
o
tRNA act as ‘adapters’ that bind to specific codon and brings aa ! polypeptide chain
o All known tRNA molecules have the following features:
" (1) Each is a single chain containing between 73 and 93 ribonucleotides
" (2) Contain
many unusual bases
(7-15); some bases modified through methylation
• Methylation can prevent formation of certain base pairs and also imparts
hydrophobic character to some regions on tRNA
" (3) The molecule is L-shaped
" (4) About half nucleotides in tRNA are paired to form double helix
• Four helical regions form to create 2 segments of double helix (A-form DNA)
o One helix has 5’ ! 3’ run horizontally; other containing anticodon vertically (L)
o 5 groups of base are not base paired in this way: 3’CCA terminus, DHU loop,
TψC loop, the ‘extra’ arm, and anticodon loop
" (5) The 5’ end is usually phosphorylated; terminal residue usually pG
" (6) Activated aa attached –OH group of adenosine residue in attachment site
" (7) Anticodon loop (near center) is at other end of L making is accessible to 3 bases
that make up anticodon
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