HONR 1034 Chapter Notes - Chapter 14: Eef2, Transfer Rna, Amine

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12 Jun 2018
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Translation and Proteins
I. Translation of mRNA depends on ribosomes and transfer RNAs
A. Translation: the biological polymerization of amino acids into polypeptide chains
1. Occurs only in association with ribosomes
B. Essential question in translation: how do triplet codons direct specific amino acids into their
correct position in the polypeptide?
C. tRNA: adapts genetic information as specific triplet codons in mRNA to their corresponding
amino acids
1. Contains anticodons: a sequence of three consecutive ribonucleotides complementary to
the codon; can base pair with the codon
2. Are small and stable in a cell
3. Have anticodon loops
4. On the 3’ end there’s an amino acid binding site where they join covalently
D. Amino acid structure
1. H+ bonds holding tRNA and mRNA close together so they can form peptide bonds
II. Ribosomal structure
A. One bacterial cell has about 10,000 ribosomes
B. Consists of two subunits: one large and one small
1. Each have an array of ribosomal proteins
2. Monosome: when the two subunits are associated with one another in a single ribosome
3. Found in both prokaryotic and eukaryotic cells → have subtle differences
4. Many ribosomal proteins are thought to promote binding of various molecules during
translation and fine-tune the process
C. Each cluster in eukaryotes consists of tandem repeats, with each unit separated by noncoding
spacer DNA sequence
III. The three steps of mRNA translation
A. Initiation
1. Initiation involves an mRNA molecule, a charged initiator tRNA, the small ribosomal
subunit, and a few other initiation factors
2. STEP 1: initiation factors bind to the subunit and the subunit binds to mRNA
3. STEP 2: the mRNA and tRNA become stabilized
4. STEP 3: the initiation factors are hydrolyzed, providing the energy needed that is released
B. Elongation
1. Charged tRNAs are transported into the complex by an elongation factor
2. The growing polypeptide is lengthened
3. Before elongation can be repeated, tRNA is released from the large subunit and moves to
the exit site, uncharged
4. Translocation: when the entire complex shifts in the direction of the P site by three
nucleotides
5. Process is repeated over and over of elongation and translocation
6. Once the elongated chain is of reasonable size, it emerges from the bottom of the large
subunit through a tunnel
C. Termination
1. Stop codons signal the termination
2. The translation complex is released
D. Polyribosome: what results from multiple ribosomes working on the same mRNA strand with
their own initiation and stop codons
IV. Variations in protein structure provides a basis for biological diversity
A. Polypeptide: the precursor to a protein
B. Amino acids have a carboxyl group, amino group, R group, and a carbon atom
C. Are hydrophilic, hydrophobic, positively charged or negatively charged
V. Levels of protein structure
A. Primary structure: the sequence of amino acids in the linear backbone of the polypeptide
B. Secondary structure: regular or repeated configurations in space assumed by amino acids
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