11: The Genetic Code and Translation
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- 11.1: Introduction
- We begin this chapter with a look at how the genetic code was broken (deciphered). The very terms genetic code, broken and deciphered came from what was at the time, the recent history of the World War II. We will look at the elegant experiments that first deciphered the amino acid meaning of a few 3-base codons, and then all 64 codons. Of these, 61 encode amino acids and three are stop codons.
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- 11.2: An Overview of the Genetic Code
- The genetic code is the information for linking amino acids into polypeptides in an order based on the base sequence of 3-base code words (codons) in a gene and its messenger RNA (mRNA). With a few exceptions (some prokaryotes, mitochondria, chloroplasts), the genetic code is universal – it’s the same in all organisms from viruses and bacteria to humans.
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- 11.3: Gene and Protein Colinearity and Triplet Codons
- Serious efforts to understand how proteins are encoded began after Watson and Crick used the experimental evidence of Maurice Wilkins and Rosalind Franklin (among others) to determine the structure of DNA. Most hypotheses about the genetic code assumed that DNA (i.e., genes) and polypeptides were colinear.
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- 11.4: Translation
- Like any polymerization in a cell, translation occurs in three steps: initiation brings a ribosome, mRNA and an initiator tRNA together to form an initiation complex. Elongation is the successive addition of amino acids to a growing polypeptide. Termination is signaled by sequences (one of the stop codons) in the mRNA and protein termination factors that interrupt elongation and release a finished polypeptide. The events of translation occur at specific A, P and E sites on the ribosome.
Thumbanil: Diagram of RNA translation. (CC BY 3.0 - unported; Kelvinsong ).