What the genetic code codes for genes specify the

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- What the genetic code codes for - genes specify the primary structure of proteins: structural, motor, enzyme, etc. - that is, the order of amino acids in each protein - and control when, where, and how much of each protein is made - also some other things, as we will see later - The genetic code is carried on deoxyribonucleic acid , or DNA - Not a protein itself - Amazing facts for your next party, not on any test: - a typical complement of human DNA in a single diploid somatic (body) cell is 46 strands of a long, narrow molecule just 20 angstroms (20 x 10 -10 meters) wide - 38,000 strands of DNA next to each other would be about as wide as one human hair - yet each strand is up to 12 cm (4 ¾ inches) long, with all 46 strands totaling about 2 meters (6 ½ feet) long! - if the DNA in one cell in your body was as large around as a human hair (75 microns, 75 x 10 -6 m), the 46 pieces would total about 750 kilometers long (450 miles)! - at this scale, single genes would range from 2 cm (less than 1 inch) long to about 75 meters (244 feet, or 81 yards) long - (500 codons x 3 bases/codon x 3.4 angstroms/base, to 2 million codons) - DNA has an unusual structure that allows the molecule to encode a huge amount of information - just what is needed for a “genetic code” - double helix structure, like a ladder twisted lengthwise (but not exactly) - two long “backbone” strands of phosphate and sugar molecules - the upright sides of the ladder - connected by the “rungs” of the ladder, made from matched pairs of nucleotide bases - there are four types of nucleotide bases: - adenine , thymine , guanine , and cytosine - the bases can be in any order along the backbone - but the bases join to the other side only in matched pairs; adenine only to thymine, guanine only to cytosine - adenine and thymine (A and T) - guanine and cytosine (G and C) - [note: thymine is a base in the structure of DNA; it is not the same as thiamine (or thiamin), which is vitamin B 1 ] - so each side of the DNA molecule is like an extremely long sequence of seemingly random selections of the four letters (the four bases) - while the other side is its complementary, inverse image
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Intro to Biological Anthro F 2011 / Owen: Molecular genetics p. 3 - DNA works as a genetic code because the sequence of the nucleotide bases determines the sequence of amino acids in a protein (the protein’s primary structure) - there are 20 amino acids, but only 4 bases - so the “code” for each amino acid is a combination of 3 nucleotide bases - these combinations of three bases are like 3-letter words - for example, the combination Guanine, Cytosine, Thymine (GCT) codes for the amino acid alanine - each of these triplets is called a codon - since each codon consists of 3 bases, and there are four possibilities for each base, there are 4 x 4 x 4 = 64 possible codons - 61 of these combinations signify amino acids - some amino acids are specified by more than one different codon - for example, GCT, GCC, GCA, and GCG all code for alanine - the remaining 3 codons indicate the beginning or end of a protein - So these are the two main players: -
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