The nucleotide sequence of a gene's DNA specifies the amino acid sequence of a protein through the genetic code. Sets of three nucleotides, known as codons, each correspond to a specific amino acid.:6 Additionally, a "start codon", and three "stop codons" indicate the beginning and end of the protein coding region. There are 64 possible codons (four possible nucleotides at each of three positions, hence 43 possible codons) and only 20 standard amino acids; hence the code is redundant and multiple codons can specify the same amino acid. The correspondence between codons and amino acids is nearly universal among all known living organisms. COUNT 5
QSN1 What specifies the amino acid sequence of a protein? ANS1 The nucleotide sequence of a gene's DNA QSN2 What are sets of three nucleotides known as? ANS2 codons QSN3 What does each codon correspond to? ANS3 a specific amino acid QSN4 What indicates the beginning and end of the protein coding region? ANS4 a "start codon", and three "stop codons" QSN5 How many possible codons are there? ANS5 There are 64 possible codons (four possible nucleotides at each of three positions, hence 43 possible codons)