DNA, genes and chromosomes

• Genes are a base sequence of DNA that code for the amino acid sequence of a polypeptide and functional RNA, located at a locus on the DNA molecule
• Genes determine the proteins of an organism, with enzymes controlling chemical reactions and an organism’s development and activities
• The genetic code requires a minimum of three bases to code for each amino acid due to the limited number of amino acids (20) and bases (4)
• Features of the genetic code:

  • Some amino acids are coded only by a single triplet
  • Most amino acids are coded for by 2-6 triplets each
  • The code is degenerate, non-overlapping, read in one direction, and universal with few exceptions
• Exons are coding sequences within genes that code for amino acids, while introns are non-coding sequences separating exons
• Chromosomes consist of two chromatids joined at a centromere, with DNA held by histones and highly coiled and folded
• Homologous chromosomes are pairs derived from maternal and paternal chromosomes, carrying the same genes but not necessarily the same alleles
• Alleles are alternative forms of a gene, with each individual inheriting one allele from each parent
• Mutations are changes in the base sequence of a gene, producing a new allele and leading to a different sequence of amino acids being coded for
• Protein synthesis involves DNA being transcribed onto RNA in the cytoplasm, with tRNA structurally suited to line up amino acids on the mRNA template