3.1 DNA, Genes and Chromosomes

• Gene - a region of DNA that codes for a particular polypeptide.
• Locus - the position of a gene on a chromosome.
• Intron - non-coding region of DNA within genes.
• Exon - coding region of DNA.
• Homologous - same genes at the same loci but may have different alleles.
• Chromosome - structure in the nucleus of a eukaryotic cell, made of chromatin (DNA + histones).
• Allele - version of a gene.
• Histone - protein associated with DNA in chromatin.
• Genome - all the genetic information within an organism.
• Proteome - all the proteins that are within an organism.
• Triplet code - a code in which each triplet of bases codes for a single amino acid.
• Universal - the same triplet codes for the same amino acid in all organisms.
• Non-overlapping - read in triplets with each base being read once.
• Degenerate -more than one triplet code can code for a single amino acid.
• Stop codons - UAA, UAG or UGA.
• Eukaryotic DNA contains introns whereas prokaryotic DNA contains exons.
• Eukaryotic DNA is longer whereas prokaryotic DNA is shorter.
• Eukaryotic DNA is linear whereas prokaryotic DNA is circular.
• Eukaryotic DNA is held in a nucleus whereas prokaryotic DNA is free in the cytoplasm.
• Eukaryotic DNA is associated with histone proteins, whereas prokaryotic DNA is not associated with histone proteins.
• DNA contains an inorganic phosphate, a deoxyribose sugar and a nitrogenous base which can be: adenine, thymine, guanine, or cytosine.
• RNA contains an inorganic phosphate, ribose sugar, and a nitrogenous base which can be: adenine, uracil, guanine, or cytosine.
• There are 46 chromosomes per somatic cell (body cell) which are arranged into 23 pairs.
• Mitochondria and chloroplasts are two other organelles (other than the nucleus) that have DNA.
• Mitochondria DNA is circular, not associated with proteins, and free in the cytoplasm.
• The bond between adjacent nucleotides is a phosphodiester bond.
• Nucleotide sequence determines genetic information.
• Genetic code is universal across all species.
• DNA has a double helix structure.
• Each strand of DNA runs antiparallel to its partner strand.