Genes and Genetic Code

DNA is condensed into chromosomes

• DNA molecules are long and need to be tightly packed to fit in the nucleus of prokaryotic cells

• DNA is wound around histone proteins forming a DNA-histone complecx

• These complexes form chromatin, which helps pack of DNA into chromosomes. Each chromosome contains just a single molecule of DNA

DNA in Eukaryotes and Prokaryotes

• Prokaryotes

  • DNA stored in the cytoplasm

  • Shorter, circular DNA molecules

  • No histones

  • No introns

• Eukaryotes

  • Store DNA in the nucleus

  • Contain long, linear DNA molecules

  • Contains Histones

  • DNA contains histones

DNA contains genes

• Gene - short section of DNA that codes for a protein

  

• In eukaryotes, genes consist of regions known as introns and exons

  • Exons - Sections of DNA that code for amino acids

  • Introns - Sections of DNA that don’t code for amino acids

• Genome - Complete set of genes within a cell

• Proteome - Full range of proteins that a cell is capable of producing

Genetic code

• Genetic code - Sequence of bases that code for an amino acid

• Each amino acid is coded for by 3 DNA bases (triplets)

• The genetic code is:

  • Universal - Each DNA triplets codes for the same amino acids in all organism

  • Non-overlapping - Each base in the DNA sequnece is only read once (CGTATC is read as CGT ATC)

  • Degenerate - Most amino acids are coded for by more than one triplet (e.g. ACA and ACG both code for cysteine)