1. How Genes Work

2. Structure of DNA DNA is composed of subunits – nucleotides Three parts Deoxyribose (5-carbon sugar) Phosphate group Nitrogen base – 2 major types Purines (adenine (A) and guanine (G)) Pyrimidines (cytosine (C) and thymine (T))

3. Structure of DNA DNA is a twisted ladder Sides of ladder Deoxyribose Phosphate Rungs (inside) of ladder Nitrogen base Bases in the middle of the DNA match up using Chargaff’s base pairing rules A=T C=G

4. DNA replication Replication – process of copying DNA Strands are complementary Process of replication – complex, requires several enzymes Preserves the sequence of bases Mutagens – causes mutations

5. Protein synthesis (building proteins) DNA  RNA  protein RNA is chemically similar to DNA Two exceptions Ribose (an additional oxygen atom) Thymine is replaced by uracil (U) Occurs in three forms Transcription uses messenger RNA (mRNA) mRNA copies the nucleotides tRNA rRNA

6. Protein synthesis (building proteins) Two stages Transcription – copying of genetic information RNA polymerase “unwinds” DNA Base pairing take place (A=U, C=G) There is NO thymine (T) in RNA Creates mRNA (messenger RNA) in the nucleus mRNA enters cytoplasm Finds ribosomes

7. Protein synthesis (building proteins) Two stages (con’t) Translation rRNA (ribosomal) translate mRNA codons into anticodons (more base-pairing) A=U C=G tRNA (transfer) brings amino acids to ribosomes

8. The Genetic Code Codon – three nucleotides in mRNA specify a particular amino acid Order of bases determines order of amino acids Order of amino acids determines structure and function of protein 64 possible codons, 20 amino acids, 3 “stop” codons