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How Genes Work

How Genes Work. 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)). Structure of DNA. DNA is a twisted ladder

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How Genes Work

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  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

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