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Genetic Expression

Genetic Expression. Feb 16, 2001. What is a gene?. Structure: Short DNA sequence of nucleotides One chromosome carries hundreds of genes Function: Each gene codes for a different protein Order of nucleotides in the DNA of the gene determines the order of amino acids in a protein.

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Genetic Expression

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  1. Genetic Expression Feb 16, 2001

  2. What is a gene? • Structure: • Short DNA sequence of nucleotides • One chromosome carries hundreds of genes • Function: • Each gene codes for a different protein • Order of nucleotides in the DNA of the genedetermines the order of amino acids in a protein

  3. Genes are Expressed as Proteins • 2 main stages 1) Transcription • DNA information copied to RNA • Occurs in the nucleus 2) Translation • RNA information used to construct a protein • Occurs in the cytoplasm The flow of genetic information

  4. Protein Synthesis • Copy the recipe from the master document (DNA gene) in the nucleus. • Use the copy of the recipe (mRNA) to produce the protein on ribosomes in the cytoplasm.

  5. The Central Dogma of Biology

  6. Proteins, Essential to Life • proteios: “primary” • Important for the operation and regulation of all life processes! • “Proteins run everything!” • Structural • E.g., collagen & keratin • Transport • E.g., hemoglobin • Movement • E.g., muscle filaments • Communication messengers • E.g., insulin & growth hormone • Communication receivers • E.g., hormone and neural receptors • Selective cellular permeability • E.g., membrane gates & pumps • Defense • E.g., antibodies • Enzymes • E.g., RNA-polymerase • Regulate all biochemical reactions Hair made of keratin, a structural protein

  7. Proteins, Essential to Life Must synthesize the right protein at the right place and at the right time! • Monomer: • Amino Acid • 20 different amino acids used to make proteins • Polymer: • Polypeptide • The precise sequence of amino acids in the polypeptide determines the function of the protein Hair made of keratin, a structural protein

  8. II. Translation: the sequence of mRNA codons determines the sequence of amino acids in the polypeptide • Codons (“words”) are RNA nucleotide triplets • Each codon represents a specific amino acid Translation of RNA codons

  9. The Genetic Code • specific mRNA codons are associated with specific amino acids • 64 codons, but only 20 aa’s • Many codons are redundant • Some are start/stop signals

  10. The Interpreters: tRNAtransfer-RNAs Carry Amino Acids • tRNA molecules match amino acids to the appropriate codon • tRNA anticodon - a triplet sequence on tRNA that base pairs with a complementary mRNA codon Structure and symbol of transfer RNA

  11. Ribosomes: the site of translation Ribosomes are bound to ER and free in cytoplasm Ribosome: Made of rRNA and protein

  12. Translation • On the ribosome • tRNAs translate the sequence of 3-base nucleotide “words” (codons) into a sequence of amino acids in a polypeptide • NOTE: the mRNA is not “turned into” protein!

  13. Initiation of Translation • mRNA binds to ribosome at start codon [AUG] • First tRNA binds to mRNA (anticodon to codon) The initiation of translation

  14. Elongation 1) Next tRNA binds to A site 2) Adjacent amino acids linked 3) tRNA in P site leaves 4) Ribosome moves to next codon Process continues Polypeptide elongation

  15. Translation: Termination • When ribosome reaches stop codon, polypeptide is released from tRNA • Ribosome then released from mRNA

  16. Fig. 7.12

  17. Making lots of protein • Many copies of mRNA can be made from one gene • Many ribosomes can make protein from the same mRNA • Amplification of information allows rapid production of proteins

  18. Protein Shape Determines Function • Post-translation modification • Specific 3-D shape • Shape is critical to function • Denaturation = loss of shape  loss of function Ribbon model of lysozyme protein

  19. Levels of Proteins Structure • Primary • Polypeptide sequence • Secondary • Folding coils & pleats • Tertiary • Complete 3-D shape • Quarternary • Combining polypeptides

  20. Review

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