Gene Expression

Gene Expression

1. Proteins

   • Fibrous
     • Structure
   • Globular
     • E.g. Enzymes or hormones
   • Coded by genes
     • Gene is a section of DNA

2. Transcription

   • FIrst stage of protein synthesis
   • Occurs in the nucleus
   • DNA unwinds + unzips
     • Coding strand
       • identical to mRNA strand, except T instead of U
     • Template strand
       • 3 bases called triplet
       • code for mRNA strand
         • 3 bases called codon
         • processed
           • introns are removed
           • exons are joined to together
           • mRNA leaves the nuclues
             • translation begins
         • using complementary base pairing rule
           • instead U replaces T
   • PURPOSE: mRNA transcribes the code for a polypeptide chain from the DNA. so the original DNA does not get damaged

3. Translation

   • mRNA enters cytoplasm and moves to the ribosome
     • the ribosome moves along the mRNA reading the code
       • the tRNA pairs with the mRNA
         • using complementary base pairing rule
         • the mRNA acts as a code for the tRNA
         • the tRNA as an amino acid joined
           • the coded for amino acids join together by peptide bonds
             • forming a polypeptide chain
               • A stop codon is read
                 • the polypeptide chain is released into the cytoplasm
                   • folds up in a particular way to produce a fuctional protein
                     • the protein is used fro cellular functions
         • 3 bases on tRNA is called anti-codon
   • PURPOSE: to use the mRNA to make a polypeptide chain/protein. so the protein can be used for cellular functions

4. Mutations

   • A change in the DNA base sequence
   • can be harmful or helpful
   • Somatic mutation
     • mutation in body cells, cannot be inherited
   • Gametic Mutation
     • mutation in gametes, can be inherited by offspring
   • Mutagen
     • causes mutations
       • e.g. UV light, chemicals
   • Deletion
     • A base is deleted
       • Frameshift
         • Making the reading of the triplets change along one.
         • the following triplets affected, resulting in different amino acids
         • different coded for protein or unfunctional protein
   • Insertion
     • A base is inserted
   • Substitution
     • one base swapped for another
     • Missense
       • changes the amino acid
     • Nonsense
       • changes the amino acid to a stop
     • silent
       • does not change the amino acid
         • no affect on protein
         • due to redundancy due to degeneracy
           • more than one codon codes for the same amino acid
             • e.g. UUU and UUC, both code for Phe

5. Metabolic Pathway

   • Linked biochemical reactions controlled by enzymes that maintain life processes in organisms
   • the reactants of one reaction are the products for the previous reaction
   • mutation occur may result in a enzyme not being produced or too much
     • causing a build up of one product
       • phenotype may be affected

6. Environmental Influences

   • genotype + environment ------> phenotype
   • temperature
   • light
   • moisture
   • minerals
   • nutrients