08 transcription, translation and mutation


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08 transcription, translation and mutation

  1. 1. Transcription, Translation and Mutation • From DNA to Protein (11.2) • Genetic Changes (11.3)
  2. 2. Answer these questions:  What is coded for in DNA? How is it coded?    What is the primary structure of a protein?   Proteins The sequence of A, T, G, C Sequence of amino acids What are proteins used for?   Structure Controlling the biochemistry of an organism  Enzymes, antibodies
  3. 3. From DNA to Protein  DNA cannot leave the nucleus  Protein is made at the ribosomes in the cytoplasm and attached to the rough endoplasmic reticulum  Therefore, a message must be sent from the DNA to the ribosome
  4. 4. From DNA to Protein  The messenger is RNA (mRNA)  DNA  Protein: occurs in 2 steps  Transcription   Making the coded message (mRNA) Translation  Reading the coded message
  5. 5. How is RNA different from DNA? RNA DNA  Single-stranded  Double-stranded  Sugar = ribose  Sugar = deoxyribose  A, U, G, C  A, T, G C
  6. 6. 3 types of Ribonucleic Acid (RNA)  mRNA    rRNA    Messenger RNA Brings instructions from DNA in the nucleus to the cytoplasm (where ribosomes are found) Ribosomal RNA Part of the ribosome that binds to the mRNA and uses the instructions to assemble the amino acids in the correct order tRNA   Transfer RNA Delivers the amino acids to the ribosome to be assembled into a protein
  7. 7. Transcription: DNA to mRNA DNA is unzipped mRNA is formed, complementary to one of the strands of DNA 1. 2.  RNA polymerase (enzyme) joins the nucleotides of RNA together
  8. 8. Transcription The mRNA is processed 3. Not all nucleotides in DNA code for making protein    Introns – noncoding sequences Exons– coding sequences Introns are removed and exonsare spliced together For protection from enzymes in the cytoplasm, the ends of the RNA strand are ‘covered’     5’ GTP cap 3’ poly-A tail
  9. 9. Translation: mRNA to Protein  ~20 amino acids and 4 nitrogenous bases (A, U, G, C)   How can 4 bases form a code for all possible proteins? A group of 3 bases code for 1 amino acid    Each group is called a codon 64 combinations are possible when a sequence of 3 bases is used, therefore there are 64 different mRNA codons Not all codons code for proteins.    UAA = stop AUG = start More than one codon can code for the same amino acid, but for any one codon, there can only be one amino acid
  10. 10. Translation: mRNA to Protein
  11. 11. Mutations Answer this question:  How does DNA encode the characteristics of an organism?   Each codon in DNA codes for an amino acid (or start/stop) used to build protein which shapes an organism's characteristics DNA  mRNA  Protein  Characteristics  A mutation is any change in the genetic code (nucleotide sequence)  Mutations are random
  12. 12. The Causes of Mutations  DNA fails to copy accurately  External influences can create mutations   Chemicals or radiation break down DNA When the cell repairs the DNA, it might not do a perfect job of the repair
  13. 13. Types of Mutations  Substitution   One base is exchanged for another This will change the codon which could…     Code for a different amino acid and change the protein Code for the same amino acid and do nothing (silent mutation) Change the code to ‘stop’ and make an incomplete protein that will probably not function Insertion  Extra base pairs are inserted into a new place in the DNA
  14. 14. Types of Mutations  Deletion   A section of DNA is lost, or deleted Frameshift  Since protein-coding DNA is divided into codons three bases long, insertions and deletions can ‘shift’ the code
  15. 15. The Effects of Mutations   All cells contain DNA = lots of places for a mutation to occur Somatic mutations occur in non-reproductive cells and won't be passed onto offspring
  16. 16. The Effects of Mutations  Germ line mutations occur in reproductive cells like sperm and eggs and can be passed to offspring and has large scale effects on evolution  The mutation could do nothing The mutation could do something small…  The mutation could have large consequences…   http://evolution.berkeley.edu/evolibrary/article/0_0_0/mutations_ 06