BIO Chapter 17

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BIO Chapter 17
2010-12-12 16:28:22
BIO Chapter genes proteins

Chapter 17: From Genes to Proteins
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  1. One gene - one polypeptide (protein) hypothesis
    • each gene dictates production of a specific polypeptide
    • ex: gene A codes for polypeptide A and variations because of different alleles
  2. Goal of transcription and translation
    transfer from nucleic acid language (DNA) to protein language
  3. Transcription
    • synthesis of RNA under direction of DNA
    • produces messenger RNA (mRNA)
    • takes place in the nucleus
  4. Translation
    • synthesis of a polypeptide (protein)
    • occurs on ribosomes
  5. The central dogma
    Cells are governed by a cellular chain of command: DNA --> RNA --> protein
  6. The genetic code
    • 4 nucleotide bases in DNA
    • 20 amino acids
    • Codons are 3 bases, read in 5' to 3' direction (each codon specifies amino acid)
  7. 2 rules of genetic code
    • No ambiguity within the genetic code - means each codon only appears once (and codes for a specific amino acid)
    • There is redundancy in the genetic code. For most proteins, there are multiple codons.
  8. RNA polymerase
    pries DNA strands apart and hooks together RNA nucleotides
  9. 3 stages of transcription
    • Initiation
    • Elongation
    • Termination
  10. Transcription: Initiation
    • brings everything together and is now ready to start transcription
    • needs to have promoter region including TATA to start
  11. Transcription: Elongation
    • RNA polymerase moves along the DNA and untwists the double helix
    • happens very quickly
    • through elongations, we get growing mRNA strand
  12. Transcription: Termination
    • In bacteria, polymerase stops transcription at the end of the terminator
    • In eukaryotes, polymerase continues transcription after the pre-mRNA is cleaved from the growing RNA chain; the polymerase eventually falls off the DNA
  13. Each end of a pre-mRNA molecule is modified
    • The 5' end receives a modified nucleotide 5' cap
    • The 3' end gets a poly-A tail
    • Cap and tail helps make it easier to get out of nucleus, helps attaching, and protects mRNA
  14. Introns
    • intervening sequences; noncoding regions
    • don't need introns in translation
  15. Exons
    • other regions; eventually expessed
    • usually translated into amino acid sequences
  16. RNA splicing
    removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence
  17. Transfer RNA (tRNA)
    • helps translate an mRNA message into protein
    • one end of tRNA has anticodon, and the other end has an amino acid. Anticodon matches up with the mRNA codon
    • *serves as adaptor molecule in protein synthesis; translates mRNA codons into amino acids
  18. Translation: Ribosomes
    Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis
  19. Ribosomal RNA (rRNA)
    • along with proteins, make up the two ribosomal subunits
    • plays catalytic (ribozyme) roles and structural roles in ribosomes
  20. 3 stages of translation
    • Initiation
    • Elongation
    • Termination
  21. Translation: Initiation
    Brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits
  22. Translation: Elongation
    • 3 steps:
    • Codon recognition
    • Peptide bond formation
    • Translocation
  23. Codon recognition
    occurs when anticodons on tRNA recognize codons on mRNA
  24. Peptide bond formation
    when we transfer amino acids from tRNA onto the elongated chain of amino acids
  25. Translocation
    everything moves down a spot
  26. Translation: Termination
    • Occurs when stop codon in mRNA reaches 'A site' of ribosome
    • our bodies need to regulate so we don't have too much or too few proteins
  27. Post-translation polypeptide modification
    • Polypeptide chains are modified after translation
    • Completed proteins are targeted to specific sites in the cell
  28. Mutations
    • changes in genetic material of a cell or virus
    • not always bad - forms natural selection
  29. Point mutations
    changes in just one base pair of a gene
  30. Types of point mutations
    • Base-pair substitutions
    • Base-pair insertions or deletions
  31. Frame
    What we read
  32. Frameshift
    when each codon is changed and frame is shifted; causes nonsense and missense from insertions or deletions
  33. Silent mutation
    aka neutral mutation because it doesn't affect the actual outcome of protein structure or function
  34. Missense
    new codon codes for an amino acid, just not the right amino acid (doesn't make sense)
  35. Nonsense
    base pair codes for a stop codon; don't get an amino acid
  36. 3 base-pair deletion
    no frameshift occurs, but one amino acid is missing
  37. Mutagen
    • physical or chemical agent that can cause mutations
    • different than carcinogen because not all mutagens have to do with cancer.
  38. Messenger RNA (mRNA)
    Carries info specifying amino acid sequences of proteins from DNA to ribosomes
  39. Primary transcript
    Is a precursor to mRNA, rRNA, or tRNA, before being processed. Some intron RNA acts as a ribozyme, catalyzing its own splicing
  40. Small nuclear RNA (snRNA)
    Plays structural and catalytic roles in spliceosomes, the complexes of protein and RNA that splice pre-mRNA