12-3 Protein Synthesis

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12-3 Protein Synthesis
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DNA vs. RNA

• Double stranded
• Sugar deoxyribose
• Thymine (no Uracil)
• Stays in nucleus
• One type
• Same copy in the cell all the time

• Single stranded
• Sugar ribose
• Uracil (instead of Thymine)
• Nucleus cytoplasm
• 3 types (mRNA, tRNA, rRNA)
• Disposable copies

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Ribose vs. Deoxyribose
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RNA

• many functions but mostly just protein synthesis
• three main types of RNA messenger RNA, ribosomal
  RNA, and transfer RNA

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Types of RNA
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mRNA

• RNA molecules that carry copies of the DNA
  instructions mRNA
• messenger RNA (mRNA) serve as messengers from
  DNA to the rest of the cell

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rRNA

• Ribosomes are made up of several dozen proteins,
  as well as a form of RNA known as ribosomal RNA
  (rRNA).

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tRNA

• During the construction of a protein, a third
  type of RNA molecule transfers each amino acid to
  the ribosome
• as specified by coded
• messages in mRNA.
• These RNA molecules
• are known as
• transfer RNA (tRNA).

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Transcription Translation
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Transcription (DNA ? mRNA)

• RNA molecules are produced by copying part of the
  nucleotide sequence of DNA into a complementary
  sequence in RNA
• required enzyme RNA polymerase
• RNA polymerase binds to DNA (in nucleus)
• separates the DNA strands
• RNA polymerase then uses one strand of DNA as a
  template
• nucleotides are assembled into a strand of mRNA
• Transcription Animation

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Where does RNA start?

• enzyme will bind only to regions of DNA known as
  promoters
• promoters are signals in DNA that indicate to the
  enzyme where to bind to make RNA (start
  sequence).
• Similar signals in DNA cause transcription to
  stop when the new RNA molecule is completed.

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RNA Editing

• Intron intervening sequence of DNA does not
  code for a protein
• Exon expressed sequence of DNA codes for a
  protein
• When RNA molecules are formed, both the introns
  and the exons are copied from the DNA
• introns are cut out of RNA molecules while they
  are still in the nucleus
• exons are then spliced back together to form the
  final mRNA

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The Genetic Code

• Proteins long chains of amino acids
  
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  (polypeptides)
• polypeptide combination of any or all of the 20
  different amino acids
• properties of proteins are determined by the
  order in which different amino acids are joined
  together to produce polypeptides

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• The language of mRNA instructions is called the
  genetic code
• RNA contains four different bases A, U, C, and G
  
• Letters read 3 at a time codon
• Codon  a group of three nucleotides on messenger
  RNA that specify a particular amino acid.

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Translation (mRNA? tRNA? amino acid chain)

• Occurs at the Ribosome
• mRNA instructions for the order of the amino
  acid sequence
• Ribosome reads the instructions of the mRNA

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Steps of Translation

• mRNA is released from the nucleus ? enters
  cytoplasm
• mRNA attaches to the ribosome
• mRNA codons move through the ribosome? proper
  amino acid brought by tRNA
• Amino acids are bound together ? polypeptide chain

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• Each tRNA carries only one type of amino acid
• The three bases on tRNA anticodon
  (complementary to mRNA)

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• The ribosome forms peptide bonds between the
  neighboring amino acids
• It also breaks the bonds between tRNA and the
  amino acids
• Translation ends when a stop codon is reached

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• Translation Animation

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What amino acids are made?

• Use the mRNA strand on the Genetic Code Chart
• DNA TAC AAA CAC GGA CCA ACT
• (antisense strand)
• mRNA AUG UUU GUG CCU GGU UGA
• tRNA UAC AAA CAC GGA CCA ACU
• Amino acids Methionine Phenylalanine
  
• Valine - Proline - Glycine - STOP

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