From Gene to Protein

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From Gene to Protein

• Chapter 17

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One Gene One Enzyme
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Genes

• The DNA provides the instructions to make the
  protein
• RNA is the link between gene and protein
• DNA codes for RNA and RNA codes for the protein

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Transcription/Translation

• The DNA and RNA molecules that are composed of
  nucleotide monomers
• When converting from DNA to RNA you are simply
  transcribing the code from the language of DNA
  nucleotides to RNA nucleotides
• Proteins are written in the language of amino
  acids
• When converting from RNA to protein we are
  translating from the nucleotide language to amino
  acid language

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RNA

• In what ways are RNA molecules different from
  DNA?
• RNA is single stranded
• In RNA, Uracil replaces Thymine
• Nucleotides have ribose instead of deoxyribose
• In eukaryotes, RNA leaves the nucleus

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What are the functions of the 4 different types
of RNA?
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The Genetic Code

• RNA consists of four letters A, U, G, and C
• Proteins consist of 20 letters the amino acids
• If 1 RNA base codes for 1 amino acid, then only 4
  amino acids can be coded for

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• How many different amino acids can be coded for
  if 2 RNAs code for 1 amino acid?
• 42 16 Not enough!
• How many different amino acids can be coded for
  if 3 RNAs code for 1 amino acid?
• 43 64 More than enough for the 20 different
  amino acids.

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There is redundancy in the code but not ambiguity!
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The Code is Universal

• The code is shared by almost all organisms
• CCG codes for what amino acid?
• Proline. This holds true for all species of
  living organisms
• Bacteria, therefore can be programmed to
  synthesize human proteins by inserting human DNA

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In prokaryotes, RNA is directly translated into
the polypeptide
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RNA in eukaryotes is processed before translation
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• The function of the cap is
• prevent mRNA degradation by hydrolytic enzymes
• helps attach to the ribosome
• Function of the 3 tail
• same functions as the 5cap
• also helps facilitate export of mRNA from nucleus

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RNA splicing

• Removes noncoding regions called introns
• snRNP (short nuclear ribonucleoproteins)
  recognize the splicing signals that are at the
  ends of introns
• The RNA in the snRNP is called snRNA (small
  nuclear RNA)
• spliceosome is the larger protein assembly that
  surrounds the snRNP
• The spliceosome cuts and releases the introns,
  and then joins exons together

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Evolutionary role of introns

• Introns may play regulatory role
• Different intron removal may lead to different
  proteins
• Introns may enhance crossing over between
  homologous regions by increasing the distance
  between exons

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Peptide Bonds Join Amino Acids
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Messenger RNA consists of leader, reading frame,
and trailer sequences.
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Ribosomes, consist of two subunits, each of which
contains rRNA and ribosomal proteins.
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tRNAs bring amino acids to the ribosomes during
translation to be assembled into polypeptide
chains.
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tRNA Assembly
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Initiation of Translation
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Elongation
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Termination
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review
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Polyribosomes
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Mutations