DNA Notes

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DNA Notes

• Section 12.3

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Transcription

• DNA is copied into a complementary strand of
  RNA
• Transferring info from DNA to mRNA

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• Occurs in the nucleus
• Why is this significant?
• DNA cannot leave the nucleus, so mRNA must carry
  the code to the ribosome

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RNA

• RNA Polymerase
• Enzyme that attaches to DNA ? separates DNA
• Synthesizes (builds) a mRNA strand
• Binds at the Promoter a site that RNA recognizes

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• A combination of 3 nucleotides of mRNA is called
  a codon
• Each codon specifies a particular amino acid to
  be placed in the polypeptide chain

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• AUG start codon ? codes for methionine
• Stop codon has no tRNA ? does not code for an
  amino acid, so the chain is finished

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• RNA

• DNA

• 1 strand (single)
• Ribose
• A, U, C, G
• U Uracil

• 2 strands (double)
• Deoxyribose
• A, T, C, G
• T - Thymine

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Transcribe

• DNA
• mRNA

• A T T C G A G
• U A A G C U C

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Translation

• Changing or decoding a mRNA molecule into
  producing a polypeptide
• Message is being translated from the language of
  nucleic acids to the language of amino acids
  (proteins)

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• To produce a protein, need
• mRNA messenger RNA
• tRNA transfer RNA
• ? carries amino acid to the ribosome
• rRNA ribosomal RNA
• ribosome site of protein synthesis

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Fig. 12.
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• tRNA will bind to mRNA
• ? the anticodon on tRNA will bind to the codon on
  mRNA

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• Use the chart (p. 338) to find what amino acids
  these codons code for
• ? Always use the mRNA codon with this chart!

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• Codon (mRNA)

• Amino Acid

Anticodon (tRNA)

• UAC
• GAU

• 1) UCG
• 2)
• 3) ACU
• 4)

________ ________ ________ ________
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• Codon (mRNA)

• Amino Acid

Anticodon (tRNA)

• AGC
• UAC
• UGA
• GAU

• 1) UCG
• 2) AUG
• 3) ACU
• 4) CUA

Serine Methionine Threonine Leucine
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The Process of Translation

• The ribosome always has 2 spots for tRNA
• tRNA leaves when it is empty
• Stop amino acid chain is finished

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• Peptide bond is the covalent bond that joins
  together two amino acids
• The polypeptide chain continues to grow until the
  ribosome reaches a stop codon on the mRNA

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• Conclusion A section of DNA a gene directs
  the synthesis of a protein

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Q Why are proteins so important? Do so many
different things!

1. Most enzymes are proteins
2. Control biochemical pathways in the cell
3. Direct the synthesis of lipids, carbohydrates,
   nucleotides
4. Responsible for cell structures
   movement