The DNA Code

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The DNA Code

• What is the message contained in DNA???
• Proteins hold the key
• Genes are responsible to protein production
• The messages in DNA is used to make proteins

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The DNA Code

• How do genes code for proteins???
• Sequence of nitrogen bases is important
• Genetic code
• Quick protein review
• What is the building block for proteins?
• Amino Acids
• How many different amino acids?
• 20

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The DNA Code

• Coding for Proteins
• Single nitrogen bases do not code
• Only 4 amino acid possibilities (A,G,C,T)
• Sequence of two bases (base pairs)
• 16 amino acid possibilities
• Still not enough possibilities

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The DNA Code

• Coding for Proteins
• Sequence of three nitrogen bases
• More than 20 different possibilities
• Codon
• Set of 3 bases that represents an amino acid

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The DNA Code

• Coding for Proteins
• The order of nitrogen bases can determine
• Type of amino acid
• Order of amino acids
• 64 different combinations of codons
• 61 code for amino acids
• 3 signal for the stopping of polypeptide chain
  synthesis

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The DNA Code

• Coding for Proteins
• More than one codon can code for the same amino
  acid
• Rememberonly 20 amino acids
• Key Point
• For any one codon, there can only be one amino
  acid

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The DNA Code
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The DNA Code

• Universal Genetic Code
• Genetic code was figured out by studying
  bacterium
• Escherichia coli (E coli)
• Genetic code is the same in all organisms
• Bacteria, viruses, humans, etc.

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Transcription

• Quick Review
• Proteins are made by ribosomes
• Cytoplasm of cell
• DNA is found in the nucleus
• Genetic information needs to make its way from
  the nucleus to the ribosomes

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Transcription

• RNA (Ribonucleic Acid)
• Different structure than DNA in 3 ways
• Single strand of nucleotides
• DNA is a double strand
• Contains ribose (simple sugar)
• DNA deoxyribose
• Four nitrogen bases (A,G,C,U)
• No thymine uracil (U)

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Transcription

• RNA (Ribonucleic Acid)

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Transcription

• RNA (Ribonucleic Acid)
• Base Pairing Rules
• Adenine with Uracil (used to be Thymine)
• Cytosine with Guanine
• IMPORTANT! (for transcription)
• Base pair for T is A
• Base pair for A is U

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DNA Replication
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Transcription

• RNA is the transport to get DNA from the nucleus
  to ribosomes
• Transcription
• A process by which enzymes (proteins) make an RNA
  copy of a DNA strand

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DNA Replication
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Transcription

• Transcription Vocabulary
• mRNA
• RNA copy that carries information from DNA out of
  the nucleus into cytoplasm
• rRNA
• Portions of the DNA for RNA is for ribosomes

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Transcription

• Transcription
• Enzymes unzip DNA molecule
• Like DNA replication
• As DNA unwinds, free RNA nucleotides pair with
  complimentary nucleotides on one of the DNA
  strands
• Follow base pairing rules (codons)
• AGC TAA CCG ------- UCG AUU GGC

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Transcription

• Transcription
• When base pairing is completed, mRNA molecule
  breaks away as DNA strands rejoin into double
  helix
• mRNA leaves nucleus and heads towards cytoplasm
  (ribosomes)
• Proteins are synthesized at ribosomes

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DNA Replication
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Translation

• When mRNA is synthesized, it carries a
  complimentary code of the DNA code to make
  proteins
• Need to convert information contained in nitrogen
  bases into amino acids

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Translation

• Translation
• The process of converting the information in a
  sequence of nitrogen bases in mRNA into a
  sequence of amino acids
• Occurs on ribosomes
• Involves a 3rd type of RNA
• Transfer RNA (tRNA)

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Translation

• Transfer RNA (tRNA)
• Function is to bring amino acids to ribosomes to
  be assembled into proteins
• Made up of about 75 nucleotides
• Each tRNA molecule ONLY recognizes ONE amino acid

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Translation

• Transfer RNA (tRNA)
• Top of tRNA molecule
• One amino acid
• Bottom of tRNA molecule
• Three nitrogen basescalled anticodons
• Anti-codons because they pair with codons on
  mRNA molecules

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Translation

• Translation
• The first codon of the mRNA attaches to a
  ribosome
• tRNA molecule (carrying the appropriate amino
  acid) approach ribosome
• tRNA anticodon pairs with mRNA codon attach
  together

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Translation

• Translation
• First codon on mRNA is usually AUG
• Codes for amino acidmethionine
• Signals for the start of protein synthesis
• mRNA continues to slide through ribosome
• More tRNA (with new amino acids) pair with codons
  on mRNA

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Translation

• Translation
• After first two amino acids are in place, enzyme
  creates a peptide bond between them
• Process continues, forming a long chain of amino
  acids, until the ribosome reaches the STOP codon
  on the mRNA strand

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DNA Replication
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DNA Replication
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Protein Synthesis

• Oh how can it be???
• Correct translation depends upon the codons on
  mRNA pairing correctly with anticodons on tRNA
• Large, complex, and various proteins are formed

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Protein Synthesis

• Proteins are very important
• How many proteins can be produced?
• Infinite
• Remember
• Only 20 amino acids
• Can form in any combinationcreates extreme
  variety
• Sequence of amino acids determines characteristics

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DNA Replication
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DNA Replication
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