History of DNA

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History of DNA
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History of DNA

• Chromosomes are made of coiled DNA and protein
• Experiments on bacteriophage viruses by Hershey
  Chase proved that DNA was the cells genetic
  material

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DNA Structure

• Rosalind Franklin took diffraction x-ray
  photographs of DNA crystals
• In the 1950s, Watson Crick built the first
  model of DNA using Franklins x-rays- double helix

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DNA Structure
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DNA

• Two strands coiled called a double helix
• Sides made of a pentose sugar Deoxyribose bonded
  to phosphate groups
• Center made of nitrogen bases bonded together by
  weak hydrogen bonds

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DNA Double Helix

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DNA Nucleotide

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Pentose Sugar

• Sugars are numbered clockwise 1 to 5

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Chargaffs Rule

• Adenine must pair with Thymine
• Guanine must pair with Cytosine
• The bases form weak hydrogen bonds

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Nitrogenous Bases

• Double ring PURINES
• Adenine (A)
• Guanine (G)
• Single ring PYRIMIDINES
• Thymine (T)
• Cytosine (C)

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DNA

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Antiparallel Strands

• One strand of DNA goes from 5 to 3 (sugars)
• The other strand is opposite in direction going
  3 to 5 (sugars)

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Question

• What would be the complementary DNA strand for
  the following DNA sequence?
• DNA 5-CGTATG-3

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Answer

• DNA 5-GCGTATG-3
• DNA 3-CGCATAC-5

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DNA and Genes
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DNA

• DNA contains genes, sequences of nucleotide bases
• These Genes code for polypeptides (proteins)
• Proteins are used to build cells and do much of
  the work inside cells

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Polypeptides

• Amino acid chains are called polypeptides

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DNA Begins the Process

• DNA is found inside the nucleus
• Proteins, however, are made in the cytosol of
  cells by organelles called ribosomes
• Ribosomes may be free in the cytosol or attached
  to the surface of rough ER

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Starting with DNA

• DNA s code must be copied(transcription) and
  taken to the cytosol
• In the cytosol, this code must be
  read(translation) so amino acids can be assembled
  to make polypeptides(proteins)
• This process is called PROTEIN SYNTHESIS

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RNA
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RNA Differs from DNA

• RNA has a sugar ribose
• DNA has a sugar deoxyribose

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Other Differences

• RNA contains the base uracil (U)
• DNA has thymine (T)
• RNA molecule is single-stranded
• DNA is double-stranded

DNA
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Types of RNA
.

• Messenger RNA (mRNA) copies DNAs code carries
  the genetic information to the ribosomes
• Transfer RNA (tRNA) transfers amino acids to the
  ribosomes where proteins are synthesized
• Ribosomal RNA (rRNA)

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Messenger RNA

• Long Straight chain of Nucleotides
• Made in the Nucleus
• Copies DNA
• Contains the Nitrogen Bases A, G, C, U ( no T )
• Sequence of 3 bases called codon

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Transfer RNA (tRNA)

• Clover-leaf shape
• Single stranded molecule with attachment site at
  one end for an amino acid
• Opposite end has three nucleotide bases called
  the anticodon

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Codons and Anticodons

• The 3 bases of an anticodon are complementary to
  the 3 bases of a codon
• Example Codon ACU
• Anticodon UGA

UGA
ACU
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The Genetic Code

• A codon designates an amino acid
• An amino acid may have more than one codon
• There are 20 amino acids, but 64 possible codons

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The Genetic Code

• Use the code by reading from the center to the
  outside
• Example AUG codes for Methionine

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Transcription and Translation
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Transcription

• The process of copying the sequence of one strand
  of DNA, the template strand
• mRNA copies the template strand
• Requires the enzyme RNA Polymerase
• Occurs in the nucleus

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Template Strand
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Question

• What would be the complementary RNA strand for
  the following DNA sequence?
• DNA 5-GCGTATG-3

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Answer

• DNA 5-GCGTATG-3
• RNA 3-CGCAUAC-5

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Translation

• Translation is the process of of decoding the
  mRNA into a polypeptide chain
• Ribosomes read mRNA three bases or 1 codon at a
  time and construct the proteins
• Occurs in the cytoplasm

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Transcription
Translation