Chapter 11 DNA and Genes

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Chapter 11DNA and Genes

• Section 1
• DNA the Molecule of Heredity

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What Is DNA?

• DNA is a molecule that determines an organisms
  traits by determining the structure of proteins.
• DNA is contained in the cells chromosomes.

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Why Are Proteins Important?

• Proteins are responsible for structure in
  organisms (skin, hair, bone, muscles.
• Proteins called enzymes are responsible for all
  life functions because they control the rate of
  chemical reactions.

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The Structure of Nucleotides

• DNA is a large molecule made up of subunits
  called nucleotides.

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The Structure of Nucleotides

• Nucleotides are made of a phosphate group, a
  deoxyribose sugar and a nitrogenous base.

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Nitrogenous Bases

• The four nitrogenous bases of DNA are
• Adenine
• Guanine
• Thymine
• Cytosine

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Structure of DNA

• Nucleotides join together to form long chains.
• Phosphate and deoxyribose form the back bone of
  the chain and the nitrogen bases stick out like
  teeth in a zipper.
• DNA is formed by two chains of nucleotides.

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Watson and Crick

• In 1953, James Watson and Francis Crick were the
  first to show the structure of DNA.

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Structure of DNA

• Watson and Crick said that DNA is shaped like a
  double helix.
• The double helix is two twisted chains of
  nucleotides.

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Rosalind Franklin

• Watson and Crick base their findings on the
  research done by Rosalind Franklin.

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• Franklins work with x-ray crystallography showed
  the DNA had a double helix shape, that phosphate
  and sugar groups made the outside of the helix
  and nitrogen bases made up the center of the atom

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Base Pairing

• Nitrogen bases are joined together in the double
  helix by weak hydrogen bonds.
• Adenine can only pair with Thymine.
• Cytosine can only pair with Guanine.

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Complementary Base Pairs

• A-T
• C-G

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Nucleotide Sequences

• Nucleotide sequences code for specific genetic
  information.
• The sequence A-T-T-C carries different
  information than the sequence T-A-C-T, even
  though the same nucleotides are present.

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Nucleotide Sequences

• Organisms with similar DNA sequences are closely
  related.
• Scientists use nucleotide sequences to determine
  evolutionary relationships between organisms

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• Apes and chimpanzees have similar DNA nucleotide
  sequences.

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DNA Replication

• When cells divide, the DNA in the chromosomes is
  copied so that each new cell can have chromosomes
  identical to the original cell. Chromosomes are
  copied by DNA replication

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DNA Replication

• DNA molecule unzips at base pairs.
• Free nitrogen bases attach to their base pair on
  the opened molecule.
• This continues until the entire molecule has been
  unzipped and copied.

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DNA Replication