dna – the molecule of heredity. what is dna? although the environment influences how an organism...
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DNA – The Molecule of Heredity
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What is DNA?
• Although the environment influences how an organism develops, the genetic information that is held in the molecules of DNA ultimately determines an organism’s traits.
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What is DNA?
• DNA achieves its control by determining the structure of proteins.
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What is DNA?
• All actions, such as eating, running, and even thinking, depend on proteins called enzymes.
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What is DNA?
• Enzymes are critical for an organism’s function because they control the chemical reactions needed for life.
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What is DNA?
• Within the structure of DNA is the information for life—the complete instructions for manufacturing all the proteins for an organism.
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DNA as Genetic Material
• In 1952 Alfred Hershey and Martha Chase performed an experiment using radioactively labeled viruses that infect bacteria.
• These viruses were made of only protein and DNA.
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DNA as Genetic Material
• Hershey and Chase labeled the virus DNA with a radioactive isotope and the virus protein with a different isotope.
• By following the infection of bacterial cells by the labeled viruses, they demonstrated that DNA, rather than protein, entered the cells and caused the bacteria to produce new viruses.
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The Structure of Nucleotides
• DNA is a polymer made of repeating subunits called nucleotides.
• Nucleotides have three parts: a simple sugar, a phosphate group, and a nitrogenous base.
Phosphate group
Sugar (deoxyribose)
Nitrogenous base
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The Structure of Nucleotides
• The simple sugar in DNA, called deoxyribose, gives DNA its name—deoxyribonucleic acid.
• The phosphate group is composed of one atom of phosphorus surrounded by four oxygen atoms.
Phosphate group
Sugar (deoxyribose)
Nitrogenous base
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The Structure of Nucleotides
• A nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen.
Adenine (A) Guanine (G) Thymine (T)Cytosine (C)
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The Structure of Nucleotides
• In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T).
Adenine (A) Guanine (G) Thymine (T)Cytosine (C)
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The Structure of Nucleotides
• Thus, in DNA there are four possible nucleotides, each containing one of these four bases.
• For this class… the NAMES are more important than the SHAPES.
Adenine (A) Guanine (G) Thymine (T)Cytosine (C)
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The Structure of Nucleotides
• Nucleotides join together to form long chains, with the phosphate group of one nucleotide bonding to the deoxyribose sugar of an adjacent nucleotide.
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The Structure of Nucleotides
• The phosphate groups and deoxyribose molecules form the backbone of the chain, and the nitrogenous bases stick out like the teeth of a zipper.
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The Structure of Nucleotides
• In DNA, the adenine is always paired with thymine, and guanine is always paired with cytosine.Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)
Straights & Curves
A-T & C-G
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The Structure of DNA
• In 1953, Watson and Crick proposed that DNA is made of two chains of nucleotides held together by nitrogenous bases.
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The Structure of DNA
• Watson and Crick also proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring.
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The Structure of DNA
• Because DNA is composed of two strands twisted together, its shape is called double helix.
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The Importance of Nucleotide Sequence • The sequence of nucleotides
forms the unique genetic information of an organism. The closer the relationship is between two organisms, the more similar their DNA sequences.
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The Importance of Nucleotide Sequence • Scientists use nucleotide
sequences to determine evolutionary relationships among organisms, to determine if two people are related, and to identify dead bodies.