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Inherited characteristics are transmitted from parent genes to offspring
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Genes are parts of the chromosomes
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Genes provide the genetic instructions for every organism
– contained in its DNA
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DNA molecules direct the life & function of each cell
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DNA is passed on from parents to the next generation
DNA structure – was determined by Watson and Crick
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Double helix
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Composed of monomers called nucleotides
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Each nucleotide has 3 parts
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Phosphoric acid (phosphate)
–
deoxyribose sugar
–
Nitrogen base- 4 possible: Adenine, Thymine, Guanine, Cytosine
DNA Structure - Double Helix
• DNA structure- arranged in a “ladder” configuration
– DNA molecule consists of 2 lchains of nucleotides
– Held together by hydrogen bonds
– Alternating phosphate and sugar groups form sides of ladder
– Rungs are composed of paired nitrogen bases
– Complementary base pairing (purine with pyrimidine)
• Adenine - Thymine (A-T)
• Guanine - Cytosine (G-C)
• The “ladder” then coils to form a helix
DNA Replication
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Variations in organis m’ characteristics is determined by the sequencing of the four simple parts of the molecule
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The 4 bases are arranged in in any order
– This occurs during S phase of the cell cycle (mitosis)
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When cells divide, DNA is copied with accuracy
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A chromosomes consists of DNA and protein
– Each double helix is the DNA components of a single chromosome
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Base pairing is the foundation of DNA replication
DNA Enzyme
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DNA Ligase
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Bonds the DNA together; completes it.
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Repairs any breaks in the sugar-phosphate backbone

Semi-conservative replication
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When the DNA divides, one parent DNA strand and its complementary daughter
DNA strand entwine into a helix formation
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Each daughter DNA molecule consists of one new chain of nucleotides that has paired up with the parent DNA molecule
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The 2 daughter DNA molecules will be identical to the parent molecule
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Semiconservative = means that the two new DNA molecules will each contain half
“old” and half “new” DNA strands.