Journal 5-3: Modeling DNA

Nucleotides Monomers of DNA Each Nucleotide has 3 parts Phosphate group Sugar (Deoxyribose) Nitrogenous Base

Nucleotides (cont) Every nucleotide has a phosphate and a sugar Nitrogenous Bases vary Purines Adenine Guanine Pyrimidines Cytosine Thymine

Nucleotides (cont) CUT the Py Purines - nucleotides with a 2-ring nitrogenous base Adenine and Guanine Pyrimidines - nucleotides with a 1-ring nitrogenous base Thymine and Cytosine CUT the Py

Nucleotide Bonding Dehydration synthesis reaction connects the phosphate group from one nucleotide to the sugar group from another nucleotide.

Base Pairing 2 bonds Nitrogenous bases connect together with hydrogen bonds 3 bonds

DNA Structure (Watson/Crick/Franklin)

DNA Replication Why does a cell replicate it’s DNA? To make an identical copy! When would a cell need to do that? When it is dividing, so… To make new cells

DNA Replication Step 1: Helicase binds to the DNA and unwinds the 2 strands (exposing nitrogenous bases) What kinds of bonds does helicase break? Helicase

DNA Replication Step 2: DNA Polymerase adds complementary nucleotides to the exposed bases on the original strand This forms a NEW strand attached to the OLD one What kinds of bonds are being formed? Helicase DNA Polymerase DNA Polymerase

DNA Replication Step 3: New DNA molecules wind back up to form a double helix Why do we say DNA replication is “Semi- conservative?” There are now two DNA molecules, each containing one OLD strand and one NEW strand Helicase DNA Polymerase DNA Polymerase

DNA Replication video