Structure & Replication Basics of DNA Structure & Replication

DNA (Deoxyribonucleic Acid) Polymer made of smaller monomers nucleotides Described as having a double helix Twisted ladder Outside = sugar phosphate backbone Inside = base pairs

Nucleotides Repeating monomer Made of 3 smaller molecules Sugar Deoxyribose Phosphate Base (4 Types) Adenine Thymine Cytosine Guanine

Base Pair Rule Adenine with Thymine Guanine with Cytosine Joined together by hydrogen bonds Pairs are in equal amounts Form the steps in the DNA ladder

DNA Replication 3 Main Stages Each strand acts as a template for the synthesis of a new strand Reaction carried out by enzymes 3 Main Stages Initiation – replication begins at an origin point Elongation – new strands of DNA are synthesized Follows the base pair rule Termination – new strand of DNA is complete

Initiation: The strands separate PO4 PO4

Elongation: Each strand builds up its partner by adding the appropriate nucleotides PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 The nucleotides are present in the nucleoplasm. The nuclear equivalent of cytoplasm PO4 PO4 PO4 PO4 PO4 Termination: 2 new and identical strands are complete.

Semi-Conservative Model

Chromosomes Found in nucleus Chromosomes are tightly wound forms of DNA

Chromosomes & Genes Different chromosomes have different genes Gene is a sequence of bases in a DNA molecule

Homologous Chromosomes Chromosomes arranged in pairs = homologous chromosomes One from mom and one from dad Have the same genes in the same order Slightly different DNA sequences

Humans have 23 pairs (46 Total) Homologous Pairs Humans have 23 pairs (46 Total) Autosomes Sex Chromosomes