DNA Structure

·The basic subunit of DNA is a nucleotide ·Each nucleotide consists of three parts: ·Deoxyribose sugar ·Phosphate group ·Nitrogen base

pyridimine purine ·There are four different types of nitrogen bases ·Adenine ·Guanine ·Thymine ·Cytosine pyridimine purine

·DNA consists of two strands that together look like a ladder This shape is called a Double Helix ·The “backbone” of the helix is formed when the phosphate groups and deoxyribose sugars bond together covalently ·Result is an alternation of sugar and phosphate

·The nitrogen bases bond together in a pattern called complimentary base pairing to form the “rungs” of the DNA ladder -Adenine always binds with Thyamine -Cytosine always binds with Guanine ·The bases bond together using hydrogen bonds

The two strands of DNA run “anti-parallel” to each other, This means that the sugar and phosphates run in opposite directions (one looks upside down) Each side has a 3’ end and a 5’ end

If a strand runs from 3’ to 5’ this means that the backbone runs from sugar to phosphate If a strand runs from 5’ to 3’ the backbone runs from phosphate to sugar

The two antiparallel strands of DNA coil into a double helix structure

·The double stranded ladder twists into a double helix shape Homework: Read and add to notes · p 65-68 (DNA and RNA are nucleic acids) ·p 243-251