DNA Structure

What is DNA made of

Composition

Composed of nucleotides

• Deoxyribose Sugar

• Phosphate group

• Nitrogenous base

  • Adenine ~ Purines: 2C

  • Thymine ~ Pyramidine: 1C

  • Guanine ~ Purines: 2C

  • Cytosine ~ Pyramidine: 1C

DNA Bonding

Phosphodiester bond

• Joins sugar and phophate group

  • Phosphate-sugar backbone

Glycosidic bond

• Joins nitrogenous base to Sugar

Strong Covalent Bonds

Base Pairing

Bases are held together by WEAK hydrogen bonds

A=T ~ 2 hydrogen bonds

C=G ~ 3 hydrogen bonds

Chargaff’s Rule

Amount of A+G = Amount of T+C

Strands

Antiparallel Strands

• Running in opposite directions

• 5 prime end alings with 3 prime end

Arranged as a double helix

• They complement eachother

Packaging

• DNA wraps around histone proteins (thread around a spool)

  • Histone proteins + DNA = nucleosome

  • Nucleosomes are the beads on a string

• Solenoids

  • Secondary lvl of packaging. Packed nucleosomes using 30nm of chromatin fiber

• Chromosomes are made of two identical chromatids

  • Held by a centromere

Terminology: DNA Packaging

Histone: Structural Proteins

Nucleosome: Section of DNA wrapped around histones

Chromatin = DNA + Histones

Eukaryotic Genomes

• Supercoiling compacts the DNA more:

• Tension builds & nucleosomes twist together more compactly