The Structure of DNA and RNA

Two types of nucleic acid DNA RNA Two strands Contains Deoxyribose Contains ACTG Remains in the nucleus One strand Contains ribose Contains ACUG Exists in the cytoplasm, originally copied from the DNA.

5 end 3 end 3 end 5 end Hydrogen bond 3.4 nm 1 nm 0.34 nm (a) Figure 16.7 5 end C G Hydrogen bond C G 3 end G C G C T A 3.4 nm T A G C G C C G A T 1 nm C G T A C G G C C G A T Figure 16.7 The double helix. A T 3 end A T 0.34 nm 5 end T A (a) Key features of DNA structure (b) Partial chemical structure Space-filling model (c)

Structure of DNA An anti-parallel double helix Form from two strands of nucleotides Each nucleotide contains a phosphate group, a deoxyribose sugar, and a nitrogenous base A, G = purines (two rings) T, C = pyrimidines (one ring) A bonds with T using two hydrogen bonds G bonds with C using three hydrogen bonds

In Eukaryotes DNA is carefully packaged into chromosomes for stability and control of gene transcription.

Nucleosome (10 nm in diameter) Figure 16.22a Nucleosome (10 nm in diameter) DNA double helix (2 nm in diameter) H1 Histone tail Figure 16.22 Exploring: Chromatin Packing in a Eukaryotic Chromosome Histones Nucleosomes, or “beads on a string” (10-nm fiber) DNA, the double helix Histones

Replicated chromosome (1,400 nm) Figure 16.22b Chromatid (700 nm) 30-nm fiber Loops Scaffold 300-nm fiber 30-nm fiber Figure 16.22 Exploring: Chromatin Packing in a Eukaryotic Chromosome Replicated chromosome (1,400 nm) Looped domains (300-nm fiber) Metaphase chromosome

Assignment: Draw a DNA molecule (not in it’s helical shape, but as if it had been unwound). Label 3’ and 5’ ends Label each part of the nucleotides Label which nitrogenous bases are pyrimidines and which are purines. Color code! Must contain a total of 12 bases (6 on each strand)