Molecular Biology

Eukaryotic Genome Structure

The human genome:nuclear and mitochondrial

components

Genetic Material in the Living Cells

Composition of Chromosome

DNA

Histones(Major proteins)

Non-histone(Small amounts)

p

q

Karyotype

chromosomes

DNA Condensation: Why?

Histones

Nucleosomes: The Basic Units of DNA Condensation

Chromatin “beads-on-a-string” structure (10 nm Fiber)

Histone H1 Binds the Nucleosome to Form the Chromatosome

Two models of the 30 nm chromatin fiber

Two models of the 30 nm chromatin fiber

Higher-Order Chromosome Structure Involves Loops and Coils

Looped chromatin fibre folds

Chromatin fibre loops along the protein scaffold

Low power high power

Scaffold protein

DNA loops

The major structures in DNA compaction

The major structures in DNA compaction (contd.)

Regulation of chromatin structure

• Post-translational modifications of histones• Exchange of canonical histones with their

alternative sequence variants.• Chromatin remodeling via ATP-dependent

complexes • DNA methylation

Chromosomes

Metaphase chromosomes in Eukaryota:–the highest level of chromatin structure (the most condensed)

–observed only during cell division

After cell division:–metaphase chromosomes disappear–chromatin condensation is reduced–genomic DNA exists in the form of

heterochromatin and euchromatin

Different forms of chromatin show differential gene activity

euchromatin

heterochromatin