chapter 11: Nucleic Acid structure, DNA Replication and Chromosome structure

Biochemical Identification
of the Genetic Material

Researchers found out that chromosomes carry the
genetic information, by the experiment done by Frederick Griffith.

Nucleic Acid Structure

James Watson and Francis Crick, Rosalind Franklin’s proposed the structure of the DNA double helix, and Erwin Chargaff did the base pairing A-T, G-C.

Levels of DNA Structure:

4- Chromosomes

5- Genome

3- Double helix

2- Strand

1- Nucleotides

DNA Replication

Conservative mechanism:
DNA replication produces 1 double helix with both parental strands and the other with 2 new daughter strands.

Semiconservative Model:
DNA replication produces DNA molecules with 1 parental strand and 1 newly made daughter strand.

Dispersive mechanism:
DNA replication produces DNA strands in which segments of new DNA are interspersed with the parental DNA.

Molecular Mechanism
of DNA Replication

Prokaryotes

single origin of replication.

Eukaryotes

multiple origins of replication.

steps for replication

DNA helicase: Binds to DNA and travels 5’ to 3’ using ATP to separate strand and move fork forward.

DNA topoisomerase: Relieves additional coiling ahead of replication fork.

Single-strand binding proteins: Keep parental strands open to act as templates.

DNA polymerase: Covalently links nucleotides, Deoxynucleoside triphosphates.

Telomeres:
Series of short nucleotide sequences (5’-GGGTTA-3’)n repeated at the ends of chromosomes in eukaryotes.

Molecular Structure of
Eukaryotic Chromosomes

Three levels of DNA compaction

30-nm fiber

Radial loop domains

DNA wrapping