Chapter 7 Molecular Organization of Chromosomes

The range of genome sizes in the animal & plant kingdoms

DNA can assume alternative conformations such as partially melted or supercoiled states

Mechanism of action of a topoisomerase

Mechanism of folding of a bacterial chromosome There are many supercoiled loops (~100 in E. coli) attached to a central core. Each loop can be independently relaxed or condensed.

Packing of DNA in an eukaryotic cell involves wrapping around a core of basic (positively charged) proteins called histones

Steps in the folding of DNA to create an eukaryotic chromosome

The rate of renaturation of single stranded DNA depends upon the concentration and sequence complexity

The rates of renaturation of DNAs with different kinetic complexities

DNA of an eukaryotic cell has several components with different kinetic complexities

DNA with low kinetic complexity is located in the middle (near the centromere) and at the ends (near the telomeres) of a chromosome

Structure of the centromere in a Saccharomyces chromosome The centromere DNA has 4 centromere determining elements (CDEs)

Replication of telomere DNA repeats

Mechanism of replication of telomere DNA by the enzyme telomerase The enzyme telomerase has a RNA molecule that serves as the template for telomere DNA synthesis.

Telomerase has protein and RNA components

Proposed 4-stranded structure of telomere DNA in two protozoans

Hydrogen bonding structure of G quartet