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