Chapter 7Chapter 7

Molecular Organization of Molecular Organization of ChromosomesChromosomes

The range of genome sizes The range of genome sizes in the animal & plant kingdomsin the animal & plant kingdoms

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

statesstates

Mechanism of action of a Mechanism of action of a topoisomerasetopoisomerase

Mechanism of folding of a bacterial Mechanism of folding of a bacterial chromosomechromosome

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

histoneshistones

Steps in the folding of DNA Steps in the folding of DNA to create an eukaryotic chromosometo create an eukaryotic chromosome

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

The rates of renaturation of DNAs The rates of renaturation of DNAs with different kinetic complexitieswith different kinetic complexities

DNA of an eukaryotic cell has several DNA of an eukaryotic cell has several components components

with different kinetic complexitieswith different kinetic complexities

DNA with low kinetic complexity is located in the DNA with low kinetic complexity is located in the middle (near the centromere) and at the endsmiddle (near the centromere) and at the ends

(near the telomeres) of a chromosome (near the telomeres) of a chromosome

Structure of the centromere Structure of the centromere in a in a

SaccharomycesSaccharomyces chromosome chromosome

The centromere DNA has 4 centromere determining

elements (CDEs)

Replication of telomere DNA repeatsReplication of telomere DNA repeats

Mechanism of replication of telomere Mechanism of replication of telomere DNA DNA

by the enzyme telomeraseby the enzyme telomerase

The enzyme telomerase has a

RNA molecule that serves as the template

for telomere DNA synthesis.

Telomerase has protein and Telomerase has protein and RNA componentsRNA components

Proposed 4-stranded structure of Proposed 4-stranded structure of telomere DNA telomere DNA

in two protozoansin two protozoans

Hydrogen bonding Hydrogen bonding structure of G quartetstructure of G quartet