DNA Organization, Telomeres, and Telomerase in Eukaryotes and Prokaryotes

Eukaryotic DNA Organization

Negatively charged DNA is wrapped around positively charged histone proteins.

Nucleosome

8 Histone proteins combine to form a Nucleosome which helps to wrap DNA.

Solenoid

6 nucleosomes are further condensed to form solenoids (also called chromatin fibres).

Chromatid

Solenoids form one chromatid.

Chromosome

Two chromatids make one chromosome.

Prokaryotic DNA Organization

Commonly only one chromosome that can be circular.

Plasmids

Smaller pieces of DNA float throughout the cell and are called Plasmids.

Supercoiling

Twisting of prokaryotic DNA to reduce the volume, like an elastic band.

Telomere

A repeating sequence of DNA at the end of a chromosome that protects coding regions from being lost during replication.

Telomeres during Replication

Telomeres shorten after each division.

Hayflick Limit

The total number of times a cell can divide; human cells can divide around 50 times before telomeres become too short.

Telomerase

An enzyme that adds more DNA to the shortening telomeres of sex cells so they can continue to divide.

Functions of Telomeres

Help to prevent chromosome ends from fusing to other chromosomes, prevent DNA degradation, assist DNA repair mechanisms, and determine how many times a cell can divide.

Telomeres and Aging

As we age, more of our cells reach the Hayflick limit and begin to die off.

Cancer Cells

Cancer cells can continue to divide indefinitely because they produce large amounts of Telomerase.

Uncoiled DNA

Uncoiled DNA is called chromatin.

Chromatosome

1 nucleosome + Histone H1 = Chromatosome.