4 DNA Organization and Telomeres

Prokaryotic DNA Organization

DNA in prokaryotic organisms consists of one circular chromosome, with less tightly bound and more easily accessible DNA.

Plasmids

Small pieces of DNA in prokaryotes that can move from one bacterium to another, typically through conjugation.

Conjugation

The process by which plasmids are transferred from one bacterial cell to another.

Histones

Positively charged proteins around which DNA is tightly wound to form nucleosomes.

Nucleosome

This cluster of 8 histones wrapped with DNA.

Supercoiling

The process by which prokaryotic DNA is twisted to fit in a compact form.

Solenoid

A 30nm-wide cylindrical fiber formed by coiling nucleosomes together, used in eukaryotic DNA packaging.

Telomeres

Repeating sequences of non-coding DNA located at the ends of eukaryotic chromosomes that protect them from degradation.

Hayflick Limit

The maximum number of times a normal somatic human cell can divide before cell division stops due to shortened telomeres.

Telomerase

An enzyme that adds new telomere sequences to the ends of chromosomes, found in stem cells and some white blood cells.

Cell Senescence

The process where cells lose the ability to divide and function after many replications due to reduced telomere length.

DNA Replication

The process by which DNA makes a copy of itself during cell division, involving leading and lagging strands.

Chromatin

The complex of DNA and proteins found in eukaryotic cells, which condenses to form chromosomes during cell division.

Active Genes

Genes that are expressed at a given time, requiring loosely packed DNA for transcription.

Telomere Shortening

The phenomenon where telomeres decrease in length with each cell division, leading to cellular aging.

Linkers

Stretches of DNA that connect one nucleosome to another.

Chromosome Ends

The tips of chromosomes where telomeres are located, preventing them from fusing with other chromosomes.