Chromosomes, Chromatin & DNA Packing

What is a chromosome?

A very long DNA molecule associated with proteins; in eukaryotes it is typically linear and highly condensed.

What is chromatin? How does it relate to chromosomes?

Chromatin is DNA wrapped around proteins (histones and other proteins) in a less-condensed form typical when the cell is not dividing. Chromosomes are a more condensed form of chromatin seen during cell division.

Why must eukaryotic DNA be packed into chromatin and chromosomes?

To fit the enormous length of DNA into the small volume of the nucleus and to regulate accessibility for gene expression and replication.

What proteins are primarily involved in the initial level of DNA packing?

Histone proteins (DNA wraps around histone octamers to form nucleosomes, the first level of packing).

What is the functional significance of chromatin being less condensed when the cell is not dividing?

Less condensed chromatin is more accessible for transcription (gene expression), DNA repair, and replication.

How many chromosomes do humans have (diploid), and how does that relate to packing needs?

Human somatic cells typically have 46 chromosomes (23 pairs); all this DNA must fit inside the nucleus, necessitating multilevel packing.