Lecture 22: Chromosome Packing

What are the two types of chromatin?

Euchromatin and heterochromatin.

What is euchromatin?

Euchromatin is lightly packed, allowing access to genetic material.

What is heterochromatin?

Heterochromatin is tightly packed DNA that cannot be accessed for transcription.

What is the role of histones in chromatin?

Histones are proteins that help package and condense DNA into chromatin.

What is the nucleosome?

The nucleosome is the basic unit of chromatin, consisting of DNA wrapped around a core of histone proteins.

How many base pairs of DNA are wrapped around a nucleosome?

About 200 base pairs of DNA are wrapped around the histone core in a nucleosome.

What is the difference between constitutive and facultative heterochromatin?

Constitutive heterochromatin is permanently condensed, while facultative heterochromatin can switch between euchromatin and heterochromatin states.

What happens during the process of chromatin condensation?

Chromatin is compacted from a loose, accessible state into a tightly packed state for cell division.

What compaction level is referred to as the 30 nanometer fiber?

The 30 nanometer fiber is a higher level of chromatin organization, sometimes called a solenoid.

What is the function of topoisomerase II in chromatin structure?

Topoisomerase II helps in forming and maintaining chromatin loops during DNA compaction.

What is the significance of the 300 nanometer fiber?

The 300 nanometer fiber represents another level of compaction of euchromatin while allowing access to genetic material.

How is DNA packaged into a cell nucleus?

DNA is compacted into chromatin to fit in the cell nucleus, achieving various levels of organization.

What are the core histones in a nucleosome?

The core histones are H2A, H2B, H3, and H4.

What occurs during mitosis regarding chromatin?

During mitosis, chromatin condenses into metaphase chromosomes.

What does it mean when chromatin is described as 'beads on a string'?

This term refers to the appearance of nucleosomes along a strand of DNA, resembling beads on a string.

Why do cells need to compact their DNA before mitosis?

Compaction of DNA is necessary to facilitate the separation of chromosomes during cell division.