Chromatin and DNA packaging

What is a typical “X” shaped chromosome indicative of in terms of cellular structure?

It represents a stage in metaphase where DNA is tightly packaged and condensed.

Why must DNA be loose during certain cellular processes?

DNA must be loose to be unwound and accessed for transcription.

How much DNA does each cell contain?

Each cell has about 6.5 feet of DNA.

What is chromatin composed of?

Chromatin is a combination of DNA and proteins, mostly histones.

What is euchromatin?

Euchromatin is lightly packed chromatin, under active transcription with a high gene concentration.

What characterizes heterochromatin?

Heterochromatin is tightly packed chromatin that mostly contains genetically inactive sequences.

What are constitutive heterochromatin areas?

Constitutive heterochromatin is genetically poor, always heterochromatic, and found in centromeres and telomeres.

What is facultative heterochromatin?

Facultative heterochromatin is not heterochromatic all the time and may go through gene silencing.

Describe the folded fiber model of DNA packaging.

The folded fiber model suggests DNA is balled up like a ball of yarn in packaging, but it is not proven.

What is a nucleosome?

A nucleosome is the unit where DNA is wrapped around histone proteins, localized areas of transcription.

How are core histones structured?

Core histones consist of H2A, H2B, H3, and H4, with two of each forming an octet.

What is the significance of linker histones?

Linker histones (such as H1) are not highly conserved and are loosely associated with the core particle.

What does the ZigZag model represent?

The ZigZag model represents supercoiling of DNA, which cannot bend easily between nucleosomes.

What is the importance of 10 nm fibers?

10 nm fibers are the primary packaging of DNA, also known as 'beads on a string,' reducing length by 7x.

What characterizes 30 nm fibers?

30 nm fibers have 6 nucleosomes and provide increased compaction through histone H1.

What sees maximum compaction of heterochromatin?

The 700 nm fiber represents the highest compaction of heterochromatin.

What proteins make up the highest compaction of heterochromatin?

Heterochromatin is composed of topoisomerase II and 15 non-histone proteins.

What happens to DNA right before mitosis?

DNA cannot be read because enzymes will not attach due to high compaction.

What is the state of chromatin during early prophase?

In early prophase, chromatin undergoes heavy condensation.

What occurs during late prophase?

During late prophase, the nuclear envelope breaks down, and the mitotic spindle forms.

What is the state of chromatin during metaphase?

Metaphase is characterized by the highest condensation of chromatin.

What type of fibers are found in G1 phase of the cell cycle?

In G1 phase, 2-10 nm fibers are present for preparation for synthesis.

What happens to chromatin in G2 phase?

In G2 phase, chromatin is further compacted into 30, 300, and 700 nm fibers.

What role do histones play in the structure of nucleosomes?

Histones help to tightly wrap and package DNA, forming nucleosomes that regulate gene expression.

What is the effect of histone tails on DNA movement?

Histone tails can influence whether DNA can move to access different genes.

How is transcription activity related to chromatin structure?

Transcription activity is higher in euchromatin, which is less compact and more accessible.

What role does topoisomerase play in chromatin structure?

Topoisomerase helps in packaging and compaction of DNA by relieving supercoiling.

Why is histone structure highly conserved across organisms?

Histones are highly conserved because they are fundamental for DNA packaging and function across different life forms.

What does the term 'gene silencing' refer to in the context of chromatin?

Gene silencing refers to the process by which certain genes are turned off and not expressed, commonly associated with heterochromatin.