Genetics: Chromosomes and Chromatin

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Questions and Answers

What distinguishes euchromatin from heterochromatin in terms of gene transcription?

Euchromatin allows for transcription as it is loosely organized and active, while heterochromatin remains compacted and is transcriptionally inactive.

What is the primary characteristic of constitutive heterochromatin?

Constitutive heterochromatin is always compacted and remains inactive in transcription.

How do histone proteins contribute to the packaging of DNA into chromosomes?

Histone proteins bind to DNA, facilitating its condensation into nucleosomes, which helps package the DNA into the compact structure of chromosomes.

Identify the phases of the cell cycle where euchromatin is active versus when heterochromatin is typically present.

Euchromatin is active during interphase and early in the S phase, while heterochromatin is compacted throughout the cell cycle, including interphase. Signup and view all the answers

Explain the relevance of the charges of histones in their interaction with DNA.

Histones are positively charged due to high levels of arginine and lysine, allowing them to bind effectively to negatively charged DNA. Signup and view all the answers

What role does the nucleosome play in the cellular context?

The nucleosome organizes DNA into a compact structure, allowing it to fit within the nucleus and plays a key role in gene regulation. Signup and view all the answers

Discuss the significance of G banding techniques in the study of chromosomes.

G banding techniques reveal the structural differences in chromosomes, particularly highlighting regions of euchromatin and heterochromatin based on their staining properties. Signup and view all the answers

What are the implications of having late replicating genes concentrated in heterochromatin?

Late replicating genes in heterochromatin typically indicate regions involved in structural functions or gene regulation, which are less accessible for transcription. Signup and view all the answers

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Study Notes

Chromosomes

The basic unit of genetic organization.
A continuous thread of DNA and proteins in eukaryotic cells.
The term comes from the Greek word for "colored thread".

Chromatin

Refers to the complex of DNA and proteins that make up chromosomes.
Two main types: Euchromatin and Heterochromatin.

Euchromatin

Loosely organized and uncoiled.
Contains active genes, replicates early in the cell cycle.
Stains lightly with G banding techniques.
Contains most of the structural genes.

Heterochromatin

Densely compacted at cell division and interphase.
Concentrated around the nuclear periphery and nucleolus.
Transcriptionally inactive (not transcribed).
Replicates late in the S phase of mitosis.
Two types: Constitutive Heterochromatin and Facultative Heterochromatin.

Histone Proteins and the Nucleosome

Low molecular weight, basic proteins with high affinity for DNA.
Five major types: H1, H2A, H2B, H3, and H4.
Rich in positively charged amino acids (arginine and lysine), giving them a positive charge.