Chromosome Structure and Chromatin

Chromosome Structure

Chromatin

• Definition: Chromatin is the complex of DNA, histone proteins, and other non-histone proteins that make up the chromosome.
• Forms:
  • Euchromatin: lightly packed, active genes, loose structure
  • Heterochromatin: densely packed, inactive genes, compact structure
• Chromatin remodeling: process of reorganizing chromatin structure to access or silence genes

Histones

• Definition: Histones are a family of basic proteins that DNA wraps around to form chromatin.
• Types:
  • H2A
  • H2B
  • H3
  • H4
• Histone modifications: post-translational modifications that alter chromatin structure and accessibility
  • Acetylation: relaxation of chromatin structure, increased gene expression
  • Methylation: condensation of chromatin structure, gene silencing

Cell Division

• Chromatin condensation: process of chromatin compacting into visible chromosomes during mitosis
• Chromosome condensation complex: protein complex that helps condense chromatin
• Sister chromatids: identical copies of a chromosome that separate during cell division
• Centromere: specialized region on the chromosome where sister chromatids attach

Chromosome Structure

Chromatin

• Chromatin is the complex of DNA, histone proteins, and other non-histone proteins that make up the chromosome.
• Euchromatin is lightly packed, has active genes, and a loose structure.
• Heterochromatin is densely packed, has inactive genes, and a compact structure.
• Chromatin remodeling is the process of reorganizing chromatin structure to access or silence genes.

Histones

• Histones are a family of basic proteins that DNA wraps around to form chromatin.
• There are four main types of histones: H2A, H2B, H3, and H4.
• Histone modifications alter chromatin structure and accessibility.
• Acetylation of histones relaxes chromatin structure, increasing gene expression.
• Methylation of histones condenses chromatin structure, silencing genes.

Cell Division

• Chromatin condensation is the process of chromatin compacting into visible chromosomes during mitosis.
• The chromosome condensation complex is a protein complex that helps condense chromatin.
• Sister chromatids are identical copies of a chromosome that separate during cell division.
• The centromere is a specialized region on the chromosome where sister chromatids attach.

Chromosome Structure in Cell Division

Interphase

• Chromatin is uncoiled and dispersed throughout the nucleus, making individual chromosomes invisible
• DNA replication occurs, resulting in two identical sister chromatids

Chromosome Condensation

• Chromatin condenses into visible chromosomes during prophase
• Each chromosome consists of two identical sister chromatids joined at the centromere
• Centromere is the specialized region where sister chromatids are attached

Chromosome Alignment

• Chromosomes line up at the center of the cell, attached to the spindle fibers during metaphase
• Each chromosome is aligned with its homologous partner, ensuring a complete set of chromosomes in new cells

Sister Chromatid Separation

• Sister chromatids separate, moving to opposite poles of the cell during anaphase
• Each chromatid becomes a separate chromosome after separation
• Microtubules pull the sister chromatids apart, ensuring each new cell receives one copy of each chromosome

Chromosome Decondensation

• Chromosomes reach the poles of the cell and begin to decondense during telophase
• Nuclear envelope reforms around each set of chromosomes
• Cytokinesis follows, dividing the cytoplasm and completing cell division

Learn about chromatin, its forms, and histones in chromosome structure. Understand the difference between euchromatin and heterochromatin and the process of chromatin remodeling.