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