Lecture Notes: Chromosome Shape, Mitosis, and the Cell Cycle

Chromosome Structure

• Chromosomes are composed of double-stranded DNA molecules.
• Chromatin: Combination of DNA and proteins.
  • Proteins are mainly histones.
• Nucleosome: Single unit of DNA wrapped around histones.
• 30 Nanometer Fiber: Zigzag structure formed by nucleosomes.
• Radical Loop Domain: Loops formed when 30 nm fibers come closer.
• Heterochromatin: Highly compacted DNA regions.
• Euchromatin: Less compacted DNA regions.

The Cell Cycle

• A series of steps leading to cell and nuclear division.
• Cytogenetics: Study of chromosomes and their structure.
• Karyotype: Display of chromosomes, showing size, gender, and number.

Chromosome Sets

• Humans: 23 pairs of chromosomes (46 total).
  • Autosomes: Chromosomes 1-22.
  • Sex Chromosomes: Determine gender (XX female, XY male).
• Diploid (2n): Two sets of chromosomes.
• Haploid (n): One set of chromosomes, found in gametes.
• Homologous Chromosomes: Pair of chromosomes at each position with similar genes.
• Alleles: Specific locations on homologous chromosomes carrying genes.

Stages of the Cell Cycle

• G1 (Gap 1): Cell growth and normal metabolism.
• S Phase (Synthesis): DNA replication.
• G2 (Gap 2): Preparation for mitosis, protein synthesis.
• M Phase (Mitosis & Cytokinesis): Division of nucleus and cytoplasm.

Mitosis

• Prophase: Chromosomes condense, nuclear envelope dissolves, spindle forms.
• Prometaphase: Spindle fibers attach to kinetochores, chromosomes begin to move.
• Metaphase: Chromosomes align in the middle of the cell.
• Anaphase: Sister chromatids separate and move to opposite poles.
• Telophase: Chromosomes decondense, nuclear envelope reforms.
• Cytokinesis: Division of cytoplasm, forming two separate cells.
  • Cleavage Furrow: Forms in animal cells.
  • Cell Plate: Forms in plant cells.

Regulation of the Cell Cycle

• Cyclin and Cyclin-dependent Kinases (CDKs): Regulate progression of the cell cycle.
• Plant hormones, steroids, and protein growth factors can influence cell growth and division.
• Cancer cells may bypass normal cycle controls, leading to uncontrolled growth.

Binary Fission in Bacteria

• Simple division process, no mitosis involved.
• Septum Formation: Division site in bacteria.
• Rapid replication, e.g., E.coli duplicates in ~20 minutes.

These notes cover the key topics and structure of the lecture on chromosome shape, the cell cycle, and mitosis. It includes essential terms and processes necessary for understanding cell division in eukaryotes and bacteria.