Cell cycle and cell division

• What are chromosomes made of?

  DNA wound around histone proteins
• What is chromatin?

  Unwound single structures of DNA that are not visible
• When are chromosomes visible?

  When the cell is dividing
• What happens to DNA before cell division?

  It replicates so that each chromosome consists of two identical DNA molecules
• What is the area where two identical DNA molecules are joined called?

  Centrosome
• What occurs at the beginning of cell division regarding chromatin?

  Chromatin condenses and becomes visible as chromosomes
• What are the two identical parts of a chromosome called?

  Chromatids
• What are sister chromatids?

  Identical chromatids joined by the centromere
• What are homologous pairs of chromosomes?

  Pairs of chromosomes that are the same size and shape but not identical
• Why are homologous pairs called so?

  Because they carry the same genes in the same gene locus
• What are alleles?

  Different forms of the same gene
• What is a diploid cell?

  A cell where the chromosomes are paired
• What is a haploid cell?

  A cell where the chromosomes are unpaired
• How do diploid and haploid cells divide?

  Diploid cells can divide by both mitosis and meiosis, while haploid cells can only divide by mitosis
• What phases are collectively called interphase?

  G1, S, and G2 phases
• What occurs during the S phase of the cell cycle?

  DNA replication happens
• What is mitosis?

  The process where chromosomes move into new nuclei
• What is cytokinesis?

  The division of the cytoplasm to form two new cells
• What does mitosis produce?

  Two daughter cells that are genetically identical to the parent cell
• What are the stages of the cell cycle?

  • Interphase: Synthesis and growth
  • Mitosis: Formation of two genetically identical daughter nuclei
  • Cytokinesis: Division of the cytoplasm to form two daughter cells
• What happens during interphase?

  • Longest phase of the cell cycle
  • Cell grows and organelles replicate
  • DNA replicates to double its quantities
  • Proteins are synthesized using ATP
  • Chromatin is dispersed and not visible
• What happens during prophase?

  Chromosomes condense, centrioles move to poles, and the nuclear envelope disintegrates
• What is the role of centrioles during prophase?

  They move to opposite ends of the cell and organize spindle formation
• What occurs during metaphase?

  Chromosomes align on the equator and attach to spindle fibers
• What happens during anaphase?

  Spindle fibers shorten, separating the chromatids and pulling them to the poles
• What occurs during telophase?

  Chromatids reach the poles, chromosomes uncoil, and the nuclear envelope re-forms
• How does cytokinesis occur in animal cells?

  By constriction of the parent cell around the equator
• How does cytokinesis occur in plant cells?

  By formation of a cell plate that develops into a cell wall
• What are the differences between mitosis in animal and plant cells?

  **Animal Cells:**

  • Shape: Cells become rounded
  • Centrioles: Present
  • Cytokinesis: Cleavage furrow from outside inwards
  • Spindle: Degenerates at telophase
  • Occurrence: In adult mammals for cell replacement

  
  

  **Plant Cells:**

  • Shape: No shape change
  • Centrioles: Absent
  • Cytokinesis: Cell plate from center outwards
  • Spindle: Remains throughout new cell wall formation
  • Occurrence: In meristems (root and shoot apex)
• Prophase?


  First stage of mitosis where chromosomes condense and the nuclear envelope breaks down. Centrioles divide and move towards opposite poles of the cell
• Metaphase?


  Complete dissapearance of the nuclear enevlope, spindle becomes fully developed. Chromatid pairs are attached to indidvidual spindle fibres and align themselves in the middle/along the equator, ready for division.
• Anaphase?


  Rapid and most obvious stage. Centrosomes split and spindle fibres contract, causing the chromatids to be pulled apart by the split centrosome. New single chromosomes are pulled to the poles.
• Telophase?


  Final phase in mitosis; chromosomes uncoil, and form the chromatin of interphase. The nuclear envelope reforms and the nucleolus reappears - essentially the opposite to prophase.
• Prophase


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• Metaphase


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• Anaphase


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• Telophase


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• Mitotic index?


  Total number of cells observed/Number of cells in mitosis​×100