Cytology: Understanding Mitosis

Cytology: Cell Division Mitosis

• Mitosis is a process where eukaryotic cells duplicate their genetic material (chromosomes) to prepare for division.
• Cytokinesis is the division of the cell's cytoplasm into two new daughter cells.
• Eukaryotic cells divide multiple times throughout an organism's life; prokaryotic cells divide through binary fission.
• Cell division is crucial for embryonic development, growth, and wound healing in animals.
• Errors in cell division can cause cell death or cancer.

Mitosis Reorganizes DNA

• Before mitosis, the cell creates an exact copy of its DNA material.
• During mitosis, the DNA copies are reorganized and packaged into two sets of chromosomes, and then are separated to opposite ends of the cell.
• Mitosis is immediately followed by cytokinesis in most organisms, where the cell body divides into two separate cells.
• The original cell (mother cell) is identical to the two resulting cells (daughter cells).

Mitosis Vocabulary

• Nucleus: Location of DNA within the cell.
• Nuclear envelope: Membrane separating the nucleus from the cytoplasm, crucial for cell division.
• DNA: Contains the genetic blueprint for cell behavior.
• Chromatin: Loosely bundled coil of DNA that is typically present in non-dividing cells.
• Histones: Proteins that hold the DNA strand together in chromatin.
• Chromosome: Highly organized form of chromatin in a tightly wrapped and knotted rope shape, present during mitosis.
• Chromatid: One half of a duplicated chromosome; contain the same genetic information.
• Centromere: Proteins that connect two chromatids.
• Microtubules: Part of the cell's cytoskeleton, involved in separating chromosomes during mitosis.
• Mitotic spindle: An organized collection of microtubules that coordinate the pulling apart of chromosomes during cell division.
• Metaphase plate: An imaginary plane equidistant between the cell's poles where chromosomes are lined up during metaphase.

Chromosome Structure

• Chromosomes are highly condensed structures of DNA that are visible during cell division.
• Each chromosome is composed of two identical chromatids held together by a centromere.
• The centromere is the point where the two chromatids are connected.

Mitosis Stages

• Mitosis is divided into five sub-phases: prophase, prometaphase, metaphase, anaphase, and telophase.

Interphase

• By late interphase, chromosomes have duplicated but are still loosely packed
• The centrosomes have been duplicated and begin to organize microtubules into an aster.

Prophase

• Chromosomes tightly coil, and sister chromatids are joined.
• Nucleoli disappear.

Prometaphase

• Nuclear envelope fragments.
• Microtubules from one pole attach to one kinetochore, while microtubules from the other pole attach to the other kinetochore.

Metaphase

• Spindle fibers push sister chromatids until they are all arranged at the metaphase plate, equidistant from the poles.

Anaphase

• Centromeres divide, separating the sister chromatids.
• Each chromatid is pulled toward the pole to which it is attached by spindle fibers

Telophase

• The cell elongates as free spindle fibers from each centrosome push off each other.
• Two nuclei begin to form surrounded by fragments of the parent's nuclear envelope.
• Chromatin becomes less tightly coiled.

Cytokinesis

• The cytoplasm divides after the formation of two nuclei, resulting in two new cells that resemble the mother cell and contain 2n chromosomes.