Mitosis - PPT 2nd Semester
Asexual Reproduction Overview
The process of asexual reproduction starts when a sperm fertilizes an egg.
Reasons for Asexual Reproduction in Cells
Cells reproduce through asexual reproduction for three main reasons:
Growth: To increase the organism's size or biomass.
Repair: To replace damaged or dead cells.
Replacement: To continuously replenish cells that have a limited lifespan.
Example: Skin cancer is an abnormal growth of skin cells that often originates from cells exposed to the sun, indicating a failure in the regulation of cell reproduction.
Cells that reproduce by asexual means often do so constantly, ensuring a steady increase in cell population.
Cell Life Cycle and Mitosis
The cell life cycle consists of several stages, prominently featuring mitosis, which is responsible for the division of cells. Mitosis includes the following stages:
Major Stages of Mitosis
Interphase
Occurs prior to mitosis.
Chromosomes are duplicated, resulting in a doubling of genetic material (n # doubles).
At the beginning, chromosomes appear as threadlike coils known as chromatin, and at the end of this phase, they are formed as sister chromatids.
Key Components:
CELL
Nucleus
MEMBRANE
Cytoplasm
Prophase
First step of mitosis where cell division starts.
Centrioles appear and move to opposite ends of the cell.
Spindle fibers form between the poles of the cell, aiding in chromosome separation.
The nucleus begins to dissolve, facilitating the upcoming processes.
Key Components:
Centrioles
Sister chromatids
Spindle fibers
Metaphase
Second step in mitosis.
Chromatids align at the cell's equatorial plane, facilitated by spindle fibers attaching to the centromere of each chromatid.
Key Components:
Centrioles
Spindle fibers
Anaphase
Third step of mitosis.
Chromatids, or pairs of chromosomes, separate and are pulled toward opposite ends of the cell by the spindle fibers.
Key Components:
Centrioles
Spindle fibers
Telophase
Fourth step in the process of mitosis.
Formation of two new nuclei occurs.
Chromosomes unwind to become chromatin (shifting from the rod-like appearance back to a thread-like form).
Mitosis ends at this stage.
Key Components:
Nuclei (two new)
Chromatin
Cytokinesis
Occurs immediately after mitosis.
The cell membrane contracts inward, resulting in the formation of two daughter cells, each with its own nucleus containing identical chromosomes.
Cell Cycle Review
The complete cell cycle can be summarized with the steps: Interphase, Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.
Mnemonic to remember the order: "IPMAT C" (Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis).
Visual Representation of Cell Cycle Processes
Animal Cell Cycle:
Major Stages: Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis.
Plant Cell Cycle:
Also follows the major stages of Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis.
Key Components and Terms
Centrioles: Structurally important for chromosome movement and spindle fiber formation during cell division.
Chromatids: The two identical halves of a duplicated chromosome.
Spindle Fibers: Structure that helps separate chromosomes during cell division.
Centromere: The region where two sister chromatids are joined.
Daughter Cells: Resulting cells after the completion of cell division, each genetically identical to the original parent cell.
The cell cycle is like a life cycle for cells, and it includes several important stages. First, in Interphase, the cell grows and copies its DNA to prepare for division. Next is Mitosis, which is where the cell divides into two new cells, and this has its own stages: Prophase, where the DNA condenses; Metaphase, where the chromosomes line up in the middle; Anaphase, where the chromosomes are pulled apart; and Telophase, where two new nuclei form. Finally, in Cytokinesis, the cell divides its cytoplasm to form two separate daughter cells, each with its own nucleus. This cycle is essential because it allows for growth, repair, and reproduction of cells in living organisms.