Cell Biology: Structure, Function, Mitosis, and Meiosis
Cell Biology: Structure, Function, and Reproduction
Cell: The fundamental physiological, morphological, developmental, reproductive, and genetic unit of organisms.
It is the smallest unit of life.
There are two main types: prokaryotic and eukaryotic.
Prokaryotes possess a cell wall but lack a nucleus.
Eukaryotes are divided into animal and plant cells.
Animal cells, unlike plant cells, contain lysosomes that absorb lipids. Plant cells, unlike animal cells, have a cell wall made of cellulose.
Cytoplasmic organelles perform various functions, such as photosynthesis in plants, lipid and protein synthesis and packaging, energy production, and housing the genetic structure.
The cytoplasmic membrane is a thin, transparent layer that regulates the entry of substances and the exit of waste products.
Nuclear components contain the genetic information that is transferred to subsequent generations.
Mitosis: Asexual Reproduction
Mitosis is a form of asexual reproduction involving somatic cells. From one cell, two identical daughter cells are produced, each containing the same quantity of DNA and cytoplasm.
Mitosis Phases
- Interphase: The cell prepares for mitosis.
- Prophase: The first stage of mitosis, where DNA condenses into chromosomes.
- Metaphase: Chromosomes align in the middle of the cell.
- Anaphase: The centrioles at each pole pull the chromosomes apart into two chromatids, and the cytoplasm begins to constrict.
- Telophase: The DNA of the chromosomes uncoils, the nucleolus and centromere reappear, the nuclear membrane reforms, and the centriole is located outside the nucleus.
- Cytokinesis: The cell divides into two, giving rise to two smaller cells.
Meiosis: Sexual Reproduction
Meiosis is the type of cell division involved in gamete formation, such as the egg and sperm in animals or pollen in plants. Sexual reproduction occurs only in eukaryotes. During gamete formation, the number of chromosomes is reduced by half, and the full number is restored when two gametes unite during fertilization. This combination allows for the formation of a new being of the same species, sharing genetic information from both parents.
Meiosis Phases
During Prophase I, a key event occurs: the pairing of homologous chromosomes.
Metaphase I: Spindle fibers are attached to the centromere of each homologous pair.
Telophase I: Each “cell” has only one set of replicated chromosomes. Depending on the species, the new nuclear membrane may or may not form.
Prophase II: During Prophase II, the nuclear membrane dissolves, and spindle fibers appear, similar to the prophase of mitosis.
Metaphase II: Chromosomes align in the equatorial plane, and spindle fibers attach to opposite sides of the centromere in the kinetochore region.
Anaphase II: During Anaphase II, the centromere divides, and the chromatids (now chromosomes) are segregated to opposite poles of the cell.
Telophase II: The DNA of the chromosomes uncoils, the nucleolus reappears in the nucleus, the centromere reappears, the nuclear membrane reforms, and the centrioles are located outside the nucleus.
Cytokinesis separates the cells.
Binary Fission: Asexual Reproduction in Microorganisms
Binary fission is a form of asexual reproduction that occurs in bacteria, yeast, fission algae, and single-celled protozoa. The mother cell divides into two daughter cells of equal size.