Eukaryotic Cell Structure, Organelles, and Mitosis Process
Structure of Eukaryotic Cells
The cells of animals and plants are known as eukaryotic cells. They share several fundamental components:
- Plasma Membrane (Cell Membrane): A thin membrane that separates the cell contents from the surrounding environment. It regulates the entry and exit of substances.
- Cytoplasm: The region inside the cell membrane, containing a great variety of structures immersed in a solution called hyaloplasm (or cytosol). Many of these cellular structures are surrounded by membranes and are called organelles.
- Nucleus: The largest and most visible structure. Its contents are separated from the rest of the cytoplasm by a double membrane.
Animal Cell Components
- Mitochondria: Oval-shaped organelles with a double membrane delimiting an interior space. They are responsible for generating the energy required for cellular functions.
- Cytoskeleton: A network of distributed filaments forming a structure throughout the cytoplasm. They form the cell's structural backbone, provide support, and are involved in cellular movements.
- Golgi Apparatus: Consists of stacks of flattened membranous sacs (cisternae) surrounded by small vesicles. These vesicles incorporate and process many of the products manufactured in the cell.
- Endoplasmic Reticulum (ER): A network of interconnected membranous sacs and canals extending throughout the cellular cytoplasm. It manufactures a wide variety of substances.
- Centrioles: They take the form of two hollow cylinders whose walls are formed by filaments. They are directly involved in the movement of cytoskeleton filaments and membrane vesicles.
- Lysosomes: Membrane vesicles containing enzymes that cause the digestion of large organic molecules.
Plant Cell Structures
Plant cells contain the following structures in addition to many organelles shared with animal cells:
- Vacuoles: Large sacs containing water and dissolved substances.
- Chloroplasts: Oval-shaped organelles that contain a green pigment called chlorophyll. Cellular photosynthesis is performed within the chloroplasts.
- Cell Wall: A thick, rigid cover disposed on the outside of the plasma membrane. It possesses pores that allow the exchange of substances with the exterior.
Shared Organelles in Plant Cells
Plant cells also contain:
- Endoplasmic Reticulum
- Golgi Apparatus
- Lysosomes
- Mitochondria
- Cytoskeleton
Cell Division and Chromosome Transmission
The process by which eukaryotic cells divide is called cell division, which includes mitosis and the subsequent division of the cytoplasm (cytokinesis).
Stages of Mitosis
- Prophase: The chromatin condenses, and the chromosomes become visible. At this stage, each chromosome is double, consisting of two identical chromatids joined at the centromere. The nuclear membrane disappears, and the chromosomes scatter across the cell.
- Metaphase: The chromosomes align in a central plane (the metaphase plate).
- Anaphase: The centromeres of the chromosomes split, and the two chromatids separate. One chromatid moves toward one end of the cell, and the other moves toward the opposite end.
- Telophase: Once at their respective ends, the daughter chromosomes are surrounded by a new nuclear membrane, completing the division of the nucleus.
After the division of the nucleus by mitosis, the cytoplasm divides either by cleavage furrow (strangulation) or by forming a phragmoplast.
Cell Cycle Chromosome States
- Chromosomes are invisible, consisting of two chromatids.
- Chromosome is invisible, but chromatids are visible.
- Chromosome is visible, chromatids are visible.
- Chromosomes are visible with single chromatids.