Cellular Processes Explained: Division, Transport, and Key Structures
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Golgi Apparatus Functions
- Packaging, modification, and distribution of materials synthesized in the cell.
- Pathway: Rough ER (cis) → Cisternae → Vesicles (trans).
Cellular Protein Export Pathway
After proteins are synthesized by ribosomes, they are transported to the rough endoplasmic reticulum where they can be modified. Vesicles carrying the protein then bud off the rough endoplasmic reticulum and are transported to the Golgi apparatus for further modification. Following this, vesicles carrying the protein bud off the Golgi apparatus and transport the protein to the plasma membrane. Here, the vesicles fuse with the membrane, expelling their content (the modified proteins) outside the cell. The membrane then returns to its original state. This process is called exocytosis.
Endocytosis is a similar process that involves the pulling of the plasma membrane inwards, leading to the pinching off of a vesicle from the plasma membrane. This vesicle can then carry its content anywhere within the cell.
Understanding the Cell Cycle: G1, S, and G2 Phases
- Interphase
- G1 Phase: Major cell growth occurs.
- S Phase: Involves the replication of DNA.
- G2 Phase: Cell grows further and makes preparations for mitosis.
Cellular Transport: Endocytosis and Exocytosis
Both endocytosis and exocytosis are vital cellular processes that occur in cells to move larger molecules across the plasma membrane. "Endo" means inside, and "exo" means outside.
| Endocytosis | Both | Exocytosis |
|---|---|---|
| Allows macromolecules to ENTER the cell. |
| Allows molecules to EXIT the cell. |
Prokaryotic Cell Division: Binary Fission
Prokaryotes divide through a process called binary fission. The steps are:
- DNA is copied.
- Two daughter chromosomes attach to different regions on the plasma membrane.
- The cell divides into two genetically identical daughter cells.
Key Proteins and Cholesterol in Cell Membranes
- Protein Channel: Facilitates active transport of substances not handled by integral proteins.
- Integral Protein: Involved in active transport, particularly of ions.
- Peripheral Protein: Primarily used for inter-cell communication.
- Cholesterol: Essential for maintaining cell shape and membrane fluidity.
Therapeutic Cloning: Somatic Cell Nuclear Transfer
Therapeutic cloning involves a procedure also known as somatic cell nuclear transfer (SCNT). In this procedure, a researcher extracts the nucleus from an egg, which contains the genetic material. Scientists also take a somatic cell (a body cell other than an egg or sperm), extract its nucleus, and inject it into the enucleated egg. The egg, now containing the new genetic material, is stimulated to divide, forming a blastocyst with an outer and inner layer. The cells in the inner layer are rich in stem cells and are subsequently isolated for therapeutic purposes.
Cancer Formation: Uncontrolled Cell Division
Cancer forms due to uncontrolled cell division that can occur in any organ or tissue. This uncontrolled growth forms a ball of cells, known as a tumor, which can potentially spread to other areas of the body (metastasis).
Mitosis Results: Two Identical Daughter Cells
The primary result of mitosis is the formation of two genetically identical daughter cells from a single parent cell.