Cell Structure and Function: A Comprehensive Look
The Cell: Vital Unit of All Life
The cell is the vital unit, anatomical, functional, and breeding unit of all life.
Basic Components
- Atom: Small particle made up of electrons.
- Molecule: Formed by the interaction of several atoms.
Bioelements
Elements found in living beings:
- Main: Present in greater proportion in the cell.
- Secondary: Present in smaller proportion in the cell.
- Trace elements: Present in very small proportion in the cell.
Biomolecules
Molecules formed in living beings:
- Carbohydrates: Molecules made up of C, H, O, and degraded for energy.
- Monosaccharides: A single sugar molecule, such as glucose.
- Disaccharides: Formed by two sugar molecules.
- Polysaccharides: Formed by more than ten sugar molecules.
- Lipids: Macromolecules consisting of C, H, O, P, and fatty oils.
- Nucleic acids: Store genetic information of all living beings.
- Proteins: Formed by amino acids and express DNA information.
- Enzymes: Responsible for chemical bonds and degrading substances.
Classification of Cells
Prokaryotes
- Have a cell membrane and cytoplasm.
- Only present cellular organelles are ribosomes.
- Circular and single-stranded DNA.
- DNA is dispersed in the cytoplasm, i.e., not enclosed in the cell nucleus.
- Many enzymes in the cytoplasm are responsible for hundreds of chemical reactions.
Eukaryotes
- Composed of three main parts: cell membrane, cytoplasm, and cell nucleus.
- DNA is a double-stranded molecule, arranged in a helical shape.
- DNA is enclosed in a cell nucleus.
Cell Membrane
The cell membrane is a structure formed of a lipid bilayer, which has selective permeability and is the major barrier between the extracellular and the intracellular environments.
- Formed by: 55% protein, 25% phospholipids, 13% cholesterol, 4% other lipids, and 3% carbohydrates.
- Consists of a lipid bilayer of phospholipids.
- Cholesterol is found along the bilayer.
- Protein membrane constituents are of two types: integral (crosses the phospholipid bilayer) and peripheral (on the surface of the membrane).
- Carbohydrates are almost always found mostly on the outer cell surface.
Cytoplasm
The cytoplasm is the internal portion of the cell containing the intracellular environment and cell organelles, except the cell nucleus.
Cell Nucleus
The cell nucleus is a spherical organelle with a nuclear envelope. Inside it is DNA, which contains the genetic information of all living beings.
Plastids – Chloroplasts
Plastids are organelles characteristic of plant cells. Chloroplasts are the cellular organelles where photosynthesis takes place. They have their own DNA and can be classified into different types, including chloroplasts.
Mitochondria
Mitochondria are cylindrical and elongated organelles that have their own DNA. They are responsible for energy production (ATP).
Endoplasmic Reticulum
The endoplasmic reticulum is a network of channels and tubules that extend throughout the cytoplasm. It has a simple membrane that connects with the nuclear membrane and possesses storage tanks. The endoplasmic reticulum can be smooth or rough.
Golgi Apparatus
The Golgi apparatus is a set of flattened saccules derived from invaginations of the nuclear membrane or rough endoplasmic reticulum, which are stacked one above the other.
Lysosome
Lysosomes are vesicles in the cytosol separated by a single membrane.
Vacuole
A vacuole is a cavity surrounded by a membrane that is in the cytoplasm of cells, mainly in plant cells.