The cell is the basic structural and functional unit of life. Every living thing, such as humans, animals, plants, and bacteria, is made of cells. According to the Cell Theory, all living things are made of cells, the cell is the basic unit of life, and every new cell comes from an existing cell. This last idea is known as “Omnis cellula e cellula,” which was stated by Rudolf Virchow. The word “cell” was first used by Robert Hooke in 1665, when he looked at thin slices of cork under a microscope. The Cell Theory was first formulated by Schleiden and Schwann together. The nucleus was discovered by Robert Brown in 1831.
There are two main types of cells. A prokaryotic cell, such as a bacterium, has no true nucleus and has 70S ribosomes. A eukaryotic cell, such as a plant, animal, or fungal cell, has a true nucleus and membrane-bound organelles, and it has 80S ribosomes. The 80S ribosome is made of two subunits, 60S and 40S.
The plasma membrane controls what enters and leaves the cell. Its structure is explained by the Fluid Mosaic Model, proposed in 1972 by Singer and Nicolson. The nucleus contains the cell’s DNA (genetic material) and acts as the control center of the cell. Nuclear pores in the nuclear envelope allow materials like RNA and proteins to move between the nucleus and the cytoplasm.
Mitochondria are called the powerhouse of the cell because they produce ATP, the cell’s energy. The infoldings of the inner mitochondrial membrane are called cristae, and they increase the surface area for ATP production. Chloroplasts are found only in plant cells, and photosynthesis takes place in them. Mitochondria and chloroplasts are both double membrane bound and semiautonomous, which means they have their own DNA and ribosomes.
Ribosomes are the sites of protein synthesis. The rough endoplasmic reticulum looks “rough” because ribosomes are attached to its surface. The Golgi apparatus modifies, packages, and sorts proteins for secretion. It also tags enzymes meant for lysosomes with mannose-6-phosphate. Lysosomes are called the “suicidal bags” of the cell because they contain digestive enzymes that can break down the cell itself. Lysosomes were discovered by the Belgian scientist Christian de Duve, who later received a Nobel Prize for this work.
Plant cells differ from animal cells mainly because they have a rigid cell wall, chloroplasts, and a large central vacuole. Animal cells have only a plasma membrane. Apoptosis is the term for programmed cell death, a controlled process in which the body removes old or damaged cells.