cell theory

• The cell theory states that all living things are made up of cells, the smallest unit of life.
• Dutch lens maker, Zacharias Jansen (1588- 1631), invented one of the microscope’s first prototypes.
• Robert Hooke (1635- 1703) reported some first clear drawings of the plant cells he had observed in thin cells of cork.
• Anton van Leeuwenhoek (1632- 1723) reported his discovery of blood cells, sperm cells, and a lively world of “animalcules” which were later found to be bacteria and protozoans.
• Robert Brown (1773- 1858) discovered the nucleus as a constant part of the plant cell.
• Felix Dujardin (1802- 1860) French Biologist, first recognized the living substance within the cell which he termed as sarcode.
• Matthias Schleiden (1804-1881) and Theodore Schwann (1810-1882) concluded that cells are the elementary particles of both plants and animals.
• German pathologist, Rudolf Virchow (1821- 1902) concluded that cell is the basic and structural unit of life and that every cell is formed from a preexisting cell.
• Certain structures in animal cells are not found in plant cells, and vice versa.
• Nerve cells may have structures not found in muscle cells.
• The nucleolus is a granular body within the nucleus, consisting of RNA protein, and is the site for ribosomal RNA synthesis and ribosome subunit assembly.
• The endoplasmic reticulum (ER) is a network of internal membranes extending through the cytoplasm, synthesizing lipids and modifying many proteins, and is the origin of intracellular transport vesicles that carry proteins.
• Chromosomes contain genes (units of hereditary information) that govern the structure and activity of the cell.
• The smooth ER lacks ribosomes on its outer surface, involved in lipid biosynthesis.
• The nucleus is a large structure surrounded by a double membrane, storing genetic information and synthesizing DNA and RNA.
• Chromosomes are composed of a complex of DNA and protein known as chromatin, and condense during cell division, becoming visible as rod-like chromosomes.
• The plasma membrane is the membrane boundary of the cell, enclosing cellular contents, regulating movement of material in and out of the cell, and helping maintain cell shapes.
• The rough ER has ribosomes studded on its outer surface, involved in the manufacture of many proteins destined for secretion or for incorporation into membranes.
• The modern Cell Theory includes three principles: all organisms are composed of one or more cells, cells are the basic unit of organization of all organisms, and all cells come from pre-existing cells.
• The cell wall is a structure that contains cellulose fibrils, found in plants, prokaryotes, fungi, and some protists, providing protection, maintaining cell shape, and preventing excessive uptake of water.
• Ribosomes are granules composed of RNA and protein, some attached to the ER, some free in the cytosol, and they synthesize polypeptides in both prokaryotes and eukaryotes.
• Cells arise only by division of a previously existing cell.
• Peroxisomes are membranous sacs containing a variety of enzymes and are the site of many diverse metabolic reactions.
• Plastids, such as chloroplasts, are double-membrane structures that enclose material in thylakoid membranes, and are the site of photosynthesis where chlorophyll captures light energy, ATP and other energy-rich compounds are formed, and then used to convert CO2 to glucose.
• The cytoskeleton consists of microtubules, microfilaments, and intermediatefilaments, which provide structural support, play a role in cell and organelle movement and cell division, and are components of cilia, flagella, centrioles, and basal bodies.
• Flagella are long projections made of two central and nine pairs of peripheral microtubules (9+2 structure), extend from the surface of the cell, covered by the plasma membrane, and are used for cellular locomotion by sperm cells and some unicellular eukaryotes.
• Cilia are relatively short projections extending from the surface of the cell, covered by the plasma membrane, and made of two central and nine pairs of peripheral microtubules (9+2 structure), used for movement of some single-celled organism and to move material on the surface of some tissues.
• Centrioles are a pair of hollow cylinders located near the nucleus, each consisting of 9 microtubule triplets (9x3 structure), and may anchor and organize microtubule formation in animal cells.
• Plant cells have cell walls that provide structure, chloroplasts for photosynthesis, and use mitochondria for energy production.
• Animal cells do not have cell walls, have many small vacuoles, use mitochondria for energy production, and have lysosomes, but plant cells do not.
• Vacuoles are membranous sacs (mostly in plants, fungi, and algae) that store materials, wastes, water, and maintain hydrostatic pressure.
• Mitochondria are sacs consisting of two membranes; the inner membrane is folded to form cristae and encloses matrix, and are the site of most reactions of cellular respiration and transformation of energy originating from glucose or lipids into ATP energy.
• Both animal and plant cells have cell membranes that enclose the cell, are filled with cytoplasm, a gel-like substance containing chemicals needed by the cell, have a nucleus where DNA is stored, have ribosomes, protein builders of cells, have mitochondria that use oxygen to breakdown food and release energy, have vacuoles that contain food, water, or waste products, have endoplasmic reticulum, where a system of tubes transports proteins, have Golgi bodies to distribute proteins outside of the cell, and have cell walls that provide structure.
• Lysosomes are membranous sacs (in animals) that contain enzymes to breakdown ingested materials, secretions, and wastes.
• The Golgi complex consists of stacks of flattened membrane sacs that modify proteins, package secreted proteins, and sort other organelles.