Cell

• • The three scientists who contributed to the development of cell theory are Matthias Schleiden, Theodore Schwann, and Rudolf Virchow.
• By the late 1830s, botanist Matthias Schleiden and zoologist Theodore Schwann were studying tissues and proposed the unified cell theory.
• The generally accepted portions of the modern Cell Theory are as follows:

  • The cell is the fundamental unit of structure and function in living things.
  • All organisms are made up of one or more cells.
  • Cells arise from other cells through cellular division.
• The expanded version of the cell theory can also include:

  • Cells carry genetic material passed to daughter cells during cellular division
  • All cells are essentially the same in chemical composition
  • Energy flow (metabolism and biochemistry) occurs within cells.
• According to the Cell Theory, cells are the basic unit of life, meaning it is the smallest living entity that exhibits the characteristics of life (reproduction, metabolism, homeostasis, etc.).
• Inside every living cells are small structures or compartments called organelles. These organelles may be grouped together according to the role they play inside the cell. Some organelles function for protection, genetic control, energy processing, breakdown and storage, manufacture and distribution, and structural support and communication.
• Microscopes were invented in 1590 and further refined during the 1600s. Cell walls were first seen on dead cells of oak bark by Robert Hooke in 1665 and living cells by Antoni van Leeuwenhoek a few years later.
• In a light microscope (LM), visible light is passed through the specimen and through glass lenses.
• Magnification is the ratio of an object's image size to its real size.
• Resolution is the measure of the clarity of the image; it is the minimum distance two points can be separated and still be distinguished as separate points.
• Contrast is the difference in brightness between the light and dark areas of an image. Methods for enhancing contrast include staining or labeling cell components to stand out visually.
• organelles are the membrane-enclosed structures within eukaryotic cells.
• Rather than focusing light, the electron microscope (EM) focuses a beam of electrons through the specimen or onto its surface.
• Cells-the basic structural and functional units of every organism-are two distinct types: prokaryotic and eukaryotic.
• Organisms of the domain Bacteria and Archaea consist of prokaryotic cells.
• Organisms of the domain Eukarya-protists, fungi, animals and plants-all consist of eukaryotic cells.
• All cells share certain basic features: They are all bounded by a selective barrier, called the plasma membrane (or the cell membrane)
• Inside all cells is a semifluid, jellylike substance called cytosol, in which subcellular components are suspended. All cells contain chromosomes, which carry genes in the form of DNA.
• All cells have ribosomes, tiny complexes that make proteins according to instructions from the genes.
• A major difference between prokaryotic and eukaryotic cells is the location of their DNA.
• In a eukaryotic cell, most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane
• In a prokaryotic cell, the DNA is concentrated in a region that is not membrane-enclosed, called the nucleoid.
• Eukaryotic means "true nucleus"
• Prokaryotic means "before nucleus"
• The interior of either type of cell is called the cytoplasm; in eukaryotic cells, this term refers only to the region between the nucleus and the plasma membrane. Within the cytoplasm of a eukaryotic cell, suspended in cytosol, are the variety of organelles of specialized form and function
• Eukaryotic cells are generally much larger than prokaryotic cells
• The smallest cells known are bacteria called mycoplasmas
• The plasma membrane functions as a selective barrier that allows passage of enough oxygen, nutrients and wastes to service the entire cell
• Larger organism do not generally have larger cells than smaller organisms-they simply have more cells
• Such cells may have long, thin projections from their surface called microvilli, which increase surface area without an appreciable increase in volume.
• The plasma membrane and organelle membranes also participate directly in the cell's metabolism because many enzymes are built right into the membranes.
• Flagella: are microscopic hair-like structures involved in the locomotion of a cell. The word “flagellum” means “whip”.
• Endoplasmic Reticulum (ER): network of membranous sacs and tubes; active in membrane synthesis and other synthetic and metabolic processes; has rough (ribosome-studued) and smooth regions.
• Centrosome: region where the cell's microtubules are initiated; contains a pair of centrioles
• Nuclear envelope: double membrane enclosing the nucleus; perforated by pores; continuous with ER
• Nucleolus: nonmembranous structure involved in production of ribosomes; a nucleus has one or more nucleoli
• Chromatin: material consisting of DNA and proteins; visible in a dividing cell as individual condensed chromosomes
• Plasma Membrane: membrane enclosing the cell
• Ribosomes (small brown dots): complexes that make proteins; free in cytosol or bound to ER or nuclear envelope
• Golgi apparatus: organelle active in synthesis, modification, sorting, and secretion of cell products