Cells

the discovery of cells

  • Robert Hooke: 1665; looked at cork (tree bark) under a microscope of sorts, noticed hollow compartments that looked like rooms in a monastery that were called “cells”
  • cell theory was developed by scientists Schleiden, Schwan, and Virehow; states that   * all organisms are made of cells   * all cells are produced by other living cells   * cells are the basic units of life
  • cells are the building blocks of all living organisms

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types of cells

  • all cells fall into one of two categories: prokaryotic cells and eukaryotic cells
  • prokaryotic cells (prokaryotes): cells that do not have a nucleus or membrane binding their organelles together   * eg. bacteria
  • eukaryotic cells (eukaryotes): cells that have a nucleus and membrane-bound organelles   * any organism that is not a prokaryote   * can be singular or multicellular   * plant cells are eukaryotes with chloroplasts, central vacuoles, and cell walls   * animal cells are eukaryotes with centrioles and lysosomes

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organelles (cell parts)

  • cytoskeleton: a network of protein fibers with many functions   * microtubules: long, hollow tubes used for cell shape, movement of organelles, manipulation of chromosomes during cellular division
  • nucleus: contains the cell’s genetic information   * DNA is contained in the nucleus and has the “instructions” for making proteins, it cannot leave the nucleus   * chromatin: spread out form of DNA which condenses into tightly-coiled chromosomes before cellular division   * RNA is used as a messenger because DNA can’t leave the nucleus   * nucleolus: inside the nucleus, responsible for making ribosomes
  • endoplasmic reticulum: an extensive network of folded membranes which produces the membranes of the cell and other organelles   * can be rough or smooth   * rough-- studded with ribosomes, looks lumpy under a microscope   * smooth--detoxifies drugs and poisons, synthesizes lipids

organelles in the cytoplasm

  • ribosomes: “factories” that make protein; made by the nucleolus and have two different subunits   * ribosomes on the rough endoplasmic reticulum make proteins destined to be exported from the cell or imbedded into the cell membrane   * ribosomes free in the cytoplasm make protein to be used within the cell, always imbedded into the cell membrane
  • golgi apparatus: layered stacks of membrane enclosed spaces that process, sort, and ship out proteins; alter proteins and send them on their way
  • vesicles: small bags from the endoplasmic reticulum used to transport proteins and substances to and from the golgi bodies
  • mitochondria: the powerhouse of the cell, responsible for making ATP (energy) through the process of cellular respiration
  • chloroplasts: found in plant cells, use CO2 and water to make sugar in photosynthesis
  • vacuole: found in plant cells, a fluid-filled sac used for storage of water, food molecules, ions, and enzymes   * central vacuole: found in plant cells, responsible for storing water, poisons, and some pigments of fruits and flowers; when it fills with water, it increases the cell’s turgor pressure     * should have high turgor pressure (keeps cell standing upright rather than wilting)   * contractile vacuole: found in protists, used to pump out excess water to prevent the cell from bursting
  • lysosomes: contain digestive enzymes to break down food, and defend against bacteria and viruses; can also recycle cell parts   * “suicide sacs”—programmed cell destruction
  • centrioles: found in animal cells, organize microtubules to form cilia and flagella   * cilia: microscopic hairs on the exterior surface of a cell; beat back and forth like oars for a boat, help move the cell and move materials around the cell   * flagella: whiplike tail for movement of the cell

cell membrane

  • cell membrane: selectively permeable substance which controls the passage of materials into or out of the cell   * selectively permeable: allows some but not all materials to pass
  • cholesterol: keeps the membrane more fluid   * carbohydrates attached serve as identification tags so cells can distinguish one cell from another

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the role of cells

  • “building blocks” of organisms   * every living being is built up of at least one cell; the human body contains trillions
  • give structure to the human body and its organs   * form bones and other organs that are critical to the structure of the human body
  • process nutrients from food and convert them to energy (ATP)   * through cellular respiration, we’re able to gain nutrients and energy from the food we consume
  • carry out specialized functions   * cells in each organ have a different set of functions from others, eg. fighting infections (white blood cells)

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