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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