A View of the cell Ch. 7

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A View of the cellCh. 7
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• Before the microscope, many believed that
  diseases were caused by curses and supernatural
  spirits.

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• Microscopes enabled scientists to view and study
  cells, the basic units of living organisms.

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• The first microscope was used by van Leeuwenhoek
  in the 1600s and it is considered a simple light
  microscope because it had only one lens.

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• Over the next 200 years, microscopes improved by
  grinding higher quality lenses. The compound
  microscope was also developed, which uses a
  series of lenses to magnify objects in steps.

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• Compound light microscopes can view objects up to
  about 1500 times their actual size.

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• Robert Hooke used a compound light microscope to
  study cork, the dead cells of Oak bark.
• He observed small geometric shapes like boxes
  which he called cells.

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• This and other discoveries gave rise to the Cell
  Theory, one of the fundamental ideas of modern
  biology.

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The Cell Theory

• 1. All organisms are composed of one or more
  cells.
• 2. The cell is the basic unit of structure and
  organization of organisms.
• 3. All cells come from preexisting cells.

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• In the 1930s and 1940s the electron microscope
  was developed . It uses a beam of electrons
  instead of light and can magnify up to 500,000
  times.

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• With better microscopes scientists observed that
  all cells contain small, specialized structures,
  called organelles.

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• Cells can be divided into two broad groups those
  that contain membrane bound organelles and those
  that do not.
• These are called prokaryotes and eukaryotes

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• Prokaryotes are cells that do not contain
  membrane bound organelles.
• Ex. Unicellular organisms such as bacteria.

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• Eukaryotes are cells that contain membrane-bound
  organelles.
• Ex. Most multicellular organisms are made up of
  eukaryotic cells. Also amoeba and some yeast and
  algae.

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• Eukaryotes are larger and contain a true nucleus.
  
• They can carry out numerous metabolic chemical
  reactions at the same time.

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• The plasma membrane maintains a state of balance
  in the cell by controlling the flow of nutrients
  into the cell and a flow of waste out of the
  cell. It does this through a process of selective
  permeability.

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• The plasma membrane is composed of a phospholipid
  bilayer which is a lipid where one of the fatty
  acids has been replaced by a phosphate group.

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• The polar phosphate group allows the cell
  membrane to interact with its watery environment
  because water itself is polar.
• The fatty tails avoid water.

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• When the phospholipid molecules come together to
  form this sandwich, a barrier is created that
  is water-soluble at its outer surfaces and water
  insoluble in the middle.

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• Water-soluble molecules will not easily move
  through the membrane because they are stopped by
  the water-insoluble layer.

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• This model is called the fluid mosaic model.
• The proteins create a mosaic or pattern with the
  phospholipids like boats with their decks above
  water and hulls beneath it.

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• Cholesterol is found in the cell membrane where
  it helps stabilize the phospholipids by keeping
  them from sticking together.

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• Transport proteins move needed substances or
  waste materials through the plasma membrane.
• Other proteins play a role in attaching the cells
  inner structure to the membrane and help the cell
  identify chemical signals.

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• All plant cells have a cell wall which gives
  support and protection to the cell. It is a
  cellulose mesh which is highly permeable.
• Fungi, bacteria, and some protists also have a
  cell wall.

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• The master set of directions for making proteins
  is found in chromatin, which are strands of DNA
  found in the nucleus.

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• The nucleolus is found inside the cell nucleus
  and makes ribosomes.
• Ribosomes are the sites where the cell produces
  proteins according to the directions of DNA.

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• Cytoplasm is the clear, gelatinous fluid within a
  cell which holds all the organelles as well as
  nutrients and waste waiting for export.

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• The endoplasmic reticulum is the site of cellular
  chemical reactions. It is folded up like an
  accordion and thus fits into a small space.

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• The golgi apparatus is a flattened stack of
  tubular membranes that modify proteins made by
  the ribosomes, which sort and package proteins
  like mail at the post office.

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• Vacuoles are temporary storage compartments used
  to store food, enzymes, and other materials.
• Most animal cells dont contain vacuoles.

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• Lysosomes are organelles that contain digestive
  enzymes. They digest excess or worn out
  organelles, food particles and engulfed viruses
  or bacteria.

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• The cell requires a large amount of energy to
  perform all its vital functions.
• Two organelles chloroplasts and mitochondria
  provide this energy.

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• Chloroplasts are organelles in plant cells that
  contain chlorphyll and capture light energy and
  convert it to chemical energy.
• They contain a double membrane which contains the
  stroma and grana which help trap the suns energy.

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• Mitochondria are organelles in plant and animal
  cells that transform energy for the cell and
  store it in the bonds of other molecules.

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• Mitochondria can occur in varying numbers
  depending on the cells function.
• Liver cells can hold up to 2000 mitochondria.

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• The cytoskeleton forms a framework for the cell
  like the skeleton. Microtubules and
  microfilaments, that can be dismantled and
  reassembled elsewhere, make up the cytoskeleton.

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• Centrioles are organelles found in animal cells
  and aid in cell division.
• Cilia and flagella are organelles on the surface
  of the cell that are made of microtubules and aid
  in locomotion and feeding

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• Cilia are short numerous and look like hairs.
  They move like oars in a rowboat.
• Flagella are longer and move in a whip-like
  motion. Cells have only one or two flagella.