Cell Structure

1
Cell Structure Function

• Unit III
• Chapter 7

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The History of the Microscope

• In the 1600s, Dutch businessman Anton van
  Leeuwenhoek became on of the first people to us a
  microscope to study nature
• In 1665, English physicist Robert Hooke used one
  of the first light microscopes to look at thin
  slices of plant tissue
• Under the microscope, the cork he was looking at
  seemed to be made of thousands of tiny chambers
  that he dubbed cells
• Before long, it became apparent that cells were
  the basic unit of life

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The Cell Theory

• The collective discoveries of many biologists are
  summarized in the cell theory
• The cell theory states the following
• All living things are composed of cells
• Cells are the basic units of structure and
  function in living things
• New cells are produced from existing cells

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Types of Cells

• Biologists divide cells into 2 categories
  eukaryotes and prokaryotes
• Prokaryotes
• Generally smaller and simpler than eukaryotes
• Do not contain nuclei (no nucleus)
• Example all bacteria are prokaryotes
• Eukaryotes
• cells have nucleus
• contain dozens of specialized structures (called
  organelles)
• Example all plants, animals, and fungi are
  eukaryotes

Prokaryote cell
Eukaryote cell
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Cell Structures Cell Membrane

• The cell membrane is a thin, flexible barrier
  around the cell that is selectively permeable
• The main function of the cell membrane is to
  regulate what enters and leaves the cell and also
  to provide protection and support
• The core of the cell membrane is a double-layered
  sheet called a lipid bilayer
• Most cell membranes also contain protein
  molecules that run through the lipid bilayer
  (form channels pumps to help move material
  across the cell membrane)
• Carbohydrate molecules form chains that are
  attached to the outer surfaces of these proteins
  (act like chemical identification cards
  allowing cells to identify one another)

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The Cell Membrane
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Cell Structures Cell Wall

• Cell walls are found in many organisms,
  including
• Plants
• Algae
• Fungi
• Nearly all prokaryotes
• ANIMAL CELLS DO NOT HAVE CELL WALLS
• The main function of the cell wall is to provide
  support and protection for the cell
• Most cell walls allow water, oxygen, carbon
  dioxide, and other substances to pass through
  them
• Plant cell walls are made of cellulose

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Cell Structures Nucleus

• Found only in eukaryotic cells
• The function of a cell nucleus is to
• Control most cell processes
• Contain the hereditary information of DNA
  contains nearly all of a cells DNA

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Cell Structure Chromatin Chromosomes

• The granular material visible within the nucleus
  is called chromatin
• Consists of DNA bound to protein
• Most of the time, chromatin is spread throughout
  the nucleus
• When cells divide, chromatin condenses to form
  chromosomes
• These threadlike structures contain the genetic
  information that is passed from once cell to the
  next

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Cell Structure Nucleolus Nuclear Envelope

• Most nuclei contain a small, dense region known
  as the nucleolus
• This is the site where the assembly of ribosomes
  begins
• The nucleus is surrounded by a double-membrane
  layer called the nuclear envelope
• Contains thousands of pores which allow material
  to move into and out of the nucleus

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Cell Structures Cytoskeleton

• The cytoskeleton of a cell is a network of
  protein filaments that helps the cell maintain
  its shape
• Also involved in many forms of cell movement
• The cytoskeleton is made up of microtubules and
  microfilaments
• Microtubules hollow tubes of protein that help
  maintain cell shape help to separate
  chromosomes during cell division
• Microfilaments long, thin fibers that function
  in the movement and support of the cell helps
  to move the organelles within the cell

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Organelles in the Cytoplasm

• The cytoplasm contains many important structures
  known as organelles
• Ribosomes
• Endoplasmic reticulum
• Golgi apparatus
• Lysosomes
• Vacuoles
• Chloroplasts
• mitochondra

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Ribosomes

• Ribosomes are the site of protein synthesis
  within the cell
• The site where proteins are assembled following
  coded instructions that come from the nucleus

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Endoplasmic Reticulum

• The endoplasmic reticulum is the organelle in
  which components of the cell membrane are
  assembled and some proteins are modified
• Rough Endoplasmic Reticulum the part of the ER
  that is involved in the synthesis of proteins
  has ribosomes on its surface
• Smooth Endoplasmic Reticulum do not have
  ribosomes on its surface contains enzymes that
  function in the synthesis of lipids

Rough ER
Smooth ER
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Golgi Apparatus

• Enzymes in the golgi apparatus attach
  carbohydrates and lipids to proteins
• From the golgi, proteins are sent to their final
  destination

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Lysosomes

• Lysosomes are small organelles filled with
  enzymes
• Lysosomes break down lipids, carbohydrates, and
  proteins for use by other parts of the cell
• Lysosomes also remove debris that might otherwise
  clutter up the cell
• known as the garbage disposals of the cell

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Vacuoles

• Vacuoles are found only in eukaryotic plant cells
• Plant cells often store materials such as water,
  salts, proteins, and carbohydrates in saclike
  structures called vacuoles
• Many plant cells have a single large, central
  vacuole filled with liquids
• Pressure in these central vacuoles allow plants
  to support heavy structures such as leaves
  flowers

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Chloroplasts

• Chloroplasts are found in plants and some other
  organisms
• Chloroplasts use energy from the sunlight to make
  energy-rich food molecules by photosynthesis

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Mitochondria

• Mitochondria are the site of ATP (energy)
  production in the cell
• Mitochondria use energy from food to make
  high-energy compounds that the cell can use for
  power

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Types of Solutions

• All of the components of a solution are evenly
  distributed throughout the solution
• The substance that is dissolved is the solute
• The substance in which the solute is dissolved is
  the solvent
• Example salt/water mixture salt is the solute
  and water is the solvent
• A solution may be
• Hypertonic
• Hypotonic
• Isotonic

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Types of Solutions

• A hypertonic solution is one in which there are
  more solutes (particles) than solvent (liquid)
• A hypotonic solution is one in which there is
  less solute (particles) than solvent (liquid)
• An isotonic solution is one in which there is an
  equal solute/solvent ratio
• NOTE the terms hyper, hypo, iso are referring to
  the outside environment in which something is
  placed

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Movement of Molecules in Solution

• A cell placed in an isotonic solution will remain
  the same as when it was put into the solution
• This is known as equilibrium
• If a cell is placed in a hypertonic solution
  (i.e. more salt in the solution than is inside
  the cell), the net movement of water will be OUT
  of the cell and the cell will SHRINK
• Because osmosis moves water from an area where
  there is more water to an area where there is
  less water
• If a cell is placed in a hypotonic solution (i.e.
  less salt in the solution than is inside the
  cell), the net movement of water will be INTO the
  cell and the cell will swell and burst
• Because osmosis moves water from an area where
  there is more water to an area where there is
  less water

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Movement Through the Membrane

• The cell membrane regulates what enters and
  leaves the cells and also provides protection and
  support (a.k.a. selectively permeable to certain
  substances)
• The core of nearly all cell membranes is a
  double-layered sheet called a lipid bilayer
• The 2 types of movement that can occur across a
  cell membrane are
• Passive transport does not require energy
• Osmosis, diffusion, facilitated diffusion
• Active transport requires energy
• Endocytosis, exocytosis, phagocytosis

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Passive Transport

• Passive transport is the diffusion (movement) of
  a substance across a membrane where NO ENERGY is
  used
• In a solution, molecules move constantly! The
  molecules tend to move from an area where they
  are more concentrated to an area where they are
  less concentrated (a process known as diffusion)
• Diffusion causes many substances to move across a
  cell membrane from an area of higher
  concentration to an area of lower concentration
  but does NOT require the cell to use energy
• Alcohol
• Water
• Small lipids

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Osmosis

• Osmosis is the diffusion of WATER through a
  selectively permeable membrane
• Although water molecules move in both directions
  across the membrane, there is a net movement of
  water into the compartment containing the most
  solutes (i.e. least water)
• Since osmosis is a form of passive diffusion, it
  requires NO energy
• Water will move across a membrane until
  equilibrium is reached

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Osmosis
(more sugar)
(more water)
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Facilitated Diffusion

• Some molecules are too large to cross the lipid
  bilayer of the cell membrane but do diffuse
  through protein channels found within the lipid
  bilayer of the cell membrane
• This process is known as facilitated diffusion
• Facilitated diffusion is the movement of specific
  molecules across a cell membrane through protein
  channels
• This process occurs WITHOUT energy and the net
  movement of the molecules will be from an area of
  higher concentration to an area of lower
  concentration

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Active Transport

• Often, material needs to move across a cell
  membrane against a concentration gradient
• Active transport is the movement of materials
  across a membrane from an area of lower
  concentration to an area of higher concentration
• Active transport REQUIRES energy
• endocytosis
• phagocytosis
• exocytosis

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Endocytosis

• Endocytosis is the process by which a cell takes
  material into the cell by infolding of the cell
  membrane
• Endocytosis is a form of ACTIVE TRANSPORT and
  requires energy

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Phagocytosis

• When large particles are taken into the cell by
  endocytosis, the process in known as phagocytosis
• Phagocytosis is the process in which extensions
  of cytoplasm surround and engulf large particles
  and take them into the cell
• Phagocytosis is a form of endocytosis
• Phagocytosis is a form of ACTIVE TRANSPORT and
  therefore REQUIRES energy

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Exocytosis

• Exocytosis is a process by which a cell releases
  large amounts of material
• During exocytosis, the membrane of the vacuole
  surrounding the material fuses with the cell
  membrane, forcing the contents out of the cell
• Exocytosis is a form of ACTIVE TRANSPORT and
  REQUIRES energy