Chapter 2 Structure and function of cells

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Chapter 2Structure and function of cells

• Plasma membrane
• Movement (diffusion/Osmosis)
• Surface area to volume ratio
• Organelles
• Tissues/Organs

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Plasma membrane
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Environments of cells

• All cells exist in a watery environment
  extracellular fluid
• Mullticellular organisms have an outer layer that
  acts as a barrier and creates an internal
  environment

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Aspects of the internal environment that need to
be regulated

• Salt concentrations
• Temperature
• Levels of nutrients
• pH
• Removal of wastes
• Ion concentrations

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• CELL MEMBRANE
• The role of the membrane is very important in
  maintaining cell stability and enabling the cell
  to operate at optimum levels.

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• The cell membrane (plasma membrane),
• - selectively controls the molecules entering
  leaving the cell.
• - allows the cytoplasm to have a different
  composition from the the surrounding environment

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Membrane Structure.

• The membrane is partially permeable. Some
  substances pass freely across the membrane while
  others are excluded.

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Phosopholipid bi-layer

• The cell membrane is formed from a double layer
  of lipids with proteins embedded in it forming
  ion channels.
• The lipid layer is capable of much movement, i.e.
  it is fluid.
• Cholesterol molecules reduce the membrane
  fluidity
• It is impermeable to water soluble substances.
• Lipid soluble substances e.g. alcohol pass
  through.

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Hydrophobic, water hating end
Hydrophillic, water loving end
When in contact with an aqueous solution, the
phospholipid molecules line up with tails
pointing in (away from sol)
EXAMPLE! Detergents cause fats to form micelles.
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Protein Channels

• These are large proteins with openings on both
  sides of the membrane.
• Allow flow of
• ions

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• Carbohydrates on the outer surface
  are important in cell
  adhesion and cell recognition.
  These are attached to recognition proteins.

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(1) Fluid (2) Mosaic Model (Draw)
Carbohydrate
Embedded protein
Phospholipid Bilayer
Protein channel
Embedded Cholesterol
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Movement into and out of the cell
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Movement in and out of Cell

• Diffusion (simple)
• Osmosis
• Facilitated diffusion
• Active Transport
• Endocytosis and Exocytosis

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Diffusion (simple)
Where? What? Energy?
Through the phospholipid bilayer small uncharged particles (water, urea, Oxygen, carbon dioxide) lipid soluble substances such as alcohol, ether, chloroform. NO

• Comments Moves down Con gradient (high to low)
  The diffusion rate increases with a high
  concentration gradient, heat, small particles and
  with gaseous substances. Movement is from a
  strong solution to a weak solution. (think sugar
  cube /water) (lungs, CO2)

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Osmosis
Where? What? Energy?
Through the phospholipid bilayer Water only NO

• Comments Osmosis is a special type of diffusion.
  The process is the same but only water moves to
  even up concentrations. Movement of water is from
  a weak solution into a strong solution.
• Example water from the gut (diarrhoea)
• Cell wall in plants

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Diffusion across the (partially permeable)
membrane.
1
2
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Active Transport.
Where? What? Energy?
Through the protein molecules spanning the membrane. Nutirent molecules, ions such as chloride ions (Cl-), sodium ions (Na), potasssium ions (K) and water Yes

• Comments Active transport is movement against
  the concentration gradient to build up rather
  than toeven up.

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Bulk Transport (endocyctosis and exocytosis).
Where? What? Energy?
Small sections of the plasma membrane. Large molecules such as enzymes, hormones and antibodies and foreign material. YES

• Comments Phagocytosis (solids - cell eating) and
  pinocytosis (cell drinking entry of liquid) are
  forms of endocytosis.

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Summary of common substances and their passage
through the cell membrane
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Surface area to volume ratio
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Surface area to volume ratio
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Organelles
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CELL THEORY

• All living things are made up of one or more
  cells.
• All cells are formed from pre-existing cells
  and these cells contain the hereditary
  information.
• The cell is the smallest organisational unit

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Organisation

• Atom /molecules ? cells ?
  tissues ? organs ? organ systems ?
  individual ? population and community ?
  ecosystem

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Properties of cells

• Most cells have some common features
• Plasma membrane
• Cytoplasm
• Nucleus
• Flagella or Cilia

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Types of cells

• There are two types of cells
• Organisms are grouped according to what type of
  cell they have
• Prokaryotes have cells that do not have a
  membrane surrounding the nucleus and lack most
  organelles (unicellular or simple multicellular
  organisms - Bacteria, cyanobacteria) (pic pg
  23)
• Eukaryotes- have cells that are usually much
  larger and more complex than prokaryote cells.
  The nucleus is surrounded by a membrane and the
  cell contains organelles (protists, fungi, plants
  animals)

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Cell Organelles

• Overview

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Mitochondrion

• Cells require a continuous supply of energy.
• Organelles where
• food molecules are broken down.
• energy is released.
• The energy is then stored in other molecules that
  can power cell reactions easily.
• Mitochondria (plural) use when you refer to
  more than one mitochondrion.

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Nucleus

• Usually the largest organelle in the cytoplasm of
  a cell.
• Directs all the activities of the cell.
• Contains genetic blueprints for the operations of
  the cell.

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Centrioles

• Self-replicating organelles
• Made up of nine bundles of microtubules
• Found only in animal cells.
• Help in organizing cell division.

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Cell membrane

• Forms the outer boundary of the cell.
• Allows only certain materials to move into and
  out of the cell.
• Food, oxygen and water move into the cell through
  the membrane.
• Waste products also leave through the membrane.
• Cells that perform photosynthesis (plants and
  some protists) take in carbon dioxide through the
  cell membrane instead of oxygen.

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Cell wall

• The cell wall is a rigid structure outside the
  cell membrane that supports and protects the cell
  (for plants, fungi, and some protists and
  bacteria but NOT animals).
• Animal cells DO NOT have a cell wall.
• The cell wall is made of tough cellulose fibres
  and other materials made by the cell.
• Note fungal cell walls contain chitin instead of
  cellulose.

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Cytoplasm

• Gel-like material inside the cell membrane and
  outside the nucleus.
• Cytoplasm is the jelly-like material inside the
  cell (but unlike gelatin it does flow cytoplasm
  constantly moves or streams.
• Contains a large amount of water (cytosol) and
  many chemicals and structures that carry out the
  life processes in the cell.
• The structures that the cytoplasm contains are
  called organelles.

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Endoplasmic reticulum

• A folded membrane that moves materials around in
  the cell.
• Extends from the nucleus to the cell membrane and
  takes up quite a bit of space in some cells.
• Two different types Smooth ER and Rough ER.
  Rough ER has ribosomes attached to its outer
  membrane, while Smooth ER does not.

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Golgi bodies

• Golgi bodies package and move proteins
• In a business, products are made, packaged, and
  moved to loading docks to be carried away.
• In cells, structures called Golgi Bodies are
  stacks of membrane-covered sacs that package and
  move proteins to the outside of the cell.
• When something is secreted, it is given off by
  the cell.
• Note Golgi Bodies are sometimes referred to as
  Golgi Apparatus.

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Vesicle

• Vesicles transport proteins.

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Chloroplasts

• Chloroplasts take in sunlight, water and carbon
  dioxide to make oxygen and sugar.
• This process is called photosynthesis.
• A plant's chloroplasts convert light energy into
  chemical energy.
• Contain a green pigment called chlorophyll. This
  is what makes plants green.

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Vacuole

• Acts as a temporary storage space for the cell.
• Vacuoles store water, food, pigments, waste or
  other materials.
• Vacuoles are large in plant cells and small in
  animal cells.
• Vacuoles can also be found in fungi and protists.

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Lysosomes

• An active cell constantly produces waste
  products.
• Contain chemicals (enzymes) that
• digest wastes and worn-out cell parts
• break down food.

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Ribosome

• One chemical that takes part in nearly every cell
  activity is protein.
• Proteins are needed for chemical reactions that
  take place in the cytoplasm.
• Cells make their own proteins on small structures
  in the cytoplasm called ribosomes.

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Cilia and Flagella

• For single-celled eukaryotes, cilia and flagella
  are essential for the locomotion of individual
  organisms.
• In multicellular organisms, cilia function to
  move fluid or materials past an immobile cell as
  well as moving a cell or group of cells.
• Cilia lining nasal passage
• Sperm

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Microfilaments

• Solid rods made of globular proteins called
  actin and are common to all eukaryotic cells.
• Long chains of the molecules are intertwined in
  a helix to form individual microfilaments.
• Filaments are primarily structural in function
  and are an important component of the
  cytoskeleton, along with microtubules.

• In association with myosin, microfilaments help
  to generate the forces used in cellular
  contraction and basic cell movements.
• They enable a dividing cell to pinch off into
  two cells and are involved in amoeboid movements
  of certain types of cells.
• They also enable the contractions of muscle
  cells.

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Microtubules

• Straight, hollow cylinders are found throughout
  the cytoplasm of all eukaryotic cells
  (prokaryotes don't have them) and perform a
  number of functions.

• Gives structure and shape to a cell,
• Serve as conveyor belts moving other organelles
  through the cytoplasm
• Are the major components of cilia and flagella,
  and participate in the formation of spindle
  fibers during cell division (mitosis).
• These filaments are composed of linear polymers
  of tubulin, which are globular proteins, and can
  increase or decease in length by adding or
  removing tubulin proteins.

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Plant cell
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Animal cell
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Copy down the characteristics of cells in the 5
kingdoms pg 26HW - Q 1- 8