Cell Biology and Genetics

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Cell Biology and Genetics

• Chapter 3

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The Cell

• The smallest unit of life
• Anything less than a cell is not living
• Cells come from preexisting cells
• Connect together to form tissues
• Many different sizes and shapes
• Most cells have many of the same structures
• All have a cell membrane

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The cell (plasma) membrane functions

• Encloses cell contents
• Supports the cell
• Attaches to other cells
• Recognizes substances
• Regulates what moves in and out of the cell

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Cell membrane structure (fluid-mosaic model)

• Made mainly of lipids (phospholipids) and
  proteins
• The lipid forms the main barrier and is made of 2
  layers of lipid (lipid bilayer)
• The proteins are scattered throughout the lipid
  bilayer and have various functions
• Cholesterol is also in cell membranes and
  function to make it more rigid

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Cell membrane proteins functions

• The membrane is dynamic, not static
• Transport
• Pores
• Receptors
• Enzymes
• Structural

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Movement across the cell membrane

• Move things in and out of the cell
• Move nutrients, minerals, water, etc. in
• Move toxins/wastes out
• Selectively permeable

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Methods used to move substances across the cell
membrane

• Simple diffusion
• Facilitated diffusion
• Active transport
• Endocytosis/Exocytosis
• Osmosis

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Simple diffusion in general

• The tendency for things to move from an area of
  high concentration to an area of low
  concentration
• Occurs naturally
• No energy needed, molecules naturally move this
  way
• Molecules move until they reach equilibrium

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Simple diffusion in cells

• No cellular energy used
• No carrier proteins needed
• Moves from an area of high concentration to an
  area of low concentration
• Molecules move through the lipid bilayer

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Facilitated diffusion

• No cellular energy used
• Carrier proteins are needed
• Moves from an area of high concentration to an
  area of low concentration
• Molecules are carried across the membrane by
  carrier proteins or, move through protein pores

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Active transport

• Cellular energy is used
• Carrier proteins are needed
• Moves from an area of low concentration to an
  area of high concentration
• Molecules are carried across the membrane by
  carrier proteins

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Endocytosis/Exocytosis

• Moves large pieces of material into (endocytosis)
  or out of (exocytosis) the cell
• Uses cellular energy (active transport)
• Moves high to low or, low to high
• Uses cellular proteins (receptors)
• Cell membrane forms a pocket containing the
  substance to be moved
• The pocket (containing substance) pinches off on
  the opposite side of the cell membrane

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Osmosis

• Movement of water across the membrane (Simple
  diffusion)
• No cellular energy
• No protein carriers
• From an area of high concentration to an area of
  low concentration
• Important in our bodies
• Osmotic pressure is pressure caused by water

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Osmosis continued

• Water moves from high to low
• Pure water is a higher concentration than water
  containing a solute because the solute takes up
  space
• Water will always move toward the higher
  concentration of solute (salt, sugar, proteins,
  etc.)

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Osmosis types of solutions

• If the solution has a higher concentration of
  solute than in the cell it is called hypertonic
• If the solution has a lower concentration of
  solute than in the cell it is called hypotonic
• If the solution has the same concentration of
  solute than in the cell it is called isotonic
• Isotonic is necessary to prevent cell death or
  damage

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Osmosis effects of different solutions

• Hypertonic
• Water will be drawn out of the cell
• Cell will dehydrate and die
• Hypotonic
• Water will be drawn into the cell
• Cell will swell and burst (lyse)
• Isotonic
• No net movement of water

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Questions

• If a blood cell contains 10 salt and the fluid
  around it contains 17 salt
• What kind of solution is this?
• What will happen to the cell?

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Cell structures cytoplasm

• Everything outside the nucleus
• Contains organelles (tiny organs) and cytosol
  (fluid)
• Cytosol
• Fluid portion
• Water, ions, dissolved molecules
• Cytoskeleton
• Supports the cell and holds organelles in place
• Can change the shape of the cell
• Made of microtubules and microfiliments

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Organelles

• Tiny organs
• Structures within the cell that perform specific
  functions
• Most have membranes similar to the cell membrane
• The membranes function to separate the organelles
  from the rest of the cell and to provide
  increased surface area for enzymes
• The number and type of organelles depends on the
  type of cell

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The nucleusin most cells

• Usually the largest organelle
• Surrounded by a double membrane with nuclear
  pores
• Contains the chromosomes (Genetic material, DNA)
• Contains nucleoli, where RNA is synthesized

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Ribosomes

• The site of protein synthesis
• Made of protein and RNA
• May be unattached (free) or attached to the
  Endoplasmic reticulum

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Endoplasmic reticulum (ER)

• A network of membranes in the cell
• Rough ER
• Has ribosomes attached which give it a rough
  appearance
• Ribosomes make proteins insert them into
  membranes to be secreted out of the cell
• Smooth ER
• Has no rbosomes
• Makes new lipids

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Golgi apparatus (complex)

• A stack of flattened membranes in the cell
• Modifies, packages, distributes products made
  in the cell
• Packages products in vesicles sends them out of
  the cell or to the properlocation in the cell

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Lysosomes

• Vesicles in the cell that contain digestive
  enzymes
• Digest large molecules brought into the cell

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Mitichondria

• Provide energy (ATP) for the cell by breaking
  down food molecules
• Has a smooth outer membrane
• And, a highly folded membrane
• Foldings are called cristae
• Foldings increase surface area and provide more
  space for enzymes to attach
• Within the inner membrane is a fluid-filled space
  containing more enzymes called the matrix
• Cells with high energy requirements, like muscle
  cells, have many mitochondria

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Centrioles

• Cylinders of microtubules
• Two in each cell
• Help in cell division

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Flagella and cilia

• Flagella
• Long whip-like structure
• For motility
• On sperm
• Cilia
• Short hair-like structures
• Usually numerous
• Motility
• Move substances through tubes

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