Cell Boundaries

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Cell Boundaries

• Structure and Movement Across the Membrane

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Cell Wall

• Found in plants, algae, fungi, and many
  prokaryotes
• Structure
• Made of cellulose - a strong carbohydrate fiber
• Component of both wood and paper

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400x
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Cell Wall

• Function
• Provide support and protection for the cell

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Cell Membrane
Cheek Cells (40X)
Cheek Cells (1000X)
Cheek Cells (400X)
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Cell Membrane

• Function
• Separate the cell from its surroundings
• Selectively permeable - regulates what enters and
  leaves the cell
• Provides protection and support

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Cell Membrane

• Structure - Fluid Mosaic Model
• Primarily composed of three substances
• Phospholipids
• Hydrophilic (likes water) head
• 2 Hydrophobic (afraid of water) tails
• Cholesterol
• Proteins

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Cell Membrane

• Structure How the substances are arranged
• - Phospholipid bilayer with interspersed
  proteins and cholesterol

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Cell Membrane

• Function of each part
• Phospholipids - form the bilayer
• The hydrophobic tails point towards each other
  and the hydrophilic heads point towards the water
  in the cytoplasm and the outside of the cell
• This creates the barrier between the cytoplasm
  and the outside of the cell

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Cell Membrane

• Cholesterol
• Maintains the membranes fluidity

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Cell Membranes

• Proteins - 2 Main Types
• Peripheral Proteins
• Attached to the surface of the membrane
• Receive signals for the cell and allow the cell
  to communicate with other cells

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Cell Membrane

• Proteins - 2 Main Types
• Integral Proteins
• Penetrate the lipid bilayer and extend from one
  side of the membrane to the other
• Transport substances into and out of the cell

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Cell Membrane

• Integral Proteins
• 3 Types
• Carrier Proteins - used in facilitated diffusion
• Channel Proteins - used in facilitated diffusion
• Membrane Pump Proteins - used in active transport

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Movement Across the Cell Membrane

• Background
• Many living cells live in a liquid environment
• Important function of the cell membrane is to
  regulate the movement of molecules from one side
  of the membrane to the other.
• Molecules move in both directions

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Movement Across the Cell Membrane

• Background
• Concentration
• Cytoplasm of the cell contains a solution of many
  different substances in water
• The substances in the solution are called
  solutes.

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Movement Across the Cell Membrane

• Background
• Concentration -
• The concentration of a solution is how much
  solute is found in a solution
• Higher concentration more solutes
• Lower concentration less solutes
• Movement across the membrane depends on the
  concentration on either side of the membrane

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Movement Across the Cell Membrane Overview

• Passive transport does not require the cell to
  use energy
• Diffusion
• Osmosis
• Facilitated Diffusion
• Active Transport requires the cell to use
  energy
• Membrane Pumps
• Endocytosis (Phagocytosis and Pinocytosis)
• Exocytosis

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Movement Across the Cell Membrane

• Types of Movement
• Diffusion (passive transport)
• In solution, particles move constantly and tend
  to spread out randomly
• Definition - particles move from an area of high
  conentration to an area of low concentration

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Movement Across the Cell Membrane

• Types of Movement
• Diffusion (passive transport)
• Equilibrium is reached when the concentration of
  solutes is the same on both sides of the membrane
• Substances diffuse across the membrane without
  requiring the cell to use energy

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Movement Across the Cell Membrane

• Types of Movement
• Diffusion (passive transport)
• Diffusion across the membrane only occurs with
  small molecules
• Carbon dioxide
• Oxygen
• Amino acids (small molecules that make up
  proteins)

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Movement Across the Cell Membrane

• Types of Movement
• Osmosis (passive transport)
• Definition The name for the diffusion of water
  across a selectively permeable membrane
• Water moves from higher concentration to lower
  concentration

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Movement Across the Cell Membrane

• Types of Movement
• Facilitated Diffusion (passive transport)
• Substances pass through a carrier protein or a
  channel protein
• Different proteins allow different substances
• Occurs quickly and is very specific

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Movement Across the Cell Membrane

• Facilitated Diffusion Contd
• Substances that cannot pass through on their own
• Examples -
• Glucose
• Glycerol

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Movement Across the Cell Membrane

• Types of Movement
• Facilitated Diffusion
• Only occurs from a high concentration to a low
  concentration
• Does not require the cell to use energy
• Animation
• Animation

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Movement Across the Cell Membrane

• Types of Movement
• Active Transport
• Requires the cell to use energy
• Types of Active Transport
• Membrane Pumps
• Endocytosis
• Exocytosis

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Movement Across the Cell Membrane

• Active Transport Contd
• Membrane Pumps
• Specialized proteins that use energy to pump
  substances across the membrane
• A way of moving substances against the
  concentration gradient (from low concentration to
  high concentration)

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Movement Across the Cell Membrane

• Membrane Pumps Contd
• This occurs when the cell needs more of a
  substance than diffusion can provide
• Moves small molecules (Na, K, Calcium)

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Movement Across the Cell Membrane

• Types of Active Transport
• Endocytosis
• Process of taking material into the cell by
  infolding or pockets of the cell membrane
• Pocket breaks off and forms a vesicle in the
  cytoplasm

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Movement Across the Cell Membrane

• Endocytosis Contd
• Occurs for large molecules, clumps of food, even
  whole cells
• Two Types
• Phagocytosis (Cell eating) - cell engulfs a
  particle

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Movement Across the Cell Membrane

• Two Types Contd
• Phagocytosis
• Examples
• Blood Cells engulf a bacteria
• Amoebas (single celled orgaisms) obtain nutrients

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White Blood Cell Engulfing a Bacteria
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Movement Across the Cell Membrane

• Two Types Contd
• Pinocytosis (Cell Drinking) - cells take up
  liquid from environment

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Movement Across the Cell Membrane

• Types of Active Transport
• Exocytosis
• Opposite of endocytosis
• Membrane of the vesicle fuses with the cell
  membrane and forces material out of the cell
• Allows cell to get rid of waste
• Animation