Chapter 4

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Chapter 4 Section 4.2 (pgs. 56 57) Chapter 5
(5.6, 5.7 and 5.8 - pgs. 88-93)
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Unit Objectives

• Students will be able to
• Describe how parts of the plasma membrane are
  used for various types of cell transport,
  regulation and exchange of substances and
  communication with the environment.
• Explain how materials move across the plasma
  membrane based on concentration gradient.
• Explain the movement of water in isotonic,
  hypotonic and hypertonic solutions and how both
  animal and plant cells are affected in each.
• Explain turgor pressure
• Compare and contrast endocytosis and exocytosis
  and explain their function.
• Compare and contrast passive and active transport
  and be able to give examples of each.

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MEMBRANE STRUCTURE AND FUNCTION

• - Each cell is surrounded by a plasma membrane
• - The plasma membrane separates the living cell
  from its nonliving surroundings
• - It allows only specific substances in and out
  of the cell (selectively permeable)
• - Passes chemical messages from external
  environment to the internal cell

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Characteristic of Membranes

• Major mechanisms of molecular transport in cells
• Regulates what enters and leaves the cell
• Permeable materials pass through freely
• Selectively Permeable Membrane Allow only
  certain substances to pass through depends on
  the cells needs.

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Factors that affect permeability

1. Size of molecules example large molecules do
   not pass as freely as smaller ones.
2. Cells needs
3. Environment
4. Solubility
5. Composition of the membrane

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Membrane Structure Review
Phosphate containing head (hydrophilic) and two
fatty acids tails (hydrophobic)
Non-polar
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Membrane Structure
- The plasma membranes lipids form a two-layered
membrane called the lipid bilayer - The lipid
bilayer is an arrangement of hydrophilic heads
and hydrophobic tails
Outside cell
Hydrophilic head
Hydrophobic tail
Cytoplasm (inside cell)
(a) lipid bilayer of membrane
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• Most membranes have specific proteins
• embedded in the lipid bilayer

This is called the fluid mosaic model of the
plasma membrane
Hydrophilic region of protein
lipid bilayer
Hydrophobic region of protein
(b) Fluid mosaic model of membrane
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Fluid Mosaic Modelof Membrane Structure
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Membrane Proteins and Their Function

• Water can cross the membrane freely but ions and
  most polar molecules cannot.
• Integral Proteins detect environmental signals
  and transmit them to the inside of the cell.
• Peripheral Proteins lie on one side of the
  membrane. They often have carbohydrates attached
  that act as labels on cell surfaces. Act as
  recognition.
• Functions
• Regulation and exchange of substances
• Communication with the environment

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Physical Laws of Motion (molecular motion)
Solids vibrate in space Liquids Flow Gases
move very freely and quickly Brownian Movement
Constant random molecular motion Molecules
move from areas of high concentration to low
concentration
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Simple Diffusion movement across a membrane

• - Net movement of molecules from regions of high
  concentration to regions of low concentration.
• - Down a concentration gradient
• - Doesnt require energy, like riding a bike
  down hill
• - Movement continues until substances are evenly
  distributed (equilibrium is reached)
• Equilibrium Concentration gradient (difference
  in the concentration of molecules across a
  distance) no longer exists, molecules still move
  but there is no net movement. Concentration of
  molecules will be the same.

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Simple Diffusion
(extracellular fluid)

Some moleculesdiffuse freelyacross
(cytoplasm)
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Diffusion of Dye in Water
RandomDispersal
Dispersing
Time 0
Time 1
Time 2
SteepConcentrationGradient
ReducedConcentrationGradient
NoConcentrationGradient
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Factors that affect the rate of diffusion

• Concentration increase in concentration
  increases the rate
• Temperature increase in temperature increases
  the rate (hot water and dye)
• Pressure increase in pressure increases the rate

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Osmosis

• Diffusion of water across a membrane
• Special case of diffusion
• Net movement of water molecules from an area of
  high water concentration to an area of low water
  concentration
• The cell has no control over osmosis, it is due
  to the concentration gradient inside and outside
  of the cell.

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Concentration Gradient
Concentration Gradient Is determined by the
concentration of solute (ex. Salt) on each side
of the membrane (differences in amount) of
molecules or substances. Remember! Osmosis is
looking at which way water moves. (Example on
Board)
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Types of solutions or Environments of Cells
What happens to a red blood cell in different
solutions? Isotonic Solution solution that has
the same concentration of dissolved particles as
the cytoplasm. Thus, water inside and outside of
the cell are equal and there will be equal
movement. (example on board)
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Types of solutions or Environments of Cells
Hypotonic Solution solution has lower
concentration of dissolved particles than the
cytoplasm of a cell. Thus, more water is outside
the cell than inside the cell so water will move
into the cell from high to low. (example on
board)
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Types of solutions or Environments of Cells
Hypertonic Solution solution that has a higher
concentration of dissolved particles (less water)
than the cytoplasm. Thus, less water outside of
the cell so water moves out of the cell from high
concentration to low, into solution . (example
on board)
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The Effects of Osmosis
Hypotonic Solution
Hypertonic Solution
Isotonic Solution
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Osmotic Factors what happened to plant cells in
isotonic, hypotonic a hypertonic conditions?

• Osmotic Pressure pressure that builds up in a
  plant cell due to osmosis.
• Isotonic Solution no change in cell
• Solution of equal water concentration and solute
  concentration
• The plants will neither gain or lose water
• Plant is normal and healthy
• Hypotonic Solution plant gains water and pushes
  the membrane up against the cell wall.
• The cell wall is strong enough to resist the
  pressure exerted by the water inside the
  expanding cell TURGOR PRESSURE
• High concentration of water and a lower
  concentration of solute (ex. sugar or salt)
• Hypertonic solution cell will shrink away from
  the cell wall plasmolysis
• This is why plants wilt
• Low concentration of water and a high
  concentration of solute (ex. sugar or salt)

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Plants Reaction to Different Solutions
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Plants Reaction to Different Solutions
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Osmotic Factors what happened to animal cells
in isotonic, hypotonic a hypertonic conditions?

• Isotonic Solution no change in cell
• Solution of equal water concentration and solute
  concentration
• Hypotonic Solution water enters the cell, cell
  will swell / burst/cell lysis. The membrane
  ruptures.
• High concentration of water and a lower
  concentration of solute (ex. sugar or salt)
• Hypertonic solution water leaves the cell,it
  will shrink / crenate
• Low concentration of water and a high
  concentration of solute (ex. sugar or salt)

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Animal Cell (red blood cell) Reaction to
Different Solutions
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Animal Cell (red blood cell) Reaction to
Different Solutions
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Cells Reaction to Different Solutions
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Types of Transport Processes

• Plasma membrane provides two types of movement
• I. Passive Transport
• Substances move into and out of cells along
  concentration gradients
• Move from an area of high concentration to low
  concentration
• Does not require energy
• Types of Passive Transport
• - Simple Diffusion
• - Osmosis
• - Facilitated Diffusion diffusion using a
  carrier protein/channel protein. Molecule is to
  large to go through the membrane.

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Facilitated Diffusion

• Facilitated Diffusion
• Down a concentration gradient, from high
  concentration to low concentration
• Entrance is via channel or carrier proteins
• Does not require energy

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Facilitated Diffusion Carriers
DiffusionChannelProtein
(OutsideCell)
Molecule inTransit
DiffusionGradient
Carrier proteinhas binding sitefor molecule
Carrier protein changesshape, transportingmolecu
le across membrane
Molecule entersbinding site
Carrier protein resumesoriginal shape
(Inside Cell)
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Types of Transport Processes

• II. Active Transport
• Substances move against a concentration gradient
• Move from low concentration to high concentration
• Requires energy (ATP)

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Active Transport

• - Requires that the cell expend energy to move
  molecules across a membrane
• - Movement of molecules against a concentration
  gradient
• - From low concentration to high concentration
• - Maintains internal (inside cell)
  concentrations of molecules that differ from
  external (out side cell) environment
  concentrations

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Active Transport the Pumping of Molecules
Across Membranes

• Transport proteins have specific binding sites
  that only accepts specific molecules. Using
  energy, the protein pumps the solute molecule
  against a concentration gradient and into the cell

Lower solute concentration
Solute
Higher solute concentration
Figure 5.15
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• Types of Active Transport

Exocytosis and Endocytosis are methods of active
transport that move large molecules across a
membrane
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Endocytosis

• Endocytosis takes material into the cell by
  forming pockets in the membrane
• Types of endocytosis

• Phagocytosis engulfing large particles cell
  eating
• Pinocytosis engulfing smaller particles cell
  drinking

Figure 5.16b
(b) Endocytosis
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Endocytosis

• In phagocytosis (cellular eating) a cell
  engulfs a large particle and packages it within a
  food vacuole

In pinocytosis (cellular drinking) a cell
gulps droplets of fluid or small particles by
forming tiny vesicles
Food being ingested
Figure 5.17
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Exocytosis

• Exocytosis

• Secretes substances outside of the cell. Removing
  particles.

Outside cell
Plasma membrane
Cytoplasm
(a) Exocytosis
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Exocytosis
1
(cytoplasm)
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Active Transport Sodium Potassium Pump

• Another example of active transport in animal
  cells is the Sodium Potassium Pump and it
  involves a carrier protein.
• The protein transports sodium (Na) ions and
  potassium (k) ions against a concentration
  gradient.
• To function normally, some animal cells must have
  a higher concentration of Na ions outside of the
  cell and higher concentration of K ions inside
  the cell.
• Sodium potassium pump maintains these
  concentration differences.
• THIS TAKES ATP

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Active Transport Sodium Potassium Pump
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The End