Download Cell Biology

The Cell
Movement Across
the Membrane
Cell Diagram: College of Dupage
Quiz
• 1. What is the type of bond within a single
water molecule?
• 2. A carboxyl group is symbolized by what?
• 3. Briefly explain what happens in a hydrolysis
reaction.
• 4. Is maltose a monosaccharide, disaccharide,
lipid, or protein?
Quiz cont.
• 5. Are lipids hydrophobic or hydrophilic?
• 6. What is the difference between a saturated
vs unsaturated fatty acid?
• 7. What does the secondary structure of
protein refer to?
• 8. How does an enzyme work?
Quiz cont.
• 9. What is the difference between filtration
and diffusion?
• 10. What happens to a rbc in a hypertonic
solution?
• A hypotonic solution?
C. Fluid Mosaic Model
Plasma membrane is oily film made of lipids
with diverse proteins embedded in
Phospholipid bilayer
– Hydrophillic heads facing water on either side of
cell membrane
– Hydrophobic tails directed to center
Proteins
-integral or transmembrane
-peripheral
Plasma Membrane
www.susanahalpine.com/anim/Life/memb.htm
Functions of the Cell Membrane
• Defines boundaries of the cell
• Governs interactions with other cells
• Controls passage of materials into and out of
cell
III. Movement Across Membrane
A. Selective Permeability
Depends on
1. Size of particle
2. Solubility in lipids
3. Charge on particle
4. Carrier molecules in membrane
Movement across membrane
occurs through:
•
•
•
•
Lipid bilayer
Membrane channels
With carrier molecules
In vesicles
Passive vs. Active Transport
Requires
___________
• Primary Active
Transport
• Secondary Active
Transport
B. Non-mediated Transport Mechanisms
1. Diffusion
2. Osmosis
3. Filtration
• Passive
• Requires no energy
Concentration Gradient
B. Non-Mediated Transport Mechanisms
DIFFUSION = when molecules
move from a higher to a lower concentration.
What type of things might affect the rate
of diffusion?
a. Magnitude of concentration gradient
b. Temperature
c. Size of diffusing particles
d. Viscosity (thickness) of solvent
Diffusion Animation: biologycorner.com
Diffusion
Osmosis: Diffusion of
water across the membrane
Water moves from an area of more
water to an area of less water
Osmotic Pressure
Whenever dissolved substances
such as glucose or protein are
confined in a space by a selectively
permeable membrane, they can pull
water into the compartment by
osmosis.
The strength of the osmotic pull is
directly related to the concentration
of the solution.
The greater the concentration, the
greater the pulling, or osmotic
pressure.
Tonicity =the ability of a solution
to affect fluid volume and pressure within a cell
Environment surrounding cells may contain amounts of
dissolved substances (solutes) that are…
equal to
less than
greater than
…those found within the cell.
Tonicity
Isotonic:
no net movement of water between cell
and environment
Hypertonic:
a higher concentration of solute.
Hypotonic : a lower concentration of solute.
Water will always move toward a hypertonic
environment!!
Diagrams:
Cell: College of DuPage
Osmosis - www.scienceaid.co.uk/biology/plants/osmosis.html
Blood Cells: Mariana Ruiz
Effects of tonicity on RBCs:
Water moves from an area of more water to an area of less water
www.tvdsb.on.ca/WESTMIN/science/sbi3a1/cells/Osmosis.htm
Effects of Tonicity on RBCs
Isotonic solutions: normal saline (0.9% NaCl),
5%D/W, and Ringer’s solution
Under special conditions, hypotonic or
hypertonic solutions may be administered IV.
Most IV solutions are isotonic.
Filtration- due to a pressure gradient
Mediated Transport Mechanisms
Characteristics
1. Specificity- carrier exhibits specificity for certain ligand, just
as an enzyme does for its substrate
2. Saturation- once all carriers occupied, adding solutes will
not make the process go any faster
Three types
1. Facilitated Diffusion
2. Active Transport
3. Bulk Transport
Facilitated Diffusion
Passive
-Proteins assist in diffusion of molecules across plasma membrane.
-Movement only occurs in the presence of a concentration gradient.
-Some molecules move across the membrane more quickly if diffusion is facilitated by a carrier
molecule.
Web References
www.susanahalpine.com/anim/Life/memb.htm
www.northland.cc.mn.us/biology/biology1111/animations/passive3.swf
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation_how_osmosis_works.html
www.tvdsb.on.ca/WESTMIN/science/sbi3a1/cells/Osmosis.htm
www.education.uoit.ca/lordec/ID_LORDEC/capillary_fluid/capillary_fluid_LO.swf
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation_how_facilitated_diffusion_works.html
Review
What are three examples of non-mediated
transport mechanisms?
Review
What are three examples of non-mediated
transport mechanisms?
1. Diffusion
2. Osmosis
3. Filtration
Review
What are three examples of non-mediated
transport mechanisms?
1. Diffusion
2. Osmosis
3. Filtration
Are these active transport or passive transport?
Review
1. Osmosis is best defined as the movement of
A) molecules from an area of high concentration to an area of lower concentration
B) molecules from an area of low concentration to an area of higher concentration
C) water molecules across a membrane from an area of low water concentration to an area of higher
concentration
D) water molecules across a membrane from an area of high water concentration to an area of lower
concentration
2. A red blood cell placed in a hypertonic solution will
A)
B)
C)
D)
Expand
Burst
Shrink
Have no change in shape
3. Facilitated diffusion requires
A) Enzymes
B) Carrier proteins
C) lipid carriers
D) carbohydrate carriers
Review
• The main difference between filtration and
diffusion is
Active Transport
Transport of solute across membrane up (against) concentration gradient
Analogous to a pump moving water uphill.
ATP Driven Active Transport
Energy from adenosine triphosphate (ATP) drives substances across the plasma membrane with the aid of
carrier molecules.
Examples: Sodium-potassium pump, bring amino acids into cell, pump Ca2+ out of cell
Diagram:
Cell, College of DuPage
Sodium-Potassium Pump
• Needed because Na+ and
K+ constantly leak out of
the cell
• One ATP utilized to
exchange three Na+ pushed
out for two K+ brought in to
cell
Functions of Na+ K+ Pump
• Regulation of cell volume
• Heat production (thyroid hormone increases
number of pumps; heat a by-product
• Maintenance of membrane potential in all
cells
• Secondary active transport (no ATP used)
Vesicular Transport
• Transport large particles or fluid droplets
through membrane in vesicles (uses ATP)
• Exocytosis
• Endocytosis
– Phagocytosis
– Pinocytosis
– Receptor mediated endocytosis
Phagocytosis = Cell Eating
Pinocytosis= Cell Drinking
Taking in droplets of ECF
– Occurs in all human cells
Membrane caves in, then pinches off into the
cytoplasm as pinocytotic vesicle
Transcytosis
 Transport of a substance across a cell
 Capture on one side and release on the other side
 Receptor mediated endocytosis moves it into cell and
exocytosis moves it out the other side
Receptor Mediated Endocytosis
Exocytosis