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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 ModelPlasma 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 centerProteins -integral or transmembrane
-peripheral
Plasma Membranewww.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 on1. Size of particle2. Solubility in lipids3. Charge on particle4. 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.Diffusion2.Osmosis3.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 toless thangreater 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 substrate2. Saturation- once all carriers occupied, adding solutes will not make the process go any faster
Three types1. Facilitated Diffusion2. Active Transport3. 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 Referenceswww.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. Diffusion2. Osmosis3. Filtration
Review
What are three examples of non-mediated transport mechanisms?1. Diffusion2. Osmosis3. 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 concentrationB) molecules from an area of low concentration to an area of higher concentrationC) water molecules across a membrane from an area of low water concentration to an area of higher
concentrationD) 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 willA) ExpandB) BurstC) ShrinkD) Have no change in shape
3. Facilitated diffusion requiresA) Enzymes C) lipid carriersB) Carrier proteins D) carbohydrate carriers
Review
• The main difference between filtration and diffusion is
Active Transport
Transport of solute across membrane up (against) concentration gradientAnalogous to a pump moving water uphill.
ATP Driven Active TransportEnergy 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 cellCapture on one side and release on the other sideReceptor mediated endocytosis moves it into cell and
exocytosis moves it out the other side
Receptor Mediated Endocytosis
Exocytosis
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