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