Membrane Transport Nestor T. Hilvano, M.D., M.P.H. (Images Copyright Discover Biology, 5 th ed.,...
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Transcript of Membrane Transport Nestor T. Hilvano, M.D., M.P.H. (Images Copyright Discover Biology, 5 th ed.,...
Membrane Transport
Nestor T. Hilvano, M.D., M.P.H.(Images Copyright Discover Biology, 5th ed., Singh-Cundy and Cain,
Textbook, 2012.)
Learning Objectives1. Describe plasma membrane and give its
functions.
2. Differentiate the types of transport of molecules across the membrane.
3. Compare and contrast diffusion and osmosis.
4. Discuss briefly what happens when a red blood cells is placed in hypotonic solution? In hypertonic solution?
Plasma MembraneFunctions: • Regulates passage of ions and macromolecules
in and out of the cell• Allows some substances to cross more easily
than others• Allows information to be transferred across the
membrane• Possesses devices for cell attachment• Receptors for hormones • Ion pumps for regulating the internal
environment
Components of Plasma Membrane • The fluid mosaic model states that a
membrane is a fluid structure with a “mosaic” of various proteins embedded in it
• Selectively permeable• Composed mainly of Bilayer of phospholipids
(selective barriers), and some proteins, cholesterol, carbohydrates
Fig. 7-7
Fibers ofextracellularmatrix (ECM)
Glyco-protein
Microfilamentsof cytoskeleton
Cholesterol
Peripheralproteins
Integralprotein
CYTOPLASMIC SIDEOF MEMBRANE
GlycolipidEXTRACELLULARSIDE OFMEMBRANE
Carbohydrate
Transport of Molecules Across the Plasma Membrane
a) Passive transport- move from [high] to [low]; requires no ATP
b) Active transport- move from [low] to [high]; needs ATP
c) Facilitated transport- via carrier protein
d) Exocytosis and endocytosis
Passive Transport
• Cell does not expend energy
• Diffusion – particles spread out from area of high concentration to an area of low concentration gradient.
i.e. O2 and CO2 are small and nonpolar molecules that easily cross the membrane.
• Osmosis – is the net diffusion of water across a selectively permeable membrane
Figure 5.3A
Molecules of dye Membrane
Pores
Net diffusion Net diffusion Equilibrium
Figure 5.4
Osmosis
Solute moleculewith cluster ofwater molecules
Watermolecule
Selectivelypermeablemembrane
Solutemolecule
H2O
Lowerconcentration
of solute
Higherconcentration
of solute
Equalconcentrations
of solute
p. 76
Tonicity • Tonicity is important in maintaining cell
volume (ability to cause a cell to loss or gain water)
• Isotonic solution – solute concentration is the same both intracellular and extracellular
An animal cell (RBC) placed in:
• Hypotonic – will gain water, swell and lyse
• Hypertonic – will lose water and crenate
Facilitated Transport • Uses specific transport proteins in the membrane• Does not requires energy• Substances move down its concentration gradient• Channel proteins- ions channels (gated channel) that
open or close in response to stimulus • Carrier proteins- binds to protein and changes it’s
shape
Fig. 7-15
EXTRACELLULAR FLUID
Channel protein
(a) A channel protein
Solute CYTOPLASM
Solute Carrier protein
(b) A carrier protein
Active Transport
• Requires expenditure of energy (ATP)
• Molecules move against the concentration gradient
• i.e. Na+ - K+ pump in nerve impulse transmission
Faciliatated diffusion and active transport: http://www.youtube.com/watch?v=1ZFqOvxXg9M&feature=related
Endocytosis and Exocytosis • Transport of large molecules
• Exocytosis – export bulky materials
i.e. tearing, insulin release into the blood
stream
• Endocytosis – cells take in macromolecules by forming vesicles/vacuoles from its plasma membrane.
a) phagocytosis, b) pinocytosis
Homework 1. Define – diffusion, osmosis, endocytosis,
exocytosis, channel proteins, carrier proteins, isotonic solution, hypotonic solution, and hypertonic solution.
2. Describe the structure of plasma membrane and give its functions. What is it’s primary component?
3. Compare and contrast passive transport, facilitated transport, and active transport across a membrane as to concentration gradients, energy expenditure, use of carrier/transport proteins, and cite an example of substances.
4. Discuss the effect of hypotonic and hypertonic solution to red blood cells.