cell membrane & cell transport
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CELL MEMBRANE & CELL TRANSPORT. Homeostasis: Maintaining a Balance. Organisms must adjust to changes in their environment. If not…DEATH! A formal definition is—maintaining a stable internal state despite what is going on externally. What Maintains Homeostasis?. - PowerPoint PPT PresentationTRANSCRIPT
CELL MEMBRANE &CELL TRANSPORT
Homeostasis:Maintaining a Balance
Organisms must adjust to changes in their environment.
If not…DEATH!
A formal definition is—maintaining a stable internal state despite what is going on externally.
What Maintains Homeostasis? The PLASMA or CELL
MEMBRANE maintains the proper concentrations of materials by controlling the passage of molecules in and out of the cell.
Therefore, the cell membrane’s function is to maintain HOMEOSTASIS through passive transport, active transport and cell communication!
Cell Membrane
X 53, 260
This electron micrograph of the cell membrane shows the appearance of the phospholipid bilayer using several staining processes. The magnification on this structure is 53,260 X
Characteristics of the Cell
Membrane
The cell membrane is Selectively Permeable
aka Semi-permeableAllows some things in/out and not
others… Oxygen, nitrogen,carbon dioxide,
and other small, nonpolar molecules can diffuse directly
Water was once thought to move directly through, but it is now understood to travel through aquaporins (a type of transport protein).
Ions, sugars, and larger molecules move through transport proteins or in vesicles.
Plasma/Cell Membrane-Structure
Phospholipid Bilayer with proteins embedded/floating in it
Phospholipid Structure: Polar Head (hydrophilic
—”water loving”) Nonpolar Tails—
(hydrophobic—”water fearing”)
PhospholipidPolar Head
Nonpolar Tails
Bilayer ArrangementOutside of cell
Inside cell
Proteins are embedded/floating in the lipid bilayer.
Protein in membrane
Cell Membrane Structure-ProteinsThese proteins are needed for the membrane to function properly.3 Types of Membrane Proteins
1. Transport—regulate what enters or leaves cell2. Marker—identify the cell3. Receptor—allow cells to communicate
Transport Proteins—Channel Proteins• Function as
“gates/passageways”• Allow polar sugars, amino
acids, and ions to cross the membrane.
• Special channel proteins:– Gated ion channels—gates
that open/close– Carrier proteins—change
shape to allow specific molecule to pass
– Aquaporins—allow water to diffuse through (called osmosis)
Channel Protein
Carrier Protein
http://personal.tmlp.com/Jimr57/textbook/chapter3/cms2.htm
Transport Protein
Marker Proteins• Cell’s “Name Tag”• Protein sticks out of
phospholipid layer• Often has carbohydrates
attached to outside end• Functions in cell
identification to identify the cell to other cells and molecules
• Important in – immunity—so various
white blood cells in your body do not mistake your cells for foreign cells
- blood typing – so you can’t receive just any ol’ type of blood
http://personal.tmlp.com/Jimr57/textbook/chapter3/cms2.htm
Marker Protein
Receptor Proteins• Function as
“messenger/receiver”• Receive information from the
environment (extracellular fluid, blood, interstitial fluid) and transmit that info to the inside of the cell
• Protein has specific shape/charge to only allow certain molecules (like hormones) to bond
• Triggers a response in cell• Ex) epinephrine can bind to a
receptor protein and send a message inside that says “break down glycogen”
http://personal.tmlp.com/Jimr57/textbook/chapter3/cms2.htm
Receptor Protein
CELL TRANSPORT• Concentration gradient - the
difference the concentration of a particular substance across a space. .
• Equilibrium is reached when the molecules become even throughout a space.
Cell Transport Types• Passive Transport—no energy required,
molecules move from high to low concentration (down or with concentration gradient)– Diffusion– Osmosis– Facilitated Diffusion
• Active Transport—energy (ATP) required, molecules move from low to high concentration (up or against the concentration gradient)– Pumps– Vesicles
Passive Transport
Diffusion, Osmosis, Facilitated Diffusion
Diffusion Diffusion - the process by which molecules spread from areas of high concentration, to areas of low concentration Molecules are said to go
“Down” or “with” the concentration gradient.
Passive Transport-requires no energy
Osmosis• Osmosis - the diffusion of watermolecules through
a semi-permeable membrane requires
no energyEx. Water will move in the
direction where there is a higher
concentration of solute (and hence a lower concentration of water).
About this diagram: this represents a cell in a solution. The cell will not let the red particles pass through the membrane. The green molecules can pass through, as can water molecules. The arrows show the direction of particle movement. The green particles are moving in to the cell where their concentration is lower, and water is moving out of the cell because its concentration is higher inside
osmosis
diffusion
Isotonic Solution• Concentration of
solute and solvent outside the cell is equal to/the same as the solution you are comparing it to (often the cytoplasm in cell)
• Water is moving in and out at equal rates, no net movement into or out of cell since
• Cell size would stay the same
Red blood cells in isotonic solutionX 1000Note that all the cells appear normal.
Hypertonic Solution There are more solute
(ex. salt) molecules in solution outside the cell when compared to the inside of cell
Water will move out of the cell
Cell would shrink Plants cells shrink
(plasmolysis) because cell membrane pulls away from cell wall, so plant wilts because water has left the central vacuole. Animal cell shrink (crenate). In both cases, the cell may die.
Crenated red blood cells in hypertonic salt solution X 1000Notice that the cells have shrunk.
Hypotonic Solution There are less solute
(ex. salt) molecules in the solution outside the cell than inside the cell.
Water will move into the cell.
Cell will swell Cell could burst
(lyse) Plant cells have
vacuoles to collect extra water
Red blood cells in hypotonic solutionX 1000Note that the pinkish cells have swollen (the little dip in the middle of a normal rbc is not visible and one side bows out).
Osmosis Links
Osmosis Examples
http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
Hypotonic, Hypertonic, Isotonic Interactive Quiz
http://www2.nl.edu/jste/osmosis.htm#Osmosis
Facilitated Diffusion (uses Transport Proteins,
passive)• Moves substances
(from high to low concentration) down the concentration gradient without using cell’s energy using channel/carrier proteins located in membrane
Active Transport in Cells
Why do cells need active transport?
• Cells must transport certain amino acids, sugars, etc. into their cytoplasm from the surrounding fluid.
• Some of these substances, however, are already in higher concentrations inside versus outside.
How does active transport work?
• Some types involve carrier proteins that function as “pumps”.
• Other types use vesicles.• Energy is provided by ATP.
Active Transport Using Pumps
Sodium-Potassium PumpProton Pumps
Example of active transport types using pumps
Sodium/Potassium Pump•Na+ pumped out of a cell•K+ pumped into a cell• Important because it prevents cells from bursting by lowering the sodium inside causing less water to enter through osmosis.
•Used by many cells, including nerve cells, to send a chemo-electric message.
Sodium-Potassium Pump
Sodium/Potassium pump:
3 Na+ out of cell (yellow diamonds)
2 K + into cell (red/purple squares)
Here the energy of a phosphate from ATP (shown in pink) is used to exchange sodium atoms for potassium atoms.
Proton PumpProton (H+) pump – forces protons out of a
membrane enclosed space (organelle or cell), often to create a proton gradient down which the protons can flow back in
Why would the cell “waste” energy on a proton pump? *Because the cell needs isolated areas of the cell with different pH for particular functions; ex) lysosomes – have proton pumps to maintain a pH=5*Because the cell only uses one ATP to pump a proton out, and that proton can be used in co-transport
Co-transport – process cells use to bring large molecules, such as sugars, into a cell with a minimum amount of energy used; usually a proton and a sugar enter a double tunneled protein at the same time; the tunnel only “works” when both molecules are present
Active Transport Using Vesicles
Endocytosis & Exocytosis
EndocytosisSubstances are moved into a
cell by a vesicle that pinches off from the cell membrane
Requires energy (ATP)
Types of Endocytosis• Pinocytosis—when the nutrient
particles are dissolved in a liquid; “cellular drinking”
• Phagocytosis—when the nutrient particles are solids; “cellular eating”
ExocytosisExocytosis- substances inside a vesicle are
released from a cell as the vesicle fuses with the cell membrane
Involves the cell getting rid of waste or the cell secreting cell products (ex. Hormones, insulin)
• Requires Energy (ATP)
Animations—Exocytosis, Endocytosis
McGraw-Hill: Cotransport, Na-K pump, Endo/Exocytosis, & Proton Pump
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter6/animations.html#
Exocytosis using ER and Golgi:
http://www.wisc-online.com/objects/index_tj.asp?objid=AP11203
Cell Membrane Physiology--Interactive
http://www.getbodysmart.com/ap/nervoussystem/neurophysiology/membranephys/menu/menu.html