Untitled Flashcards Set

Topic 2.4: Plasma Membranes 

• Phospholipids are amphipathic (polar head is hydrophilic and nonpolar tail is hydrophobic), head is phosphate group tails are 2 fatty acid chains 

• Phospholipids form bilayer in aqueous environments (tails located inside) 

• Peripheral proteins- loosely bound to surface of membrane, hydrophilic with charged and polar side groups  

• Integral proteins (transmembrane proteins)- span the entire membrane, hydrophilic w charged and polar side groups protrude the membrane and hydrophobic w nonpolar side groups that penetrate interior (tails) of bilayer 

• Proteins can shift in membrane and change shape slowly and laterally 

• Fluid Mosaic Model- membrane is not static and is held together by hydrophobic interactions which are weaker than covalent bonds, lipids and proteins in membrane can shift and flow 

• Cholesterol is wedged between phospholipids and regulates fluidity under different environmental conditions (@ warm temps it restrains movement and @ cool temps it maintains fluidity) 

• Glycoproteins- one or more carbs attached to a membrane protein 

• Glycolipids- lipid w one or more carbs attached (in membrane) 

• Cell recognition- recognize each other by binding to surface molecules which are carbs attached to the membrane (can be covalently bonded to glycolipids or glycoproteins) 

Topic 2.5: Membrane Permeability 

• Selective permeability is a direct consequence of membrane structure  

• Small nonpolar (hydrophobic)molecules pass freely (N2, O2, CO2, hydrocarbons, lipids)bc tails dont like anything w a charge (ions) 

• Hydrophilic substances such as large polar molecules and ions CANNOT pass freely, small polar molecules such as H2o can pass occasionally in small amounts 

Transport proteins: 

• PASSIVE- Channel proteins- hydrophilic tunnel spans the membrane and allows target molecules to pass  

• ACTIVE- Carrier proteins (protein pumps)- spans the membrane and changes shape to move a molecule from one side of the membrane to the other (Na+ and K+) 

• Pump has areas for ions to bond to, phosphate from ATP transfers to protein which changes its  

• ONLY IN PLANTS: Cell wall is structural boundary bc it maintains shape of cell, prevents against rupture when internal water pressure is high, helps plants stand against force of gravity 

• It's also a permeable barrier bc of plasmodesmata (small holes between plant cells that allow transfer of nutrients, waste, etc) 

• Cell wall is made of cellulose (complex carbohydrate) 

Topic 2.6: Membrane transport 

• Concentration gradient- when a solute is more concentrated in one area than another (membrane separating them) 

• Passive transport IS HIGH TO LOW- net movement of molecules from HIGH TO LOW concentration (no energy needed) ALSO KNOWN AS DIFFUSION (no membrane proteins) 

• Facilitated diffusion- movement of molecules from high to low concentration through transport proteins 

• Active Transport IS LOW TO HIGH- requires the direct input of energy (ATP)to move molecules from LOW TO HIGH concentration, establishes and maintains concentration gradients  

• Endocytosis- cell uses energy to TAKE IN macromolecules and particulate matter by forming new vesicles derived from the plasma membrane 

3 types of endocytosis: 

• Phagocytosis- cell takes in large particles 

• Pinocytosis- cell takes in extracellular fluid containing dissolves substances 

• Receptor-mediated endocytosis- receptor proteins on cell membrane are used to capture specific target molecules  

• Exocytosis- internal vesicles use energy to fuse with the plasma membrane and secrete large macromolecules OUT OF THE CELL (signaling proteins, hormones, waste) 

Topic 2.7: Facilitated diffusion 

• Facilitated diffusion works through transport proteins that move large and small polar molecules 

• Large amounts of water can pass through aquaporins 

• Charged ions (Na+ and k+) require channel proteins 

• Cotransport- secondary active transport that uses energy from electrochemical gradient to transport 2 different ions across the membrane through a protein 

• Symport- 2 different ions transported in the same direction 

• Antiport- 2 different ions transported in opposite directions 

• Electrochemical gradient- type of concentration gradient  

• Membrane potential- electrical potential difference (voltage) across a membrane  

• Membranes may become polarized by movement of ions 

Topic 2.8: Tonicity and osmoregulation 

• Osmosis- diffusion of free water across membrane via aquaporins 

• Osmolarity- the total solute concentration in a solution 

• Solvent (usually water) dissolves the solute 

• Tonicity- measurement of concentrations of solute inside and outside of the cell 

• Internal cell environments can be... 

• Hypertonic- more solute less solvent  

• Isotonic- equal concentrations 

• Hypotonic- less solute more solvent  

• Water moves to areas of higher SOLUTE concentration 

• Solute moves from high to low concentration 

• Osmoregulation- in plant cells it maintains water balance and allows control of internal solute composition/water potential 

Plant cells: 

• Environmental hypertonicity- less cellular solute and more cellular water (plasmolysis) 

• Isotonic solution- equal solute and water (flaccid) 

• Environmental hypotonicity- more cellular solute and less cellular water (turgid), water flows into plant vacuoles via osmosis causing vacuoles to expand and press against cell wall, cell wall expands until it exerts pressure on the cell- turgid pressure (critical for overall plant structure) 

• Turgidity is the optimum state for plant cells 

Animal cells: (same order as above) 

• Shriveled  

• Normal 

• Lysed 

Topic 2.8 #3:  

• water potential- measures the tendency of water to move by osmosis or potentiAL  (calculated from pressure potential and solute potential) 

• Water moves from area of high water potential to low water potential 

• Values of water potential can be positive, 0 (pure water), or negative  

• The more negative the water potential, the more likely water will move into the area (negative water potential is low water potential) 

• Increasing the amount of solute in water will cause an INCREASE in solute potential and a DECREASE in water potential (more solute=less water potential) 

• Increasing water potential will cause increase in pressure potential and vice versa  

• Components of water potential: 

• Solute potential- reflects the effect of dissolved solutes on water potential 

• Pressure potential- physical pressure exerted on or by water 

• In an open system, pressure potential is 0, so water potential is equal to solute potential always (-) 

I= ionization constant (1 w sucrose 2 w sodium) 

C= molar concentration 

R=pressure constant (o.083?) 

T=temp in k (c+273) 

• Over time as the potato cells gain water, the water that entered exerts pressure against the plant cell walls, raising the overall water potential in the potato core cells