Chapter 7 Flashcards
Plasma membrane
Exhibits selective permeability allowing some substances to cross easier than others
What does plasma membrane consist of?
Phospholipid bilayer(most abundant component) ; Amphipathic (hydro philic and phobic)
How is plasma membrane fluid mosaic
Lipids and proteins float and move within the membrane, embedded proteins are held by hydrogen regions, most lipids and proteins move move laterally, in animal cells the PM includes a ECM containing 25% cholesterol which regulates membrane fluidity
PM fluidity is influenced by:
Temperature (hibernating animals, ectothermic animals, endothermic animals) ; Composition (unsaturated fatty acids, cholesterol)
Types of membrane proteins
Peripheral proteins (bound to the surface of the membrane), integral proteins (penetrate the hydrophobic core), transmembrane proteins (integral proteins that span the membrane)
Transmembrane proteins
R group can be nonpolar and hydrophobic or polar and hydrophilic ; characteristics determine if protein is inserted into nonpolar bilayer and how
What are the functions of cell-surface membrane proteins?
Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to the cytoskeleton and ECM
Peripheral and transmembrane protein functions
Cell-cell recognition, transmembrane protein regulation of transport (passive vs active)
Cell-cell recognition
Distinguish one type of neighboring cell from another, crucial to the functioning of an organism, cells recognize other cell by binding to surface molecules
What are recognition sites?
Cell membrane carbohydrates ; glycolipid=carb+lipid, glycoproteins=carb+protein, proteoglycan=protein+longer carb chains
Why is a cell’s surface proteins medically important?
HIV must bind to the immune cell-surface protein CD4 and a “co-receptor” CCR5 in order to infect
What key roles do transmembrane proteins play in regulating transport?
Hydrophobic (nonpolar) molecules can dissolve in the lipid bilayer and pass through the he membrane rapidly ; Polar and hydrophilic molecules don’t cross the membrane easily
Passive transport
Doesn’t require metabolic energy (substance moves down concentration gradient)
Active transport
Does require input of metabolic energy (substance moves against its concentration gradient)
Diffusion
Random movement toward equilibrium ; net movement from regions of greater concentrations to lesser concentrations
Passive transport (more info)
Can occur by simple diffusion through the phospholipid bilayer ; speed of diffusion depends on: size of molecule, temperature of solution, concentration gradient
Osmosis
Diffusion of water ; depends on the concentration of water molecules on either side of the membrane (water moves down its concentration gradient)
Osmoregulation
The control of solute concentrations and water balance ; necessary adaptation for life in such environments ; hypertonic or hypotonic environments create osmotic problems for organisms that have cells without rigid walls
Facilitated diffusion
Passive transport that requires channel proteins or carrier proteins ; considered passive b/c there is no ATP
Channel protein
Form channels across the membrane through which some substances can pass ; high specificity
Aquaporins
Channels that allow large amounts of water to move along its concentration gradient
Active transportation
Uses energy to move solutes against their gradient ; requires ATP ; allows cells to maintain concentration gradients that differ form their surroundings
How does ATP release energy?
It stores energy in the last phosphate bond ; when the last bond is broken (hydrolysis) the energy is released and ATP is converted into ADP
Voltage across plasma membrane
Na+/K+ pumps create differences in ions across the membrane (voltage) ; voltage across membrane is called membrane potential ; inside of cell is negative compared to the outside
Electrogenic pumps
Animal cells=sodium potassium pump, plant cells=proton pump ; electrogenic pumps help store energy that can be used for cellular work
Bulk transport
Occurs by exocytosis and endocytosis across PM ; requires energy ; small molecule and water enter or leave through lipid bilayer via transport proteins, large molecule cross the membrane via vesicles
Types of endocytosis
Phagocytosis (cellular eating), pinocytosis (cellular drinking), receptor-mediated endocytosis
Phagocytosis
Specialized cell engulf large solid particle or another cell ; food vesicle (phagosome) forms and usually fuses w/ a lysosome where the contents are digested
Pinocytosis
Molecules dissolved in droplets are taken up when extracellular fluid is “gulped” into tiny vesicles
Receptor-medicated endocytosis
Binding of specific solves to receptors triggers vesicle formation ; receptor proteins, receptors, and other molecules form the extracellular fluid are transported in the vesicles ; emptied receptors are recycled to the plasma membrane
