Chapter 2 Flashcards
Selectively Permeable
feature/function of the plasma membrane that maintains homeostasis by regulating the passage of some substances while preventing others from entering the cell.
Hydrophilic
water insoluble; “water-loving”
Hydrophobic
water soluble; “water-fearing”
Lipid bilayer
- composed of two layers of polar phospholipids **A phospholipid contains a polar hydrophillic head and two hydrophobic tails (tails on the inside of the layer and heads on the outside)
- membrane also contains proteins and cholesterol
Amphipathic
containing both a polar and non-polar portion
**phospholipids are amphipathic
Fluid-mosaic
Used to describe the feature of the plama membrane.
- Fluid: the phospholipid are constantly moving and rearranging.
- Mosaic: several different components of the membrane (different types of lipids, proteins, and carbohydrates).
Brownian movement (Diffusion)
random moving of particles; dependent upon temperature and mass of the molecule.
-Does not require ATP
Flux
quantity of molecules moving from one sector to another in a defined volume.
-dynamic equilibrium=flux is 0.
Permeability coefficient
“Diffusion” coeffecient (P); volume that will flow in an amount of time.
-takes into account: solubility, pore size of the membrane,membrane thickness
Osmotic pressure
the pressure that needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane
Isotonic
equal osmotic pressure
Hypertonic
having higher osmotic pressure than other solution
Hypotonic
has lower osmotic pressure than other solution
Crenate
Process in osmosis where red blood cells shrink; This happens if placed in a hypertonic solution
Hemolyze
Process in osmosis where red blood cells swell and burst ; this can happen if placed in a hypotonic solution
Electrogenic pump
pumps unequal numbers of like charges in opposite directions; some active pumps pump 3 Na+ out of the cell while only 2 K+ are moving into the cell.
Electroneutral pump
pumps equal numbers of like charges in opposite directions
Endocytosis
Cells absorb molecules by engulfing them;
- pinocytosis= “cell drinking”, fluid endocytosis
- receptor-mediated endocytosis= endocytosis mediated by recoptors on the surace of the membrane; ligand binds to a receptor protein; clathrin coated pit; membrane invaginates to form vesicle
- phagocytosis
Exocytosis
mechanism where cell can release certain particles from the cell that are too large to pass the membrane.
Tmax
Transport maximum; maximum amount of transported molecule. point at which increases in concentration do not result in an increase in movement of a substance across a membrane.
Transduction
a major process of membranes that refers to the conversion of one form of energy to another.
Translocation
a major process of membranes that refers to the selective movement of substances from one location to another.
Phospholipids
- derived from either glycerol (phosphoglycerides) or sphingosine (sphingomyelin)
- hydrophobic fatty acid tails; probably what decreases the membrane’s permeability to polar molecules
- hydrophilic heads
Glycolipids
sugar containing lipids found mostly in plasma membranes.
-derived from sphingosine (like sphingomyelin)
Cholesterol
- Some plasma membranes contain one molecule of cholesterol for every molecule of phospholipid.
- smaller cholesterol molecules serve to add stability to the membrane and tends to decrease its fluid nature and increase its viscosity.
- Also prevents cystallization of fatty acyl chains by fitting between them.
- Cholesterol is largely nonpolar, hydrophobic but when combined with protein, its solubility in water increases.
Common activities of membranes
- Receptor sites- for hormones and other chemical messengers
- Energy Conversion- oxidative phosphorylation, which produces ATP, occurs on mitochondrial membranes
- Transcellular Transport and Extracellular Communication- molecules are transported through the membrane by a variety of ways (active and passive)
- Intracellular Compartmentalization- divides the cytoplasm into structures such as the nucleus, endoplasmic reticulum, and Golgi apparatus
3 major classes of membrane lipids
- phospholipids
- glycolipids
- cholesterol
Integral vs peripheral
Membrane proteins are classified as either integral or peripheral on the basis of how well they can be dissociated from the membrane.
Integral Proteins
- interact very extensively with the hydrocarbon chains; only be released by agents that can compete for these non-polar interactions (detergents); disruption of the bilayer is necessary to remove these.
- membrane-spanning proteins man span the membrane once or a number of times.
- have both hydrophobic and hydrophilic portions
- provides a lot of the asymmetry of the membrane
- some may serve as receptor sites; a class that serve as receptors for hormones, neurotransmitters, and some drugs are couple to G proteins and are termed G protein-coupled receptors; span membrane with 7 alpha-helical domains; outer portion contain ligand binding site, inner portion binds to G protein.
Peripheral proteins
- bound to membranes by electrostatic and hydrogen bonds; more easily disrupted
- Water-soluble
- some bound to surface of integral proteins
Functions of cell membrane proteins
- structural elements- and within and between cells (tight junctions)
- enzymes- surface or cytoplam
- receptors- ligand will evoke intracellular changes
- transporters- carriers or channels
Aquaporins
water channels in membrane
Carbohydrate of cell membranes
- cell membranes may contain 2-10% carbohydrate.
- associated with either lipids or proteins on the outer surface of the cell
- Function: interaction between cells, structural
Osmosis
movement of water from an area of higher concentration to an area of lower concentration.
Key determinants of Diffusion
lipid solubility, size, and charge
Passive Transport
- Does not require an input of chemical energy
- Simple Diffusion
- Facilitated Diffusion
Simple Diffusion
- type of passive transport
- does not require an input of chemical energy
- small, non-polar molecule passes through a membrane
Facilitated Diffusion
- does not require an input of chemical energy
- movement of molecules from a higher concentration to a lower concentration with the help of proteins found in the membrane.
- gated channels allow ions and small polar molecules to pass through at certain times.
- Protein carriers assist larger molecules; important characteristic: specificity, saturation, competition
Symporters (sodium, potassium, and chloride)
name for transporters that transport ions in the same direction
Antiporters (sodium and hydrogen)
transport ions in opposite directions
Uniporters (glucose)
transport only single molecules
Active Transport
- May also be called a pump
- Movement of substances from an area of low concentration to an area of high concentration
- ATP required
ATPases
name for many of the active transporters
Sodium/ Potassium pump
Secondary active transport
- takes advantage of the concentration gradient that exists for many ions
- The downhill transport of one molecule provide the energy for the uphill transport of another molecule
- countertransport= opposite direction
- cotransport= same direction
transcytosis
transport of substances across the cell; endocytosis and exocytosis
