Plasma Membrane Flashcards
plasma membrane
a thin, flexible, lipid bilayer that separates the contents of the cell from its surrounding
molecular gradients
ECF: Na+, Ca++ and Cl-
(positive outside)
ICF: proteins -, phosphate -, K+
(negative inside)
membrane potential
slight negative charge on the inside of the cell and slight positive charge on the outside of the cell
phospholipid molecule
- head: negatively charged, polar, hydrophilic
- tail: uncharged, nonpolar, hydrophobic
membrane protein functions
- channels for passage of small ions
- carriers for transport of substances
- docking-marker acceptors for secretory vesicles
- membrane bound enzymes
- receptors for responding to chemical messengers (endocrine system)
- cell adhesion molecules that hold cells together
myasthenia gravis
- muscle weakness
- channel proteins issue
- binding to receptors and openings of the channels are missing in MG
receptor proteins- insulin insensitivity
- DMII
- have insulin but can’t go into the cell
- receptors don’t recognize insulin
hereditary spherocytosis
- anchor proteins
- RBC are spherical
fluid mosaic model
-relates to the membrane fluidity and the mosaic pattern of free floating proteins in the bilayer
cell to cell adhesions
- the extracellular matric binds cells together
- three types of proteins: collagen, elastin (elastic), fibronectin (reticular)
- also held together by desmosomes, tight junctions, and gap junctions
collagen
- flexible nonelastic fibers or sheets that provide tensile strength(resistance to being stretch lengthwise)
- most abundant protein in the body
elastin
- allows tissues to stretch and recoil
- found in the lungs
fibronectin
-promotes cell adhesion and holds cells in position
desmosomes
- act like “Velcro” and anchor two adjacent non-touching cells
- most abundant in tissues that are subject to stretching
- pair of dense, buttonlike, cytoplasmic thickenings called plaques
- has strong filaments containing cadherins that extend across the plaques
- they bind adjacent plasma membrane together so they resist being pulled apart
tight junctions
- firmly bond adjacent cells together
- seal off passageway between the two cells
- found in primarily in sheets of epithelial tissue
- prevents leaks within epithelial sheets
- lines the internal cavities
- kiss sites are strands of proteins known as claudins that fuse the outer surfaces
gap junctions
- between adjacent cells linked by small connecting tunnels formed by connexons
- extend through the thickness of the membranes
- communicating junctions
- permits unrestricted passage of small nutrient molecules between cells, and water soluble molecules
- abundant in cardiac and smooth muscle, can transmit electrical activity throughout an entire muscle mass and allows synchronized contraction of a whole muscle mass
membrane transport-permeability
- if a substance can cross the membrane it is permeable to that substance
- can’t pass through membrane, it is impermeable
- plasma membrane is selectively permeable: allows some particles to pass while preventing others
particle solubility and size
- the two properties of particles that influence whether they can permeate cell membrane without assistance
- lipid solubility and particle size
- highly lipid-soluble particles dissolve in the lipid bilayer and pass through the membrane
- non-lipid particles require assisted transport to move across the membrane (charged particles and polar molecules)
simple diffusion kinds
- diffusion through lipid bilayer, diffusion through protein channel, osmosis
- passive
carrier-mediated transport
-facilitated diffusion, primary active transport, secondary active transport (symport or antiport)
net diffusion
refers to the difference between two opposing movements
unassisted membrane transport
- particles that can penetrate the plasma membrane on their own
- passively driven across the membrane
- diffusion down a concentration gradient
- movement along an electrical gradient
simple diffusion
- unassisted, passive membrane transport
- uniform spreading out due to random intermingling
- move from high to low concentrations
- occurs until equilibrium is reached
- crucial to survival of every cell
fick’s law of diffusion
- directly proportional: concentration gradient of substance, surface area of membrane, lipid solubility
- inversely proportional: molecular weight, distance (thickness)
molecules using simple diffusion
- nonpolar molecules dissolve through down their concentration gradients
- small ions can move down electrochemical gradients through open protein channels
- cations move towards area more negatively charged and vise versa with anions
ions and channels
- ions can across the membrane through protein channels
- channels are specific to one ion
- can be opened or closed
ions move through channels:
- down their concentration gradient
- down the electrical gradient
water transport
- water can easily pass through membrane
- through the tails of the phospholipids
- aquaporins
aquaporins
- channels specific for the passage of water
- the driving force is the concentration gradient
- different cells have different density
osmosis
- water moves passively down concentration gradient
- semi-permeable membrane
- area of high concentration of non-penetrating solutes to low concentration
osmolarity
-of a solution is measured by total solute particles per liter
osmotic pressure
- of a solution is the pressure that must be applied to the solution to completely stop osmosis
- the magnitude of the osmotic pressure is equal to the magnitude of the opposing hydrostatic pressure
tonicity
- of a solution refers to the effect the solution has on cell volume
- if the cell stays the same size, shrinks or swells
isotonic
-same concentration of nonpenetrating solutes as normal body cells do
hypotonic solution
- below-normal concentration of nonpenetrating solutes
- water diffuses in
- cell swells
hypertonic solution
- above normal concentration of nonpenetrating solutes
- water leaves cell
- cell shrinks
assisted membrane transport
- small particles are transported across the membrane by their carrier proteins
- protein flips to move particle from side to side
- facilitated and active transport
facilitated diffusion
-carrier moves the particle down its concentration gradient
active transport
-carrier moves particle against its concentration gradient
facilitated diffusion: passive
- substances move from a higher concentration to a lower concentration
- requires a carrier molecule
- does not require energy
- how glucose is transported into cells
facilitated diffusion: active transport
- substance against concentration gradient
- primary: direct use of ATP
- secondary: driven by ion concentration gradient, established by primary active transport, has symport and antiport
symport
- cotransport
- the transported solute moves in the same direction as the gradient of the driving ion
antiport
- counter transport or exchange
- the transported solute moves in the direction opposite from the gradient of the driving ion
carrier-mediated transport characteristics
- specificity
- saturation
- transport maximum (Tm)
- competition
specificity
-each carrier transports a specific substance or a few closely related compounds
saturation
-a limited number of carrier binding sites are available
transport maximum
-the amount of a substance transported in a given time
competition
-several closely related compounds may compete for transport on the same carrier
resting membrane potential
-70mV
Na+ and K+ pump
- small contribution to the resting membrane potential
- 3 Na+ out for every 2 K+ in
- loses more positive charges than it gains
- inside becomes more negative
- actively maintain the Na+ and K+ concentration gradients
equilibrium potentials
K+: -90mV
Na+: +60 mV
-resting membrane is 25 to 30 times more permeable to K+ than Na+
-closer to K+’s equilibrium potential
contributions of K+ and Na+
- more K+ diffuses out the cell
- excessive of positive charge outside of cell
- when -70mV is reached no net movement of K+ and Na+ occurs
excitable cells
- nerve and muscle cells can rapidly alter their membrane permeability
- fluctuates membrane potential
- fluctuations are responsible for producing electrical impulses in nerve and muscle cells
transport pathophysiology
-diffusion: pneumonia
-facilitated diffusion: GLUT4 in DM
voltage gated Na channel inhibited by tetrodotoxin (puffer fish) and saxitoxin (shell fish)
-CHF: Na+ and K+ pump inhibited by digitalis
-H+-K+ pump inhibited by omeprazole
-Na-glucose co-transporter - in GI mucosa and PCT, oral rehydration
familial hypercholestrolemia
- mutations in LDL receptor protein
- LDL particles not taken up by cells
- more in blood
- ??
chronic granulomatous disease
- inability of phagocytes to kill microbes
- normal functioning is mediated by: nicotinamide adenine dinucleotide phosphate (NADPH) oxidase
- oxidative burst kills the phagocyte
