lect 4: membranes II Flashcards
what is the movement of substances across cell membranes?
selectively permeable (helps maintain homeostasis)
-permits some solutes to pass through but not others
some permeability factors
-molecular size
-lipid solubility
-ions need transporters to get through hydrophobic region
what are the differences in ion concentrations between extra and intra cellular space?
creates gradients through transports
what are the types of membrane transport?
what is simple diffusion?
small, nonelectrolyte solutes
-fit through gaps between membrane lipids
-non-polar/minimal polarity
substances transported across membrane by simple diffusion
-gases (e.g. O2, NO)
-lipid solutes: fatty acids, steroid hormones
-a few other organic molecules
what is the difference between diffusion and osmosis?
what is the movement of water across membranes?
not all cells are equally permeable to water (kidney versus skin cells)
aquaporins
-small integral protein
-4 subunits
-each subunit has a central channel: lined with hydrophobic amino acids specific for H2O (selectivity filter)
-passive, facilitated transport
what are ion channels?
-membrane impermeable: K, Na, Ca, Cl (for specific)
-specialized integral proteins
-traverse lipid bilayer
-provide a pathway for an ion(s) to move
-do not bind ion(s)
-usually selective bases on mass and charge (anion/cation) (amino acids in channel interact noncovalently)
-driving force is the electrochemical gradient of the ion(s)
what are channel gating mechanisms?
-open or closed conformation
-gated-number of mechanisms
-activation results in conformational change
what are voltage-gated potassium channel (K+)?
-patch clamping allows for electrochemical study of single channel proteins
-can exist in three different states: open, inactivated, and closed
-once opened, more than 10 million K ions can through per second
-after the channel is open for a few milliseconds, the movement of K ions is “automatically” stopped (inactivated)
-activation is the opening of the channel in response to stimuli
-inactivation is a cessation of conduction despite that the stimuli is still present
what is the bacterial KcsA potassium channel?
structure dictates function (selectivity)
selectivity filter (specific part) (where what allowed to pass through is decided)
-amino acids line it, with there carbonyl sides facing the pore
-8 C=O groups with forms ring 3.0A (particular diameter)
-coordinate interaction with K ion (K+2.7A)
-other ions dont efficiently interact
what is carrier protein facilitated diffusion?
movement facilitated by membrane protein
-carrier or transporter
-specific for solute
not just a pore (like channels)
-does not require stimuli or energy
-actually needs conformational change
-carrier has a solute binding site (on extracellular side)
-solute binding causes conformational change in carrier
-slower than channels
-principle mode of passive transport polar organic solutes across membranes (glucose, amino acids
what is the summary of carrier protein facilitated diffusion?
what are the kinetics of simple vs facilitated diffusion?
what is the physiological examples of facilitated diffusion?
glucose transporters
-insulin regulates blood sugar levels
-increased blood glucose causes insulin secretion which causes glucose uptake into cell
-glucose transporters moved to cell surface (increases amount of carriers)
what is active transport?
-cells maintain an imbalance of ions across the plasma membrane, which cannot occur by either simple or facilitated diffusion
-electrochemical gradients are generated by active transport
-coupled energy input needed like ATP hydrolysis, absorbance of light, electron transport, or the flow of other substances down their gradients?
what are electrochemical gradients?
what are the two types of active transport?
two types
-primary active transport
-secondary active transport
-classified based on whether ATP is used directly or indirectly
-protein is both an enzyme and transporter (pump)
-energy provided by hydrolysis of ATP phosphate bond (is an ATPase)
-transporter is phosphorylated by ATP
typically transport inorganic ions
-Na-K ATPase
-H-K ATPase
-Ca-ATPase
what is an important point about active transport?
pumps move ions which can influence cell’s electrical properties
-electroneutral
-electrogenic
what is a the Na+/K+ ATPase an example of?
primary active transport: coupling transport to ATP hydrolysis
-found only in animal cells, 10 membrane-spanning helices
-2 K in and 3 Na out (inhibited by ouabain)
-P-type pump: phosphorylation causes changes in conformation (E1/E2)/ion affinity
-transport against gradients
what is H/K ATPase an example of?
electroneutral pump (in parietal cell)
-stomach proton (H+) pump
-acidifies stomach
-exchanges 2 H+ for 2 K+
what is co-transport?
co-transport (active transport): coupling transport to existing ion gradients
-potential energy stored in ionic gradients can be utilized to perform work
-intracellular [Na+] kept low by a Na/K ATPase pump
-diffusion of [Na+] down a concentration gradient drives the cotransport of glucose
what is secondary active transport?
co-transport
2 types
-symporter
-antiporter (exchanger)
what are neurons and what are the parts?
neurons are specialized cells that use changes in membrane potential to transmit information
-dendrites receive incoming information
-cell body contain the nucleus and metabolic center of the cell
-axon is a long extension for conducting outgoing impulses
what is bioelectricity?
what is the resting membrane potential (RMP)?
-result of differences in ion concentration and membrane permeability to ion
-most important ion in RMP generation is K+
what is the action potential?
cell is stimulated: Na channels open which causes membrane depolarization
one of two things can happen
1. small depolarization=membrane returns to RMP
2. threshold level of depolarization achieved (voltage gated Na channels open->action potential)
action potentials are all-or-none
what is the propagation of action potentials?
-local membrane currents depolarize adjacent membrane regions
-unidirectional
-nerve impulse retains intensity/strength with propagation
what is determines the speed of the propagation of action potentials?
-speed of neural impulse depends on axon diameter and myelination
in myelinated axons, Na ion channels reside in unwrapped gaps (nodes of ranvier)
-only site where action potentials can be generated
-saltatory conduction
