bmsc 207 cell membranes Flashcards
cells, tissue, organ, organ system
cell: smallest unit of structure capable of carrying out life processes
tissue: collection of cells carrying out related functions
organs: formation of tissues into a structural and functional unit
organ system: intergrated groups of organs
emergent properties
properties of a complex system that cannot be explained by knowledge of a systems individual components
ex) emotion or intelligence in humans cannot be prediceted by knowing properties of nerve cells
extracellular fluid
extracellular fluid: surrounding cells is a buffer between cells and the external environment
local and reflex control
local control: restricted to tissues or cells involved (small region of the body)
activce cells–> reduced O2 levels in tissue
endothelial cells send local signals, sense when O2 levels drop and restore it
reflex control: uses long distance signaling, changes widespread throughtout the body and uses more complex systems to maintain homeostasis ex)blood pressure
broken down into two parts
response loop
feedback loop: modulates the response loop
feedback loop and response loop
feedback loops modulates the response loop
negative/positive feedback and feedfoward
reflex control aquarium example
stimilus: water temp below the setpoint
sensor: thermometer
input signal: signal passes from the sensor to control box through the wire
integrating center: control box
output signal: wire to heater
target: heater turns on
response: water temp increases
negative feedback
a pathway in which the response opposes or removes the stimulus signal
stabilizes a system
homeostatic
example is high blood glucose
negative feedback for blood glucose concentration
stimulus: rising blood glucose level
insulin secreting cells of pancreas detects it
releases insulin into the blood
liver takes up glucose and stores it as glycogen
most body cells take up more glucose, glucoe level declines to set point
glucagon cells in the pancrease detect decling blood glucose levels
reflex control systems (baroceptor reflex/inc blood pressure example)
stimulus: stretch of artery wall due to inc pressure
sensor: baroreceptor
input signal: mechanical stretch is converted to AP that travels back to CNS
integrating center: medulla
output signal: AP are sent out toward the target tissues
target: heart and peripheral arterioles
response: reduced heart rate, stroke volume
positive feedback loops
not homeostatic
reinforce a stimilus and drive the system away from normal value rather than decreasing it
example) child birth
functions of the cell membrane
physical isolation: physical barrier seperating ECF and ICF, seperates cell from environment
regulation of exchange with the environment: controls entry, elimination and release
communication b/w the cell and its environment: contains proteins that allows it
structural support: proteins in the membrane are used to make cell-to-cell connection and to anchor the cytoskeleton
cell membrane composition
55% protein
45% lipids
small amount of carbs
- not all cell membranes are created equally
the 3 lipids found in the cell membrane are…
phospholipid 50-60% major lipid
sphingolipids 30% formlipid rafts (elevated or caveolae)
cholesterol 20%
squeezes between phospholipid head and inc in viscosity and help make membrane imperable to small water soluble molecules
cell membrane proteins
integral proteins: are integrated in the membrane have to disrupt the membrane to obtain the proteins
Transmembrane proteins
lipid anchored proteins anchored in the lipid bi layer
roles: membrane receptors, cell adhesion molecules, transmembrane movement, enzymes, mediators of intracellular signaling
peripheral: attached to integrated proteins
loosely attached to phospholipid head
roles: participate in intracellular signalling
form submembraneous cytoskeleton protein (that links cytoskelton to the membrane)
lipid rafts and lipid anchored proteins
lipid rafts are made up of sphingolipids
lots of lipid anchored proteins in the lipid rafts meaning they asscoiate with sphignolipids not really phospholipids
two types of rafts
1) planar lifted raft, elevated region
2)Caveolae: addition proteins that form a indentation instead of sticking out
cell membrane carbohydrates
carbs found on the extracellular side
1) glycoproteins carb attached to protein
2) Glycolipids carb attached to lipid
small protein chains
both form a protective coat (glycoalyx)
cell-cell recognition/interaction
body fluid compartments
intracelluar fluid all the fluid within cells in the boyd
extracellular fluid: acts as a buffer between the external environment and internal environment , all fluid in our body surrounding cells consist of:
interstitial fluid is fluid existing adjacent cells (75%)
blood plasma liquid component of your blood (25%)
body is mostly water
60% of body weight is water
1/3 inECF and 2/3 in ICF
osmosis, extracellular and intracellular compartments are in osmotic equilibrium
fluid concentration are equal, the amount of solute per volume solution
osmosis: the movement of water across a membrane in response to a solute concentration gradient
region of low solute conc to region of high conc and can move freely between the intracellular and extracellular spaces
water moves because of aquaporins
adipose tissue vs skeletal muscle
adipose tissue very little water, 90% lipids
skeletal muscle: 75% water, 18% protein
distribution of ions in ICF and ECF (chemical disequilibrium)
there is osmotic equilibrium but does not mean we are chemical equilibrium hence the distribution of ions
higher in ECF: Na, Cl, Ca, HCO3
higher in ICF: K, anions, proteins
osmosis and osmotic pressure
Two compartments are seperated by a membrane that is permeable to water but not glucose
glucose is dumped in, they wont be in osmotic equilibrium
after dumping it in water will start to move into the column with higher solute concentration,
excess soulte in one of the compartments water will move to keep that osmotic equilbrium
osmotic pressure can be applied to make the water not move, it opposes osmosis
isosmotic, hyperosmotic, hyposmotic
normal osmolarity in human body is 280-296 mOsM
isosmotic: solutions have identical osmolarities
hyperosmotic: (higher than) desribes the solution with the higher osmolarity
hyposmotic: less than, the solution with the lower osmolarity
osmolarity
describes the number of particles in solution
osmotic movement of water can be predicted by knowing the solute particle concentrations of each solution
not molarity (number of dissolved solutes/litre of solution) because we are interested in osmolarity active individual particles as opposed to entire molecules
know the overall number of particles that contribute to the conc gradient, drives the movement of water
molarity x particle/molcule =osmolarity
tonicity vs osmolarity
osmolarity is the number of particles dissolved in solution and can be measured, tonicity cannot be measured, comparable term
osmolarity is used to comapred two solutions, tonicity always compares a solution and a cell and desribes the solution
osmolarity does not tell you what happens to the cell because changes in cell volume depend on non pentrating solutees. tonicity tells you what happens to cell volume when placed in solution
tonicity depends on non-pentrating solutes
tonicity
desribe a solution and how that solution would affect cell volume if a cell were placed in the solution
hypotonic: cell swell
isotonic: nothing happens
hypertonic: cell shrinks
osmolarity vs osmolality
osmolarity= osmoles oer litre of solution
osmolality= osmoles per kg of solvent
small concentrations of solute they are near identical
solvent weght is differnet because osmolarity takes in account solute content whereas osmolaity excludes solutes
diffusion (definiton and general properties)
the movement of molecules form an are of high conc to area of low conc
general properties: uses the kinetic energy of molecular movement and does not require an outside energy source
moleucles diffuse from are high to area of low
diffusion continues until cocentrations come to equilbrium
diffusion is faster: along higher conc gradients, over shorter distances, at higher temperatures, for smaller molecules
diffusion can take place in an open system
how can diffusion be faster
along higher concentration gradients
over shorter distances
at higher temperatures
for smaller molecules
simple diffusion
for small uncharged lipophilic molcules: O2, CO2, lipids, steroids
the rate of diffusion through a membrane is faster if:
membrane surface area is larger, the membrane is thinner, the concentration gradient is larger, the membrane is more permeable to the molecule
membrane permeability to a molecule depends on: the molecules lipid solubility, the molecules size, and the lipid composition of the membrane
Ficks law of diffusion
rate of diffusion=
membrane premability=
ficks law incldues equlbrium when finding permeability
rate of diffusion= surface area x conc gradient x membrane permeability
membrane permeability= lipid solubility/molecular size
changing the composition of the lipid layer can inc or dec membrane permeability
protein mediated transport
facilitate diffusion or
active transport
channel proteins
channel proteins create a water filled pore
made of membrane spanning protein subunits that create a cluster of cylinders with a pore through the center
mainly smaller substances pass through
open channels
and
gated channels (chemically, voltage, mechanically)
channel protein (selectivity)
determined by the size of pore and the charge of the AA lining in the pore
carrier proteins
large complex proteins
change conformation to move molecules
slow
never form an open between the two sides of the membrane (ECF and ICF)
ex) carrier open to ICF then later open to the ECF
molecule gets in from ECF opening then ECF side closes then molecules goes out the ICF side
facilitated diffusion
some molecules and ions appear to move into and out of the cell by diffusion, but based on their chemical properties, this cannot be simple diffusion across the lipid bilayer
use channel or carrier proteins
ion moves down their concentration gradient or electrochemical gradient
no energy required (passive)
stops once equilibrium is reached (when the concentration of molecule is equal on the inside and outside
active transport
moves molecules against their concentrations gradients: from an area of low conc to an area of high conc
supports a state of disequilibrium, requires energy, uses carrier proteins
primary active transport: energu to move molecules come directly from hydrolyzing ATP (ATPase)
secondary transport: uses the potential energy stored in the conc gradient of one molecule to push another molecule against their conc gradient
primary transport example
Na/K ATPase cretates the state of disequilbrium
3 Na out and 2 K in
1) 3 sodium from the ICF bind to high affinty sites (affinity meaning sticky will bind)
postassium has low affinity
ATP hyrdolyzed ADP + energy
2) ATPase is phosphorylated with Pi from aTP
3) Na binding sites lose their affininty for Na and relase 3 Na into the ECF
High affininty sites for K appear
4) 2 K from the ECF bind to high affinity sites
5) high affininty binding sites for Na appear
K binding sites lose their affininty for K and release 2 K into the ICF
specificity
specificity refers to the ability of a transporter to move one molecule or a closely related group of molecule
one or a group
if it carries multiple it is a lower specificity
e.g., GLUT transporters moves naturally occuring 6 carbon sugars but will not move disaccahride maltose
secondary active transport (Na)
the majority harnesses the kinetic energy of Na moving down its conc gradient to move a second molecule against its conc gradient
can move in the same direction (symport) or opposite (antiport)
competition and saturation
competition: a carrier may move several members of a related group of substances but these substances competition with one another.
saturation: rate of transport depends on concentration and number of transporters
transport normally increases with increasing concentration until transport maximum is reached (all transporters are in use)
saturation occurs when transport max is reached
vesicular transport
macromoleucles that cannot fit rhough a carrier or channel: phagocytosis, endocytosis, exocytosis all use bubble like vesciles crated from the cell membrane
phagocytosis
creates vesicles using the cytokskleton
requires ATP to move the phagsome to a lysosome
the phagocytic white blood cell encounters a bacterium that binds to the cell membrane
it will uses the cytoksleeton to push its cell membrane around the bacterium, creating a large vesicle (phagosome)
the phagosome goes into the cytoplasm and the bacterium dies
endocytosis- transport into the cell
differs from phagocytosis: membrane indents (inward not outward), vesicles are much smaller, can be sensitive, also requires ATP
non selective:
pinocytosis: allows ECF to enter
selective: receptor mediated transport
1) ligan binds to membran receptor
2) receptor ligand migrates to clathrin coated pit
3) endocytosis
4
exocytosis
transport out of the cell, transport vesicle and cell membrane fuse
receptors inserted back into the membrane
vesicles can be ffilled with large lipophobic molecules such as proteins
can occur continuously (goblet cell in the intestine)or intermittently (hormones, electrical)
requries ATP
can be regulated by Ca
aquaporins are an example of what type of channel
leak
epithelial transport
secetion/ absorption
substances entering and exiting the body or moving between compartments often must cross a layer of epitheial cells )line lumen or surface structure in the body)
digestive tract, airways, kidneys etc
from lumen of organ to ECF= absorption
from ECF to lumen of organ= secretion
tight junctions
seperate the apical membrane from the basalateral membrane
any protein created in the apical membrnae stays there doesnt go to the basalateral membrnae vice versa
they are variety of transmembrane proteins that link the adjacent epithelial cells
transcellular, paracellular, transcytosis
smaller substances that can diffuse across or fit through a carrier or channel is trans and para
transcellular: across epithelial cell,
paracellular: beside, between tight junctions
diffusion no transporters that exist between the space of cells
the tightness of tight junctions depends on the rate
transcytosis: larger substances like protiens that cant fit through channel
epitheial cells basallateral apial endocytosis on one vesicles transported to the baslateral and it exocytosised
properties for basalaterla and apical
different properties
polarized disribution of membrane transporters ensures one way movement
membrane transport summary
passive transport: it does not rquire energy, substances move down the gradient two types simple and facillitated diffusion
active transport: requires energy, substances move uphill (against gradient)
two types: primary and secondary
vesicular transport: it does require energy
three types: phagocytosis, endocytosis, exocytosis
epithelial transport: it sometimes requires energy (transcellular and transcytosis)
three types: parracellular, transcellular, transcytosis
major cations and anions
major cations: intracellular K, extracellular Na
anions: intracellular phosphate ions, proteins
extracellular Cl
membrane potential (what is it and how its created)
the electrical disequilbrium that exists between the ECF is called the membrane potential
when we begin there is no membrane potential, the ECF and ICF are electrically neutral
we insert a leak channel for K, K starts to move out of the cell down its conc gradient
the inside of cell becoming more negative and the outside of the cell becoming more positive. some potasium cell starts to get drawn back in to the negative charge, eventually the amount leaving and coming in is equal (equilbrium potenital)
nernst
equation used to find the equilbrium of an ion
need to know charge of ion and conc gradient of the ion
