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MEMBRANE DYNAMICS and Cell Signaling (PROPERTIES OF CARRIER MEDIATED…
MEMBRANE DYNAMICS
and Cell Signaling
Cell Membrane
phospholipid bilayer
cholesterol
proteins: integral/transmembrane and peripheral
glycolipids
glycoproteins
Passive Transport
(doesn't require energy)
simple diffusion across a permeable membrane
allows for movement of lipophilic substances
requires conc. gradient (substances move :arrow_up: to :arrow_down: conc.)
Factors that influence diffusion rate
general properties: uses kinetic energy of molecular movement and uses conc. gradient
MEMBRANE
properties
S.A.
Thickness
SOLUTE
PROPERTIES
M.W. (size)
Lipid Solubility
Lipid Conc.
Uses
Membrane Transport Proteins
cylinder
shaped (move water & ions) :droplet:
gated
(open or closed)
chemically gated :female-scientist::skin-tone-5:
voltage gated :zap:
channel
proteins (generally do not change shape)
carrier
proteins (bind substances & carry them across membrane; undergo conformational change) :baggage_claim:
Types
Uniport: transports 1 substance
Symport: 2+ substances in
same
direction
Antiport: 2+ substances in
opposite
directions
Primary Active Transport
(Uses ATP directly :explode:)
1) Molecule (or ion) binds to transport protein
2) ATP is hydrolyzed to ADP and P gets released
3) Phosphate binds to transport protein. Phosphorylation causes protein to change shape, substrates are on other side of membrane
4) Transport protein releases phosphate & returns to reg. shape
Secondary Active Transport
(uses potential energy from conc. gradient as energy source)
needed ATP to set up conc. gradient :explode:
glucose is transported against its conc. gradient when Na+ moves down its conc. gradient (SYMPORT)
sodium-glucose transporter [Na+ gradient created by pump]
PROPERTIES OF
CARRIER MEDIATED TRANSPORT
Binding Affinity:
depends on formation of a set of weak, non-covalent bonds
Competition
: Diff substances may compete for binding sites on transporters
Specificity:
protein can only bind to 1 or 2 other molecules (Transport proteins only bind to specific molecules)
Terms
Antagonist
: binds to receptor but doesn't activate it, blocks agonist activity
Agonist/ Ligand:
substance fully activates receptor that it binds to
Saturation:
rate of transport
VESICULAR TRANSPORT
(transports molecules too lrg. for protein channels or carriers)
endocytosis
- transports materials into cells via membrane bound vesicles
exocytosis
- releases lrg. molecules out of cell
RESTING MEMBRANE POTENTIAL
due mostly to potassium (K+) ions conc. gradient created by Na+/K+ pump
Cell membrane separates electrical charges in the body
an uneven distribution of ions (electrical charge) between the ICF and ECF
CREATION OF A MEMBRANE (ex. with an artificial cell)
:check:cell is initially electronically neutral (NO MEM POTENTIAL) (+)ions= (-) ions
:check:Insert K+ leak channel into the cell...K+ leaks outside the cell
down its conc. gradient
resulting in a
net negative charge
inside
the cell and a
net positive charge
outside
the cell. The cell now has a
membrane potential diff.
The resulting (-) membrane potential attracts K+ back into the cell, however K+ wants to move out due to conc. gradient. K+ ions eventually stop moving which results in an equivalent potential of (Ek= -90mV)
:check:Insert a Na+ leak channel into the cell. Cl- contributes to a (-) charge outside of the cell. Na+ moves back out of the cell attracted to a (-) charge. (Ena= +60mV)
NOTE: Cells are permeable to more than 1 ion. Most cells are
more
permeable to K+. Human body cells are 40x more permeable to K+ so resting membrane potential is -70 mV