Lecture 7: Membranes, Composition and Function Flashcards
Plasma membrane
Plasma membrane has selective permeability to maintain differences in composition between the inside and outside of the cell (cell homeostasis)
Selective permeabiltiy
molecules can pass through membrane through transporters or ion channels
- lipid soluble molecules can pass
- O2, N2 and CO2 (gases) can pass membrane
Order of cell
Organism> Organ> Tissues > Cell > Organelle
Membranes are:
- asymmetric
- proteins can move laterally
- form specialized compartments within cell for ex. organelles
Cilia
- detect sound
- borders hair cells around ear
Intercalated discs
- heart
- allow electron coupling of cells
Synapse
site of chemical communication between adjacent cells
Cholesterol
-mostly resides within plasma membrane but smaller amounts are found within mitochondrial, Golgi complex and nuclear membranes
Membrane fluidity
the kink in the tail of the unsaturated fatty acid increases membrane fluidity
What increases plasma membrane fluidity?A.Phospholipids with unsaturated fatty acids.
B.Phospholipids with saturated fatty acids.
C. Glycolipids
D.Surrounding water molecules.
A.Phospholipids with unsaturated fatty acids.
Ions are
Hydrophilic or lipophilic and need ion channels to pass membrane
The permeability coefficient
measures the ability of a molecule to diffuse across a permeability barrier
The drug prednisone is a corticosteroid that is used to treat many inflammatory diseases including asthma
The lipid bilayer permeability coefficient of prednisone is:
A.Equal to that of water. B.Lower than that of water.
C.Higher than that of water.
C.Higher than that of water.
This drug is has rings which make is hydrophobic so its harder to pass through the membrane than water
Active transport
Movement of molecules against concentration gradient using energy
Simple diffusion
molecules diffuse through the lipid bilayer
- driven by the transmembrane gradient of substrate
Facilitated diffusion
movement of molecules with the aid or a protein, transporter or ion channel
Uniport
transport a single species across membrane in one direction
Symport
transport a two species across membrane in the same direction
Antiport
transport a two species across membrane in the opposite direction
Aquaporins
- water channels
- always open
- cells regulate water movement
Ion channels
- permeability of a channel depends on charge, the extent of hydration and size
- maybe always open
- often active transporters
The concentration of sodium Na+ is:
A.higher inside than outside the cell?
B.equal between the inside and outside of the cell?
C.higher outside than inside the cell
C.higher outside than inside the cell
3 Na+ out for every 2 K+ in
Sodium potassium pump
-Powered by ATP
-2K+ into cell
3Na+ out of cell
-net +1 increase in charge outside
Weak acid
pH>pKa Ionized form charged
pH
Weak base
pH>pKa Unionized form uncharged
pH
Fluid base pinocytosis
random and nondirected
Absorptive endocytosis
selective and occurs in coated pits
Gap Junctions
-allow direct flow of molecules from one cell to another
Exocytosis
releasing of hormones out of cell
peripheral vs integral proteins
Integral proteins are embedded in the whole bilayer
Peripheral proteins is only located in the inner or outer surface of the phospholipid bilayer
Mosaic
constant fluid movement in membrane
-Proteins and phospholipids can move laterally in the membrane
The majority of cholesterol resides
within
plasma membranes
- smaller amounts are found within mitochondrial,
Golgi complex, and nuclear membranes
What other ways regulate fluidity and permeability?
The hydroxyl group of the cholesterol faces water and the tail inside
away from water
So how other molecules are transported through the membrane?
-Large molecules bind to receptors - Glucose binds to a specific ping-pong receptor -Ions are transported via pumps or ion channels
Molecules with low membrane permeability are
hydrophilic or lipophobic
Molecules with high membrane permeability are
hydrophobic or lipophilic
The lipid bilayer permeability coefficient of prednisone is:
A. Equal to that of water.
B. Lower than that of water.
C.Higher than that of water
C.Higher than that of water
(GLUT) Glucose transporter
- facilitated transport
- helps to transport insulin through the membrane (cell)
“AQUAPORINS”
water channels - always open -Cells regulate water movement by controlling # of aquaporin proteins inserted into the plasma membrane
P (in P-type) transporter
signifies phosphorylation (these proteins autophosphorylate). - Ca2+ ATPase (SR); Na+ -K \+ -ATPase (PM)
F (in F-type) transporter
signifies energy coupling factors
-mt ATP synthase of oxidative phosphorylation
V (in V-type) transporter
signifies vacuolar
-The ATPase that pumps protons into lysosomes and synaptic vesicles
ABC transporter
signifies ATP-binding cassette transporter (all have two nucleotidebinding domains and two transmembrane segments)
-CFTR protein (PM); MDR-1 protein (PM)
Uionized vs ionized as far as diffusion
Unionized forms can diffuse across cell membranes
Ionized forms will be have low lipid solubility and will be harder to cross cell membranes
Diffusion of weak acid and weak base drugs through
plasma membrane depend on
pH
A caveolae
is an invagination in the
plasma membrane. The protein caveolin appears to play an important role
in the formation of caveolae and occurs as a dimer
Cystic fibrosis causes
Mutations in the gene encoding the
CFTR protein, a Cl–
transporter
