Biological membranes Flashcards
What are membrane functions
- barrier
- cellular organization
- transport
- signal transduction
- cell-cell communication
membrane lipids are ____which mean they have a hydrophobic and hydrophilic component.
amphipathic
What is the hydrophobic and hydrophilic region of glycerophospholipid
diacylgycerol; phosphorylated alcohol
What is the hydrophobic and hydrophilic region of sphingomyelin
ceramide; phosphorylcholine
what is the hydrophobic and hydrophilic region of glycosphingolipid
ceramide; sugar residues
what is the hydrophobic and hydrophilic region of cholesterol
hydrocarbon rings; OH group at carbon 3
Inner and outer leaflets of single membranes have different compositions:
One layer exposed to environment and one layer exposed to interior of cell.
What gets flipped out to exterior of cell during apoptosis and serves as a signal for phagocytosis
Phosphatidylserine; usually very little on outer leaflet, entirely internal
What does flipase do
move PE (phosphatidylehanolamine) and PS (phosphatylserine) from outer to cystolic leaflet
What does amount of membrane movement depend on
percentage of unsaturated fatty acids
What does floppase do
moves phospholipids from cystolic to outer leaflet (one used by phosphotidylserine)
What do scramblase’s do
moves lipids in either direction, toward equilibrium
What physical factors affect fluidity of membrane
- temperature
- pressure
- membrane potential
what chemical factors affect fluidity of membrane
- head group of phospholipid
- FA chain length
- FA unsaturation
- cholesterol
what indirect factors affect fluidity of membrane
- hormones
- adaptation to stress
- cell cycle
- cell differentiation
Unsaturated has more fluidity bc:
they cannot pack as tightly as saturated
% of saturated fats affects melting temp bc:
more long chain saturated fats inc melting temp due to packing
Lateral diffusion of cell-surface proteins is very fast:
- virus induced fusion
2. mixture of labeled proteins from the membranes in heterokaryon (hybrid cell)
Flourescence recovery after photobleaching is a techniqe to monitor lateral diffusion of lipids and proteins in membranes. How does it work?
- Shine light on it –> bleaches out flourescence
- Fourescence intensity goes very down
- Wait and it starts to recover as other still labeled monomers come to that region
- This shows that there is a lot of movement within our membranes.
What is the fluid mosaic model
lipid bilayer composed of phospholipids and sphingolipids. There are peripheral proteins, integral proteins, glycolipids
what are the membrane proteins
- peripheral
- amphitropic
- integral
- lipid (GPI) -linked
What are amphitropic proteins
proteins that bind loosely to suruface of lipid bilayer and can be released.
what is a glycophorin
a well characterized membrane protein of RBC’s.
- Hydrophobic domain
- Hydrophillic domain (intracellular)
- Membrane spanning (hydrophobic)
what are integral proteins
All have an alpha helical, hydrophobic region of aa that will be the membrane spanning portion.
what are lipid rafts
stable microdomains of cholesterol and sphingolipids that can form on either the inner or outer leaflet that serve as sites for lipid -linked protein attachment
What is a caveolin
protein dimers that are lipid-linked to the cell membrane, they produce invaginations in the cell membrane
what processes cause membrane fusion
- building of vesicles from golgi complexes
- exocytosis
- endocytosis
- viral infection
- fusion of sperm and egg
what is exocytosis
membrane fusion and nuerotransmitter release
what proteins does exocytosis use
SNARE’s and SNAP25; form zipped up component and keeps pulling it toward fusion until you get an opening for contents of vesicles to be released.
what is endocytosis
- phagocytosis of particulate matter
- pinocytosis take up extracellular fluid
- receptor mediated endocytosis
What is receptor mediated endocytosis
LDL receptors bind to LDL particles that cause them to be endocytosed.
What is familial hypercholesterolemia
People who have defective LDL receptors accumulate high levels of LDL in their blood that cause them to have heart attacks and atherosclerasis
What are the 2 types of active transport
- Primary active transport: Directly use ATP hydrolysis to move things in and out
- Secondary active transport: Use ATP hydrolysis to create a conc. gradient that is used to symport other things in and out
Lipid bilayer is not a barrier for :
- gases (oxygen, CO2)
- ethanol (polar molecules and small uncharged)
- water
what can’t cross lipid bilayer
- large molecules - glucose
- ions
- polar charged molecules - aa, nucleotides, sugar phosphates
What is solute movement across membranes like
movement of charged solutes will depend on a combination of chemical and electrical gradients: electrochemical potential
Transporter reduces delta G of _____
diffusion; makes it more efficient to get it in and out
What are the 6 major types of membrane transport
- Simple diffusion: nonpolar compounds only, down conc gradient (high to low)
- Fascilitated diffusion: uses protein; from high to low
- Primary active transport: against electrochemical gradient
- Secondary active transport:
- ion channels:
- ionophores:
What are general classes of transporters
- uniporters: carry 1 molecule back and forth
- symporter: take 2 molecules in same direction
- antiport: taking one in and one out at the same time
what is the driving force in Simple diffusion
entropy
what is hypertonic
high salt solution than intracellularly so water diffuses out and cell shrivels
what is isotonic
salt conc is same inside and out. cell is in equilibrium
what is hypotonic
higher salt conc inside than outside, so water goes inside cell to make equal conc. cells swell
What is a good ex of fasciliated diffusion
- chloride bicarbonate exchanger. it uses an antiporter
2. GLUT1 Transporter
What are three types of Primary active transporters
- P type: Na/K ATPase, SERCA calcium pumps
- F type: uses proton gradient; ex is mitochondrial ATP synthase
- ABC Type: dimer with 2 ATPase. Ex: CFTR
How does Na/K+ ATPase work
Sets up membrane potential. Makes it more negative on the inside and more positive on outside. Ships 3 Na out and 2 K+ in. Low sodium inside, high potassium
What are ion channels
- Resting is always open
- Voltage gated: responds to change in membrane potential
- Ligand gated: responds to extracellular neurotransmitter
- signal gated: responds to int cellular signal transduction events.
How do voltage gated K+ channels work
Contain R residues that are pulled toward - charged cytosol. When membrane depolarizes, pull is lessened, conformation changes, pore opens.
what are ionophores
masks charge and shuttle ions across membrane.
