Biological Membranes Flashcards
Explain general properties of membranes, their functions, channels & association
What are primordial germ cells
Stem cells that make reproductive gametes
What did Hooke discover?
Cell theory
How are prokaryote types separated ?
By ribosomal RNA sequences
What are the types of prokaryotes?
Archaea, Eubacteria
Describe the characteristics of gram negative prokaryotes
Periplasmic space, thin layer of peptidoglycan
Describe gram positive bacteria
large layer of peptidogylcan
Give an example of gram positive bacteria
staphyloccal, streptococcaal
Give an example of gram negative bacteria
E.coli salmonella
What is a lysosome?
an organelle in the cytoplasm of eukaryotic cells containing degradative enzymes enclosed in a membrane
What charge do nuclei have?
Negative
What does fluorescence microscopy allow?
Visualisation of proteins and lipids in fixed cells
What cells have a specialised plasma membrane?
Rod and cone cells
What is the key role of phosphoinositides?
Responding to growth factors
What type of bonds does acetone form with water?
Electrostatic interactions
Why does acetone form electrostatic interactions with water?
It is polar
What type of bond does 2-methyl propane form with water and why?
none - non-soluble so forms a crystalline ice cage due to non-polarity
Name the features of epithelial cells
Highly organised cells, very motile, ALWAYS polarised, apical and basolateral domains, always exposed to environment
What is the function of white blood cells
secrete antibodies
What are acinar cells
exocrine cells of the pancreas
What is the function of acinar cells
secrete lots of digestive enzymes to assist with digestion of food
What are the properties of the Plasma membrane
Barrier and selectively permeable
What is the PM composed of
Lipids, proteins and carbohydrates
What carbohydrates is the PM composed of and how do they bond?
Glycoproteins and glycolipids that covalently link to proteins and lipids
What are oligosaccharides?
carbohydrates composed of a small number of monosaccharide units
How are phospholipids held together?
non-covalent forces; Van der Waals and hydrogen bonding
Why are phospholipids amphipathic?
polar head group and hydrophobic tail
What is the charge of phospholipids?
Neutral
Why do phospholipids have a neutral charge?
Choline is positively charged and phosphate has a negative charge
What are the four main membrane phospholipids?
Phosphatidyl-ethanolamine
Phosphatidyl-serine
phosphatidyl-choline
Sphingo-myelin
Which major membrane phospholipid has a negative charge?
phosphatidyl-serine
TRUE or FALSE - all major membrane phospholipids have a neutral charge except phosphatidyl-serine
TRUE
What form do fatty acid chains normally take in nature?
Cis
What forms the polar head group in phospholipids
choline
describe cis fatty acids
have kinks/bends so cant pack closely together
what is lacking in bacterial membranes
cholesterol and sphingomyelin
What do phospholipids form in aqueous solutions
micelles or bilayers - more energetically favourable
What is the structure of a liposome?
spherical structure of phospholipids arranged around a water molecule
What the applications of liposomes?
drug delivery into cells, DNA delivery and cosmetics
What phospholipid movement rarely occurs
flip-flop
Describe the effect of cholesterol on the membrane
increases fluidity at high temperatures and decreases permeability
What are tetraspanins?
scaffolding proteins
What is the function of tetraspanins?
Anchor multiple proteins to one area of the membrane, important in the immune system
Describe micro-domains
Joining of proteins and lipids, thicker than the rest of the bilayer, accumulation of proteins allows rafts to stick together
What are the types of phospholipid movement?
Lateral diffusion, flexion, rotation, flip-flop
Describe lateral diffusion
rotation or exchange in the lateral plane of the membrane
Which phospholipid movement is the most energetically favourable
lateral diffusion
Describe the effect of unsaturated hydrocarbon chains with cis double bonds on the membrane
Increases fluidity
What is the effect of saturated hydrocarbon chains on the membrane and why
Decreases fluidity because they pack tightly together
What type of hydrocarbon chain increases membrane fluidity
more double bonds, shorter chains
What type of animals have more double bonds
cold blooded animals
Describe the structure of cholesterol
small polar head group, steroid ring, rigid structure
What does cholesterol prevent at high concentrations
congealing and crystallisation
What does no recovery/repopulation after fluorescence photobleaching show?
no mobility
What does fluorescence recovery after photobleaching allow?
measure the rate of mobility
What is the effect of a tethered nuclear membrane on mobility
no mobility
What are the types of secondary structure
alpha helix, beta sheet, random coil
Which way do side project in an alpha helix
outwards
describe the structure of beta sheets
kinked stable structures, parallel or antiparallel, polypeptide chains project above and below
What are the two types of protein association with the membrane?
Peripheral and integral
How do peripheral membrane proteins associate with the membrane?
covalently bind to lipids or associate directly with integral membrane proteins
How do integral membrane proteins associate with the membrane?
Insert directly via a hydrophobic domain
How many times do G-protein coupled receptors span the membrane?
7
What are the advantages of lipid anchoring on membrane proteins?
Mobility, rapid release into extracellular space, regulate binding and release of proteins to membrane
Proteins linked to … move more rapidly
phosphatidylinositol
What bonds hold together single pass transmembrane proteins?
Disulphide bonds
What do hydropathy plots measure
hydrophobicity of amino acids
What are beta barrels function in bacteria?
pore forming proteins
What is the effect of detergents on membranes?
solubilise phospholipids in membranes, causes proteins to acquire a negative charge
What is an example of a harsh membrane detergent
sodium dodecyl sulphate
What is the effect of sodium dodecyl sulphate on the membrane
linearises membranes
what are the functions/types of integral proteins
enzymes, carriers, channels, receptors, cell-cell recognition
What are the functions/types of peripheral membrane proteins?
cell shape determination, communication with internal and external environment, cell signalling
What happens to red blood cells in a hypotonic solution?
creates RBC ghosts, form a pure preparation of the plasma membrane
What is SDS polyacrylamide gel electrophoresis used for
analyse proteins and separate them based on size
what does spectrin form
dimers
what is spectrin
cytoskeletal protein that lines intracellular side of PM in eukaryotic cells
What is spectrin important for
mechanical stability of RBCs
What do mutations in spectrin cause?
types of haemolytic anaemia
What are the peripheral proteins in RBC cytoskeleton
spectrin, actin, ankyrin
What are the transmembrane proteins in RBC cytoskeletons
glycophorin, band 3
What is the RBC biconcave shape maintained by
mesh of proteins lining inner surface of the membrane
What protein is NOT freely diffusible in the RBC cytoskeleton
Band 3
What are the restraints on protein movement
Physical structures and direct interactions with the cytoskeleton
What do tight junctions prevent in the PM
free diffusion in cytoplasmic leaflet and partial lipid barrier
What are the restraints on lipids
sequestation by binding to specific proteins, segregated into domains, physical barriers
What is the glycocalyx
the cell coat
How is the glycocalyx formed
association of sugar residues with transmembrane and peripheral proteins at extracellular surface
What blood group is the universal donor
O
What blood group is the universal acceptor
AB
What is blood group determined by?
structure of the oligosaccharide attached to sphingomyelin and proteins in the RBC membrane
What is the function of scramblase
abolish asymmetry by
equilibrating lipids, transferring lipids and catalysing flipping of phospholipids
What is the NET charge on the cytoplasmic side of RBCs
negative
What does the net equilibrium favour under normal condition in RBCs PM
translocase
what is the function of translocase in RBCs PM
transfer phosphatidyl-serine from outer leaflet to the inner leaflet
What type of molecules can move freely across the PM
hydrophobic molecules EG O2, CO2, N2 and benzene
What do the rate that molecules move across the membrane depend on
charge, size and polarity
What type of molecules do membrane transport proteins move
solutes like sugars, amino acids, nucleotides and ions
What are the two main classes of membrane transport protein
carriers and channels
What are membrane transport proteins
multi-pass integral membrane proteins
What type of interaction do carriers have with the solute?
Direct interaction - binding
Which membrane transport protein is the fastest
channels
What type of interaction do channels have with the solute
weak
what do ion channels form
narrow hydrophilic pores through the membrane
What do ion channels allow
rapid movement of ions down concentration or electrical gradient
How do ions move through ion channels
the selectively filter means ion fit through interactions with carbonyl groups in pore
What are ion channels regulated by?
binding of ions, changes in voltage or binding of small molecules
Mutation in what channel causes congenital insensitivity to pain
SCN9A - voltage gated sodium channel
How do carriers transport solutes
undergo conformational change
What are the types of carrier?
uniport, symport and antiport
what creates the electrochemical gradient
membrane potential and concentration gradient
What is the electrochemical gradient established by?
ionic concentration differences on either side of the membrane
What pumps use active transport
ATP-driven pumps, light driven pumps
What is the uptake of glucose driven by
Electrochemical gradient of Na+
What type of transport moves glucose
coupled transport
How do sodium and potassium move by a sodium potassium ATPase
3Na+ move out, 2K+ move in
