Cell Membrane 2 Flashcards
-Flexibility: ?
-Fluidity: ?
-How? → ? interactions of lipids in the bilayer
-Vesicles: ?
-Flexibility: Ability to change shape without losing integrity or becoming leaky
-Fluidity: Ability to flow
-How? → noncovalent interactions of lipids in the bilayer
-Vesicles: Intra- and extra-cellular structures consisting of liquid enclosed by a lipid bilayer
-Recognised that
individual lipid molecules can diffuse ? within ? bilayers
- Liposomes: ?
- Black membranes: ?
Synthetic lipid bilayers form ? when in solution
-Recognised that
individual lipid molecules can diffuse freely within lipid bilayers.
- Liposomes (bilayers as closed spherical vesicles), commonly used as model membranes in experimental studies
- Black membranes (planar bilayers, formed across a hole in a partition between two aqueous compartments), are used to measure the permeability properties of synthetic membranes
Synthetic lipid bilayers form liposomes when in solution
-Catalysis of transbilayer movement of lipids by: ? (3)
-Transversal Diffusion
Flip-flop: ?
-Lateral Diffusion
diffusion in the plane: ?
-Catalysis of transbilayer movement of lipids by:
* Flippases
* Floppases
* Scramblases
-Transversal Diffusion
Flip-flop: happens rarely
(unless the process is catalysed)
-Lateral Diffusion
diffusion in the plane: happens readily and rapidly
CELL MEMBRANE FLUIDITY
-The ? of a lipid bilayer must be precisely regulated –> depends on its ? and ?
-Membrane phase transition: ?
Fluidity depends on: ? (3)
-At low temperatures: ?
-At higher temperatures (20-40°C / 68-104°F): ?
Lipid bilayer is stabilized by ? interactions between lipids’ fatty acid chains
CELL MEMBRANE FLUIDITY
-The fluidity of a lipid bilayer must be precisely regulated –> depends on its composition and temperature
-Membrane phase transition: the change of a lipid bilayer from a liquid state to a two- dimensional rigid crystalline state (gel) at a characteristic temperature (melting point)
-Fluidity depends on:
1. Phospholipid content (FA length and saturation) 2. Cholesterol content
3. Temperature
-At low temperatures: less lipid movement
Lipid bilayer is in paracrystalline state (more rigid state)
-At higher temperatures (20-40°C / 68-104°F): more lipid movement Lipid bilayer becomes more fluid
-Lipid bilayer is stabilized by hydrophobic interactions between lipids’ fatty acid chains
CELL MEMBRANE FLUIDITY/FA
-Influence of cis-double bonds in membrane phospholipids ? (3)
-Influence of shorter hydrocarbon chain ?
CELL MEMBRANE FLUIDITY/FA
-Influence of cis-double bonds in membrane phospholipids :
Unsaturated FA make more difficult to pack the hydrocarbon chains together
lower melting point (liquid at colder temperatures)
Also form a thinner membrane as the phospholipids will be further spread apart
-Influence of shorter hydrocarbon chain –> lower melting point
CELL MEMBRANE FLUIDITY/FA
Saturated FA ?
Saturated FA:
-Tend to form paracrystalline structures (less space between phospholipid tails)
-↑ saturated fatty acids content of a lipid bilayer
-↑ Paracrystalline-to-fluid transition temperature of the membrane
(↑ melting point)
Unsaturated FA:
-Cis-double bonds → kinks (more space between tails) Inhibits the paracrystalline conformation
-↑ Unsaturated fatty acids content of a lipid bilayer
-↓ Paracrystalline-to-fluid transition temperature of the membrane (↓ melting point)
CELL MEMBRANE FLUIDITY/CHOLESTEROL
-Eukaryotic plasma membranes can contain very large amounts of ?
-Cholesterol molecules improve the ?-barrier properties of the lipid bilayer
-Cholesterol can ? or ? phase transitions
-High temp?
-Low temp?
CELL MEMBRANE FLUIDITY/CHOLESTEROL
-Eukaryotic plasma membranes can contain very large amounts of cholesterol
-Cholesterol molecules improve the permeability-barrier properties of the lipid bilayer
-Cholesterol can inhibit or delay phase transitions
at high temperatures
Cholesterol helps keep the membrane more stable, stiffening the bilayer and making it less fluid and less permeable
at low temperatures, acts as ‘antifreeze’
Cholesterol also helps the membrane remain fluid by preventing fatty acid tails from interacting with each other and ‘clumping up’
*ECM
-EXTRACELLULAR MATRIX: made up of what ?
-What are its functions?
-EXTRACELLULAR MATRIX: Basement membrane and Interstitial matrix
Functions: Structural and biochemical support to surrounding cells.
Common functions: cell adhesion, cell-to-cell communication and differentiation.
Animal ECM:
?: present between different animal cells (in intercellular spaces)
Each type of ? tissue in animals has a different type of ECM:
Bone tissue: consists of ? fibers and ? mineral
Loose connective tissue: reticular ? and ground substance
Blood: ECM is ? ?
???: sheet-like depositions, special type of ECM that lines the basal side of epithelial and endothelial tissues
Animal ECM:
Interstitial matrix: present between different animal cells (in intercellular spaces)
Each type of connective tissue in animals has a different type of ECM:
Bone tissue: consists of collagen fibers and bone mineral
Loose connective tissue: reticular fibers and ground substance
Blood: ECM is blood plasma
Basement membranes/basal lamina: sheet-like depositions, special type of ECM that lines the basal side of epithelial and endothelial tissues
Macromolecules in the ECM are mainly produced ? by cells in the matrix and secreted via ?.
Fibroblasts
* Fibroblasts ? and ? ECM
* In connective tissue mainly ? ?
Can differentiate into
* Chondroblasts- ?
* Osteoblasts- ?
* Myofibroblasts – ?
Macromolecules in the ECM are mainly produced locally by cells in the matrix and secreted via exocytosis.
Fibroblasts
* Fibroblasts produces and secretes ECM
* In connective tissue mainly collagen fibers
Can differentiate into
* Chondroblasts- cartilage
* Osteoblasts- bone tissue
* Myofibroblasts – muscle tissue
1) Glycosaminoglycans ?
2) Fibrous proteins ?
3) Non-collagen fibrous proteins?
1) Glycosaminoglycans (GAGs, e.g. cartilage): large and highly charged polysaccharides
GAG + proteinsproteoglycans
GAG + PROTEOGLYCANS = Ground Substance (amourphous gelatinous material, fill the space between fibers and cells)
2) Fibrous proteins like collagen (e.g. skin and bone)
3) Non-collagen fibrous proteins (elastin, fibronectin, laminin)
COLLAGEN ?
Rich in ? and ? amino acids
The fibrils are glycosylated
COLLAGEN are fibrous, long, stiff, triple-stranded helical proteins
forming fibrils.
Rich in proline and glycine amino acids
The fibrils are glycosylated
-ELASTIN gives tissues their ?
-Elastin is a hydrophobic protein rich in ? and ? (like collagen) but is not ?
-Joint by what bonds?
An elastin molecule can do what?
-ELASTIN gives tissues their elasticity
(skin, blood vessels, lungs are strong and elastic enough to function properly)
-Elastin is a hydrophobic protein rich in proline and glycine (like collagen) but is not glycosylated
-Joined by covalent bonds
-An elastin molecule can extend and contract
-THE BASAL LAMINA (or basement membrane) ? ? ?
-LAMININ is the ? organizer of the sheet structure of the basal lamina
Composed of three long ? chains held together by ? bonds
-THE BASAL LAMINA (or basement membrane) is a specialized form of ECM
Basal lamina is thin, flexible and tough –> essential component of all epithelia
-LAMININ is the primary organizer of the sheet structure of the basal lamina
Composed of three long polypeptide chains held together by disulfide bonds
Integrins
Family of transmembrane proteins synthesized in several types of cells ? ? ? (3)
Family of transmembrane proteins synthesized in several types of cells
* Facilitate cell adhesion (link cytoskeleton filaments with the ECM)
* Mediate cellular signals (signal transduction pathways, cell recognition, cell movement)
* Can be receptors for certain viruses (adenovirus, hantavirus, foot and mouth disease, polio virus…)
