Membrane 2 (cell bio) Flashcards
Cell Membrane
FLUID MOSAIC MODEL FOR MEMBRANE STRUCTURE
recap:
fusion: membrane not damaged
fission: same
KNOW EXAMPLES FOR THEM!
visualization techniques (freeze membrane and break it down and then do metal-carbon coating and then can visualize it with SEM and TEM microscope)
N/A
CELL MEMBRANE - MEMBRANE DYNAMICS
Features of all biological membranes:
* Flexibility: Ability to change shape without losing ? or becoming ?
* Fluidity: Ability to flow How?
→ ? interactions of lipids in the bilayer (same as ? in the same sentence) isn’t strong so can fluid)
The structure and flexibility of the lipid bilayer depend on:
- ? composition
- changes in ?
Vesicles:
(v imp in process of fission and fusion e.g. vesicle coming out of the ER or GA)
* ?- and ?-cellular structures consisting of liquid enclosed by a lipid bilayer
* Form naturally during:
- ? (exocytosis)
- ? (endocytosis)
- ? transport
(FA one has tail but this will be more like a cone-shaped (lipid composition - micelles))
CELL MEMBRANE - MEMBRANE DYNAMICS
Features of all biological membranes:
* Flexibility: Ability to change shape without losing integrity or becoming leaky
* Fluidity: Ability to flow How?
→ non-covalent interactions of lipids in the bilayer (non-covalent interaction) isn’t strong so can fluid)
The structure and flexibility of the lipid bilayer depend on:
- lipid composition
- changes with temp.
Vesicles:
(v imp in process of fission and fusion e.g. vesicle coming out of the ER or GA)
* intra- and extra-cellular structures consisting of liquid enclosed by a lipid bilayer
* Form naturally during:
- secretion (exocytosis)
- uptake (endocytosis)
- membrane transport
(FA one has tail but this will be more like a cone-shaped (lipid composition - micelles))
CELL MEMBRANE - THE LIPID BILAYER: A 2-dimensional FLUID
Around 1970 researchers first recognised that individual lipid molecules can diffuse ? within ?
* First demonstrations resulted from studies of ? bilayers
Two types of preparations were effective for these studies:
1. ? (bilayers as closed spherical vesicles), commonly used as model membranes in experimental studies
2. ? membranes (planar bilayers, formed across a hole in a partition between two aqueous compartments), are used to measure the permeability properties of synthetic membranes
(black membrane uses lipid bilayer membrane in the lab (in vitro) set up and called it black membrane cuz visually its dark and they also had synthetic lipid bilayer and w use of these e- microscopes/micrographs they started to understand the characteristics of membrane)
CELL MEMBRANE - THE LIPID BILAYER: A 2-dimensional FLUID
Around 1970 researchers first recognized that individual lipid molecules “can diffuse freely within lipid bilayer”.
* First demonstrations resulted from studies of synthetic bilayers
Two types of preparations were effective for these studies:
1. liposomes (bilayers as closed spherical vesicles), commonly used as model membranes in experimental studies
2. 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
Later they figured out PLs can move:
(laterally, in and out, or can just change the side of the bilayer)
- ? diffusion
- flip-flop diffusion ( -> commonly or rarely? occurs bc the polar head of the PL needs to go through the hydrophobic part of the membrane so lateral diffusion as there’s just an interaction of heads and interaction of tails)
- ? (tails move a little bit inside of ? part)
- ?: PL rotating along (due to the ? and ? of the polar head of the PL and also depending on which sort of ? or other ? is going through the membrane at that time)
so 1. ? diffusion 2. flip flop diffusion 3. ? 4. rotation
Later they figured out PLs can move:
(laterally, in and out, or can just change the side of the bilayer)
- lateral diffusion
- flip-flop diffusion ( -> rarely occurs bc the polar head of the PL needs to go through the hydrophobic part of the membrane so lateral diffusion as there’s just an interaction of heads and interaction of tails)
- flexion (tails move a little bit inside of ? part)
- rotation: PL rotating along (due to the ? and ? of the polar head of the PL and also depending on which sort of ? or other ? is going through the membrane at that time)
so 1. lateral diffusion 2. flip flop diffusion 3. flexion 4. rotation
CELL MEMBRANE - Phospholipid movement
MOVEMENT OF PHOSPHOLIPIDS WITHIN THE LIPID BILAYER
Catalysis of transbilayer movement of lipids by:
* ?
* ?
* ?
special ? proteins that move phospholipids and other lipids in the membrane
Transversal Diffusion
Flip-flop: happens usually or rarely?
(unless the process is ?)
Lateral Diffusion
diffusion in the where?: happens ? and slowly or rapidly?
CELL MEMBRANE - Phospholipid movement
MOVEMENT OF PHOSPHOLIPIDS WITHIN THE LIPID BILAYER
Catalysis of transbilayer movement of lipids by:
* flippasses
* floppases
* scrambles
special transporter proteins that move phospholipids and other lipids in the membrane
Transversal Diffusion
Flip-flop: happens rarely
(unless the process is catalyzed)
Lateral Diffusion
diffusion in the plane: happens readily and rapidly
(membrane shouldn’t be too fluid or too rigid
temp: butter is made of saturated FA and if u put in hot temp. it melts and if in fridge then solid so temp. matters
low temp. so lipid bilayer come close together and are more RIGID, high temp then they want to spread around to be far away from each other thus FLUIDIZATION TAKES PLACE)
CELL MEMBRANE - FLUIDITY
The fluidity of a lipid bilayer must be precisely regulated
- depends on its ? and ?
Some organisms can adapt to environmental temperature fluctuations, adjusting the ? content of their membranes to maintain a relatively constant ?.
?: the change of a lipid bilayer from a ? state to a 2D or 3D? rigid or fluid? crystalline state (gel) at a characteristic ? (melting point)
CELL MEMBRANE - FLUIDITY
The fluidity of a lipid bilayer must be precisely regulated
- depends on its composition and temp.
Some organisms can adapt to environmental temperature fluctuations, adjusting the FA content of their membranes to maintain a relatively constant fluidity.
MEMBRANE PHASE TRANSITION: the change of a lipid bilayer from a liquid state to a 2D rigid crystalline state (gel) at a characteristic temp. (melting point)
FLUIDITY
Lipid bilayer is stabilized by ** ? interactions ** between lipids’ fatty acid chains
Fluidity depends on:
1. ? content (FA length and saturation)
2. ? content
3. ?
At low temperatures: less lipid movement
Lipid bilayer is in ? state (more fluid or rigid? state)
At higher temperatures (20-40°C / 68-104°F): more lipid movement Lipid bilayer becomes more fluid or rigid?
FLUIDITY
Lipid bilayer is stabilized by ** hydrophobic interactions ** between lipids’ fatty acid chains
Fluidity depends on:
1. PL content (FA length and saturation)
2. Cholesterol content
3. Temp.
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 *hot so they want to spread out and kinks/bends in tail i.e. unsaturated helps with this)
CELL MEMBRANE
Influence of cis-double bonds in hydrocarbon chains in membrane phospholipids:
Unsaturated FA make it more difficult to pack the hydrocarbon chains together due to ?
-> lowers the ? point (it’ll be more liquid at colder temperatures)
-> Also form a ? membrane as the phospholipids will be further spread apart bc they spread out and have kinks
Influence of a shorter (double or single bond?) hydrocarbon chain in membrane phospholipids:
-> increases or reduces? the tendency of hydrocarbon tails to interact with one another → The membrane remains fluid at lower or higher? temperatures
the shorter the hydrocarbon chain FA -> lower or higher? the melting point
- Hydrocarbon chain of membrane phospholipid tails can vary from 14-24 C, most are between 18-20 C
CELL MEMBRANE
Influence of cis-double bonds in hydrocarbon chains in membrane phospholipids:
Unsaturated FA make it more difficult to pack the hydrocarbon chains together due to kinks
-> lowers the melting point (it’ll be more liquid at colder temperatures)
-> Also form a thinner membrane as the phospholipids will be further spread apart bc they spread out and have kinks
Influence of a shorter (double bond) hydrocarbon chain in membrane phospholipids:
-> reduces the tendency of hydrocarbon tails to interact with one another → The membrane remains fluid at lower temperatures
the shorter the hydrocarbon chain FA -> lower the melting point
- Hydrocarbon chain of membrane phospholipid tails can vary from 14-24 C, most are between 18-20 C
CELL MEMBRANE - fluidity/FA
Saturated fatty acids (double or single bond?)
Tend to form * ? * structures (less space between phospholipid tails)
↑ ? fatty acids content of a lipid bilayer
↑ Paracrystalline-to-fluid transition temperature of the membrane
(↑ melting point)
Unsaturated fatty acids:
Cis-double bonds → kinks (more space between tails) Inhibits the ? conformation
increases or decreases? Unsaturated fatty acids content of a lipid bilayer
↓ ?-to-? transition temperature of the membrane (↓ melting point)
(saturated FA is tightly packed as no kinks, so will increase the melting point and if the hydrocarbon chain is shorter then it helps keep PLs apart lowering the melting point-as not tightly packed so easier to melt them)
CELL MEMBRANE - fluidity/FA
Saturated fatty acids (single bond)
Tend to form * paracrystalline (rigid) * structures (less space between phospholipid tails)
↑ saturated fatty acids content of a lipid bilayer
increase Paracrystalline-to-fluid transition temperature of the membrane
(↑ melting point)
Unsaturated fatty acids:
Cis-double bonds → kinks (more space between tails) Inhibits the paracrystalline conformation
increases Unsaturated fatty acids content of a lipid bilayer
decreases Paracrystalline-to-fluid transition temperature of the membrane (↓ melting point) note: Paracrystalline-to-fluid transition temperature of the membrane (↓ melting point)
CELL MEMBRANE -
Eukaryotic plasma membranes can contain very large amounts of cholesterol: up to one molecule for every phospholipid molecule
Cholesterol molecules improve the ? properties of the lipid bilayer
* Orient themselves in bilayer with their hydroxyl (i.e. polar) groups close to the ? heads of the phospholipid molecules
* The ? ? ring can support the hydrocarbon chains and stabilize them
Cholesterol can ? or ? phases transitions
(pic: polar head of cholesterol is binding with polar head of PL
& hydrocarbon tail of PL will be binding and hydrophobic interaction with tail of PL so thats how cholesterol molecule will configure itself between PL molecules of PM)
(-prokaryotic cells don’t contain CHOLESTEROL (v rare)
-cholestrol keeps the PL together so it doesn’t spread apart too much and not too fluid then this struc. here so in high temp. the cholesterol will try to keep the tails together
CELL MEMBRANE -
Eukaryotic plasma membranes can contain very large amounts of cholesterol: up to one molecule for every phospholipid molecule
Cholesterol molecules improve the permeability-barrier properties of the lipid bilayer
* Orient themselves in bilayer with their hydroxyl (i.e. polar) groups close to the polar heads of the phospholipid molecules
* The rigid steroid ring can support the hydrocarbon chains and stabilize them
Cholesterol can inhibit or delay phases transitions
(pic: polar head of cholesterol is binding with polar head of PL
& hydrocarbon tail of PL will be binding and hydrophobic interaction with tail of PL so thats how cholesterol molecule will configure itself between PL molecules of PM)
CELL MEMBRANE - cholesterol
-> at high temperatures
Cholesterol helps keep the membrane more ?, ? the bilayer and making it more or less? fluid and more or less? permeable (thinner membrane = easier to pass through membrane)
-> at low temperatures, acts as ‘antifreeze’
Cholesterol also helps the membrane remain fluid by ? fatty acid tails from interacting with each other and ‘clumping up’
CELL MEMBRANE - cholesterol
-> at high temperatures
Cholesterol helps keep the membrane more stable, stiffening the bilayer and making it less fluid and less permeable (thinner membrane = easier to pass through membrane)
-> 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’
-> cholestrol should be in right place at right time e.g. when talking about bad protein -> lipoprotein strugglin in blood vessels
CELL MEMBRANE - Extra Cellular Matrix (ECM)
Tissues are not made solely of cells
-> cells are contained in a complex and intricate network of macromolecules, known as the:
? MATRIX:
* ? membrane and
* ? matrix
THE CELL AND ITS “SOCIAL“ CONTEXT: THE EXTRACELLULAR MATRIX (ECM)
- The extracellular matrix in biology is a collection of extracellular molecules secreted by cells
? and ? support to surrounding cells
Common functions: cell ?, cell-to-cell ? and ?
Animal ECM:
Interstitial matrix: present between different animal cells (in intercellular spaces)
* Gels of polysaccharides and fibrous proteins fill intercellular spaces, act as ? ? to the ECM (helps with resisting mechanical stress)
Basement membranes/basal lamina: ?-like depositions, special type of ECM that lines the basal side of epithelial and ? tissues
Each type of connective tissue in animals has a different type of ECM:
Bone tissue: consists of ? fibers and bone ?
Loose connective tissue: ? fibers and ?
Blood: ECM is blood ?
CELL MEMBRANE - Extra Cellular Matrix (ECM)
Tissues are not made solely of cells
-> cells are contained in a complex and intricate network of macromolecules, known as the:
EXTRACELLULAR MATRIX:
* basement membrane and
* interstitial matrix
(e.g. small intestine epithelial cell, epithelial cell on which microvilli is present, as shown in pic, needs something to attach to so that’ll be basal lamina of ECM, in the connective tissue and interstitial fluid present under it)
THE CELL AND ITS “SOCIAL“ CONTEXT: THE EXTRACELLULAR MATRIX (ECM)
- The extracellular matrix in biology is a collection of extracellular molecules secreted by cells
structural and biochemical support to surrounding cells
Common functions: cell adhesions, cell-to-cell junctions and differentiation
Animal ECM:
Interstitial matrix: present between different animal cells (in intercellular spaces)
* Gels of polysaccharides and fibrous proteins fill intercellular spaces, act as compression buffers to the ECM (helps with resisting mechanical stress)
Basement membranes/basal lamina: sheet-like depositions, special type of ECM that lines the basal side of epithelial and endothelial tissues
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
CELL MEMBRANE EXTRACELLULAR MATRIX - ECM
EXTRACELLULAR MATRIX
? in the ECM are mainly produced ? by cells in the matrix and secreted via ?.
Fibroblasts
* Fibroblasts produces and secretes ?
* In connective tissue mainly ? fibers
Can differentiate into
* “Chondro”blasts- ?
* “Osteo”blasts- ? tissue
* “Myofibro”blasts – ? tissue
CELL MEMBRANE EXTRACELLULAR MATRIX - ECM
EXTRACELLULAR MATRIX
Macromolecules in the ECM are mainly produced locally by cells in the matrix and secreted via exocytosis
Fibroblasts
* Fibroblasts produce and secretes ECM
* In connective tissue mainly collagen fibers
Can differentiate into
* “Chondro”blasts- cartilage
* “Osteo”blasts- bone tissue
* “Myofibro”blasts – muscle tissue
CELL MEMBRANE - ECM
MAJOR CLASSES OF MACROMOLECULES IN THE ECM (MAMMALS HAVE > 300 MATRIX PROTEINS):
ALL THESE GUYS BELOW ARE PRODUCED BY FIBROBLASTS!!
1) Glycosaminoglycans (GAGs) esp. in cartilage: small or large? and ? charged polysaccharides
GAG + proteins -> ?
GAG + PROTEOGLYCANS = ? (morphous or amorphous? , which receives mechanical stress look at pic in previous flashcard, gelatinous material, fill the space between fibers and cells)
2) ? proteins like collagen (e.g. skin and bone)
3) ? fibrous proteins (elastin, fibronectin, laminin)
Structural proteins: ? collagen and ?
Adhesive proteins: ? and ?
CELL MEMBRANE - ECM
MAJOR CLASSES OF MACROMOLECULES IN THE ECM (MAMMALS HAVE > 300 MATRIX PROTEINS):
1) Glycosaminoglycans (GAGs) esp. in cartilage: large and highly charged polysaccharides
GAG + proteins -> proteoglycans
GAG + PROTEOGLYCANS = Ground substance (amorphous 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)
Structural proteins: fibrous collagen and elastin
Adhesive proteins: laminin and fibronectin
CELL MEMBRANE - ECM
COLLAGEN are ?, long, stiff, ?-stranded helical proteins forming ?
-> Rich in ? (secondary AAs) and (primary AAs) amino acids
-> The fibrils are ?
in picture (in ANS, below) can see fibroblasts which are producing collagen fibers that are laying flat as soon as they are produced.
CELL MEMBRANE - ECM
COLLAGEN are fibrous, long, stiff, triple-stranded helical proteins forming, fibrils
-> Rich in proline and glycine (secondary AAs) and (primary AAs) amino acids
-> The fibrils are glycosylated
in picture (in ANS, below) can see fibroblasts which are producing collagen fibers that are laying flat as soon as they are produced.
CELL MEMBRANE - ECM
- ? * gives tissues their elasticity
(?, ?, lungs are strong and elastic enough to function properly)
Scanning electron micrograph of a dog‘s aorta (low magnification) - in pic
Network of longitudinally oriented elastin fibers (high magnification)
Elastin is a hydrophobic protein rich in ? and ? (like collagen) but is not ?
A RUBBER BAND:
* The molecules are joined together by ?
bonds to generate a cross-linked network
* Each elastin molecule can ? and ? in a manner resembling a random ?, so that the entire assembly can stretch and recoil like a ?
CELL MEMBRANE - ECM
- ELASTIN * gives tissues their elasticity
(skin, blood vessels, lungs are strong and elastic enough to function properly)
Scanning electron micrograph of a dog‘s aorta (low magnification)
Network of longitudinally oriented elastin fibers (high magnification)
Elastin is a hydrophobic protein rich in PROLINE and GLYCINE (like collagen) but is not glycosylated
(glycosylated: having undergone glycosylation; glycosylation: the controlled enzymatic modification of an organic molecule, especially a protein, by the addition of a sugar molecule.
In living organisms, glycosylation typically enhances (or enables) the function of a protein)
A RUBBER BAND:
* The molecules are joined together by covalent bonds to generate a cross-linked network
* Each elastin molecule can extend and contract in a manner resembling a random coil, so that the entire assembly can stretch and recoil like a rubber band
CELL MEMBRANE - ECM
In the ECM there are also ? with ? domains each with specific binding sites for other matrix macromolecules and for receptors of the cell surface.
? (2500 amino acids long!) is a ? ? glycoprotein that plays an important role in tissue ?, regulating cell ? and ? and in embryogenesis
(integrin in pic is attached to actin and is helping it move; integrin in also attached to fibronectin, located below integrin,)
CELL MEMBRANE - ECM
In the ECM there are also glycoproteins (proteins + carbohydrate chain) with MULTIPLE domains each with specific binding sites for other matrix macromolecules and for receptors of the cell surface.
FIBRONECTIN (2500 amino acids long!) is a multifunctional adhesive glycoprotein that plays an important role in tissue repair, regulating cell attachment and movement and in embryogenesis
(integrin in pic is attached to actin and is helping it move; integrin in also attached to fibronectin, located below integrin, so amoebic movement by e.g. neutrophil: protrude and then attach and take rest of cell to that place and FIBRONECTIN in ECM to move and attach to actin filament and helps actin to move)
CELL MEMBRANE - ECM
THE BASAL LAMINA (or basement membrane) is a specialized form of ?
Basal lamina is ?, ? and ? -> essential component of some of all? epithelia
? is the primary organizer of the sheet structure of the basal lamina
Composed of ? long polypeptide chains held together by ? bonds
(-> LAMININ has diff. binding area for other protein, also its a multidomain protein like fibronectin and big as well and responsible for attachment of cells to the basal lamina)
CELL MEMBRANE - ECM
THE BASAL LAMINA (or basement membrane) is a specialized form of ECM
Basal lamina is thin, flexible and tough -> essential component of some of all epithelia
LAMININ is the primary organizer of the sheet structure of the basal lamina
Composed of 3 long polypeptide chains held together by disulfide bonds
(-> LAMININ has diff. binding area for other protein, also its a multidomain protein like fibronectin and big as well and responsible for attachment of cells to the basal lamina)
CELL MEMBRANE - Integrins
Family of transmembrane proteins synthesized in several types of cells
- Facilitate cell ? (link ? filaments with the ECM)
- Mediate ? (signal transduction pathways, cell recognition, cell movement)
- Can be ? for certain viruses (adenovirus, hantavirus, foot and mouth disease, polio virus…)
CELL MEMBRANE - Integrins
Family of transmembrane proteins synthesized in several types of cells
- Facilitate cell adhesion (link cytoskeleton filaments with the ECM)
- Mediate cellular signal (signal transduction pathways, cell recognition, cell movement)
- Can be receptors for certain viruses (adenovirus, hantavirus, foot and mouth disease, polio virus…)
(integral protein synthesized inside of the epithelial cell and they will go to the membrane and there will be transmembrane proteins so they help attachment with basal lamina but also responsible for cellular signaling e.g. connection with other cells so tell them if cells need to grow or need to do anything special so FOR EXAMPLE can be receptors for certain viruses
so INTEGRIN NOT JUST FOR ADHESION BUT ALSO FOR CELLULAR COMMUNICATION)
