Plasma Membrane Flashcards
Plasma Membrane Structure, Receptors and Signaling, Movement of Drugs Across Membrane
What is the plasma membrane of animal cells made of?
It is a phospholipid bilayer. A phospholipid is made of a glycerol bonded to 2 fatty acids and a phosphate group. The phosphate head is hydrophilic and fatty acids are hydrophobic (an amphipathic molecule). The bilayer is made of two rows of phospholipids with the fatty acid tails facing inwards towards each other.
Why is the phospholipid bilayer described as the fluid mosaic model?
‘Fluid’- components like carrier proteins can move freely within the membrane.
‘Mosaic’- Components of different size and shapes fit together.
What is the role of membranes?
Compartmentalisation- Membranes separate different cells and organelles so they can carry out their individual function.
Selectively permeable- This allows the membrane to control what enters and leaves the cell.
Communication- Used in cell signalling via receptors on the surface of the plasma membrane.
Chemical reactions- The plasma membrane is also a site where chemical reactions take place.
What are intrinsic proteins?
Intrinsic proteins are found embedded in the membrane.
An example of an intrinsic protein is a carrier protein. How does a carrier protein work?
Carrier proteins transports substances across a membrane by changing shape. Carrier proteins can actively transport substances against a concentration which would require ATP. Carrier proteins can also transport molecules along the concentration gradient, which would not require ATP and be known as facilitated diffusion.
Other than carrier proteins, what is another example of an intrinsic protein?
Channel proteins.
Channel proteins helps with transporting substances via facilitated diffusion. The substances transported through these channels are polar or charged so cannot simply diffuse through the membrane. Channel proteins have specific function; different channel proteins transports specific molecules. For example, aquaporins are channel proteins that only transport water molecules. There are also sodium and potassium ion channels.
Why are proteins able to lie in the phospholipid bilayer?
A proteins tertiary structure is composed of polar, charged and non charged regions. The polar and charged regions of a protein is unable to interact with the fatty acid tails of the phospholipid bilayer. Hence, the protein arranges itself in a certain way so that the polar and charged region is found on the interior and the non-charged regions are found on the exterior (these proteins are globular).
What are extrinsic proteins? Give 2 examples of extrinsic proteins.
Extrinsic proteins are found partially embedded in the plasma membrane. Two examples of extrinsic proteins are glycoproteins and glycolipids. Glycoproteins or glycolipids is where a carbohydrate chain is attached to either a phospholipid or protein in the membrane.
What are some functions of glycoproteins and glycolipids?
The carbohydrate chain on glycoprotein or glycolipid can be used as an antigen. The shape of the carbohydrate chain is specific to different cells; the carbohydrate chain on a bacteria cell would be different from the one on a body cell. This is what white blood cells use to differentiate pathogens from body cells in an immune response.
Receptors for cell signalling. The carbohydrate chains can also be receptors, where molecules like hormones can bind on to. The carbohydrate chain is typically from a glycoprotein, because the protein attached tends to be an enzyme, which initiates a reaction as a result of hormone signalling.
What is cholesterol and its function?
Cholesterol is a lipid molecule found in the plasma membrane that regulates the fluidity of the membrane. The cholesterol molecules contains an -OH group that cannot interact wit the fatty acid tails. This -OH group is found facing out of the membrane.
What forces are found in the phospholipid bilayer? Where are they found?
Weak intermolecular forces are found between fatty acid tails on different phospholipids. They are also found between proteins and phospholipids. These intermolecular forces stabilises the structure of the membrane, but, phospholipids and other components are still able to move around a bit.
How does increasing temperature affect the phospholipids in the membrane?
Increasing temperature means giving thermal energy.
Thermal energy transferred to kinetic energy.
Kinetic energy causes phospholipids to vibrate.
When they start to violently vibrate, intermolecular forces between the phospholipids start to break.
This reduces stability of the membrane and opens up gaps in the membrane.
More molecules can simply diffuse through, hence, permeability increases.
How does increasing temperature affect the proteins in the membrane?
Increasing temperature causes the proteins to denature as bonds are broken in the tertiary and quaternary structure of the protein.
A denatured protein changes shape of the protein, so the protein may no longer be able to transport molecules across the membrane. Hence, the permeability of the membrane is altered.
How does non-polar solvents affect the fluidity of the membrane?
Non-polar solvents are able to interact with the fatty acid tails in the phospholipid bilayer. For this reason, non-polar solvents are able to slip between fatty acid tails and stay there. This in turn disrupts the intermolecular forces between the fatty acid tails and causes them to break. The phospholipids move further apart, leaving gaps in the membrane. Now molecules are able to simply diffuse through the membrane more easily and hence, permeability as well as fluidity increases.
How does ethanol as a non-polar solvent bring about the side affects of alcohol?
Ethanol is an alcohol that can be consumed. In nervous transmission, the nerve impulses are brought about by the the movement of ions across the membrane. If ethanol as a non-polar solvent is able to disrupt the membrane (make membrane more permeable), there will be more movement of ions across the membrane. This unwanted ion diffusion across the membrane can bring about unwanted nerve impulses.
Ethanol at high concentrations can be used as a disinfectant. How does this work?
High concentration of ethanol means there is more alcohol molecules. Hence, the membrane can be disrupted at a higher rate and can even be broken down, due to a lack of intermolecular forces. Using high concentrations of ethanol in alcohols as a disinfectant can kill bacterial cells, by breaking down its membrane.
Define diffusion.
Diffusion is the net movement of particles down the concentration gradient.
What is facilitated diffusion?
This is diffusion across protein channels in the membrane. The proteins in the membrane is what makes a cell selectively permeable. The permeability of the cell (and plasma proteins present) can be linked to the function of the cell.
How does temperature affect diffusion rate?
A higher temperature means more kinetic energy is given to the system. With the increased KE, phospholipids starts to vibrate and move apart slightly. Gaps in the membrane means more molecules can diffuse across. (An increased kinetic energy also means molecules can move faster).
How does concentration gradient affect the rate of diffusion?
A steeper concentration gradient means more molecules are likely to move from an area of high concentration to low concentration.
Other than temperature and concentration, what other two factors affect the diffusion rate?
Surface area to volume concentration, and thickness of membrane.
Define osmosis.
Osmosis is the net movement of water down a water potential gradient across a partially permeable membrane.
What units is water potential measured in?
Pa, or kPa
What does it mean if a solution has a water potential of 0kPa?
This means the solution is pure water and there is no solutes present.
How does values of water potential vary with concentration of solutes in a solution?
Water potential can always ever be 0 or less than 0. A solution with more solutes will have a more negative value.
What does it mean if a cell is surrounded by a hypotonic solution?
What is the direction of the net movement of water?
How does this movement of water affect an animal cell?
How does this movement of water affect a plant cell?
If a cell is surrounded by a hypotonic solution, it means the solution has a higher water potential than that of the cell, as it contains less solutes.
Hence, this means that the net movement of water will be going from the solution outside to inside the cell- in this sense, it is moving along the water potential gradient.
This net movement of water into an animal cell will put too much pressure on the cell surface membrane and will cause it to burst or undergo lysis.
The net movement of water into a plant cell will cause it to become turgid. It does not burst because the strong plant cell is able to withstand the pressure of the water.
What does it mean if a cell is surrounded by a hypertonic solution?
What is the direction of the net movement of water?
How does this movement of water affect an animal cell?
How does this movement of water affect a plant cell?
If a cell is in a hypertonic solution, the solution has a lower water potential than that of the cell, as the solution contains more solutes.
In this sense, the net movement of water will be from inside the cell to the surrounding solution outside (travelling along the water potential gradient).
The net movement of water out of an animal cell will cause it to shrivel up or undergo crenation.
The net movement of water out of a plant cell will cause it to undergo plasmolysis. The general shape of the plant cell is maintained, but the cell surface membrane detaches itself from the cell wall and goes inwards.
What does it mean if a cell is surrounded by a isotonic solution?
What is the direction of the net movement of water?
How does this movement of water affect an animal cell?
How does this movement of water affect a plant cell?
If a cell is in an isotonic solution, the water potential of the solution is the same as the water potential inside the cell.
Hence, this means the rate of movement of water into the cell is equal to the rate of movement of water outside the cell.
If an animal cell is in an isotonic solution, it will exist in its normal state.
If a plant cell is in an isotonic solution, it is flaccid (its normal state), where the cell surface membrane is just touching the cell wall.
Define active transport.
This is the movement of particles against a concentration gradient, using ATP and involving protein carriers.
ATP is required in active transport, within protein carriers. How is the ATP used?
ATP is hydrolysed to ADP and a phosphate ion. The binding of the phosphate ion to the carrier protein brings about a conformational change, which then allows the carrier proteins to carry molecules across the membrane. When the phosphate ion is released, the carrier protein returns to its original shape.
What is bulk transport?
When we refer to active transport, we normally refer to the movement of small molecules and ions. Bulk transport is the movement of large molecules, like glucose or bacteria.
Endocytosis is a type of bulk transport. What is endocytosis? Provide examples.
Endocytosis is the bulk transport of molecules into a cell.
An example is phagocytosis, where white blood cells engulf foreign matter.
Another example is pinocytosis, which is the engulfing of liquids.
Another type of bulk transport is exocytosis. What is exocytosis?
Exocytosis is the bulk transport of molecules outside of a cell.
An example is if a protein synthesised in a cell is an extracellular enzyme, the enzyme is packaged into vesicles and fuses with the plasma membrane to leave the cell.
What is the difference between integral and peripheral proteins?
Integral proteins are embedded in the membrane, where as peripheral proteins are attached to just surface of the proteins. Peripheral proteins are JUST proteins, and not glycolipids or glycoproteins (can be mistaken as glycolipids and glycoproteins are found on the exterior of the membrane).
What are transmembrane proteins?
Transmembrane proteins are a subset of integral proteins. Some integral proteins are partially embedded in the membrane and serves as different functions, like being enzymes or receptors. Transmembrane proteins are integral proteins that spans the whole lipid bilayer, and a lot of these transmembrane proteins aids in transport- channel proteins.
As transmembrane proteins spans the whole bilayer, they are in contact with the external aquiesce evironment as well as the bilayer, making them an amphipathic molecule.
What is a glycocalyx?
A glycocalyx is a protective layer formed when glycolipids and glycoproteins join together. It functions in holding cells together.
What are the things on the plasma membrane of a red blood cell that determines our blood type?
It is shape of antigens on the surface of red blood cells that determines our blood type. Antigens are glycolipids, so it is essentially the shape or the carbohydate chain.
What are the different classes of lipids in the plasma membrane?
Phosphoglycerides (or known as phospholipids), sphingolipids and steroids.
How does saturation of fatty acids in the plasma membrane affect the fluidity of the membrane?
If fatty acids are unsaturated, they have a double bond. The more the unsaturated fatty acids in the membrane, the more fluid the membrane is.
The fluidity increases with unsaturation because the double bonds provides a kink within the bilayer. The bilayer prevents phospholipids packing closely together, and hence, increases the fluidity of the membrane.
Why do animals living in colder environements benefits by having more unsaturated fatty acids in their plasma membrane?
In reezing temperatures, a bilayer with saturated fatty acids would freeze and solidify (due to compression from the cold); this in turn affects many functions, like transport across the membrane, or the membrane being a site of chemical reactions.
Whereas, is unsaturated fatty acids are compressed from decreasing temperatures, their ‘kinks’ pushes adajacent phospholipids away, maintaining space and fluidity.
How does membrane fluidity change with temperature?
In higher temperatures, the weal intermolecular forces break spreading phospholipids apart and increasing fluidity.
In colder temperatures, phospholipids compress together, and can freeze and solidify, decreasing fluidity.
What is the role of cholesterol?
Cholesterol is essentially a buffer to changes in membrane fluidity (which can change due to many factors, like non-polar solvents and temperature). In colder temperatures, cholesterol keeps phospholipids apart and stops them from freezing. In warmer tempertaures, cholesterol binds phospholipids tighter together to reduce fluidity.
What factors can affect membrane fluidity?
Presence of saturated/unsaturated fatty acids, temperature and cholesterol.
What is co-transport?
Works by transporting 2 molecules (or ions) at a time, through the same transport protein, and using the diffusion of one of the solutes to force the other solute against its gradient.
What is uniport?
Transporting a single substance through a transport protein in one direction.
What is symport?
This is where two substances are transported in the same direction through the same transport protein (one substance diffuses through, and the other substance uses the energy released from the first substance’s diffusion).
