Plasma Membrane
A microscopic membrane of lipids and proteins that forms the external boundary of the cytoplasm of a cell or encloses a vacuole
If a molecule is ATTRACTED to water it is said to be...
Hydrophilic
If a molecule is REPELLED by water it is said to be...
Hydrophobic
Phospholipids are unusual because part of a phospholipid molecule is ___________ and part is ___________
Hydrophilic, Hydrophobic
Molecules with this property are described as...
Amphipathic
Explain how hydrophilic and hydrophobic properties of the phospholipid bilayer allow a membrane to maintain its structure
The attraction between the hydrophobic tails and the hydrophilic heads and the surrounding water makes membranes stable
Draw and label a simplified (2D) diagram of the plasma membranes
...
Outline the structure if the Davson-Danielli model of the cell membrane:
#NAME?
Why was the model proposed, what did it help explain?
Despite being very thin membranes are an effective barrier to the movement of certain substances
Describe the evidence from the electron microscopy that supported this model
#NAME?
Outline how the electron micrograph image to the right was obtained and why it undermines the Davson-Danielli model of the cell membrane
#NAME?
How did insights gained from new techniques undermine the Davson-Danielli model?
#NAME?
What did the experiments with the markers find out and what conclusions could be drawn from them?
-Within 40 minutes the red and green markers were mixed throughout the membrane of the fused cell
-This showed the membrane proteins are free to move within the membrane rather than being fixed in a peripheral layer
Outline the Singer-Nicholson model of the cell membrane:
#NAME?
TRACIE
Transport: protein channels (facilitated) and protein pump (active)
Receptors: peptide based hormones (insulin, glucagon, etc)
Anchorage: cytoskeleton attachment and extracellular matrix
Cell recognition: MHC proteins and antigens
Intercellular joinings: tight junctions and plasmodesmata
Enzymatic activity: metabolic pathway (e.g. electron transport chain)
State the functions of glycoproteins found in the plasma membrane
-Proteins with an oligosaccaride (olgio=few, saccaride=sigar) chain attached
-Important for cell recognition by the immune system and as hormone receptors
Cholesterol is a type of lipid, but is not a fat or oil. What group does it belong to?
Steroid
Where in the plasma membrane can cholesterol be found?
Hydroxyl groups head and tails attracted to the heads and tails of phospholipids
What properties cause it to be located in this position?
Their polar and non polar charges
It is important to regulate the degree of fluidity in order that:
#NAME?
Cholesterol in the membrane restricts the movement of phospholipids and other molecules. How does the affect the physical properties of the membrane?
This reduces membrane fluidity
Cholesterol disrupts the regular packing of the hydrocarbon tails of phospholipid molecules. What impact does this have on the physical properties of the membrane?
Increases the flexibility as it prevents the rails from cyrstallising and hence behaving like a solid
What chemical properties of the membrane are affected by cholesterol?
Affected the order fluctuation of membranes and the diffusional motion of lipid molecules
Cholesterol also encourages the membrane to take on a concave shape. What structures and processes does this aid?
Cholesterol also reduces the permeability to hydrophilic/ water soluble molecules and ions such as sodium and hydrogen
Selectively permeable
Controlled entry/exit of molecules
Diffusion
PASSIVE movement of particles from areas of high concentration to areas of low concentration
Osmsis
When a cell is emerged in water, the water molecules pass through the cell membrane from low solute (outside) to high solute (inside)
Distinguish between solute, solvent, and solution
Solute-dissolved in solvent
Solvent-Able to dissolve another substance
Solution-A liquid mixture in which the solute is distributed with the solvent
State 4 ways to maximize the rate of diffusion of substances across a membrane
1. Alveoli in the lungs
2. Membrane folds in mitochondria and in cristae in the chloroplasts
3. Root hairs for water and mineral ion uptake
4. Villi for absorption of digested food molecules
By which method does each of the following types of molecules travel across a membrane?
Water: osmosis
Non-polar molecules (with concentration gradient): simple diffusion
Polar molecules (with the concentration gradient): facilitated diffusion
Any molecule against the concentration gradient: active transport
State the name of the specialised type of membrane protein used to transport water
Aquaporin
Give examples of cells that use facilitated diffusion as well as simple diffusion.
Animal cells
Why is facilitated diffusion used if water can move by simple diffusion?
It has to use a particular molecule
Explain what is happening in this diagram:
The solutions were not isotonic and for them to be equal they added more water to the side with more particles to even it out
What solutions, compared to cells can be described as isotonic, hyper, or hypotonic. Define these terms:
Isotonic-equal
Hypertonic-more ouside
Hypotonic-less outside
Explain what would happen to the cells of tissues and organs immersed in these solutions
Isotonic-H2O enters and leaves cell
Hypertonic-H2O enters cell
Hypotonic-H2O leaves cell
List common medical procedures in which an isotonic saline solution is useful:
#NAME?
Explain how ATP releases energy, using a simple diagram
Particles enter the pump from the side where the concentration is low.
Particles bind to a specific site. Some particles are unable to bind, and cannot get inside the cell
Energy from ATP is used to change the shape of the pump.
Particle is released on the other side, where the concentration is higher. The pump then returns to its original shape
Distinguish between uniport, symport, and anitport.
Uni- one at a time
sym-two at a time
anti- 3+ at a time
Annotate the diagram below:
1. At stage during a nerve impulse there are relatively more positive charges inside
2. This voltage change causes potassium channel to open allowing potassium ions to diffuse out of the axon
3. Once the voltage conditions change the channel rapidly closes again
What is a macromolecule? Give one example of a macromolecule.
Large molecules necessary for life
Proteins
What is a vesicle?
Small spherical packages that bud off the ER and the Golgi Apparatus
Outline the uses of vesicles within cells.
#NAME?
Differentiate between endocytosis and exocytosis
Exocytosis: release of substances from a cell (secretion)
Endocytosis: Taking of external substances
Endocytosis is characterized as either being phagocytosis or pinocytosis.
Pinocytosis: cell drinking "fluid intake"
Phagocytosis: cell eating "solid intake
How does the cell membrane break and reform for endosytosis and exocytosis:
Vesicle approaches the plasma membrane. All membranes are made of the phospholipid bilayer so they have the same properties
Membrane begins to fuse. Remember the fluidity of the plasma membrane the phospholipids can flow around each other
For a moment, there is a simple phospholipid bilayer at the point of contact
The membrane pores open, alowing the contents to pass through. Notice that through the whole process, there is never an unbroken section of the bilayer