IB Bio 1.3 and 1.4
Terms in this set (46)
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...
If a molecule is REPELLED by water it is said to be...
Phospholipids are unusual because part of a phospholipid molecule is ___________ and part is ___________
Molecules with this property are described as...
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:
-A protein-lipid sandwhich
-Lipid bilayer composed of phospholipids (tails inside, heads outside)
-Proteins coat outer surface
-Proteins do not permeate the lipid bilayer
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
-In high magnification electron micrographs, membranes appeared as two dark parallel lines with a lighter coloured region in between
-Proteins appear dark in electron micrographs and phospholipids appear light-possibly indicating proteins layers either side of a phospholipid core
Outline how the electron micrograph image to the right was obtained and why it undermines the Davson-Danielli model of the cell membrane
-The fracture occurs lines of weakness, including the centre of membranes
-The fracture reveals an irregular rough surface inside the phospholipid bilayer
-The globular structures were interpreted as trans-membrane proteins
How did insights gained from new techniques undermine the Davson-Danielli model?
-This is contrary to the Davson-Danielli model which only includes proteins coating the surface of the membrane
-A new model is needed to explain the presence of as trans-membrane proteins
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:
-Phospholipid molecules form a bilayer
-Phospholipids are fluid and move laterally
-Peripheral proteins are bound to either the inner or outersurface of the membrane
-Integral proteins permeate the surface of the membrane
-The membrane is a fluid mosaic of phospholipids and proteins
-Proteins can move laterally along membrane
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?
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:
-It needs to be fluid enough that the cell can move
-It needs to be fluid enough that the required substances that can move across the membrane
-If too fluid however the membrane could not effectively restrict the movement of substances across itself
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
Controlled entry/exit of molecules
PASSIVE movement of particles from areas of high concentration to areas of low concentration
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?
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
Give examples of cells that use facilitated diffusion as well as simple diffusion.
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:
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:
-Through IV for rehydration
-Damanged skin moist
-Frozen and packed donor organs
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
What is a vesicle?
Small spherical packages that bud off the ER and the Golgi Apparatus
Outline the uses of vesicles within cells.
-Carry out proteins produced by ribosomes on the ER
-To the Golgi Apparatus, where they are prepared for export from a cell to another vesicle
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