Biology PAP - Membrane Structure Quiz
Describe and distinguish between glycolipids and glycoproteins. Describe how these molecules contribute to membrane function.
*Glycolipids* are lipids ( most likely phospholipids ) with a carbohydrate attached by a glycosidic bond. *Glycoproteins* are any class of proteins that have carbohydrate groups attached to the polypeptide chain. These molecules serve in Cell-Cell recognition by providing a bonding surface for cellular recognition.
What are the similarities and differences between integral and peripheral proteins?
*Similarities*: - both are proteins - perform protein functions - they are part of the cell membrane *Difference*: - Integral proteins penetrate the hydrophobic interior of the lipid bilayer and span the membrane - Peripheral proteins are loosely bound to the surface of the membrane on one side - Integral proteins are on both sides of the membrane, while peripheral is only on one side - can not perform the same functions
What does it mean when a phospholipid is described as amphipathic?
*amphipathic* : (of a molecule, especially a protein) having both hydrophilic and hydrophobic parts. A molecule is amphipathic when it contains a hydrophobic and hydrophilic region.
Identify and describe the six main functions of cell membrane proteins.
- *Transport* : one of the most important functions ( allows for cell membrane's selective permeability through the use of binding carrier proteins and channel proteins ) - *Enzyme activty* - *Attachment to the cytoskeleton and extracellular matrix ( ECM )* - *Cell - cell recognition* : cell recognize each other by binding to surface molecules, often containing carbohydrates ( glycolipids & glycoproteins ), on the extracellular surface of the plasma membrane [ name tag ] - *Intercellular joining* - *Signal transduction* : cell communication *citeas*
How can temperature affect membrane fluidity and how does cholesterol help in maintaining membrane fluidity?
- As temperature cool, membranes switch from a fluid state to a solid state - the temperature at which a membrane solidifies depends on the types of lipids - *a membrane remains fluid at a lower temperature if it is rich in phospholipids with unsaturated hydrocarbon tails* - membranes must be fluid to work properly; they are usually about as fluid as salad oil - *cholesterol reduces membrane fluidity at moderate temperatures, but at low temperatures hinders solidification.* -------------------------------------------------------------- *Unsaturated: more fluid* *Saturated: less fluid; adhesive* *Cholesterol: less fluid; hinders solidification*
How do you identify fatty acid tails of phospholipids in a cell membrane diagram?
Look at all the lines branching off the white spheres in the inner region of the cell membrane. There are two tails per sphere. ( Diagram: two rows of tails can be seen inside the cell membrane [ in the hydrophobic region ] ).
How do you identify a glycolipid in a cell membrane diagram?
Look at all the phospholipid heads that form the exterior of the cell membrane. A glycolipid will be a phospholipid head that has a green carbohydrate chain. Make sure the green carbohydrate chain is NOT attached to a protein. ( Diagram: white phospholipid head with green chain, located on the right of the diagram )
How do you identify the heads of phospholipids in a cell membrane diagram?
Look at all the white spheres that make up the outer or hydrophilic region of the cell membrane. It is the most abundant physical feature of a phospholipid in this diagram. ( Diagram : two rows of hydrophilic phospholipid heads can be seen in the diagram )
How do you identify a peripheral protein in a cell membrane diagram?
Look at the protein that does not go through the entire membrane and do not have a green carbohydrate chain, but are only visible on one side of the membrane. ( Diagram: three outside and inside the cell. )
How do you identify an integral protein in a cell membrane diagram?
Look at the protein that goes through the entire membrane. ( Diagram: there are five )
How do you identify a glycoprotein in a cell membrane diagram?
Look at the proteins that are peripheral and are outside of the cell membrane. Make sure they have a carbohydrate chain and that it is NOT attached to a phospholipid. ( Diagram: purple sphere with green chain branching off. )
How do you identify the hydrophilic section of the lipid bilayer in a cell membrane diagram?
Look at the region above the phospholipid tails, where all the heads are located. ( Diagram: all of the heads of phospholipids )
How do you identify cholesterol in a cell membrane diagram?
Look at the yellow hexagons inside of the cell membrane. Specifically, it is between the phospholipids that make up the cell membrane. ( Diagram : six cholesterols can be seen in the diagram )
How do you identify a phospholipid in a cell membrane diagram?
Look for the molecule with a hydrophilic head and two hydrophobic tails. It is the most abundant molecule in the cell membrane. ( Diagram: white sphere with two tails, makes up the cell membrane )
How do you identify the hydrophobic section of the lipid bilayer in a cell membrane diagram?
Look in the region between the phospholipids, where all the tails are located. ( Diagram: lined region between the phospholipid heads )
Describe the fluid mosaic model of the cell membrane and movement that can be seen at the membrane level.
The fluid mosaic model explains various observations regarding the structure of functional cell membranes. According to this biological model, there is a lipid bilayer in which protein molecules are embedded. The lipid bilayer gives fluidity and elasticity to the membrane. *Most lipids and some proteins in a mebrane can shift laterally ( side to side ). The lateral movement of phospholipids is rapid; proteins move more slowly because they are larger than phospholipids.* The model states that *the membrane consists of protein molecules bobbing in a fluid bilayer of phospholipids*. *The hydrophilic heads of the phospholipids face the interior and exterior of the cell. The hydrophobic tails form the interior of the bilayer.*
Explain what it means for the cell membrane to be "selectively permeable".
The plasma membrane exhibits selective permeability, *allowing some substances to cross it more easily than others*. Selective permeability of the cell membrane refers to its *ability to differentiate between different types of molecules, only allowing some molecules through while blocking others*. Selective permeability is the ability of the cell membrane that allows for a controlled exit or entry of certain molecules, allowing for a system resistance and passage. *Hydrophobic ( nonpolar ) molecules, such as hydrocarbons , can dissolve in the lipid bilayer of the membrane and cross easily. However, polar molecules, such as sugars, do not cross the membrane easily.*
What are the two main molecules that compose a cell membrane?
proteins and phospholipids
