Unit 2 (Week 4) Flashcards
What is any membrane made by living cells; can be the plasma membrane or an internal membrane that surrounds an organelle?
Biological membrane (all 5-10 nm) 5,000-10,000 of these stacked on top of each other to be as thick as paper.
What are the two primary components of a membrane?
Phospholipids that form the basic matrix of the membrane and proteins which are embedded in the membrane or loosely attached to its surface.
Carbohydrates may or may not be attached to the membrane lipids and proteins.
What is the phospholipid bilayer?
The basic framework of a biological membrane, consisting of two layers of phospholipids.
What is a leaflet and what are the two in the phospholipid bilayer?
Leaflets are one half of the bilayer and faces different regions. There are two which are called the cytosolic leaflet and the extracellular leaflet.
T/F The bilayers are symmetrical.
False.
Lipid composition may be more abundant in one leaflet compared to the other. Glycolipids are found primarily in the extracellular leaflet of the plasma membrane. The carbohydrate portion protrudes into the extracellular medium.
What is a protein that has one or more regions that are physically embedded in the hydrophobic region of a membrane’s phospholipid bilayer?
Transmembrane protein
They are folded into “a helix.” The nonpolar amino acids interact favorably with the nonpolar lipid tails.
What is a type of integral membrane protein that is attached to the membrane via a lipid molecule?
Lipid-anchored protein
What are proteins such as a transmembrane protein or a lipid-anchored protein that cannot be released from the membrane unless the membrane is dissolved with an organic solvent or detergent called?
Integral membrane proteins
What is a protein that is noncovalently bound to a region of an integral membrane protein that projects out from the membrane or noncovalently bound to the polar head group of a phospholipids?
Peripheral membrane proteins (hydrogen and/or ionic bonds)
Roughly, how many medications today exert their effects by binding to membrane proteins?
70%
What is a property of biological membranes in which individual molecules remain in close association yet have the ability to move rotationally or laterally within the plane of the membrane? Membranes are semifluid.
Fluidity
What is a property of biological membranes in which movement of membrane components occurs only in two dimensions?
Semifluid
Fluid would be movement in 3 dimensions.
What enzyme allows the polar region of a phospholipid to flip to the other leaflet and does not happen spontaneously like rotational or lateral movements?
Flippase (energetically unfavorable since energy input in the form of ATP is needed)
How fast can a lipid traverse a bacterial cell? An animal cell?
1 second and 10 to 20 seconds.
What is in a membrane, a group of lipids, sometimes including associated proteins, that float together as a unit in a larger sea of lipids?
Lipid raft
Typically have a high amount of cholesterol and/or unique set of transmembrane and lipid-anchored proteins.
What is a key property that affects the fluidity of the phospholipid bilayer?
The length of lipid tails. Ranges from 14-24 carbon atoms with 16-18 being the most common. Shorter tails are less likely to interact with each other, which makes the membrane more fluid.
What is another property in phospholipid tails that help it remain more fluid in the context of carbon-hydrogen relationship?
The double bonds between carbon and hydrogen. (Remember: saturated fats are solid at room temperature versus olive oil that remains more fluid. Olive oil have double bonds while saturated fat is saturated with hydrogen bonds.
T/F Cholesterol is found in plant and animal cells.
False.
Plants have phytosterols that resembles cholesterol’s chemical structure.
What is the third factor that helps plasma membrane’s retain their fluidity and why?
Cholesterol, a short and rigid molecule.
It stabilizes cell membranes based off of lipid composition and temperature.
How does the change in temperature affect cholesterol in the membrane?
At high temperatures, cholesterol makes the membrane less fluid.
At lower temperatures, the opposite happens and prevents it from freezing.
This phenomenon helps animals cope with changing temperatures to make sure their cells operate optimally.
Why might transmembrane proteins move around the phospholipid bilayer?
They could be bound to components of the cytoskeleton or attached to molecules outside the cell like the extracellular matrix (ECM) of animal cells
Discuss how transmembrane proteins are important in the binding of cells to each other and the binding of cells to the extracellular matrix.
Transmembrane proteins called cell adhesion molecules bind to each other to promote cell-to-cell adhesion. In addition, they can bind to filaments in the extracellular matrix, such as collagen fibers, thereby causing a cell to adhere to the extracellular matrix.
Where does the synthesis of most lipids by the cytosol and endomembrane system occur?
The cytosolic leaflet of the smooth ER membrane.
[Synthesis of membrane phospholipids at the ER membrane] What are the steps needed for fatty acids to enter the ER? (5)
- Fatty acids are activated with the attachment of a CoA molecule.
- This fatty acids are then bonded to glycerol-phosphate and inserted into the cytosolic leaflet of the ER membrane via acyl transferase.
- The phosphate is removed by phosphatase enzyme.
- A choline already linked to phosphate is attached via choline phosphotransferase.
- Flippases transfer some of the phospholipids to the other leaflet into the ER lumen.