Section 2 Week 1 Flashcards
What is the plasma membrane?
The protein-containing lipid bilayer that surrounds a living cell.
It serves to separate and protect the cell’s chemical components from the external environment.
What is the composition of the plasma membrane?
Composed of a 2-ply sheet of lipid molecules about 5nm thick with inserted proteins.
All cell membranes share a common structure of lipids and proteins.
What are the main functions of the plasma membrane?
- Prevent content from escaping the cell
- Facilitate exchange of nutrients and molecules
- Act as sensors or receptors for environmental changes
These functions are critical for cell survival and communication.
What does it mean that the plasma membrane is self-healing?
If torn or penetrated, it quickly reseals itself.
This property helps maintain cellular integrity.
How do eukaryotic cells differ from bacteria in terms of membrane structure?
Eukaryotes have internal membranes enclosing organelles, while bacteria tend to have a single membrane.
Organelles include the endoplasmic reticulum, Golgi apparatus, endosomes, and mitochondria.
Define lipid bilayer.
Thin pair of closely juxtaposed sheets composed mainly of phospholipid molecules.
It forms the structural basis for all cell membranes.
What are phospholipids?
The major type of lipid molecules in cell membranes, generally composed of two fatty acid tails linked to a phosphate-containing polar group.
Phosphatidylcholine is a common example.
What does amphipathic mean?
Having both hydrophobic and hydrophilic regions.
This property is crucial for the formation of lipid bilayers.
What drives the formation of a lipid bilayer?
The conflicting forces between hydrophilic heads attracting water and hydrophobic tails avoiding it.
This results in a stable and energy-favorable bilayer structure.
Describe the fluidity of a lipid bilayer.
The lipid bilayer acts as a 2D fluid, allowing molecules to move and change places within the membrane.
This fluidity is essential for membrane function.
What factors affect the fluidity of a lipid bilayer?
- Length of hydrocarbon tails
- Number of double bonds in the tails
Shorter tails and unsaturated bonds increase fluidity.
What role does cholesterol play in membrane fluidity?
Cholesterol makes the lipid bilayer less flexible and helps maintain fluidity.
It fills spaces between phospholipids caused by unsaturated tails.
Where does membrane assembly begin in eukaryotic cells?
In the endoplasmic reticulum (ER).
Enzymes in the ER manufacture new phospholipids.
What is the function of scramblase?
A transporter protein that removes randomly selected phospholipids from one half of the bilayer and inserts them into the other.
This helps maintain even bilayer distribution.
What distinguishes the cytosolic monolayer from the non-cytosolic monolayer?
The cytosolic monolayer faces the cytosol, while the non-cytosolic monolayer is exposed to the exterior or lumen.
This asymmetry is crucial for cell function.
What are membrane proteins?
Proteins associated with the lipid bilayer of a cell membrane that carry out various functions.
Each membrane contains a unique set of proteins reflecting its specialized functions.
Define transmembrane proteins.
Membrane proteins that extend through the bilayer with domains on both sides.
They are amphipathic, with hydrophobic regions in the bilayer.
What is a polypeptide chain’s typical structure in a transmembrane protein?
It usually crosses the lipid bilayer as an alpha helix.
Hydrogen bonding within the polypeptide facilitates this structure.
What are detergents used for in membrane protein studies?
Detergents solubilize lipids and membrane proteins by disrupting the lipid bilayer.
They form micelles to separate proteins from phospholipids.
What is meant by membrane domains?
Functionally and structurally specialized regions in the membrane characterized by specific proteins.
They allow for localized functions within the cell membrane.
What does FRAP stand for?
Fluorescence recovery after photobleaching.
It measures the rate of protein diffusion within a membrane.
What is the role of glycolipids in cell membranes?
They are primarily located in the non-cytosolic half of the bilayer and have sugar groups facing the cell exterior.
They are synthesized in the Golgi apparatus.
