The Plasma Membrane Flashcards
What is the biologic membrane composed of?
Lipids and proteins
What type of lipids are found in the membrane?
- Phospholipids
- Glycolipids
- Cholesterol
What are two choline-containing phospholipids that are abundant in cell membranes?
- Phosphatidylcholine (Lecithin)
2. Sphingomyelin
What are two amine phospholipids present in some cell membranes?
- Phosphatidylethanolamine (Kephalin)
2. Phosphatidylserine
What is phosphatidylinositol (a type of phospholipid) important for, in the cell?
Cell to cell signaling
Where in the plasma membrane is glycolipids present and what is their function?
Found in the outer layer of the bilayer.
Participate in the formation of the glycocalyx.
(Has sugar residues)
Where in the plasma membrane is cholesterol present and what is their function?
Between phospholipid tails.
Increase the stability and rigidity of the cell membranes.
What are the two classes of membrane transporting proteins?
Peripheral and transmembrane (integral).
What does peripheral proteins bind to?
Phospholipids or transmembrane proteins.
What are the two classes of transmembrane proteins?
Single-pass proteins
Multi-pass proteins
What protein classifications can we find in/at the cell membrane?
Transporters, linkers, receptors, enzymes. (One protein can perform more than one function)
What can freely diffuse through the plasma membrane?
Gasses and hydrophobic molecules. (Hydrophilic molecules are transported across via specific transport proteins)
Give 3 examples of Ion channels.
- Sodium channels
- Calcium Channels
- Proton (hydrogen) Channels
How does ions get transported passively across the membrane?
Via ion channels acording to concentration gradient.
What are the different types of channels?
- Voltage-gated channels (open due to electrical potential change) Ex: Nerve cells.
- Ligand-gated (open due to signaling molecule) Ex: Postsynaptic membrane.
- Mechanically-gated channels (stress-activated) Ex: Inner ear, striated muscle cells.
(Some channels are constantly open. Withdrawed and inserted into membrane when needed) Ex: Potassium leak channel, water channels (aquaporins).
In what structures are aquaporins(water channels) especially important?
Renal tubules. Responsible for the final concentration of urine.
What does carrier proteins do?
Transports small molecules passively according to the concentration gradient. Changes conformation. No energy required.
How does pump proteins work?
Transports molecules across the plasma membrane by changing conformation. Use ATP to pump against the concentration gradient.
Ex:
Sodium potassium pump.
Calcium pump.
Proton pump.
Define antiport, symport and uniport. (Carriers and pumps)
Antiport: Transports molecules in different directions.
Symport: Transports more than one molecule in the same direction simultaneously.
Uniport: Transports only one molecule in any direction.
What is the function of translocons?
Allow for large proteins to cross the membrane.
What does the abbreviation ABC transporters stand for?
ATP-binding cassette transporters.
Transports large molecules across membranes: drugs and peptides
What is meant by the term membrane trafficking?
All the pathways of vesicular transport.
What is vesicular transport?
The predominant mechanism for transport of large molecules like lipids and peptides across the membrane.
What are the steps of the anterograde pathway?
ER –> Golgi –> Cell Membrane
What are the steps of the retrograde pathway`?
Cell Membrane –> Endosomes –> Lysosomes
How thick is the cell membrane?
7.5 nm (trilaminar structure in microscope)
What is the outer sugar coat of the cell membrane called? And what is its function?
Glycocalyx.
Strands of proteins and sugars bound together. Up to 50 nm thick. Cell recognition, endocytosis, protects cells, aids in attachment of cells to matric components.
What are 4 adhesion molecules?
- Cadherins - cell to cell (same type cell).
- Selectins - cell to cell (different type cell)
- Immunoglobulin superfamily - cell to cell adhesion (different type cell)
- Integrins - cell to extracellular matrix adhesion. Some times cell to cell (same type).
What is lipid rafts?
Subdomains of the membrane that contains high amounts of cholesterol and glycolipids.
What is Caveolae?
Formed by attachment of protein caveolin and are invagination in the membrane. It contains receptors and transporters (transports Ca2+). Participate in pinocytosis.
What are coated pits?
Surrounded by protein clathrin. Participate in receptor-mediated endocytosis.
What is meant by saying that the phospholipid bilayer is asymmetric?
The phospholipid bilayer is asymmetric because there is an unsymmetric distribution of phospholipids in the bilayer.
What is spectrin?
Spectrin is a cytoskeletal protein that lines the intracellular side of the plasma membrane.
How does the cell membrane grow?
The cell membrane grows only by the incorporation of new components. It cannot be produced de novo.
The membranes of which organelles does NOT participate in membrane trafficking?
The membranes of mitochondria and peroxisomes do not participate in membrane trafficking.
