DSA 2: Cell Membranes and Transport Flashcards
What is the most important physiological role of the cell membrane?
- Selective permeability of various metabolites
- Transport and exchange of materials (nutrients, oxygen, waste, ions)
Describe the structure and composition of cell membrane
- Composed of lipids, proteins, and carbs
- Semi permeable
- hydrophilic tail and hydrophobic head
What are the two types of phospholipids found in a membrane?
Glycerophospholipid and Sphingolipids
What is the structure of a Glycerophospholipid?
-Glycerol backbone with 2 fatty acids and phosphate group
What is the structure of sphingolipids?
Sphingosoine backbone with:
- Hydrocarbon
- Fatty Acid
- Phosphate and Choline
What is the most common Sphingolipid in the outer leaflet of the PM?
Sphingomyelin
Where can you find cholesterol in cell membrane?
Cholesterol is embedded in lipid bilayer. The hydrocarbon side chains interact with hydrophobic tails of lipid membranes.
What are the two types of sphingosine?
- Type of phospholipid (third group is phosphate and choline)
- Type of glycolipid (third group is a mono or oligosaccarhide - sugar)
What is the location and function of Phosphatidylserine in the plasma membrane?
Phosphatidylserine is a type of sphingomyelin
In healthy cells, PS is found in the inner leaflet of bilayer. During apoptosis, PS is displayed on outer leaftlet.
**ON EXAM LAST YEAR
What are integral membrane proteins?
Proteins embedded in membrane and stabilized by hydrophobic interactions with lipids.
-includes transporters, ion channels, and receptors
*If they span entire lipid bilayer and interact with both external and internal env. - polytopic transmembrane proteins
What are peripheral proteins?
Proteins that are loosely bound to membrane via electrostatic interactions with lipids or proteins.
What are lipid anchored proteins?
Proteins tethered to membranes via covalent attachment to a lipid
Where can you find carbohydrates on membrane?
They are found extracellularly. Attached via covalently to lipids and proteins
What is a glycocalyx and what are its functions?
A carbohydrate shell made up of glycolipids and glycoproteins.
- Protection
- Cell adhesion
- Cell identification
What factors influence membrane fluidity?
Remember membrane follows fluid mosaic model.
1. Temperature
High temp: too fluid
Low Temp: too rigid
2. Lipid Composition
Many Saturated FA: decrease fluidity
Unsaturated FA present: increase fluidity
3. Cholesterol (Balancer)
Helps rigid cell membranes by intercalating into membrane to prevent close packing
Helps fluid cell membranes by fitting in the kinks created by the tails of lipids.
What are two types of passive transport?
- Simple Diffusion
- Facilitated Diffusion
What sort of molecules can use Simple Diffusion?
Small molecules that are non-polar, or uncharged polar.
Small Nonpolar Examples
O2, N2, Ethanol, Diethylether, Benzene
Small polar uncharged Examples
Water, CO2, Urea, NH3
What are ligand gated channels?
Ion channels that respond to ligands (hormonees or NT)
Allow rapid transport of ions
What is Mimantine / Namenda?
Glutamate receptor antagonist (prevents opening of an ion channel)
Treats Alzheimer’s disease
*I think this was on last year exam
What are voltage gated ion channels?
Ion channels that open/close in response to membrane potential
*Example: Sodium/Potassium channels in action potentials
Tetradotoxin can bind to sodium channels and inhibit them - lethal! (also anesthetics but they don’t kill you)
What are P Type ATPases? (Primary Active Transport)
Energy comes from hydrolysis of ATP (breaks down to ADP+P)
Protein transporter is phosphorlyated which occurs on aspartate residue
Conformational change that facilitates transport of ions from one side to the other
Examples: Na+/K+ ATPase and Ca2+ ATPase
What are ABC transporters?
ATP is also hydrolyzed but protein transporter does not get phosphorylated.
Pump out small molecules against gradient concentration
What is secondary active transport? What are examples?
Unfavorable flow of one species coupled with Favorable flow of another species - gradient established
Examples: Sodium/Glucose Transporter (SGLT) and Sodium/Calcium Exchanger (NCX)
What does SGLT move and how?
Sodium and Glucose
- Both are moved from intestinal lumen to epithelium of SI and renal tubules
- Sodium moves down its gradient
- Glucose moves against its gradient
