Cell Membrane Flashcards
Primary Function of Cell membrane
proteins/complexes is controlled transport of molecules into and out of the cell through channels, gates, and active carriers
Secondary Function of Cell Membrane
proteins/complexes is cellular communication (signaling) through receptors and amplification of secondary messengers
What is the Cell membrane made up of?
Phospholipid bilayer; hydrophilic region pointing towards water and hydrophobic region pointing inwards away from water
What is the location and function of Cardiolipin (diphosphatidylglycerol)?
Location: inner mitochondrial membrane
Function: stabilizes the electron transport system of mitochondria; decrease blood clots, stabilize respiratory chain enzymes in mitochondria, moves proteins and cholesterol, assists in proper folding of mitochondrial proteins, possibly helps regulate DNA synthesis
Changes of cardiolipin composition can lead to what diseases?
Heart failure, diabetes, Alzheimer’s disease, and Parkinson’s disease
Barth Syndrome
defects in the enzyme that metabolizes cardiolipin
decreased phosphorylation of ADP to ATP
symptoms: cardiomyopathy, muscle weakness and exercise intolerance
Treponema Pallidum
Bacterium responsible for syphilis; produces antibodies against cardiolipin
Phosphatidylserine (PS)
major acidic phospholipid in brain
intercellular communication; “flipped” (flippase enzyme) to outer membrane of platelets during platelet activation where it promotes thrombin formation (coagulation); cofactor for the anticoagulant protein C pathway
Phosphatidylethanolamine (PE)
predominantly cytoplasmic side; located in both the interior and exterior of cell membranes
regulates membrane curvature; secreted in VLDL
Phosphatidylcholine (PC)
located on both sides of cell membrane but usually on exterior
compound of pulmonary surfactant and used to calculate fetal lung maturity
promotes anticoagulant protein C pathway but less than PS
Phosphatidylinositol
Located in the interior and exterior of cell membrane as well as nuclear membrane
secondary messenger
Flippase
Enzyme that catalyzes the process of moving particular phospholipid molecules from one side of the bilayer to the other when needed
What maintains membrane fluidity and why is it important? Diseases associated with it?
Cholesterol maintains membrane fluidity; very important to keep membrane fluidity as to not destroy the cell
Bacteria and viral infections, malaria, entamoeba histolytica, migraines and virgin olive oil (beneficial changes in carbohydrates and lipid metabolism)
What is the worst thing that can happen to a cell membrane?
Crystallization
How does cholesterol maintain membrane fluidity?
Stiffens lipid bilayer but also prevents crystallization of membrane at colder temperatures
What bonds are associated with the lipid bilayer?
Hydrogen bonds and van der wall forces
Where are Lipid Rafts found?
Portions of cell membrane saturated with cholesterol and other lipids
Role of Polyene Antifungals
binds to ergosterol (like cholesterol but only in fungi); decreases membrane fluidity and creates hydrophilic channel through membrane - causes cell leakage and death
Does not effect human cells since we don’t have ergosterol
Peripheral and Integral Proteins
Peripheral located on either side of the bilayer; Intergral proteins located within or across the entire width of bilayer
membrane proteins can contain carbohydrates (glycoproteins)
Which proteins maintain RBC cell membrane shape?
Spectrin and ankyrin; important in the stabilization of the normal biconcave shape of RBC
Two diseases that result in the defects in RBC proteins that maintain the RBC cell membrane shape?
Elliptocytosis and spherocytosis
Hemoglobinopathies
disorders of the globin side chains of hemoglobin (sickle cell anemia, hemolytic anemia, thalassemias) - changes in globins lead to cell deformation - lead to cell death
One point mutation
Most important cell membrane function
maintain separate chemical environments allowing concentration gradients (due to van der wall forces) of ions/molecules to move in and out of the cell for cellular functions (size and charge also effect permeability)
What are the three methods of Membrane Channels?
- simple diffusion (no energy) - concentration gradient driven (through membrane)
- Facilitated Diffusion (no energy) - concentration gradient but speed can change depending on shape of
gated channel protein - Active Transport - (energy required) - involves carrier protein and changes shape via the release of energy or phosphorylation from nucleotide molecules
Sodium Potassium Pump
Active transport carrier protein - NOT A MEMBRANE CHANNEL or GATED CHANNEL PROTEIN
Ionophore Antibiotics/Antifungals
Same outcome of polyene; mechanism is different though; DOES NOT BIND TO ERGOSTOL
Distrupts the balance of various ions inside and outside of cells by interfering with the cell’s maintenance of its membrane function of membrane channels
Calcium Channel Blockers
Decrease the total transport of calcium into muscle cells thereby decreasing heart contraction and increase the diameter of blood vessels leading to decrease blood pressure (treat hypertension and high blood pressure)
H2 blockers and proton pump inhibitors
block transport of Hydrogen transport; decrease hydrogen in stomach to reduce heart burn, gastritis, ulcers and reflex disease
Aquaporins (-1 and -2) Function
integral membrane proteins found the kidney and other organs which help to regulate water flow in and out of cells
Group I intracellular receptor proteins
signal passes through membrane by diffusion and binds to intracellular target
Group II cell surface receptors
transmit a message from one side of the lipid bilayer to the other
Secondary Messengers used by Group II surface signaling
cAMP, Ca2+, DAG, Tyr-P, IP3, PIP
Intracellular Steroid Receptors
lipid soluble and can cross the membrane; binds with cytoplasmic receptors or activate signaling or continue to receptors in the nucleus to activate transcription factors and DNA snythesis
Genomic
steroid hormones that affect DNA synthesis
Nongenomic
Steroid hormones that do not affect transcription
Purpose of G-proteins
conversion of GDP to GTP to convey an external signal to the inside of the cell
Gs
cAMP production via adenyl cylase and protein kinase A signaling multiple targets
Gi
inhibits cAMP production; minor role in stimulation of phospholipase C
Gq
stimulates phospholipase C
G12/13
activation leads to changes in the actin cytoskeletion and therefore, regulation of cell cycle and motility
Gt
transducin molecules found in rods and cones couple visual signals between rhodopsin and cGMP phosphodiesterase
Second Messengers (signaling enzymes)
Adenyl cyclase, protein kinase A, phospholipase C, protein kinase C
Phospholipase C - Protein Kinase C (PKC) Signaling
Activation of phospholipase C (via the alpha-subunit of Gq) results in the cleavage of the membrane lipid PIP2 into DAG and IP3
Soluble Receptor-Associated Tyrosine Kinases
Found on cell membrane; receptor tyrosine kinases, Janus kinases, and Integral guanyl cyclase (aka guanylyl or guanylate cyclase)
Janus Kinase and Signal Transducer and Activator of Transcription (JAK-STAT)
end result: DNA leading to expression of certain genes
