DLA1 Membrane Structure and transport: Integrated Basic Principles Flashcards
Why is the plasma membrane described as a fluid mosaic of lipids and proteins?
Because of the lateral movement
What is a lipid raft?
Very small membrane patches of unique protein and lipid composition-used for signal transduction
-site of virus infection
What are short lived planar lipid rafts composed of? (3)
- Cholesterol
- Glycolipids
- Sphinogmyelin
What are long lived signal conduction sites called?
Caveolae-form an invagination of the plasma membrane stabilized by caveolins
Fluidity of plasma membrane determined by 2 things
- Fatty acid composition
- Amount of free cholesterol
What happens at low temperatures in a plasma membrane?
Fatty acyl groups stiffen and cholesterol prevents decrease of membrane fluidity (separate acyl chains and prevent close packing)
What happens at high temperature in the plasma membrane?
Fatty acyl groups are fluid and cholesterol prevents increaseof membrane fluidity by slowing down the movement of the esterified fatty acids.
Composition of outer layer in the plasma membrane?
- Mostly sphingomyelin (SM) and phosphatidylcholine (PC) (both have polar head)
- Some Phosphatidylethanolamine (PE) and NO phosphatidylserine
- Many glycosphingolipids which form together creating (glycocalyx)
Inner layerof the plasma membrane is composed of what?
- Mostly Phosphatidylethanolamine (PE) and Phosphatidylserine (PS)-negatively charged
- Phosphatidylinositol (PI)-only found in the inner layer and can be used as PIP2 in the calcium messenger center
What are the 6 functions of Integral Membrane Proteins?
- Pumps/Carriers/Transporters-specific ions (Na, K), metabolic precursors (Sugars, AAs)
- Channels-passive diffusion, aquaporins, gap junctions
- Receptors
- Linkers
- Enzymes
- Structural proteins
What is the freeze fracture technique and what is it used for?
- Tissue soaked in cyroprotectant eg glycerol-then frozen
- Struck with a knife which fractures the hydrophobic part
- Creates 2 faces (E and P)
- Using EM we view integral membrane proteins
What are the permeable molecules?
Hydrophobic, non-polar uncharged
Ex: N2, benzene, CO2, O2
Less permeable molecules?
Small, polar, uncharged
Ex: H20, urea, glycerol
Highly impermeable molecules
LARGE, CHARGED, POLAR
H+, glucose, sucrose
GLUT-1 Tissue distribution and things to know
- Found in most tissues-abundant in RBC and blood-brain barrier
- High affinity glucose transporter
- Basal glucose uptake remains constant (at low or normal glucose levels)
GLUT-2 Tissue distribution and things to know
- Liver, kidney, pancreatic beta cells, serosal side intestinal mucosa cells
- High capacity, low affinity transporter
- May be used as a BG sensor for insulin release from beta cells
GLUT-3 Tissue distribution and things to know
- Found in most tissues (abundant in brain neurons)
- High affinity glucose transporter
- Major transporter in the CNS
GLUT-4 Tissue distribution and things to know
- Found in fat cells, skeletal muscle and heart
- High affinity glucose transport system that is INSULIN SENSITIVE-this leads to increase of GLUT-4 on the cell surface
GLUT-5 Tissue distribution and things to know
- Found on the mucosal side of intestinal mucosa cells (dietary fructose) and in semen
- Preference for fructose transport and only transports glucose at very high concentrations
How do we test for GLUT-1 deficiency?
Rare encephalopathy
Test RBCs!
Symptoms: epilepsy-like seizures in first few months of life. Also develop ataxia, delayed psychomotor development, movement disorders, impaired speech
GLUT-2 transport in detail for small intestine
Facilitates release of all dietary monosaccharides from the intestinal mucusa cells on the serosal side into the hepatic portal vein
What is the SGLT?
SGLT-1 and SGLT-2
Sodium-dependent glucose co-transporter
SGLT-1 found in intestinal mucosa for uptake of dietary glucose/galactose
SGLT-2: found in kidneys to reabsorb glucose into tubular system
What is primary active transport by ABC transporters? What is an example?
ATP-Binding Cassette
Bile salts, cholesterol, conjugated bilirubin into the bile ducts
Form of Primary Active transport (ATP)
What is the CFTR and why is it important?
Cystic Fibrosis Transmembrane conductance Regulator
Uses a gated channel with a ATP Binding Cassette-only opens or closes with stimulus using the cAMP messenger system
-CFTR does NOT pump chloride ions, they flow with the gradient when the channel opens
Deficiency of CFTR leads to?
Signs/Symptoms
Cystic Fibrosis-Signs
1. Meconium ileus-requires immediate medical treatment
2. Salty skin-impaired reuptake of chloride ions
Symptoms:
1. Poor growth and low weight
2. Lung infections
3. Pancreatitis
4. Steatorrhea (excessive fluid in stools)
5. Infertitility
