Biochemistry Flashcards
Fluid mosaic model
Describes biological membranes.
Phospholipid bilayer containing embedded proteins.
Fluid because lipids and protein molecules move laterally.
Lipid rafts
“Microdomains” in the plasma membrane that contain:
- sphingolipids/sphingomyelin
- cholesterol
- glycosphingolipids
Signal transduction Membrane fluidity Membrane protein trafficking Facilitate virus infection Regulating neurotransmission and receptor trafficking
Where is free cholesterol found in the plasma membrane?
Free cholesterol found in both inner and outer leaflet.
Where is glycocalyx (glycolipids/glycoproteins) found?
Found in the outer leaflet.
Lipids found in outer leaflet
Phosphatidycholine
Sphingomyelin
Phosphatidylethanolamine
Glycosphingolipids
Lipids found in inner leaflet
Phosphatidylethanolamine Some phosphatidylcholine *Phosphatidylserine Phosphatidylinositol PIP2
What determines the fluidity of the plasma membrane?
Determined by:
- fatty acid composition of phospholipid
- By free cholesterol
Role of cholesterol in fluidity
and
Where is cholesterol found
Decreases fluidity by polar heads.
Increases fluidity inside bilayer.
Cholesterol prevents extreme changes in fluidity due to temperatures.
Cholesterol is found in the cis-bond regions of fatty acids (kink).
Fluidity of intracellular membranes
NO cholesterol.
Shorter fatty acids & unsaturated fatty acids=membrane more fluid.
ie arachidonic acid (20:4, Ω 6)
ie docosahexaenic acid (2:6, Ω 3)
Passive transport: transporter facilitates diffusion
A compound flows with the [] gradient from a high [] to a low [].
Process is SPECIFIC and SATURABLE.
NO energy required in process.
Glucose Transporters
Sodium independent
*Facilitated diffusion transport system
High affinity transporters—
GLUT-1: Brain, RBC
GLUT-3: Neurons
GLUT-4: Skeletal muscle, heart & fat cells (insulin dependent)
Low affinity transporters—
GLUT-2: LIVER, KIDNEY, beta-cell, intestine
GLUT-5: Intestine, seminal vesicles
*Glucose uptake from the blood
Glucose Transports
Sodium dependent
*Secondary active transport system
SGLT-1: INTESTINE (epithelial cells at the lumen side)
SGLT-2: KIDNEY (epithelial cell in renal tubules)
GLUT-1
Abundent in RBC
Also found in BBB and kidneys
GLUT-3
Dominant in neurons and brain
GLUT-4
*Insulin dependent
Abundant in fat cells, skeletal muscles, and heart.
GLUT-4 stored in cells and can be mobilized by insulin or vigorous exercise of skeletal muscles.
GLUT-2
*Low affinity transporter
Capable of transporting large amts of glucose molecules at high []s.
Found in: Intestinal mucosal cells Hepatocyptes Renal tubular cells Beta-cells of pancreas
GLUT-5
Found in:
Intestinal mucosal cells on the luminal side of the intestinal membrane
Seminal vesicle
Mainly transports dietary fructose. (Glucose ONLY if in high [])
Hereditary GLUT-1 deficiency
Deficiency of GLUT-1 leads to microcephaly and epilepsy-like seizures
Individuals develop: Ataxia Delayed psychomotor development Movement disorder Impaired speech
Primary active transport
and
Secondary active transport
Primary active transport is performed by Na+/K+-ATPase
Active pumping=3 Na+ out, 2 K+ in
One ATP needs to be cleaved
Against [] gradient
———
Secondary active transport is coupled to Na+/K+-ATPase
Transports both Na+ and a specific molecule into the cell. Molecules may be taken up against a [] gradient.
Secondary active transport
SGLT-1=symporter
Transports Na+ and glucose/galactose against [] gradient.
ABC Transporters
and
CFTR
ATP Binding Cassette
Allow the active transport of molecules from cytosol to extracellular space.
Needs hydrolysis of ATP.
Mostly transporting lipids.
——-
CFTR (cystic fibrosis transmembrane conductance regulator)
Chloride ion channel. No pump, but cleaves ATP (passive). Flows with gradient.
*Gated channel with pore for chlorine ion.
Found in: airway ducts pancreatic ducts reproductive ducts intestinal lumen and skin
Cystic fibrosis cause and diagnosis
CFTR is impaired in the sweat glan, leading to a lack of re-uptake of chloride ions which leads to salty skin.
Characterized by lung congestion/infection and malabsorption of nutrients by the pancreas.
Diagnosis- Sweat test. [] of NaCl is measured.
