Flashcards in Membranes & Transport Deck (68):
Membranes are composed of lipids, proteins, and carbs and are arranged in an ______ belayer
Hydrophilic head group facing the aqueous environment outside
Hydrophobic tail facing the interior
How are carbohydrate molecules attached to membrane lipids or proteins?
Most abundant lipids found in biological membranes
Phospholipids (glycerophospholipids and sphingoolipids)
Glycerophospholipids are composed of:
Glycerol backbone + phosphate + 2 fatty acids
(Ex: phosphatidylcholine, phosphatidylserine, phosphatidylinositol)
Sphingolipids are composed of:
Sphingosine backbone + long chain fatty acid + phosphorylcholine
(Eg: sphingomyeline— most common SL in outer leaflet)
Sphingosine backbone with carbohydrate (oligosaccharide) residue(s)
Found in outer leaflet of lipid bilayer
Steroid nucleus + hydroxyl group + hydrocarbon side chain (interact with hydrophobic tails)
Which 3 membrane lipids are located in the outer sheet?
What 3 membrane lipids are located in the inner sheet?
What is a marker for apoptosis?
Describe how it works
During apoptosis, it is displayed on the outer leaflet, where it serves as a tag for phagocytes to recognize
What is the deficiency in Niemann-Pick disease? Describe what this normally does
Acid sphingomyelinase (A-SMase)
This is a lysosomal enzyme which breaks down sphingomyelin
What does the deficiency in Niemann-Pick disease cause?
SM accumulation in the lysosomes of the liver, spleen, CNS, and bone marrow
What are the symptoms of Niemann-Pick disease?
Enlargement of the liver and spleen, neurological damage
CHERRY RED SPOT in eye
Firmly embedded in the membrane
Stabilized by hydrophobic interactions with lipids
Integral membrane proteins
Integral membrane proteins
Span entire lipid bilayer
Weave in and out of membrane
Interact with internal and external environment
Include: transporters, ion channels, and receptors (regulate movement of molecules and transmit signals from external environment)
Polytopic transmembrane proteins
Loosely bound to membrane through electrostatic interactions with lipids or proteins
Tethered to membranes via covalent attachment to a lipid
Carbohydrates are attached to lipids/proteins that face ______
The glycocalyx is a carbohydrate shell. Discuss its 3 functions
Protection: mechanical injury or premature enzymatic degradation
Cell adhesion: tissue formation and fertilization
Cell identification: own healthy cells vs. diseased foreign cells; RBCs!!
RBCs have antigens on their surfaces. These can be either
H antigen (O blood type), A antigen, B antigen, or A+B antigen
Plasma produces antibodies. These can be eitherR:
Anti-A & Anti-B (for blood type O)
Anti-B for blood type A
Anti-A for blood type B
None for blood type AB
Type O (RBCs have no blood group antigen)
Type AB (plasma does not contain any antibodies)
Rh antigen is actually the ___ antigen and is inherited in an autosomal dominant fashion
Describe what occurs in erythroblastosis fetalis
There is incompatibility between the blood of mother and fetus
Mom is Rh- and the fetus is Rh+
More common in second pregnancy because the mom will have produced the antibodies already
Membranes switch from fluid to rigid state
Melting temp (Tm)
Temp >>> Tm = ?
Temp > Tm = ?
Temp < Tm = ?
What is the effect of saturated lipids on the membrane and why?
They decrease fluidity because they are more tightly packed
What is the effect of unsaturated lipids on the membrane and why?
They increase fluidity because of the kinks in the fatty acid chains
What happens if cholesterol is inserted into a membrane that is too rigid?
It increases fluidity by preventing close packing of the lipids
What happens if cholesterol is inserted into a membrane that is too fluid?
It decreases fluidity by fitting in thee gaps created by the kinks
Describe what occurs in spur cell anemia
Elevated levels of cholesterol in the RBC membrane lead to decreased fluidity —> RBCs lyse in the spleen
The membrane is permeable to what type of molecules?
The membrane is impermeable to what type of molecules?
Facilitate the transport of specific molecules across PM
Function as transporter proteins
Integral membrane proteins
What have a high concentration extracellularly?
Sodium, chloride, calcium
What has a high concentration intracellularly?
What are the 2 types of passive transport?
Simple diffusion & facilitated diffusion
This type of diffusion occurs unaided
Transports molecules that are small, non-polar, and uncharged polar
This type of diffusion requires the assistance of transmembrane proteins
Large/charged molecules —> via proteins that act as ion channels or transporters
Ex: voltage-gated Na channel and glucose transporters
Allow charged/polar molecules (ions and water) to move across membranes down their concentration gradient
Describe ligand-gated ion channels
Binding of ligand (neurotransmitter or hormone) causes conformational changes in protein —> opening of channel
Down concentration gradient
Ex: glutamate receptor
What is an antagonist of the glutamate receptor that is often used to treat Alzheimer’s disease?
Describe what occurs with voltage-gated ion channels
Depolarization occurs due to an influx of positively charged ions —> open channels —> ions go down concentration gradient
Found in excitable cells such as neurons
Ex: sodium channel
Active transport is mediated by?
Integral membrane proteins
This type of active transport uses ATP directly
This type of active transport uses energy stored in a concentration gradient and is coupled to a primary transport system
There are 2 types of primary active transport. Describe them:
1. P type ATPases: ATP is hydrolyzed, protein gets phosphorylated
2. ABC transporters: ATP is hydrolyzed but does not phosphorylated the transporter
In this type of primary active transport, the following occurs:
ATP breaks down into ADP an phosphate
Transporter forms a covalent bond with phosphate to form an intermediate
Phosphorylation on a conserved aspartame residue —> conformational changes
Ex: Na+/K+-ATPase and Ca2+-ATPase
P type ATPases
Type of primary active transport:
Pump wide range of small molecules out of cells against their gradient
Use ATP as energy source
Ex: P glycoproteins, multi-drug resistant proteins
Thermodynamically unfavorable flow of one species of ion against a gradient coupled to a favorable flow of another species down a gradient
Eg: sodium-glucose transporter and sodium-calcium exchanger
Secondary active transport
Describe an antiporter and give an example:
Go in opposite directions
Sodium calcium exchanger (NCX)
Describe a symporter and give an example:
Go in same direction
Describe a uniporter and give an example:
Can go either way depending on concentration
Mitochondrial calcium transporter
Present in epithelial cells that line the small intestine and renal tubules
Mediates unidirectional movement of Na+ and glucose
Movement of Na occurs down gradient; movement of glucose occurs against gradient
Sodium-glucose transporter 1
Antiporter that functions to maintain low levels of intracellular calcium
Imports 3 Na+ down gradient and exports 1 Ca2+ again gradient
Describe the transport mechanisms in the uptake of dietary monosaccharides:
D-glucose and D-galactose enter intestinal epithelial cells from lumen along with Na+: secondary active transport mediated by SGLT1 in apical surface
Transported across enterocyte into blood: facilitated diffusion using GLUT2
Fructose: facilitated diffusion using GLUT5 on apical side and GLUT2 on basal side
Na+: transported in by SGLT1; primary active transport mediated by Na+/K+-ATPase in basolateral membrane
What causes cystic fibrosis? What does it normally do?
Mutation in CFTR (cystic fibrosis transmembrane conductance regulator) gene —> misfolds and won’t leave ER
CFTR is a chloride channel that mediates active transport of Cl- from inside cells to the outside via airways and sweat ducts
What does the deficiency in cystic fibrosis cause?
Buildup of Cl- inside the airway epithelial cells —> increased Na+ —> water follows salt decreasing the water content of the mucous layer —> thicker mucous susceptible to bacterial infections
What is the defect in cystinuria?
Defect in transport responsible for uptake of diametric amino acid cystine and other dibasic amino acids
COAL: cystine, ornithine, arginine, lysine
What does the defect in cystinuria cause?
Cystine crystals or stones in the kidney
Positive nitroprusside test
What is the defect in Hartnup disease?
Defect in a transporter for non-polar or neutral amino acids (alanine, valine, threonine, leucine, tryptophan, etc)
This transporter is typically found in the kidneys and intestine
What does the deficiency in Hartnup disease cause?
Tryptophan is a precursor for serotonin, melatonin, and niacin (precursor for NAD+), so all of those are lacking
Cerebellum ataxia— lack of muscle coordination
Photodermatitis and photosensitivity