Membranes and Transport Flashcards
(50 cards)
1
Q
Physiological Role of Membranes
- physical ______ _______ around cells and organelles
- gives cell its _______ ______
- separates the _______ environment from the ______ medium
- ____________ of organelles
- aids in _____ recognition
- provides _________ site for cytoskeletal elements
- ________ site for hormones and enzymes
- maintain ________ potential (membrane excitability)
- interlocking surfaces _____ cell together (tissue structure/gap junctions)
- _______ permeability of metabolites
- ______: exchange of material (nutrition, oxygen, waste, ions)
A
- protective barrier
- characteristic shape
- intracellular, external
- compartmentalization
- cell
- anchoring
- binding
- electrochemical
- binds
- selective
- transport
2
Q
General Structure and Composition
- membranes are composed of ____, _____, and __________
- arranged in ______ bilayer
- ____ permeable (allows small molecules and lipid soluble molecules to diffuse through)
- primary components of membranes are ________
A
- lipids, proteins, carbohydrates
- asymmetric
- semi
- phospholipids
3
Q
- main component of membranes
- amphiphatic: contain a hydrophilic head group and a hydrophobic tail group
A
phospholipids
4
Q
Membrane Composition
- lipid bilayer serves are the _______ in which a variety of lipids and proteins are embedded, attached, or anchored
- carbohydrate molecules are ________ attached to some membrane lipids or proteins
A
- foundation
- covalently
5
Q
What are the two types of phospholipids?
A
glycerophospholipids and sphingolipids
6
Q
- phospholipid
- glycerol backbone with a phosphate and two fatty acids esterfied to backbone
- e.g. phosphatidylcholine, phosphatidylserine, phosphatidylinositol
A
glycerophospholipids
7
Q
- phospholipid
- sphingosine backbone with a long chain fatty acid and phosphorylcholine
- sphingomyelin (most common SL present in outer leaflet)
A
sphingolipids
8
Q
What are the 3 types of membrane lipids?
A
phospholipids, glycolipids, cholesterol
9
Q
- membrane lipid
- sphingosine backbone with carbohydrate (oligosaccharide) residue(s)
- found in outer leaflet of lipid bilayer
A
glycolipids
10
Q
- membrane lipid
- embedded in lipid bilayer
- steroid nucleus with hydroxyl group and hydrocarbon side chain
- the hydrocarbon chain interacts with hydrophobic tails of membrane lipids
A
cholesterol
11
Q
What are the 3 types of membrane proteins?
A
intergral, peripheral, and lipid-anchored
12
Q
- membrane protein
- firmly embedded in the membrane and stabilized by hydrophobic interactions with lipids
- polytopic membrane proteins (includes transporters, ion channels, and receptors
A
integral membrane proteins
13
Q
- integral membrane proteins that span the entire lipid bilayer, weave in and out of the membrane several times and interact with both the internal and external environment
- include transporters, ion channels, and receptors that regulate the movement of molecules across membrane and receive and transmit signals from external environment of the cell
A
polytopic transmembrane proteins
14
Q
- membrane protein
- loosely bound to membrane through electrostatic interactions with lipids or proteins
A
peripheral proteins
15
Q
- membrane protein
- tethered to membranes via covalent attachment to a lipid
A
lipid-anchored proteins
16
Q
- carbohydrate molecules are ______ attached to specific membrane lipids and proteins that face extracellular space
- outer sheet of some membranes covered with a carbohydrate shell called ______ due to presence of glycolipids and glycosylated proteins
A
covalently, glycocalyx
17
Q
What are the 3 key functions of glycocalyx?
A
- protection: protects membrane components from mechanical injury or premature enzymatic degradation
- cell adhesion: makes more stable contacts with other cells, important during tissue formation and fertilization
- cell identification: allows body to differentiate between its own healthy cells from forge in, very important in red blood cells
18
Q
Membrane Fluidity
- proteins and lipids \_\_\_\_\_ and move \_\_\_\_\_\_ in membranes
- gives it a fluid like quality
- crucial for \_\_\_\_\_\_
allows proteins and lipids to undergo \_\_\_\_\_\_\_\_\_\_ changes and/or to move to specific areas within membrane to carry out \_\_\_\_\_\_
- factors that influence fluidity:
A. temperature
B. lipid composition
C. cholesterol
A
- rotate, laterally
- function
- conformational, function
19
Q
What are the 3 factors that influence membrane fluidity?
A
temperature, lipid composition, cholesterol
20
Q
What is the temp at which membranes switch from fluid to rigid state?
A
melting temp (Tm)
21
Q
Temperature
- below Tm membrane lipid molecules show ordered packing which makes membranes _____
- above Tm membranes are more _____
- Temp > Tm is optimal fluidity
A
- rigid
- fluid
22
Q
Lipid Composition
- lipids that contain long, saturated fatty acids ______ membrane fluidity due to tight packing which reduces their mobility
- lipid with short, unsaturated fatty acid chains ______ membrane fluidity because the kinks in their fatty acid chains do not allow tight packing
A
- decrease
- increase
23
Q
saturated lipids = ______ fluidity
unsaturated lipids = _______ fluidity
A
decrease, increase
24
Q
Cholesterol in Membrane
- can either increase or decrease fluidity
- if membrane is too rigid (high sat fats or temp below Tm), cholesterol intercalates into membrane and _______ fluidity by preventing close packing of the lipids
- if membrane is fluid (high unsat fats), cholesterol ______ fluidity by fitting in gaps created by kinks in the tail lipids
- ______ large changes in fluidity caused by temperature
A
- increases
- stabilizes
- reduces
25
cholesterol in rigid membrane = ______ fluidity
| cholesterol in fluid membrane = ______ fluidity
increase, decrease
26
Membrane Transport
- plasma membrane is ____-_______
- permeable to ______ molecules, move easily via diffusion (e.g. steroids)
- impermeable to ________ molecules, need a specific transport mechanism
- integral membrane proteins embedded in membrane function as ______ proteins
- membranes ______ the flow of biomolecules into and out of cells
- control biochemical properties of cell
- semi-permeable
- lipophilic
- hydrophilic/polar
- transporter
- regulate
27
In terms of Na+, K+, and Cl-, what are the conc intra and extracellularly
Na+ and Cl- higher extracellularly,
| K+ higher intracellularly
28
- energy-independent movement of molecules down a gradient (higher conc to lower conc)
- two types: simple diffusion and facilitated diffusion
passive transport
29
- passive transport
- occurs unaided
- molecules that are small, non-polar and uncharged polar diffuse freely across the membrane
- steeper the gradient, faster the diffusion
simple diffusion
30
- passive transport
- needs the assistance of transmembrane proteins
- molecules that are large and charged are unable to cross the membrane
- need a facilitator (proteins that help movement)
- proteins function as ion channels or transporters
- greatly increase rate of transport
facilitated diffusion
31
- pores or gates in membrane which allow charged and polar molecules (e.g. ions and water) to move across membranes down their concentration gradient
- open/close in response to stimuli
- channels high throughout (transport millions of molecules per second)
ion channels
32
- ion channel
- binding of ligand (e.g. neurotransmitter or hormone) to ion channel causes conformation changes in the protein
- facilitate opening of the channel, allowing rapid transport of ions across membrane
- ions move down concentration gradient
- dissociation of ligand closes the channel
- example: glutamate receptor: antagonist of glutamate receptor used to treat Alzheimer's disease (Mimantine/Namenda)
ligand-gated ion channels
33
- ion channel
- open/close in response to changes in membrane potential
- electrical voltage across the lipid bilayer created by large excess of negative charge inside the cell
- depolarization (increase in membrane potential due to influx of positively charged ions) triggers the opening of these channels permitting specific ions to cross the bilayer down their conc gradient
- found in excitable cells, such as neurons
- example: sodium channel
voltage-gated ion channels
34
- puffer fish example: has toxin called tetradotoxin which binds to sodium channel and inhibits neurotransmission
- topical anesthetics: block sodium channel, inhibit nt, used in clinic to block pain
consequences of blocking ion channels
35
- membrane transport
- energy-dependent, protein-assisted movement of molecules against their concentration gradient
- mediated by integral membrane proteins (polytopic transmembrane protein transporters)
- bind to a specific molecule on one side of membrane and release it on the other side
- 2 types: primary (uses ATP directly) and secondary (coupled to primary transport)
active transport
36
- active membrane transport
- uses ATP directly
- P type ATPases: ATP hydrolyzed, protein gets phosphorylated
- ABC transporters: ATP hydrolyzed, protein not phosphorylated
primary active transport
37
- active membrane transport
- does not use ATP, uses energy stored in concentration gradient
- thermodynamically unfavorable flow of one species of ion against a gradient coupled to a favorable flow of another species down a gradient
secondary active transport
38
- monosaccharides derived from digestion need to be transported from intestinal ____, across the ______ into the _____ ______
- this transport process is facilitated by ______ diffusion (passive) and ______ transport
- lumen, enterocyte, blood stream
| - facilitated, active
39
Transport Mechanisms in Uptake of Dietary Monosaccharides
- D-_____ and D-______ enter intestinal ________ cells from lumen along with ___ by _______ active transport mediated by sodium-glucose transporter 1 (_____) in apical surface
- ______ transported only by ______ diffusion down its concentration gradient using GLUT5 transporter on _____ side and _____ transporters on _____ side of enterocyte
- ___ transported in by SGLT1 is delivered to the blood stream using a ______ active transport process mediated by _________ in the basolateral membrane
- glucose, galactose, epithelial, Na+, secondary, SGLT1
- fructose, facilitated, apical, GLUT2, basal
- Na+, primary, Na+/K+-ATPase
40
- caused by deficiency in the activity of an enzyme called acid sphingomyelinase (A-SMase)
- A-SMase is a lysosomal enzyme which breaks down sphingomyelin (SM) into ceramide and phosphorylcholine
- defective A-SMase leads to accumulation of SM in lysosomes of liver, spleen, CNS, and bone marrow
- leads to: enlargement of liver and spleen
- causes neurological damage
- hallmark "cherry red spot" in the eye
- fatality: type A is 85% by 18 months of age
Niemann-Pick disease
41
- in healthy cells, phosphatidylserine (PS) found in inner leaflet of bilayer
- during apoptosis, PS is transferred to outer leaflet of bilayer
- serves as tag/label for dying cells to be recognized and removed by phagocytes
phosphatidylserine as a marker for apotosis
42
- type of hemolytic anemia
- associated w/ beta lipoproteinemia and advanced alcoholic cirrhosis
- chronic liver dysfunction impairs cholesterol metabolism in liver, results in excess free cholesterol
- elevated levels of cholesterol bound to RBC membrane
- decrease fluidity and flexibility of membrane
- creates rough, thorny projections on RBC's, acanthocytes
- cause RBC's to lyse as they pass through capillaries of spleen = reduced RBC survival
- prognosis is poor, median survival is a few months
- liver transplantation represents the only potentially curative option
spur cell anemia
43
- autosomal recessive disorder
- caused by defect in transporter responsible for uptake of dimeric amino acid, Cystine, and dibasic amino acids such as Arginine, Lysine, and Ornithine
- results in formation of cystine stones in kidney
- patients present with renal cholic (abd pain that comes in waves and is linked to kidney stones)
cystinuria
44
- autosomal recessive disorder
- caused by defect in a transporter for non-polar or neutral amino acids (e.g. alanine, valine, threonine, leucine, tryptophan, etc.)
- primary in kidneys and intestine
- deficiency in tryptophan (precursor for serotonin, melatonin, and niacin) affects health
- manifests in infancy as failure to thrive
- clinical findings: intermittent cerebellar ataxia (lack of muscle coordination), nystagmus (rapid and repetitive eye movement), tremor, photo dermatitis, and photosensitivity
- triggered by sunlight, fever, drugs, or stress
- period of poor nutrition almost always precedes and attack
Hartnup disease (pellagra-like dermatosis)
45
Cardiotonic Drugs
- cardiac _____ such as ouabain and ______ act as potent cardio tonic (contraction-inducing) drugs
- _____ the Na+/K+-ATPase in cardiac myocytes
- leads to ______ in intracellular Na+
- this impairs activity of the secondary transporter _____ ______ ______ (NCX) which is coupled to the Na/K-ATPase
- impairment of NCX leads to secondary _______ in ___ in sarco-endoplasmic reticulum, which in turn ______ the ________ force of cardiac ______
- therapeutic use: congestive heart failure, atrial fibrillation, dysrhythmias
- historically: plant extracts containing cardiac glycosides (foxglove, oleander, lily of the valley) have been used as arrow coatings, homicidal/suicidal aids, rat poisons, diuretics, and emetics
- purified extracts/synthetic analogues now used for tx of CHF and arrhythmias
- glycosides, digoxin
- inhibits
- increase
- sodium calcium exchanger
- increase, Ca+, increases, contractile, myocytes
46
- autosomal recessive disorder
- mutation in _____ ______ transmembrane conductance regulator (CFTR) gene
- defective CFTR protein is misfiled and does not leave ER after translation
- CFTR protein is a chloride ion channel that mediates active transport of Cl- from inside to outside cells in airways and sweat ducts
- uses energy of ATP hydrolysis
- defective CFTR causes buildup of Cl- inside airway epithelial cells
- compensated by increase in Na+, which makes NaCl (salt)
- water flows into airway cells to compensate for increased salinity, decreasing the water content of surface mucous layer
- this leads to thicker mucous and leaves airways susceptible to bacterial infections
cystic fibrosis
47
red blood cells have _____ on their surface, which are different ________ attached to proteins (______) and lipids (________) on RBC membrane
antigens, carbohydrates, glycoproteins, glycolipids
48
Why is important to cross-match blood types when performing a blood transfusion?
Because plasma of recipient may contain antibodies to one or more of the ABO and Rh antigens. Incompatible transfusion could result in acute hemolysis, renal failure, and shock.
49
- RBC antigens that are applied to D antigen
- inherited in an autosomal dominant fashion
- (+) individuals express D antigen, (-) individuals do not
Rh factor
50
- disease in which there is incompatibility between blood of mother and fetus
- when mom is Rh- and fetus is Rh+, the mom produces antibodies during pregnancy which can cross the placenta and attack fetus
- risk is greater in subsequent pregnancies
hemolytic disease in newborns (erythroblastosis fetalis)
