Membrane Transport Flashcards
1
Q
Plasma membrane is selectively permeable
A
2
Q
membrane though which nothing can pass
A
Impermeable membrane
2
Q
any substance can pass through it
A
Freely permeable membrane
3
Q
____________ permits free passage of some materials and restricts passage of others
* Distinction may be based on ____, _______, _______, or ______
A
Selectively permeable membrane;
size;
electrical charge;
molecular shape;
lipid solubility
4
Q
The smaller the molecule and more nonpolar, the more rapidly it will diffuse across the lipid bilayer such as O2 and CO2
A
4
Q
More slowly lipid bilayers are highly impermeable to charged molecules (ions), no matter how small
A
5
Q
Determine permeability of membrane to the following:
Gases: CO2, N2, O2
A
Permeable
6
Q
Determine permeability of membrane to the following:
Small uncharged polar molecules: Ethanol
Urea, Water
A
Permeable
Slightly permeable
7
Q
Determine permeability of membrane to the following:
Large uncharged polar molecules: Glucose, Fructose
A
Impermeable (needs a transport protein)
8
Q
Determine permeability of membrane to the following:
Ions: K+, Mg2+, Ca2+, Cl-, HCO3-, HPO4^2-
A
Impermeable (needs a transport protein)
9
Q
Determine permeability of membrane to the following:
Charged polar molecules: Amino acids, ATP, Glucose 6-phosphate, proteins, nucleic acids
A
Impermeable
10
Q
- The differences in the concentration of the 2 sides of membrane
- Drives passive transport and determines its direction (higher to lower)
A
Concentration gradient
11
Q
Concentration gradient and electrical gradient combine to form a net driving force
A
Electrochemical gradient
12
Q
Diffusion from a higher to lower concentration
A
Passive transport
13
Q
Active transport occurs when a molecule is transferred from a lower concentration to a higher concentration
A
14
Q
2 Types of passive transport
A
Channel-mediated
Transporter-mediated
15
Q
(Concentration gradient, Electrochemical gradient) = involves no membrane potential
(Concentration gradient, Electrochemical gradient) = involves a membrane potential
A
Concentration gradient;
Electrochemical gradient
16
Q
2 Types of transport
A
Passive transport
Active transport (needs ATP)
17
Q
A membrane protein that uses the movement of one substance down its electrochemical gradient to transport another substance against its gradient.
A
Coupled transporter
Symport or antiport
18
Q
A type of membrane protein that uses energy from ATP hydrolysis to transport substances against their gradient.
A
ATP-driven pump
Na⁺/K⁺ pump (Na⁺/K⁺-ATPase), which pumps 3 Na⁺ out and 2 K⁺ in per ATP molecule.
19
Q
Uses energy from light (typically sunlight) to move ions or molecules across membranes.
A
Light-driven pump
20
Q
Transport Processes in the Membrane
A
- Simple diffusion = lipid-soluble solutes pass through
- Channel-mediated facilitated diffusion = involves a channel protein
- Carrier-mediated facilitated diffusion = involves a transport protein
21
Q
2 main classes of 2 membrane proteins
A
- Carrier proteins/Transporters
- Channel proteins
22
Q
__________ bind specific solutes and transfer them across the lipid bilayer
- This involves undergoing conformational changes that expose the solute-binding site sequentially on 1 side of the membrane and then on the other.
A
Transporters/ Carrier proteins
Outward open
Occluded
Inward open
23
Membrane Carriers: ______
Carries only one solute at a time
Uniporter
24
Several Features Distinguish Uniport Transport from Passive Diffusion
* The rate of facilitated diffusion by uniporters is far higher than passive diffusion
* Transport occurs via a limited number of uniporter molecules, rather than throughout the phospholipid bilayer (selective)
25
membrane proteins that facilitate the transport of glucose over a plasma membrane
Glucose transporter (Gluts)
26
Example of uniporter:
- After glucose is transported into the erythrocyte, it is rapidly phosphorylated, forming ____________, which cannot leave the cell. Because of this reaction, the 1st step in the metabolism of glucose, is rapid, the intracellular concentration of glucose does not increase as glucose is taken up by the cell.
glucose 6-phosphate
27
______ causes a rapid stimulation of glucose uptake in adipose tissue and muscle tissue by re-locating _______ from intracellular storage vesicles into the membrane.
Insulin;
GLUT4 glucose transporters
28
______ is responsible for the production of insulin (pancreas)
Beta cell
29
Insulin release and action. Glucose enters beta cells via the _______ and ATP is generated by ______. This results in closure of ATP-sensitive K+ channels, depolarization of the plasma membrane, and opening of voltage-dependent Ca2+ channels. The influx of ____ leads to the release of insulin (1), which is carried in the bloodstream to cells throughout the body where it binds to insulin receptors. This results in autophosphorylation of insulin receptors and phosphorylation of tyrosines on a variety of cellular proteins. The phosphorylated proteins provide docking sites for SH2 domains of several proteins that activate different signaling pathways (dashed lines). This results in translocation of the glucose transporter (GLUT4) and uptake of glucose by the cell; alterations in glucose, lipid, and protein metabolism; and changes in gene expression and cell growth.
glucose transporter (GLUT2);
glycolysis;
Ca2+
30
Membrane Carriers: ________
carries 2 or more solutes simultaneously in same direction (cotransport)
Symport
31
_______ Import Amino Acids and Glucose into Animal Cells
Na-Linked Symporters
32
2 Na+ out + glucose out -><- 2 Na+ in + glucose in
33
Membrane Carriers: ______
* carries 2 or more solutes in opposite directions (countertransport)
* sodium-potassium pump brings in ___ and removes ___ from cell
Antiport;
K+;
Na+
34
Antiporter: _______
* Helps maintain resting potential
* Regulate cell volume
sodium-potassium pump
35
Na-Linked Antiporter Exports ____ from Cardiac Muscle Cells
Ca2+
36
In muscle cells, a rise in the cytosolic ___ concentration in muscle triggers contraction.
Ca2
3Na+ out + Ca2+ in = 3Na+ in + Ca2+ out
37
Ca2+ pump
- accounts about 90% of the membrane protein of organelle
- responsible for moving Ca2+ from the cytosol back into the sarcoplasmic reticulum
High calcium in cytosol = muscle contraction
Low calcium in cytosol = muscle relaxation
38
Sodium-Potassium Pump
1. Binding of cytoplasmic Na+ to the pump protein stimulate phosphorylation by ATP.
2. Phosphorylation causes the protein to change its shape.
3. The shape change expels Na+ to the outside, and extracellular K+ binds.
4. K+ binding triggers release of the phosphate group.
5. Loss of the phosphate restores the original conformation of the pump protein.
6. K+ is released and Na+ sites are ready to bind Na+ again; the cycle repeats.
39
ATP-driven Pumps
1. P-class pumps
2. V-class proton pumps
3. F-class proton pumps
4. ABC superfamily
40
Transmembrane proteins that utilize the energy of ATP binding and hydrolysis to translocate various substance
* Substrates: sugar, amino acids, ions, peptides, hormones, etc.
ABC transporter: ATP binding cassette transporter
41
ABC transporters
* In humans are found in ____, ______, _____, and ______.
* Eukaryotic ABC are exporters
liver;
blood brain barrier;
kidney;
intestine
42
E. coli ABC transporter
Outer membrane
Periplasmic space
Inner membrane (found here)
43
refers to the phenomenon where microorganisms, including bacteria and cancer cells, develop resistance to multiple, structurally and mechanistically unrelated drugs, making them difficult to treat.
Multidrug resistance (MDR)
44
P. falciparum resistance to _______
chloroquine
45
* ABC transporter
* Control the flow of ions
* Dysfunctional CFTR (__________) causes cystic fibrosis
Cystic fibrosis transmembrane conductance regulator (CFTR)
46
Normal CFTR channel moves chlorine ions to the outside of the cell.
Mutant CFTR channel does not move chloride ions, causing sticky mucus to build up on the outside of the cell.
47
* Forms hydrophilic pores throughout the membrane
* concerned specifically with inorganic ion transport
* Passive transport
Channel proteins
48
2 important properties distinguish ion channels from simple aqueous pores
* Ion selectivity
- Only ions of appropriate size and charge can pass
* Are not continuously open, they are gated
49
Types of channel (based on stimulus)
1. Ligand-gated = opens in response to certain molecules
2. Mechanically-gated = opens in response to physical forces
3. Voltage-gated = Opens when a membrane potential opens at a certain value
50
is the difference in electric potential between the interior and the exterior of a biological cell
Membrane Potential
51
The equilibrium condition, in which there is no net flow of ions across the plasma membrane
Resting membrane potential
52
____________: travelling wave of electrical excitation, or nerve impulses
- is triggered by a depolarization of the plasma membrane that is, by a shift in the membrane potential to a less negative value
Action potential
53
Function of neurons
receive, conduct, and transmit signals
54
Parts of a neuron
Dendrites = Collect electrical signals
Cell body = Integrates incoming signals and generates outgoing signal to axon
Axon = Passes electrical signals to dendrites of another cell or to an effector cell
55
Voltage-gated Na+ channels
Closed: At the resting potential, the channel is closed
Open: In response to nerve impulse. Na+ enters the cell
Inactivated: For a brief period following activation, the channel does not open in response to a new signal.
56
How voltage-gated channels work
At the resting potential, voltage-gated Na+ channels are closed.
When the membrane is depolarized, conformational changes open the voltage-gated channel.
57
mutation in a voltage-gated Na channel that is expressed in the heart causes _______ and _______.
ventricular fibrillation;
heart attacks
58
Mutations in other Na channels, expressed mainly in the brain, cause _______ and ________
epilepsy;
febrile seizures
59
Transmitter-gated ion channels
_______ are the junctions where neurons release a chemical neurotransmitter that acts on a postsynaptic target cell, which can be another neuron or a muscle or gland cell
Synapses
60
Synaptic vesicles
Postsynaptic target cell
61
Transmitter-gated ion channels
small signal molecules which are stored in membrane-enclosed synaptic vesicles and released by exocytosis
E.g. acetylcholine
Neurotransmitter
62
Neurotransmitters Are Transported into Synaptic Vesicles by _______
H-Linked Antiport Proteins
63
Vesicles are 40–50 nm in diameter, and their lumen has a low pH, generated by operation of a V-class proton pump in the vesicle membrane
64
Transmitter-gated Ion Channels Convert Chemical Signals into Electrical Ones at _______
1. Import of neurotransmitter
2. Movement to active zone
3. Vesicle docking at plasma membrane
4. Exocytosis of neurotransmitter triggered by influx of Ca2+
5. Reuptake of neurotransmitter
6. Recovery of synaptic vesicles via endocytosis
Chemical Synapses
65
* Transmitter-gated ion channel
* Opens in the presence of acetylcholine
Acetylcholine receptors
66
The Acetylcholine Receptors at the Neuromuscular Junction Are Transmitter-gated Cation Channels
67
__________
* open cation channels, causing an influx of Na+ that depolarizes the postsynaptic membrane toward the threshold potential for firing an action potential.
* acetylcholine, serotonin
* __________: mediates most of the excitatory signalling in the vertebrate brain.
Excitatory neurotransmitters;
Glutamate
68
_________
* open either Cl-channels or K+ channels, and this suppresses firing by making it harder for excitatory influences to depolarize the postsynaptic membrane
* y-aminobutyricacid (GABA) and glycine
Inhibitory neurotransmitters
69
Transmitter-gated Ion Channels Are Major Targets for Psychoactive Drugs
* a drug from a plant that was originally used by South American Indians to poison arrows.
* Blocks acetylcholine receptors on muscles
Curare
70
Bind to GABA receptors, potentiating the inhibitory action of GABA by allowing lower concentrations of this neurotransmitter to open Cl channels
Valium and Librium
71
* act by inhibiting the uptake of serotonin
Prozac
72
* Strong poison, used as pesticide
* Inhibitory neurotransmitter
* binds to glycine receptors and blocks the action of glycine, causes muscle spasms, convulsions, and death.
Strychnine
73
Importance of Transporters
* Drug targets
* Drug resistance
74
is a target for major antidepressant drugs, the selective serotonin reuptake inhibitors (SSTIs)
SERT/5HTT (sodium-dependent serotonin transporters)
75
* Decreased uptake of drugs
* Enhanced efflux
* Overexpression of multidrug resistant protein
Drug resistance
76
A bundle of axons is called a ______
Nerve
77
Absolute refractory period
Neuron will not respond to a stimulus
78
Relative refractory period
79
Myelin sheaths (Schwann cells = PNS, Oligodendrocytes = CNS) speed up transmission through a process called ____________-
Saltatory conduction
80
Gaps between each Schwann cells
Nodes of Ranvier
81
Small stimulus = graded potential
