4 - Membrane Transport Flashcards
1
Q
- restricts passage of most polar molecules
- different concentration of solutes in the cytosol and extracellular fluid
- membrane transport proteins
- transporters and channels
A
Membrane transport
2
Q
2 main classes of membrane proteins
A
- Transporter (carriers)
- Channels
3
Q
3 Solute carrier (SLC) transporters
A
- Uniporter
- Symporter
- Antiporter
4
Q
An ABC transporters
A
pump
5
Q
Principles of membrane transport
A
transport by carriers can be either active or passive, solute flow through channel proteins is always passive.
6
Q
Moevement of solute in uniporter
A
facilitated diffusion
7
Q
Symporter, antiporter, and pump move solute using active or passive transport?
A
Active transport
8
Q
uses primary active transport
A
pump
9
Q
Use secondary active transport
A
Symporter and antiporter
10
Q
lipid bilayers are impermeable to ___
A
ions
11
Q
The passage of molecules across membrane depends on ___ and _____
A
size and hydrophobicity
12
Q
Example of hydrophic molecules
A
- O2
- CO2
- N2
- Steroid hormones
13
Q
Example of small uncharged polar molecules
A
- H2O
- Urea
3.Glycerol - NH3
14
Q
Example of large uncharged polar molecules
A
- glucose
- Sucrose
15
Q
Example of ions
A
- H+
- Na+
- HCO3-
- K+
- Ca2+
- Cl-
- Mg2+
16
Q
transfer solutes across cell
membranes
A
membrane transport proteins
17
Q
- transfer specific molecular
species or a class of molecules - highly specific
A
transport proteins
18
Q
Example genetic disorder that is due to single-gene mutation in transport proteins
A
cystinuria
19
Q
- single-gene mutation
- autosomal-recessive defect in the reabsorptive transport of cystine from the urine or intestine into the bloodstream.
- Csytine accumulates in the urine. This build up leads to the formation of cystine stones in the kidney
A
cystinuria
20
Q
All membrane proteins that have been studied in detail are ____ ____ ___
A
multipass transmembrane
proteins
21
Q
means that their polypeptide chain cross the lipid bilayer multiple times
A
multipass transmembrane protein
22
Q
pathway formed by membrane proteins which allows specific hydrophobic solutes to cross
A
protein-lipid pathway
23
Q
transporters are also known as
A
carriers or permeases
24
Q
- bind
- conformational changes
A
transporters
25
form continuous pores
channels
26
"downhill” transfer
passive transport
27
Movement of uncharged molecule across membrane is driven by
concentration gradient
28
Movement of charged molecule aross membrane is driven by
membrane potential
29
- uphill
- against their electrochemical
gradients
active transport
30
In most biological cells, the inside of the cell has ___ ___ ___
Negative electrical potential
31
negative
insided
electrical potential
32
Tightly coupled with energy
transporter
33
Process by which transporter transfer a solute resembles an ___-___ reaction
enzyme-substrate react
34
transporters have specific ___ sites for its solute
binding
35
transporters undergo a ___ ___ ___ after binding to their substrate molecules.
reversible conformational change
36
In some transporter proteins, an intermediate state called the ___ state exists during the transport cycle
occluded
37
represents a conformation where the binding site for the substrate is inaccessible from either side of the membrane.
Occluded state
38
3 Confirmational changes in transporters
1. Outward-open
2. Occluded
3. Inward-open
39
3 main ways for cells to perform active transport
1. Coupled transport
2. ATP -driven pumps
3. Light-or-redox-driven pumps
40
use energy stored in concentration gradients
Coupled transport
41
used energy from hydrolysis of ATP
ATP-driven pumps
42
Use energy from light
light- or redox-driven pumps
43
2 main type of transporter
1. Uniporter
2. Coupled transporters
44
- passive transport
- move one type of solute across membrane
uniporters
45
- transfer of one solute depends on the
transport of a second
- move 2 different solute at the same time
Coupled transporters
46
2 types of coupled transporters
1. Symporters
2. Antiporters
47
- transfer 2 different solute in the same direction
Symporters
48
transfer 2 different solute in the opposite direction
Antiporters
49
harvest energy stored in the electrochemical gradient
Coupled transport
50
Example of coupled transporters
* Na+ - co-transported ion
* Na+-K+ pump
* Na+-driven symporters
* Na+ and glucose, and neurotransmitters
51
Example of symporter
Na+ - co-transported ion
52
Example of primary active transporter
Na+-K+ pump
53
Transporters have 10 or more ___ ____ that span
the membrane
a helices
54
are located midway through
the membrane
solute- and ion-binding sites
55
56
Allows the transporter to alternately open and close on other side of membrane
pseudosymmetric or inverted repeats
structure
57
Inverted repeats are also known as
pseudosymmetric
58
2 channels that evolved from coupled transporter in which gating mechanism were lost, allowing the channels to open simultaneously on both sides of the membrane
aquaporin water channel and
the Sec61 channel (ER)
59
3 classes of ATP-driven pumps
1. P-type pumps
2. ABC (ATP-binding cassette) transporters
3. V-type pumps
60
-phosphorylates
-phosphorylate themselves during the transport cycle
P-type pumps
61
-pump small molecules
ABC (ATP-binding cassette) transporters
62
- turbine-like
- made from multiple different subunits
- pumps H+ ions into organelles like lysosomes, vacuoles, and synaptic vesicle
V-type pumps
63
structurally related to V-type pumps but function in reverse manner
F- type (ATP synthase)
64
use the H+ gradient across the membrane to drive synthesis of ATP
F-type (ATP synthase)
65
Pumps Ca2+ into the sarcoplasmic reticulum in muscle cells
P-type ATPase
66
pumps Ca2+ out of the cell
Ca2+ ATPase
67
intracellular storage of Ca2+ in
muscle cells
sarcoplasmic reticulum
68
release of Ca2+ into the cytosol (Ca+-release channels) can trigger ____ _____
muscle contraction
69
P-type ATPase structure
10 transmembrane α helices
connected to three cytosolic
domains
70
3 cytosolic domains
1. nucleotide-binding domain
(N)
2. phosphorylation domain (P)
3. activator domain (A)
71
Binds and hydrolyzes ATP, providing the energy needed for ion transport.
nucleotide-binding domain
(N)
72
Becomes phosphorylated during the transport cycle, which is essential for the conformational changes that drive ion transport
phosphorylation domain (P)
73
Regulates the dephosphorylation of the P-domain and resets the pump after each cycle.
activator domain (A)]
74
established Na+
and K+ gradient across the
plasma membrane
Na+-K+ pump/Na+-K+ ATPase
75
Has higher concentration in the cell
K+
76
Has low concentration in the cell
Na+
77
Na+-K+ pump has ___-____ antiporter
ATP-driven antiporter
78
___ out, ____ in
Na+
K+
79
Na+-K+ pump regulate ____ __
cytosolic pH
80
The pump creates an ____ because it moves more positive charges (Na⁺) out than it brings in (K⁺), contributing to the cell's negative internal charge.
electrogenic
81
create an
electric potential
electrogenic
82
-contains highly conserved ATPase domains (ATP-binding
“cassettes)
ABC transporters
83
ABC transporters contains highly conserved ______ ______
ATPase domains (ATP-binding cassettes)
84
brings together two domains
ATP binding
85
leads to domain dissociation
ATP hydrolysis
86
alternately expose solute-binding sites
ABC transporters
87
ABC transporters expose their ___-___ sites alternately
solute-binding sites
88
ABC transporters were first found in ____
bacteria
89
In bacteria, it captures nutrients and deliver them to ABC transporters
auxiliary mechanism
90
-pump hydrophobic drugs out of the cytosol
ABC transporter
91
What do ABC transporters pump out of the cytosol?
hydrophobic drugs
92
- A member of ABC transporter family that pump hydrophobic drugs out of
the cytosol
- present at elevated levels in human cancer cells and makes the cell simultaneously resistant to a variety of chemically unrelted cytotoxic drugs that are widely used in cancer chemotherapy
multidrug resistance (MDR) protein
or P-glycoprotein
93
causes malaria, pumps out chloroquine
Plasmodium falciparum
94
P. falciparum have amplified a gene encoding an ABC transporter that pumps out ___
chloroquine
95
TAP transporter
transporter associated with
antigen processing
96
-pumps peptides from the cytosol to ER lumen
transporter associated with
antigen processing (TAP transporter)
97
peptides in cytosol are prodced by?
protein degradation in proteasomes
98
peptides are carried from ER to ___ ___, where they are displayed for scrutiny by cytotoxic T lymphocytes
cell surface
99
-scrutinize the peptides on the cell surface
- kills the cell if the peprides are derived from virus or other microorganism
cytotoxic T lymphocytes
100
- member of the ABC transporter family which was discovered through studies of cystic fibrosis
-Cl- transport protein
- regulates ion concentrations in the extracellular fluid, esp. in lung
cystic fibrosis transmembrane conductance regulator protein (CFTR)
101
caused by mutation in the gene encoding CFTR
cystic fibrosis
102
- form pores across membrane
-one class found in virtually all animals forms gap junctions between adjacent cell
- not energy coupled, “downhill”
- diffuse down electrochemical
gradients
Channels
103
– connects the cytoplasm of two cells
gap junctions
104
- inorganic ion transport
ion channels
105
- water channels
- allow water to move more rapidly
- narrow pore that allows water molecules to traverse the membrane in single file
aquaporins
106
2 properties of ion channels that distinguish them from aqueous pores
1. Ion selectivity
2. gated
107
-allow inorganic ions to pass
- has selectivity filters
ion selectivity
108
the permeating ions have to shed most or all of their water molecules to pass through the narrowest part of the channel called____
selectivity filters
109
4 Main types of stimuli known to cause ion channels to open
1. Voltage-gated
2. Ligand-gated (extracellular ligand)
3. Mechanically gated
110
open briefly and then close again
gated
111
2 typesnof ligand-gated channel
1. Extracellular mediator
2. Intracellular mediator
112
extracellular mediator
transmitter-gated channel
113
intracellular mediator
ion-gated channels or
nucleotide-gated channels
114
- voltage-gated
- membrane potential
- K+ leak channels
- active electrogenic pumping and
from passive ion diffusion
ion channels
115
Opens even in an unstimulated or "resting" cell
K+ leak channels
116
purpose of k+ leak channels
making plasma membrane much mkre permeable to K+ than to other ions.
117
bacterial K+ channels are made from
4 identical transmembrane subunits
118
Together form a central pore through the membrane
four identical transmembrane
subunits
119
selectivity filter
pore helix
120
each four identical transmembrane
subunits contributes two transmembrane __ ____
a helices
121
the polypeptide chain that connects the 2 transmembrane helices forms a short __ __ and ___ ___
a helix (pore helix) and crucial loop
122
pore helix and crucial loop that protrudes into the wide section of cone to form ___
selectivity filter
123
To enter selective filter, K+ ions must?
K+ ion must lose almost all of its
bound water molecules
124
K+ ions interact with ___ ___ lining the filter
Carbonyl oxygen
125
oxygen are rigidly spaced at the exact distance to accomodate a __
K+ ion
126
Cannot enter selectivity filter because the carbonyl oxygen are too far away from them to compensate for the energy expense associated with the loss of water molecules required for entry
Na+ ions
127
What do the structure of a closed K+ channel shows
tilting the inner helices
128
structural and functional diversity of voltage-gated Ca2+ channels is due to
alternative splicing of RNA transcripts
129
Voltage-gated Ca2+ (also K+ and Na+) channels belong to a __ superfamily
large
130
Cause of nerve, muscle, brain, or heart disease
mutant genes encoding ion
channels
131
mutation in genes that encode voltage-gated Na+ channels in skeletal muscle cells can cause ___
myotonia
132
A condition in which there is a delay in muscle cell relaxation after voluntary contraction, causing painful muscle spasms
myotonia
133
mutation in genes that encode Na+ or K+ channels in the brain can cause ___
epilepsy
134
-mechanically gated ion channels
-capable of responding to mechanical forces
- extremely rare channel
mechanosensitive channels
135
How many mechanically gated ion
channels are found in hair cells of human cochlea
50-100
136
Open in response to mechanical stretching of the lipid bilayer
mechanosensitive channels found in bacterial plasma membrane
137
mechanical stretching of the
lipid bilayer
hypotonic
138
When bacterium experience hypotonic condition, what happens tomthe cell
Cell swells as water seeps in due to an increase in the osmotic pressure
139
It will open when pressure rises to dangerous levels to allow small molecules to leak out
mechanosensitive channels
140
receive, conduct, and transmit signals
neurons
141
Fundamental task of neurons
receive, conduct, and transmit signals
142
Despite the varied significance of signaks carried by different classes of neurons, the form of signal is always the same, consisting ?
changes in the electrical potential across the neuron’s plasma membrane
143
-traveling wave of electrical excitation
- carry a message without attenuation from one end of a neuron to the other
- consequence of the properties of voltage-gated cation channels
action potential or nerve impulse
144
- electrically excitable cells
- responsible for generating the action potentials
voltage-gated cation channels
145
triggers an actional potential
depolarization of the plasma membrane
146
In nerve and skeletal cells, a stimulus that causes sufficient depolarization promotly open ___
open Na+ channels
147
open Na+ channels, Na+ enters the cell
self-amplification
process
148
The electrical potential in the local region of membrane has shifted from its resting value of about
-40mV to +50mV
149
- photosensitive ion channels
- contains covalently bound retinal group
- light-driven cation channel
- revolutionized the study of neural circuits
channelrhodopsins
150
- increase the rate at which the axon can conduct an action potential
- formed by glial cell
myelination
151
myelin is formed by
glial cells
152
glial cells that myelinte axons in peripheral nerves
Schwann cells
153
glial cells that myelinte axons in central nervous system
oligodendrocytes
154
little current can leak across it
myelin
155
- interrupt myelin sheath
- where almost all the Na+ channelsnin the axon are concentrated
-allows for saltatory conduction
nodes of Ranvier
156
- demyelinating disease
- immune system destroys myelin sheaths in some region of CNS
multiple sclerosis
157
where neuronal signals are transmitted
synapses
158
____ cell – ____cleft – ____cell
presynaptic cell – synaptic cleft –
postsynaptic cell
159
Release of neurotransmitter is from
presynaptic cell
160
neurotransmitter bins to and opens
transmitter-gated ion channel in the postsynaptic cell
161
transmitter-gated ion channel as receptor
highly selective binding sites
162
-highly selective binding sites
- selective in the type of ions that they let pass across the plasma membrane
-neurotransmitter receptors
transmitter-gated ion channel
163
- open cation channels
- influx of Na+ or Ca2+
- firing an action potential
excitatory neurotransmitters
164
- open Cl- or K+ channels
- suppresses firing
inhibitory neurotransmitters
165
Used as excitatory neurotransmitters
acetylcholine, glutamate, serotonin
166
Used as inhibitory neurotransmitters
γ-aminobutyric acid (GABA) and glycine
167
2 major classes of neurotransmitter receptors
ionotropic receptors
metabotropic receptors
168
ion channels and feature at fast chemical
synapses
ionotropic receptors
169
– G-protein coupled receptors that bind to all
other neurotransmitte
metabotropic receptors
170
- well-studied transmitter-gated ion channel
- composed five transmembrane polypeptides
acetylcholine receptors
171
__ acetylcholine binds →___change → ___
channe
two
conformational
open
172
involves the sequential activation of five
different sets of ion channels
neuromuscular transmission
