Transmembrane Transport Flashcards
1
Q
what is facilitated diffusion done via
A
channel or carrier proteins
2
Q
what is active transprot done via
A
pumps
3
Q
Concentration gradients move from what
A
high to low
4
Q
What determines how well a substance can diffuse through a lipid bilayer
A
hydrophobicity of substance
size
steepness in concentration gradient
lipid/protein composition in the bilayer
Charge difference between the 2 compartments
5
Q
what can diffuse through the membrane
A
small gasses (O2, CO2, N2) nonpolar molecules some small uncharged polar molecules
6
Q
what does hydrophobicity have to do with rate of diffusion
A
more hydrophobic = faster diffusion
7
Q
What cant diffuse through the bilayer
A
ions
large uncharged polar molecules (sugar)
Charged polar molecules (amino acids, proteins, ATP)
8
Q
four main classes of ATP powered transport proteins
A
P-class pumps v-class pumps F-class pumps ABC
9
Q
What are active transport pumps
A
transmembrane proteins that have ATP binding site in cytoplasmic domain
10
Q
Why do we need active transport
A
cells want to bring in nutrients from environment even if cytoplasm has high concentration of that nutrient
11
Q
How to active pumps function
A
to strictly control the pH and ionic composition of the cytosol
12
Q
What ionic gradients exist between the cytosol and extracellular fluid
A
pH
Na+
K+
Ca2+
13
Q
What do P class pumps transport
A
ions only
14
Q
What is special about the P class pumps
A
it is the only pump to get phosphorylated
15
Q
what are the subunits of P pumps
A
alpha catalytic subnuit- binds to ATP and transports ions
beta- regulatory unit
16
Q
what gets phosphorylated in the p class pumps
A
the alpha sub unit
17
Q
Where is Ca2+ stored
A
sarcoplasmic reticulum
18
Q
What is the sarcoplasmic reticulum
A
smooth ER of muscle cells
19
Q
How does Ca effect muscles
A
release of Ca into cytosol triggers muscle contraction
in order for muscle to relax Ca must be pumped back in
20
Q
Examples of P class pumps
A
Sarcoplasmic reticulum Ca2+ pump
Na+/K+ pump
21
Q
How do sarcoplasmic reticulum Ca2+ pumps work
A
- cytoplasmic portion of alpha subunit binds to two Ca ions and a molecule of ATP
- ATP is hydrolyzed into ADP +P
- this phosphorylation causes a conformational change in the pump
- Ca ions come off and go into lumen
- the phosphate is removed and the protein goes back to its original conformation
22
Q
What do the Na+/K+ pumps help
A
keep high K+/ low Na+ in cytosol and high Na+/low K+ in the extracellular
23
Q
How do Na+/K+ pumps work
A
- 3Na+ ions and ATP bind to the alpha subunit
- ATP hydrolyzed and P is transferred as before
- Conformational changes allow Na+ to be released outside
- 2 K+ ions bind to the other sites in the alpha subunit
- phosphate removed, protein reverted back to original conformation
- bound K+ ions are released into cytosol
END RESULT: 3 Na+ out and 2K+ in
24
Q
what do V class proton pumps pump
A
protons only
primary function to pump protons into lysosomes, endosomes and plant vacuoles
25
Why is a pump needed to pump protons into a lysosome
it is very acidic in a lysosome so protons are pumped in against a concentration gradient
26
what are the two v class pump domains
V1 hydrophilic cytosolic domain
| V0 hydrophobic transmembrane domain
27
How V class pumps work
ATP is bound and hydrolyzed by the V1 subunit
provides power to pump H+ through the V0 domain
Nothing is phosphorylated
28
why must a Cl- must be pumped when a H+ is transported into lysosome
to keep the charge balance neutral
29
What is the structure of ABC pumps
2 transmembrane domains (T) and 2 cytosolic domains (A) that function to bind to ATP
comes together where two T units meet also where it opens
30
What do ABC pumps pump
various dif substances
| sugars, amino acids, toxins not just ion
31
where are ABC pumps found
all over bacterial and eukaryotic plasma membranes
32
what are the ABC pumps in bacteria called
permeases
33
type of mammal ABC pumps
MDR1 (multidrug resistance transport protein)
pumps various toxins and drugs from cytosol to outside
CFTR = chloride pump that when mutated leads to cystic fibrosis, Cl required to keep mucus thin and moving through lungs
34
what is a hydrophilic passageway
channel proteins create them and water ions and small organic molecules move across
35
what makes up a hydrophilic passageway
single polypeptide folded
| complex dif polypeptides
36
what is the difference between gated and non gated channels
gated open and close in response to stimuli of changes in voltage while non gated are unaffected by these factors
37
What channel proteins does water diffuse through
aquaporins
38
Is there ever a difference in water concentration
no but there can be a difference in amount of free water molecules
39
what are free water molecules
not bound to anything
| capable of diffusing as they are not associated to an ion or something else
40
high solute concentrations will have what levels of water
low
41
Water diffuses in what way
area of low solute to area of high solute
42
Hypotonic
environment containing less solute
43
Hypertonic
environment contain more solute
44
Isotonic
when solute concentration is equal in the 2 environments
45
What would happen if osmosis went unchecked
water would constantly rush into the cell as there is an enormous amount of solute in the cytoplasm
cause osmotic lysis
46
How is osmotic lysis prevented in plant fungal cells
cell walls allow for cell swelling
| the swelling causes turgor pressure which prevents more water from coming in
47
How is osmotic lysis prevented in animal cells
they do not contain a cell wall so they constantly ship out ions into the extracellular fluid in an attempt to make fluid isotonic with respect to cytoplasm
48
How is osmotic lysis prevented in protozoans
contractile vacuole that is constantly collecting extra water from cytoplasm and shipping it out
49
What are aquaporins made of
4 identical subunits containing 6 membrane spanning alpha helices
50
what provides specificity in aquaporins
hydrogen binding- hydrophilic R groups extend in middle of channel and perfectly hydrogen bond with water molecules
51
Non-gated ion channels are
highly selective
52
Structure of non gated ion channels
must contain 4 subunits arranged around a central pore
each subunit contains a loop that extends into the pore
each loop perfectly takes place of water shell that forms around ion
53
membrane potential
difference in charge between two sides of the membrane
54
which side is more negative in plasma membrane of eukaryotic cells
more negative on the inside
55
Why is the inside more negative then the outside
cytoplasm contains high concentration of large anionic molecules that are unable to exit the cell
K+ is allowed to move down its concentration gradient and diffuse out of the cell
56
Why is K+ being allowed to move down its concentration gradient make it more negative within the cell
makes it more positive outside of the cell as Na+ and Ca2+ are not allowed to diffuse into the cell easily
57
What is normal resting membrane potential
-70 mV
58
What is the patch clamp technique used to measure
ion flow through channels
measure inward or outward flow of ions through a single ion channel complex
59
How does the patch clamp technique work
utilizes 2 electrodes
1. one attached to membrane that should only contain a few ion channels
2. one inserted into the cytoplasm
use frogs as they have huge cells
60
Patch clamp technique with Na+ ions
if measuring how many Na+ ions leave the cell, the intracellular electrode will remove an e-
measures how long these channels stay open and how many ions move through the channel in that time
61
What is oocyte expression
frog eggs cotnain few or no ion channels so can inject mRNA encoding ion channel into egg, thus ion channel will be made and inserted into plasma membrane
62
Stimuli that trigger ion channels to open/close
1. voltage
2. ligands- NT and hormones bind to ion channel causing them to change conformation
3. activated g proteins
4. light
5. many others
63
Structure of voltage gated ion channels
4 polypeptides or 1 polypeptide with 4 separate domains arranged in cylinder with central pore
voltage sensing alpha helices that contain lots of lysine and arginines (+ charge)
64
When and what blocks the pore of voltage gated ion channels
after alpha helices return to their original position
channel inactivating protein
65
Structure of neuron
cell body - nucleus and other organelles
dendrites- receive signals from environment or from other neurons
axon- send electrical impulses to another cell
axon termini - contact these other cells
66
Steps of impulse generation on a neuron
1. small depolarization (Na+ into cell causing a more positive)
2. depolarization triggers opening of Na+ voltage gated channels
3. Na+ rush into cytoplasm which causes K+ channels to open
4. Na+/K+ pumps send Na+ back out and K+ back in
67
Ligand gated ion channels
channel that open following binding of a specific environmental chemical ligand
68
What is nicontinic acetylcholine receptor (NAR)
prototypical ligand gated ion channel
involved in transfer of electrical impulse from neuron to muscle cell
receptor and channel in one
69
How is NAR activated
secretion of acetylcholine triggered from arrival of action potential at end of axon
binds to NAR on muscle cell, triggers Na+ to flow into cell
action potential is initiated
70
What does a G protein do
regulates opening of some ion channels
71
How does a G protein work
binding of a ligand to its receptor signals for the recruitment and activation of G protein
G leaves receptor and binds to nearby plasma membrane ion channel
bind to channel and induce conformational change
channel opens and allows for the diffusion of some ion
72
What is special about G protein binding
it is delayed
73
What are transporters
integral membrane proteins that grab various ions/nutrients undergo conformational change and transport cargo across membrane
74
types of transporters
uniporters- bind to single substance
symporters- 2 or more in same direction
antiporters- 2 or more in opposite directions
75
How a cotransporter works
one moves with gradient thus causing release of energy and this energy is used to transfer second agains the gradient
76
example of uniporter
GLUT1 with 2 conformational states
77
example of cotransporters
Na+/ glucose symporter - Na+ moves into cell with gradient and the energy released is used to bring glucose in with it against its gradient
Na+/ amino acid symporter
Na+/Ca+ antiporter
pH controlling antiporter
78
what would increase rate of glucose update in liver cells
increase glucose in medium
transfect cells with wild type GLUT-1 gene
79
What does the CO2 transport in blood transport require
Cl-/ HCO3- antiporter
80
CO2 and O2 in systematic capillaries
High CO2
| Low O2
81
CO2 and O2 in pulmonary capillaries
low CO2 and High O2
82
What forms of transport require a protein
facilitated, active, cotransport
83
What forms of transport has solute against gradient
active, cotransport
84
What forms of transport couple to ATP hydrolysis
Active
85
What forms of transport is driven by movement of another ion down its gradient
cotransport
86
Example of molecules transported in simple diffusion
O2, CO2, steroid hormones, many drugs
87
Example of molecules transported in facilitated
glucose and amino acids (uniporters) ion and water (channels)
88
Example of molecules transported in active transport
ions, small hydrophilic molecules, lipids
89
Example of molecules transported in cotransport
glucose, amino acids (symporters) various ions and sucrose (antiporters)
