Membrane Transport Flashcards
Which membrane components make the plasma and intracellular membranes selectively permeable?
Lipids and proteins
What are the three types of molecules that can cross the membrane without assistance?
Lipophilic molecules, certain gases, and small polar uncharged (e.g. water)
Based on Flick’s Law of Diffusion, what is membrane permeability dependent on?
surface area, concentration gradient, membrane thickness, and membrane permeability
Ion movement tends to be in the direction that ___ the electrical gradient.
lowers
What are the two main types of membrane proteins?
channel and transporter (carrier)
Channels are the main way ____ crosses into the cell.
water
Channels are a continuous path from the cytosol to the extracellular region. Are these gated or not?
Gated
What kinds of molecules go through channel proteins?
Ions, water, small hydrophilics
T/F. Channel proteins use facilitated diffusion to transfer molecules.
True.
Transport proteins bind with ____ specificity to their substrate, inducing a conformational change necessary to function.
high
Which is faster: channel or transporter?
channel
What are the four types of transport protein classes?
uniport, symport, antiport, and ATP powered pump
A uniporter transports ___ substrate from high to low concentration.
one
Does symport directly require ATP?
No. The movement of molecules does not require ATP. ATP is used to form a gradient.
Symport is also called _____ active transport.
secondary
In antiport, what direction are substrates being moved?
Can be moved with or against gradient
ATP powered pumps have built in _____ activity.
ATPase
T/F. Aquaporins can be continuously open or gated.
True
Are ion channels always open, gated, or both?
Can be both open always or gated
Leak channels are an example of ____ channels. These channels are always open and let ions leak ___.
ion, in
What are the three types of gated ion channels that open only with stimulus?
voltage gated, ligand gated (chem signal like hormone), and mechanical gated
Charge of ion, size, and amount of water in the selectivity shell all contribute to ___ ____ selectivity.
Ion channel
How is the hydration shell removed from ions entering an ion channel?
Carboxylic acid residues line selectivity pore
GLUT 3’s low Km value makes it extremely valuable for ___ cells.
neural
What are two examples of cotransporters in the body?
- SGLT-1 (Glc, sodium symport. Found in small intestines and kidneys. Secondary active transport)
- Chloride, bicarbonate exchanger (antiport, increased carbon dioxide carrying capacity of RBC).
P class pumps are reversibly phosphorylated during transport. What is an example?
Sodium-Potassium pump.
Explanation: E1 conformation has high sodium affinity. ATP is cleaved and the alpha subunit is phosphorylated. E2 conformation. Low affinity for sodium now but high affinity for potassium. Potassium binds, dephosphorylation occurs, and the E1 conformation is returned.
What are two sodium potassium pump inhibitors?
Drogoxin and ouabain
V-class proton pumps move hydride ions from the cytosol to ______ ____. This lowers the ___.
intracellular organelle, pH
Where are F class proton pumps most commonly found?
plasma membrane of bacteria, mitochondria, and chloroplasts
Where do ABC transporters bind ATP?
ABC domain
When is ATP cleaved in ABC transporters?
When the substrate binds
T/F. ABC transporters can only be used to bring substrates in.
F.
Explanation: ABC transporters (e.g. ABCB1 or MDR1) can be used to remove toxic contents from cell. In MDR1, drug resistant cells in cancer patients remove the lipophilic drug from the cell.
Which of these transporters is essential in lowering the acidity of the lysosome?
V Class
Protons flow through this pump to form ATP.
ATP synthase (e.g. F class pump)
How does energy state affect membrane diffusion?
No effect. Membrane diffusion is passive and does not require energy.
How is digoxin used to treat heart failure? A. Increase extracellular sodium B. Increase extracellular potassium C. Increase bicarbonate intracellularly D. Decrease chloride intracellularly
B.
Explanation: by inhibiting Na+/K+ ATPase, will have increased K+ outside because this pump lets 3 Na+ out and 2K+ in (PUMPKIN, pumps K in!)
Which of these pumps do not undergo reversible phosphorylation during transport? Na+/K+ ATPase F class ATP synthase V class SGLT1
SGLT 1
Skeletal muscle and fat cells rely on this insulin sensitive glucose transporter
GLUT 4
Patients with Cystic fibrosis involves mutations in which type of channel?
ABC transporters
What type of transport mechanism is used to move glucose into intestinal cells from the intestinal lumen?
Secondary active transport via SGLT-1
What type of transport mechanism is used to move glucose from the intestinal cell to the interstitial fluid?
Facilitated diffusion via GLUT-2
What class of ATP-powered pumps is the Na+/K+-ATPase?
P class
What cannot cross the membrane?
Ions, sugars, and amino acids
Most channels are ______ and partake in _____ transport.
gated, facilitated
What cannot travel through an aquaporin?
charged molecules
What do monovalent cation channels allow to pass?
Cation with plus one charge
How does insulin control blood glucose levels with GLUT 4?
When insulin binds, GLUT 4 goes to outside of cell membrane, binds glc, transports it in. Without insulin on the surface, GLUT 4 goes back in and is kept in an endosome until needed.
Where is each one found:
- GLUT 1
- GLUT 2
- GLUT 3
- GLUT 4
- RBCs (second lowest Kt)
- Pancreatic beta cells and liver cells (fourth lowest)
- Neurons (lowest Kt)
- Muscle and fat cells
SGLT1 is found in….
small intestines and kidneys
How many sodiums transported per glucose in SGLT-1?
Two sodium per one glucose
What is phosphorylated in Na/K pump?
Asp
Most ABC transporters are ______ in eukaryotes.
exporters
