66 Questions
What is the number of transmembrane segments in a major facilitator superfamily integral membrane protein?
12
What is the structural arrangement of the α-helices in the glucose transporter?
4-5 amphipathic α-helices are packed to form a hydrophilic channel
What is the mechanism by which glucose transport occurs in GLUT1?
Gated Pore Mechanism
How many GLUT family members exist in the human genome?
12
What is the primary function of GLUT1 in erythrocytes?
Transporting glucose into erythrocytes
What is the superfamily of sugar transporters that GLUTs belong to?
Major Facilitator (MF) superfamily
What is the main function of GLUT1?
basal uptake of glucose to the blood brain barrier and erythrocytes, defective in De Vivo disease
In cases of defective GLUT1, why do patients present with brain-related symptoms?
Due to impaired glucose transport into the brain
Explain why a ketogenic diet is standard care for patients with defective GLUT1.
ketone bodies derived from lipids metabolism is used as an alternative energy source to glucose
What is the role of GLUT2 in the liver and kidney?
Transport glucose into liver and kidney when blood glucose is high
How does GLUT4 respond to high blood glucose levels in adipocytes?
By triggering the exocytosis of GLUT4 to the cell membrane
What happens to GLUT4 transporters when insulin levels decrease?
They are removed from the cell membrane by endocytosis
What is the main function of SERCA pumps?
Transporting Ca+2 from the cytoplasm to the sarcoplasmic reticulum
How does the E1 conformation of SERCA differ from E2?
E1 exposes the Ca+2 binding sites on the cytoplasmic side, while E2 exposes the Ca+2 binding site on the lumenal side of the membrane. E1 has higher affinity towards Ca2+ than E2
What is the role of Plasma membrane Ca+2-ATPase? (PMCA)
Pumping Ca+2 out of the cell
How does Na+K+ ATPase of the plasma membrane move ions across the membrane?
By coupling the phosphorylation-dephosphorylation of Asp to the movement of 3 Na+ out and 2 K+ in, against their electrochemical gradient.
What can inhibit the Na+K+ ATPase of the plasma membrane?
Ouabain and digitoxigenin (foxglove)
How much of the energy (ATP) used by cells goes towards the function of the Na+K+ ATPase?
Up to 30%, and in nerve cells, it can be up to 70%.
How does Digitoxigenin, an inhibitor of Na+/K+ ATPase, stimulate cardiac contraction?
Digitoxigenin increases cardiac contraction by inhibiting the Na+/K+ ATPase, leading to an increase in intracellular sodium and calcium, which results in increased contraction force.
What is the main function of V-Type ATPases?
involved in acidifying of compartments such as vacuoles, lysosomes, endosomes, and secretory vesicles.
What is the difference between F0 and F1 in F-type ATPases?
F0 is the integral proton channel, while F1 is the peripheral ATP-binding site with ATPase activity.
What is the role of ABC ATPases?
ABC ATPases are involved in the transport of various molecules across membranes using ATP energy.
What is the function of F-type ATPases in mitochondria and chloroplasts?
F-type ATPases synthesize ATP in mitochondria and chloroplasts using the energy from the proton gradient.
What is the common feature of ABC ATPases?
2 NBD (ATP binding site- conserved) and 2 TMD (each with 6 helices)
What is the main difference between primary active transport and secondary active transport?
Primary active transport creates a gradient of one solute, whereas secondary active transport uses the exergonic downhill movement of one solute to drive the endergonic movement of another solute up its concentration gradient.
What is the role of P-type ATPases in primary active transport?
They are cation transporters that use ATP to pump ions across the membrane, undergoing phosphorylation and conformational change in the process.
What is the source of energy for primary active transport?
Energy can be derived from absorption of sunlight, oxidation reactions, hydrolysis of ATP, or simultaneous flow of another chemical species down its electrochemical gradient.
What is the significance of maintaining low cytoplasmic Ca+2 levels?
Maintaining low cytoplasmic Ca+2 levels is important for cell signaling.
What is the common structural feature of all P-type ATPases?
integral protein with 8-10 TM sections in a single polypeptide, conserved Asp region that undergoes phosphorylation, sensitive to inhibition by vanadate .
What is the physiological role of the erythrocyte Anion Exchange Protein (AE1)?
Shuttling CO2 from tissues to lungs via the blood
What type of exchange does the Band 3 Transporter (AEP) perform?
The Band 3 Transporter (antiport) performs one-for-one exchange of Cl- for HCO3-, making it electro-neutral.
Why is the coupling of Cl- and HCO3- considered obligatory in the AE system?
AE is a co-transport system. In the absence of Cl-, HCO3- transport cannot be carried out
Where is the enzyme that converts CO2 to HCO3- located in the red blood cell?
In the cytosol
How many times does the AEP span the membrane?
14 times
what does ABCB1 (gene) encode for?
Encodes for MDR1 P-glycoprotein
Which ABC transporter is known as P-glycoprotein 1 and plays a role in multidrug resistance in humans?
ABCB1
What is the function of the ABCG2 transporter?
Overexpressed in breast cancer cells major exporter of anticancer drugs
Which ABC transporter is known as the cystic fibrosis transmembrane conductance regulator protein?
ABCC7
What is the significance of Multidrug transporter (MDR1), also known as ABCB1, in human organisms?
In placental membranes and BBB it removes toxic compounds and is responsible for resistance of tumors to anti cancer drugs
How does the Cystic Fibrosis Transmembrane conductance Regulator Protein (CFTR) transport ions?
Transports Cl- across plasma membrane when both NBDs have ATP bound
what is the enzyme that converts co2 to HCO3- called
carbonic anhydrase
which ABC gene is defective/mutated in tangier disease
ABCA1
what is the role of ABCA1
use in reverse cholesterol transport
What is the target for treatment of diabetes that Gliflozins inhibit in the kidney?
SGLT2
What type of channels are K+-channels in mammals?
Voltage-gated
Where are bacterial porins typically found?
Outer membrane of Gram-negative bacteria
What is the minimum number of β-strands required to form a barrel in bacterial porins?
8
What is the structural basis for voltage-gating in K+-channels?
S4 helix with Arg residues
What is the general role of SGLT2 inhibitors in the treatment of type 2 diabetes?
Lower blood glucose
What is the quaternary structure of the ligand-gated Acetylcholine-receptor ion channel?
5 subunits, alpha2-beta-gamma-delta (α2βγδ)
What is the mechanism by which Na+ selectivity is dictated in ligand-gated ion channels?
Rings of negative side chains at top and bottom entrance to the channel
What are the competitive antagonists that block the ligand-gating of Acetylcholine-receptor ion channels?
curare (poison arrows), bungarotoxin (snake venom)
Which neurotransmitters trigger the opening of cation channels in ligand-gated ion channels?
Acetylcholine & other neurotransmitters
What is the essential principal subunit in mammalian channels and how many homologous domains does it have?
alpha subunit, with 4 homologous domains
What drives the co-transport of lactose in E. coli's lactose permease (LacY) transporter?
H+ gradient
What happens to the transport function of LacY if cytochrome oxidase of the electron transport chain is inhibited by CN-?
LacY acts as a passive transporter
In eukaryotic cells, what ion gradient generated by the sodium-potassium ATPase drives the sodium-glucose symporter?
Na+ gradient
What provides the energy needed for the transport of glucose into eukaryotic cells by the sodium-glucose symporter?
Na+ flow
What is the role of the Na+-glucose symporter located on the apical surface of animals' intestines?
Takes up glucose
What is the main function of the glucose uniporter GLUT2 located on the basal surface of certain cells?
Transport glucose out
Which aquaporin is predominantly found in the lens and has low water permeability?
AQP0
In which tissue is AQP7 predominantly found with high permeability to water, glycerol, and urea?
Adipose tissue
Where is AQP3 predominantly located with high permeability to water, glycerol, and moderate permeability to urea?
Basolateral plasma membrane
Which aquaporin is mainly distributed in the salivary gland, lacrimal gland, sweat gland, and has high water permeability?
AQP5
Where can AQP10 be found with low water permeability and high permeability to glycerol and urea?
Small intestine
Which aquaporin is primarily located in the kidney, testis, liver, and pancreas, with high water permeability?
AQP8
Test your knowledge on the membrane topology of glucose transporters from the Major Facilitator (MF) superfamily. Understand how integral membrane proteins with 12 transmembrane segments facilitate the passage of glucose through hydrophilic channels. Explore the arrangement of amphipathic α-helices and the distribution of charged/polar amino acids along the channels.
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