Cell Biology Active Transport Quiz

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Questions and Answers

Which class of ATP-powered pumps primarily transports small molecules?

ABC superfamily (correct)

P-class pumps

V-class proton pumps

F-class proton pumps

What is the main function of Na+/K+ ATPase in animal cells?

Transports small molecules across the membrane

Regulates pH levels in plant vacuoles

Maintains low cytosolic Na+ and high cytosolic K+ concentrations (correct)

Pumps protons into the cytosol

Which class of pump is primarily involved in maintaining the pH of plant vacuoles?

F-class pumps

ABC superfamily

V-class pumps (correct)

P-class pumps

What distinguishes F-class pumps from V-class pumps?

F-class pumps support ATP synthesis Signup and view all the answers

Where are F-class pumps predominantly found?

Cell membranes of bacteria and in mitochondria and chloroplasts Signup and view all the answers

Which of the following ions is primarily pumped out of the cytosol by certain Ca2+ ATPases?

Ca2+ ions Signup and view all the answers

What role do P-class pumps play in the cytosolic environment?

Maintain specific ionic concentrations within the cytosol Signup and view all the answers

Which of the following statements is incorrect regarding the structural characteristics of ATP-powered pumps?

P-class pumps contain identical structures to F-class pumps. Signup and view all the answers

What is the primary function of ATP-powered pumps in active transport?

To use the energy from ATP hydrolysis to move substances against the concentration gradient Signup and view all the answers

How do non-gated ion channels primarily function?

By continuously allowing the movement of ions down their gradients Signup and view all the answers

What determines the direction of transport for charged molecules across a membrane?

Both the electrochemical gradient and electric potential Signup and view all the answers

What is the role of uniporters in cellular transport?

To transport a single type of molecule down its concentration gradient Signup and view all the answers

What is primarily responsible for generating the membrane potential in animal cells?

The movement of cytosolic K+ ions through resting channels Signup and view all the answers

What characterizes gated channel proteins?

They respond to specific signals to open or close Signup and view all the answers

In the context of GLUT1, where is the glucose concentration typically higher?

In the extracellular medium Signup and view all the answers

Which statement about the electrochemical gradient is TRUE?

It includes the effects of both concentration gradient and membrane potential Signup and view all the answers

What happens to the affinity of the Na + binding sites during the E1 to E2 transition of the Na + /K + ATPase?

It decreases, leading to dissociation of bound Na + ions. Signup and view all the answers

How are the Na + ions transported during the mechanism of the Na + /K + ATPase?

They dissociate one at a time despite a high extracellular Na + concentration. Signup and view all the answers

What role do drugs like ouabain and digoxin play in the function of the Na + /K + ATPase?

They inhibit ATPase activity, disrupting Na + and K + ion balance. Signup and view all the answers

What is the result of the transition from the E2 conformation back to E1 in the Na + /K + ATPase?

K + ions are transported inward and released into the cytosol. Signup and view all the answers

In the Na + /Glucose symport system, what primarily drives the transport of glucose into the cell?

The Na + gradient created by the Na + pump. Signup and view all the answers

What is the function of ABC transport proteins in bacteria such as E. coli?

Transporting nutrients against concentration gradients Signup and view all the answers

Which domains are present in the structure of ABC transporters?

Two transmembrane and two cytosolic ATP-binding domains Signup and view all the answers

What is the primary role of CFTR in normal airway function?

Facilitating the movement of chloride ions out of airway cells Signup and view all the answers

What is the consequence of faulty CFTR channels in cystic fibrosis?

Thick mucus buildup in the airways Signup and view all the answers

How do ABC transporters contribute to cancer treatment challenges?

They pump chemotherapy drugs out of cancer cells Signup and view all the answers

What creates a hypoosmotic state in the airways under normal conditions?

Movement of chloride ions out of cells Signup and view all the answers

What types of substances do ABC transporters typically transport?

Amino acids, sugars, and drugs Signup and view all the answers

What structural feature of ABC transporters contributes to their substrate specificity?

The configuration of membrane-spanning helices Signup and view all the answers

What occurs during Step 4 of the Ca2+ ATPase mechanism?

Ca2+ ions dissociate from low-affinity binding sites into the SR lumen. Signup and view all the answers

What is characteristic of P-class ion pumps?

They are phosphorylated on a conserved aspartate residue. Signup and view all the answers

How many sodium ions are transported out of the cell per ATP molecule hydrolyzed by the Na+/K+ ATPase?

Three Na+ ions out and two K+ ions in. Signup and view all the answers

In the E1 conformation of the Na+/K+ ATPase, how many high-affinity Na+ binding sites are present?

Three high-affinity binding sites. Signup and view all the answers

What results from the hydrolysis of the aspartyl-phosphate bond in the mechanism of the Ca2+ ATPase?

Dephosphorylation powers the E2 to E1 conformational change. Signup and view all the answers

What distinguishes the Na+/K+ ATPase from the Ca2+ ATPase?

It pumps ions in both directions across the membrane. Signup and view all the answers

Which statement is true regarding the composition of the Na+/K+ ATPase?

It is a tetramer composed of two beta and two alpha subunits. Signup and view all the answers

What is the main function of the Na+/K+ ATPase?

To maintain intracellular concentrations of Na+ and K+. Signup and view all the answers

Study Notes

Active Transport

Active transport uses energy to move molecules from a low concentration to a high concentration.
ATP-powered pumps use energy from ATP hydrolysis to move molecules across a membrane against their concentration gradient.

Transport through Membranes

Channel proteins transport water and ions down their concentration or electric potential gradients.
Non-gated channels are open most of the time.
An inside-negative electric potential exists across the plasma membrane of all cells, generated mostly by K+ ions moving through channels.
The electrochemical gradient drives transport of charged molecules across a membrane, taking into account both the concentration gradient and the membrane potential.
Gated ion channels open in response to specific chemical or electrical signals.

Transporters

Uniporters transport a single molecule down its concentration gradient through facilitated diffusion.
Glucose and amino acids enter most mammalian cells through uniporters.
GLUT1 is a uniporter that transports glucose from the extracellular medium into cells.

ATP-Powered Pumps

ATP-powered pumps are classified into four classes: P-class, V-class, F-class, and ABC superfamily.
P, F, and V classes transport ions, while the ABC superfamily primarily transports small molecules.
P-class pumps include the Na+/K+ ATPase, which maintains low Na+ and high K+ concentrations in animal cells.
Ca2+ ATPases pump Ca2+ out of the cytosol or into the endoplasmic reticulum or sarcoplasmic reticulum.
Another P-class pump found in the stomach pumps H+ out and K+ into the cell.
V-class pumps maintain low pH in vacuoles and vesicles in animal cells by pumping protons against a proton electrochemical gradient.
F-class pumps are found in bacteria, mitochondria, and chloroplasts.
F-class pumps power ATP synthesis from ADP and Pi, moving protons down their electrochemical gradient.

Na+/K+ ATPase

The Na+/K+ ATPase is a P-class pump found in the plasma membrane of all animal cells.
It moves three Na+ ions out of the cell and two K+ ions into the cell per ATP molecule hydrolyzed.
It is a tetramer with two alpha and two beta subunits.
It utilizes a similar mechanism to the muscle calcium pump, but pumps ions in both directions across the membrane.
Drugs like ouabain and digoxin inhibit its ATPase activity, disrupting the Na+/K+ balance in cells.

Na+/Glucose Symport

The Na+ pump, at the basal end of the cell, contributes to lower [Na+] inside the cell compared to the fluid bathing the apical surface.
The Na+ gradient drives uphill transport of glucose into the cell at the apical end via glucose-Na+ symport.

ABC Superfamily Transporters

ABC stands for ATP-Binding-Cassette.
They contain two transmembrane (T) domains and two cytosolic ATP-binding (A) domains.
T domains form the transport pathway and determine substrate specificity.
Bacteria use ABC proteins to import nutrients against concentration gradients.
The human genome contains 48 genes for ABC transporters, including CFTR, TAP, and drug pumps.
CFTR is a chloride channel that is defective in cystic fibrosis, leading to thick mucus that clogs airways.
MDR proteins pump small compounds like drugs and toxins out of eukaryotic cells.

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Description

Test your understanding of active transport mechanisms in cell biology. This quiz covers energy usage in molecular transport, the role of ATP-powered pumps, and the function of various membrane proteins. Discover how substances move across membranes and the importance of concentration gradients.