Biochemistry : Integrins

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #1 : Integrins

Which of the following is false about integrin structure and function?

Possible Answers:

Integrins can set off signaling pathways in the cell, indicating the nature of the extracellular matrix.

Typically, integrins are attached to actin or intermediate filaments.

Integrins are made of a single subunit.

Integrins bind a cytoskeleton to the extracellular matrix.

Integrins are central to blood clotting.

Correct answer:

Integrins are made of a single subunit.

Explanation:

Integrins have two subunits, alpha and beta. They do indeed bind the cell's cytoskeleton to its matrix, and can indicate to the cell the nature of that matrix. Integrins attach to a cell's actin and intermediate filaments. Blood platelets contain integrins, which bind proteins, like fibrinogen, in the matrix. This permits blood clotting, and the absence of certain integrins can cause a pathology in which people's blood does not clot well.

Example Question #2 : Integrins

Which of the following statements is true?

Possible Answers:

Transport proteins are identical in structure to gap junctions

All transport proteins are asymmetric across the plasma membrane.

All transport proteins are symmetric across the plasma membrane.

All transport proteins are heterotetramers

Some transport proteins are symmetric, while others are asymmetric across the plasma membrane.

Correct answer:

All transport proteins are asymmetric across the plasma membrane.

Explanation:

Transport proteins (such as the GLUT1 transporter) are asymmetric. They have two conformational states that accept the ligand from the extracellular environment and release it inside the cell after transport.

Example Question #3 : Integrins

Which of these transporters involves the formation of a high energy intermediate?

Possible Answers:

Lactose permease

Sodium-potassium ATPase

Calcium-hydrogen ATPase

More than one of these answers

GLUT1 transporter

Correct answer:

More than one of these answers

Explanation:

The sodium-potassium ATPase and the calcium-hydrogen ATPase (active transporters) are both correct and form high energy aspartyl phosphate intermediates inside the cell.

Example Question #4 : Integrins

The sodium-potassium pump is used in many different cells to control the concentration and movement of ions across the membrane. Which of the following is true about the sodium-potassium pump?

Possible Answers:

It is active transport, effectively making the cytosol more negative

It uses ATP to exchange one potassium ion and one sodium ion

It uses ATP to bring sodium into the cell

The pump allows sodium and potassium to flow down their electrochemical gradients

It is passive transport, making the cytosol polarize

Correct answer:

It is active transport, effectively making the cytosol more negative

Explanation:

Many of the distractors have partially correct statements. In full, the sodium-potassium ATPase pump is an active exchanger, meaning it is a transporter that uses ATP to move two different ions across the membrane. In this case, the transporter hydrolyzes ATP to move 3 sodium ions out of the cell and 2 potassium ions into the cell. This means that with every transport the cell looses a negatively charged cation, making the cytosol a little more negatively charged. 

The sodium-potassium pump often moves the molecules against their concentration gradients. 

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