Biochemistry : Integrins
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Example Question #21 : Signal Transduction Pathways
Which of the following is false about integrin structure and function?
Integrins are made of a single subunit.
Integrins bind a cytoskeleton to the extracellular matrix.
Typically, integrins are attached to actin or intermediate filaments.
Integrins are central to blood clotting.
Integrins can set off signaling pathways in the cell, indicating the nature of the extracellular matrix.
Integrins are made of a single subunit.
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 #22 : Signal Transduction Pathways
Which of the following statements is true?
All transport proteins are heterotetramers
All transport proteins are symmetric across the plasma membrane.
All transport proteins are asymmetric across the plasma membrane.
Some transport proteins are symmetric, while others are asymmetric across the plasma membrane.
Transport proteins are identical in structure to gap junctions
All transport proteins are asymmetric across the plasma membrane.
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 #23 : Signal Transduction Pathways
Which of these transporters involves the formation of a high energy intermediate?
More than one of these answers
Sodium-potassium ATPase
GLUT1 transporter
Lactose permease
Calcium-hydrogen ATPase
More than one of these answers
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 #24 : Signal Transduction Pathways
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?
It uses ATP to exchange one potassium ion and one sodium ion
It is active transport, effectively making the cytosol more negative
It is passive transport, making the cytosol polarize
It uses ATP to bring sodium into the cell
The pump allows sodium and potassium to flow down their electrochemical gradients
It is active transport, effectively making the cytosol more negative
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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