Question

1)

The import cycle for a nuclear protein begins with binding of the protein to a receptor. Place the remaining four steps of the cycle in the correct order by matching them to the proper number: 1, 2, 3, or 4.

Binding of Ran-GTP to receptor

Release of protein in nucleus

Binding of receptor/protein complex to nuclear pore fibrils

Translocation of receptor/Ran-GTP complex through nuclear pore fibrils

2)

Match each description of transmembrane transport with the correct classification of the process. At least one of the classifications will have to be selected twice.

- Uniport

-Symport

-Antiport

a) The sodium-potassium pump transports 3 Na⁺ ions
out of a cell,and 2 K⁺ ions in, using energy from ATP.

b)

An open potassium channel allows K⁺ ions to flow into or
out of a cell, depending on their electrochemical gradient.

c)

The basolateral NKCC1 protein in sweat gland epithelium
transports 1 Na⁺, 1 K⁺, and 2 Cl^- ions into cells from the blood.

d) The proton pump bacteriorhodopsin, found in some archaea, uses energy from sunlight to translocate H⁺ from the cytosol to the exterior side of the plasma membrane.

3)

Soluble or membrane-associated proteins that normally function in the endoplasmic reticulum are sometimes incorporated into ER vesicles destined for the Golgi apparatus. When these proteins reach the cis-Golgi, ____________________.

	a)	their ER retrieval/retention signals will be recognized by receptors, and they will be returned to the ER
	b)	they will accumulate and disrupt normal Golgi function
	c)	they will be rapidly degraded
	d)	they will be modified by addition of mannose-6-phosphate and exported to lysosomes

Answer 1

1. The correct order is as:

1..Binding of Ran-GTP to receptor.

2. Binding of receptor/protein complex to nuclear pore fibrils.

3. Translocation of receptor/Ran-GTP complex through nuclear pore fibrils.

4. Release of protein in nucleus.

2.

a.

The sodium-potassium pump transports 3 Na⁺ ions out of a cell,and 2 K⁺ ions in, using energy from ATP.

Answer: Antiport: In antiport transpot the substances or molecules or ions move in opposite directions. Here sodium is pumped out of cell and potassium is pumped into the cell. Thus it is an antiport transport.

b.

An open potassium channel allows K⁺ ions to flow into or out of a cell, depending on their electrochemical gradient.

Answer: Uniport : In uniport the molecules/ions move alone without involving any other type of molecule or ion, either through active or passive transport. Here only potassium ions move. Thus, this transporter is an example of uniporter.

c.

The basolateral NKCC1 protein in sweat gland epithelium transports 1 Na⁺, 1 K⁺, and 2 Cl^- ions into cells from the blood.

Answer: Symport : In symport the molecules/ions move in the same direction. In symport the electrochemical gradient of one species is used to move another type of molecule in the same direction even against the chemical gradient. Here all the three Na⁺, K⁺ and Cl^{​​​​​-}  all move into the cells.

d.

The proton pump bacteriorhodopsin, found in some archaea, uses energy from sunlight to translocate H⁺ from the cytosol to the exterior side of the plasma membrane.

Answer: Uniport : Again this is uniport because only one kind of ions, H⁺ are pumped out of the cell.

3.

The correct option is :

a. Their ER retrieval / retention signals will be recognised by receptors, and they will be returned to the ER.