Receptor-mediated Endocytosis

Question 1

A highly selective form of endocytosis that begins when receptors on a cell’s surface bind specific substances, triggering the plasma membrane to form a vesicle around them, drawing them into the cell.

Answer 1

Receptor-mediated endocytosis

Question 2

Fill in the blanks.

First Step: A ___ binds to a specific receptor on the cell’s plasma membrane, forming a ___ complex.

Answer 2

A ligand binds to a specific receptor on the cell’s plasma membrane, forming a ligand-
receptor complex.

Question 3

Each receptor is associated with a protein known ___.

Answer 3

Clathrin

Question 4

The regions of the plasma membrane in which these receptors and their associated clathrin molecules.

Answer 4

Clathrin-Coated Pits

Question 5

Fill in the blank

Second Step: The ___ sinks into the cell, forming a ___ that contains the ligand-receptor complexes. This vesicle becomes ___ from the plasma membrane and enters the cytoplasm.

Answer 5

The clathrin-coated pit sinks into the cell, forming a vesicle that contains the ligand-receptor complexes. This vesicle becomes detached from the plasma membrane and enters the cytoplasm.

Question 6

Fill in the blank

Third Step: Once in the cytoplasm, the ___ coating the outer edge of the vesicle ___, and associate with ___ on the plasma membrane.

Answer 6

Once in the cytoplasm, the clathrin molecules coating the outer edge of the vesicle leave, and associate with new receptors on the plasma membrane.

Question 7

Fill in the blank

Fourth Step: The uncoated vesicle fuses with an ___, and the ___ and receptors ___, collecting at ___ ends of the endosome.

Answer 7

The uncoated vesicle fuses with an endosome, and the ligands and receptors separate, collecting at opposite ends of the endosome.

Question 8

Fill in the blank

Fifth Step: Sections of the endosome containing unbound receptors ___ off, forming ___ that ___ the receptors to the plasma membrane.

Answer 8

Sections of the endosome containing unbound receptors pinch off, forming transport vesicles that return the receptors to the plasma membrane.

Question 9

Fill in the blank

Sixth Step: The remaining vesicles, which now contain ___ ___, fuse with a ___.

Answer 9

The remaining vesicles, which now contain free ligands, fuse with a lysosome containing
digestive enzymes.

Question 10

Fill in the blank

Seventh Step: The lysosome’s digestive enzymes break the ___ down into smaller molecules, which are then released into the cytoplasm of the cell for use in a number of cell processes.

Answer 10

The lysosome’s digestive enzymes break the ligands down into smaller molecules, which are then released into the cytoplasm of the cell for use in a number of cell processes.

Question 11

In simple terms, enumerate the steps of receptor-mediated endocytosis.

Answer 11

1. A ligand binds creating a ligand-receptor complex.
2. Clathrin-coated pit sinks forming a vesicle, entering the cytoplasm.
3. Clathrin molecules leave and associate with new receptors.
4. The created vesicle fuses with an endosome, with ligands and receptors located oppositely.
5. Section of endosome with unbound receptors pinch off, forming transport vesicles returning the receptors to the membrane.
6. The remaining vesicles containing free ligands fuse with a lysosome.
7. The lysosome breaks the ligands down.