recap

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6.5 recap

Endocytosis and exocytosis are the processes by which large particles and molecules are transported into and out of the cell. Endocytosis may be mediated by a receptor protein in the cell membrane.

learning outcomes

You should be able to:

  • Compare and contrast the three types of endocytosis.

  • Describe the process of receptor-mediated endocytosis.

  • Provide examples of processes that involve endocytosis and/or exocytosis.

Question 1

What are the differences between phagocytosis and pinocytosis?

Phagocytosis involves a large cell membrane–derived vesicle forming around macromolecules. Pinocytosis involves smaller vesicles forming around water and its dissolved solutes.

Question 2

Describe receptor-mediated endocytosis and give an example of a process involving this phenomenon.

In receptor-mediated endocytosis, a molecule binds to a cell membrane protein receptor and causes the membrane to form a vesicle around the molecule and receptor. The vesicle with its contents enters the cell and usually fuses with a lysosome. An example is the endocytosis of lipoprotein particles from blood into liver cells.

Question 3

Key Concept 27.2 describes the diatoms, which are protists that have complex glassy structures in their cell walls (see Figure 27.8 and the photo below of eight diatom cells inside their ornate cell walls). These structures form within the Golgi apparatus. How do they reach the cell wall without having to pass through a membrane?

Diatom wall components move from the Golgi apparatus to the cell wall by exocytosis.

image