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By the end of this section, you will be able to:
  • Describe endocytosis, including phagocytosis, pinocytosis, and receptor-mediated endocytosis
  • Understand the process of exocytosis

In addition to moving small ions and molecules through the membrane, cells also need to remove and take in larger molecules and particles (see [link] for examples). Some cells are even capable of engulfing entire unicellular microorganisms. You might have correctly hypothesized that the uptake and release of large particles by the cell requires energy. A large particle, however, cannot pass through the membrane, even with energy supplied by the cell.

Endocytosis

Endocytosis is a type of active transport that moves particles, such as large molecules, parts of cells, and even whole cells, into a cell. There are different variations of endocytosis, but all share a common characteristic: The plasma membrane of the cell invaginates, forming a pocket around the target particle. The pocket pinches off, resulting in the particle being contained in a newly created intracellular vesicle formed from the plasma membrane.

Phagocytosis

Phagocytosis (the condition of “cell eating”) is the process by which large particles, such as cells or relatively large particles, are taken in by a cell. For example, when microorganisms invade the human body, a type of white blood cell called a neutrophil will remove the invaders through this process, surrounding and engulfing the microorganism, which is then destroyed by the neutrophil ( [link] ).

This illustration shows a plasma membrane forming a pocket around a particle in the extracellular fluid. The membrane subsequently engulfs the particle, which becomes trapped in a vacuole.
In phagocytosis, the cell membrane surrounds the particle and engulfs it. (credit: Mariana Ruiz Villareal)

In preparation for phagocytosis, a portion of the inward-facing surface of the plasma membrane becomes coated with a protein called clathrin    , which stabilizes this section of the membrane. The coated portion of the membrane then extends from the body of the cell and surrounds the particle, eventually enclosing it. Once the vesicle containing the particle is enclosed within the cell, the clathrin disengages from the membrane and the vesicle merges with a lysosome for the breakdown of the material in the newly formed compartment (endosome). When accessible nutrients from the degradation of the vesicular contents have been extracted, the newly formed endosome merges with the plasma membrane and releases its contents into the extracellular fluid. The endosomal membrane again becomes part of the plasma membrane.

Pinocytosis

A variation of endocytosis is called pinocytosis    . This literally means “cell drinking” and was named at a time when the assumption was that the cell was purposefully taking in extracellular fluid. In reality, this is a process that takes in molecules, including water, which the cell needs from the extracellular fluid. Pinocytosis results in a much smaller vesicle than does phagocytosis, and the vesicle does not need to merge with a lysosome ( [link] ).

This illustration shows a plasma membrane forming a pocket around fluid in the extracellular fluid. The membrane subsequently engulfs the fluid, which becomes trapped in a vacuole.
In pinocytosis, the cell membrane invaginates, surrounds a small volume of fluid, and pinches off. (credit: Mariana Ruiz Villareal)

Questions & Answers

A skeleton is any film structure that gives mechanical support to the body and provides protection to the softer parts of the body.
Patrick Reply
nice
Kabir
A skeleton is a frame or bony part of a body that aid in the movement of different parts of the body.
hamidat
What is a skeleton?
Chipo Reply
is a bone without meat
Stanley
what is an electron microscope?
Chr Reply
what is biochemist
Lenard Reply
biochemistry:-is the study of chemical reaction with living organisms
Kabir
HOW MANY DNA STRANDS DOES CORONA VIRUS HAVE?
Baramox
what are the scientific method
Precious Reply
describe the functioning of the Golgi body in animal cells
Naiga Reply
what features does red blood have that allows it to effectively move through the blood and transport oxygen? list at least four features and explain how they help RBC's carry out their functions.
Alice Reply
has nucleus, haemoglobin
favour
what is biology
kenneth Reply
it's the study of living organisms and their interactions with one another and the environment
Precious
Biology is the study of life.
hamidat
describe the structure of DNA
Mafashion Reply
it a double helical structure negatively charged as a results of a phosphate backbone and the two strands are joined together by hydrogen bonds
Ebenezer
Bring out clearly the process of clothing
Irene Reply
How is the region of unwinding called
Irene
what is hoemositasis
Violet
homeostasis is the regulation of a constant internal environment
hamidat
is an unfavourable conditions cost by capavic bacteria
hashim Reply
no idea
hamidat
no idea
Precious
Describe the following terms used in nutrition, parasitism, saprophytic, symbiosys
Meymo Reply
parasitism involves gaining and losing
hamidat
a saprophyte does not cause harm to it Host.
hamidat
in symbiosis the two organisms are benefiting
hamidat
what is meiosis?
Emmanuel Reply
Meiosis is a two successive cell division with only one duplication of chromosomes
Amos
what are types of white cells
Kennedy Reply
phagocytes and lymphocytes
Luyando
Lymphocytes and phagocytosis
Sylvester
which plant tissue conducts sucrose in solution?
Luyando
granulocytes and agranulocytes
dilip
phloem
dilip
granulocytes and agranulocyte
Irene
types of asexual reproduction
Iradukunda Reply
what is prokaryotic
Iradukunda
a bacteria
Jewell
what is the right medication for heart burn?
Emmy

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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