Cytoplasmic Vesicles

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There are two types of Membrane-bound cytoplasmic vesicles: secretory vesicles and storage vesicles.

Secretory vesicles

Proteins that will be released from the cell are contained in secretory vesicles [1].

Storage vesicles

The content that is held within storage vesicles never departs from the cytoplasm. Two examples of storage vesicles are lysosomes and peroxisomes.

Lysosomes use enzymes which break down old organelles and bacteria, acting as a digestive system for the cell. Most of the broken down molecules are thrown out of the cell, however, if still useful to the cell, they can then be reabsorbed into the cytosol to be reused. Lysosomal enzymes are very inactive at the normal pH level of 7.0-7.3 [2] in the cytoplasm. They only become activated when the pH is about 4.8-5.0 [3]. This inactivity at a normal PH level is essential as if the lysosome breaks unintentionally leaks out some of the enzymes they will not react to digest the surrounding material. This stops lysosomes from destroying the cell that there contained in.

Peroxisomes contain a different set of enzymes to lysosomes and are much smaller. The reactions that tke place inside them generate a toxic molecle called hydrogen peroxide (H2O2) which gives them their name. Peroxisomes degrade potentially toxic foreign moelecues aswell as long fatty acid chains[4].

References

  1. Silverthorn, Human Physiology, An Integrated Approach, 5th edition (2010) Pearsons Benjamin Cummings, pg69
  2. Silverthorn, Human Physiology, An Integrated Approach, 5th edition (2010) Pearsons Benjamin Cummings, pg70
  3. Silverthorn, Human Physiology, An Integrated Approach, 5th edition (2010) Pearsons Benjamin Cummings, pg70
  4. Silverthorn,Human Physiology, An integrated Approach, 5th edition (2010) Pearsons Benjamin Cummings, pg70
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