Chapter 2.2.7: Peroxisomes

Peroxisomes

It used to be thought that peroxisomes are formed by the budding of
smooth Endoplasmic Reticulum (ER). However, now it is thought that they
form through self-assembly. (reference)
The peroxisome is another major source of Oxygen utilization (along with
the mitochondrion). There are specific proteins associated with the
peroxisomes membrane, also there are 3 oxidation enzymes associated with
peroxisomes:

D-amino acid oxidase

Urate Oxidase

Catalase

The enzyme contents vary with various types of cells. One of the main
functions of peroxisomes in liver cells is detoxification. This is
done by the oxidation of substances like:

Alcohol - About 1/2 of the ethanol one drinks is converted to
acetaldehyde by oxidation.

Phenols

Formic acid

Formaldehyde

Why peroxisomes are not like lysosomes.

Peroxisomes are organelles that contain oxidative enzymes, such as D-amino acid
oxidase, urate oxidase, and catalase. They may resemble a lysosome, however,
they are not formed in the Golgi complex. Peroxisomes are distinguished by a
crystalline structure inside a sac which also contains amorphous gray material.
They are self replicating, like the mitochondria. Components accumulate at a
given site and they can be assembled into a peroxisome. They may look like
storage granules, however, they are not formed in the same way as storage
granules.


Peroxisomes function to rid the body of toxic substances like hydrogen
peroxide, or other metabolites. They are a major site of oxygen utilization
and are numerous in the liver where toxic byproducts are going to accumulate.

The peroxisome is made as a phospholipid bilayer, encapsulating oxidative
materials. They would be 'sphere-ish' in shape, not necessarily a
perfect sphere, and sometimes, they may take other shapes. But most
electron micrographs I have seen (2 dimensions) show them as circles.
(As you may be aware, the Cell membrane is also a phospholipid bilayer.)
Peroxisomes have membrane proteins that are critical for peroxisomal function,
to import proteins into their interiors, proliferate or segregate to daughter cells
(reference)
The main differences would be:

1. Types of phospholipids used.

2. Size of the membrane (i.e. peroxisomes are MUCH smaller
than the cell).

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Please send questions/comments/suggestions to: Mark Dalton at markwdalton@gmail.com.