Biology Reference
In-Depth Information
Endoplasmic Reticulum (ER)
The endoplasmic reticulum (ER) is a complex network of cisternae or tube-like struc-
tures occupying a considerable percentage of the cell's internal volume
[13]
. The portion
of the ER with attached ribosomes is known as the rough ER. It is the site for biosynthesis
of non-cytoplasmic proteins that are either secreted, internalized into the lysosome, or
become PM proteins. The portion of ER devoid of ribosomes is known as the smooth
ER. Functions of the smooth ER include sterol biosynthesis, drug detoxification, calcium
regulation, and fatty acid desaturation. A specialized ER, the sarcoplasmic reticula has but
one function
regulation of intra-cellular calcium levels. The endoplasmic reticula were
first seen by Keith R. Porter, Albert Claude, and Ernest F. Fullam in 1945
[14]
.
e
Golgi Apparatus
The Golgi apparatus
[15,16]
is a series of stacked, disk-shaped tubules. The Golgi is named
after the man who discovered it in 1898, Carmillo Golgi. For this, in 1906 Golgi was awarded
one of the first Nobel Prizes. It is in the Golgi that post-translational modification of glycopro-
teins synthesized originally in the ER and destined for secretion takes place. Other possible
final destinations of proteins from the Golgi include incorporation into the PM or to the lyso-
some. Characteristic Golgi-resident enzymes involve sugar modification of proteins and
include glucosidases and glycosyl transferases.
Lysosome
The lysosome contains some 40 hydrolytic enzymes whose function is to degrade macro-
molecules into component parts for re-use in the cell
[17]
. As a result lysosomes are often
referred to as the 'cell's garbage disposal'. The organelle was discovered in the early 1950s
and, in 1955, it was named lysosome, by Belgian cytologist Christian de Duve, for its ability
to lyse membranes.
Peroxisome
Peroxisomes contain a battery of oxidative enzymes that are involved in breakdown of
small molecules
[18]
. Important peroxisomal enzymes include D-amino acid oxidase and
catalase, the enzyme responsible for the degradation of dangerous peroxides. Peroxisomes
are also involved in drug detoxification and the biosynthesis of essential ether-phospholipids
known as plasmalogens (discussed in Chapter 5). Peroxisomes were also discovered by
Christian de Duve in 1967
[19]
. For discovering lysosomes and peroxisomes, de Duve was
awarded the 1974 Nobel Prize for Medicine (
Figure 1.4
).
Mitochondria
Mitochondria are the 'powerhouse' of the cell, producing most cellular ATP. The processes
of electron transport and oxidative phosphorylation are housed in the highly folded mito-
chondrial inner (Cristae) membrane
[20]
. The mitochondrial aqueous interior chamber, called
