Page 205 - Color Atlas of Biochemistry
P. 205
196 Organelles
Structure of cells B. Structure of an animal cell
In the human body alone, there are at least
A. Comparison of prokaryotes and 200 different cell types. The illustration out-
eukaryotes linesthe basicstructuresof an animal cell in
an extremely simplified way. The details
Present-day living organisms can be divided given regarding the proportion of the com-
into two large groups—the prokaryotes and partments relative to cell volume (highlighted
eukaryotes. The prokaryotes are represented in yellow) and their numbers per cell fre-
by bacteria (eubacteria and archaebacteria). quency (blue) refer to mammalian hepato-
These are almost all small unicellular organ-
isms only a few microns (10 –6 m) in size. The cytes (liver cells). The figures can vary widely
from cell type to cell type.
eukaryotes include fungi, plants,and animals The eukaryotic cell is subdivided by mem-
and comprise both unicellular and multicel- branes. On the outside, it is enclosed by a
lular organisms. Multicellular eukaryotes are plasma membrane. Inside the cell, there is a
made up of a wide variety of cell types that are
specialized for different tasks. Eukaryotic cells large space containing numerous components
in solution—the cytoplasm. Additional mem-
are muchlarger thanprokaryotic ones (vol-
ume ratio approximately 2000 : 1). The most branes divide the internal space into
important distinguishing feature of these cells compartments (confined reaction spaces).
Welldefined compartments of this type are
in comparison with the prokaryotes is the fact
that they have a nucleus (karyon in known as organelles.
The largest organelle is the nucleus (see
Greek—hence the term). p. 208). It is easily recognized using the light
In comparison with the prokaryotes, eu- microscope. The endoplasmic reticulum (ER),
karyotic cells have greater specialization and a closed network of shallow sacs and tubules
complexity in their structure and functioning.
Eukaryotic cells are structured into compart- (see pp. 226ff.), is linked with the outer mem-
brane of the nucleus. Another membrane-
ments (see below). The metabolism and syn-
thesis of macromolecules are distributed bound organelle is the Golgi apparatus (see
p. 228), which resembles a bundle of layered
through these reaction spaces and are sepa- slices. The endosomes and exosomes are bub-
rately regulated. In prokaryotes, these func-
tions are organized in a simpler fashion and ble-shaped compartments ( vesicles) that are
involved in the exchange of substances be-
are spatially closely related. tween the cell and its surroundings. Probably
Although the storage and transfer of ge- the most important organelles in the cell’s
netic information function according to the metabolism are the mitochondria, which are
same principle in the prokaryotes and euka-
ryotes, there are also differences. Eukaryotic around the same size as bacteria (see
DNA consists of very long, linear molecules pp. 210ff.). The lysosomes and peroxisomes
10
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with a total of 10 to more than 10 base pairs are small, globular organelles that carry out
specific tasks. The whole cell is traversed by a
(bp), only a small fraction of which are used framework of proteins known as the cytoske-
for genetic information. In eukaryotes, the
genes (20000–50000 per genome) are usu- leton (see pp. 204ff.).
In addition to these organelles, plant cells
ally interrupted by non-coding regions (in-
trons). Eukaryotic DNA is located in the nu- (see p. 43) also have plastids—eg., chloro-
plasts, in which photosynthesis takes place
cleus, where together with histones and other (see p. 128). In their interior, there is a large,
proteins it forms the chromatin (see p. 238).
In prokaryotes, by contrast, DNA is ring- fluid-filled vacuole. Like bacteria and fungi,
6
shaped, much shorter (up to 5 10 bp), and plant cells have a rigid cell wall consisting of
located in the cytoplasm. Almost all of it is polysaccharides and proteins.
used for information storage, and it does not
contain any introns.
Koolman, Color Atlas of Biochemistry, 2nd edition © 2005 Thieme
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