Biology Reference
In-Depth Information
Fig. 4.10
synthesize proteins. Both mitochondria and chloroplasts contain their own DNA and
their own ribosomes, which in their detailed molecular properties resemble those
from proteobacteria and cyanobacteria, but differ from the DNA and ribosomes in
the nucleus and cytosol. Like chloroplasts, mitochondria contain the genes for less
than 1% of all the organellar proteins, the vast majority residing in the nucleus.
Thus plant cells are more complex than animal cells, in the sense that they all con-
tain three genetic systems, whereas animal cells contain only two. It has also been
established that mitochondria and chloroplasts are inherited directly from the par-
ent cell in the form of smaller membrane-bound structures, termed promitochondria
and proplastids. This fact recalls the adage “All cells from cells”, referred to in the
section entitled
The Principles of Molecular Biology
.
The Origin of Eukaryotes
You will note from Fig. 4.10 that comparison of whole genome sequences from
Bacteria, Archaea and Eukarya show that eukaryotic genomes contain some genes
more closely related to those found in Bacteria today, and other genes related
to those from Archaea today. Most interestingly, these genes can be largely
grouped into two distinct classes, depending on the functions of the proteins they
encode. Thus the archaeal-related genes encode proteins involve in informational
