Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

GENETIC INFORMATION IN EUKARYOTES
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anaerobic cell derived
from an archaeon
primitive
nucleus
early aerobic
eukaryotic cell
nucleus
Figure 1–29 The origin of mitochondria.
An ancestral anaerobic predator cell (an
archaeon) is thought to have engulfed the
bacterial ancestor of mitochondria, initiating
a symbiotic relationship. Clear evidence of
a dual bacterial and archaeal inheritance
can be discerned today in the genomes of
all eukaryotes.
internal
membranes
bacterial outer membrane
aerobic bacterium
bacterial plasma
membrane
loss of membrane
derived from
archaeal cell
mitochondria with
double membranes
or to swallow up other cells. Fungi, it seems, have turned from hunters into scavengers:
other cells secrete nutrient molecules or release them upon death, and
fungi feed on these leavings—performing whatever digestion is necessary extracellularly,
by secreting digestive enzymes to the exterior.
Eukaryotes Have Hybrid Genomes
The genetic information of eukaryotic cells has a hybrid origin—from the ancestral
anaerobic archaeal cell, and from the bacteria that it adopted as symbionts.
Most of this information is stored MBoC6 in m1.34/1.29
the nucleus, but a small amount remains
inside the mitochondria and, for plant and algal cells, in the chloroplasts. When
mitochondrial DNA and the chloroplast DNA are separated from the nuclear DNA
and individually analyzed and sequenced, the mitochondrial and chloroplast
genomes are found to be degenerate, cut-down versions of the corresponding
bacterial genomes. In a human cell, for example, the mitochondrial genome consists
of only 16,569 nucleotide pairs, and codes for only 13 proteins, 2 ribosomal
RNA components, and 22 transfer RNAs.
chloroplasts
chlorophyllcontaining
membranes
(A)
10 µm
(B)
inner
membrane
outer
membrane
Figure 1–30 Chloroplasts. These
organelles capture the energy of sunlight
in plant cells and some single-celled
eukaryotes. (A) A single cell isolated
from a leaf of a flowering plant, seen
in the light microscope, showing the
green chloroplasts (Movie 1.3 and see
Movie 14.9). (B) A drawing of one of the
chloroplasts, showing the highly folded
system of internal membranes containing
the chlorophyll molecules by which light is
absorbed. (A, courtesy of Preeti Dahiya.)