Biomedical Engineering Reference
In-Depth Information
dence and is widely accepted as the best explanation for the origin of eu-
karyo tic cells.
According to the endosymbiotic model, the mitochondria inside today's
eukaryotic cells arose when prokaryotic cells efficient at making ATP (aer-
obic cells) became engulfed by the
plasma membrane
of larger host cells (an-
aerobic cells) that lacked an efficient way to make ATP (fig. 1.11). When the
symbionts
began living inside the larger host cells, both types of cells gained
something from the new association. host cells gained ATP from the sym-
bionts, and symbionts gained protection and the stability of a controlled en-
vironment in which to live from the host cytoplasm. This scenario explains
the structure and function of today's mitochondrion—its double mem-
brane, circular DnA molecule, and inner membrane that produces ATP.
The structure and function of chloroplasts—double-membraned, DnA-
containing organelles responsible for photosynthesis inside plant cells—
are similarly explained. for me, it is profound to realize that every cell in
my body (and in the body of every other eukaryotic organism) is actually
a community of organisms working together to maintain the life of a vast
assemblage of communities that i call myself.
The Unity of life
Just as interesting as the origin of cells is what the biology of cells reveals
about the unity of life. By “unity,” i mean shared likenesses. The most sig-
nificant of life's shared likenesses are the common ancestry and the inter-
dependent ecological relationships among all living things. formed over
eons of biological evolution, common ancestry and ecological interdepen-
dencies connect all members of the living community to each other. A
common ancestry for all living things is reflected in the structures of genes
and proteins and their genetic and metabolic functions (steele and Penny
2010; Theobald 2010). ecological interdependencies are all around us—
from animals inhaling life-sustaining oxygen produced by green plants to
flowering plants' reliance on insects and bats for their pollination. This
tightly woven web of inherited and ecological connections is the funda-
mental fabric of nature.
Search WWH ::
Custom Search