Self and the Beginning of Life 29“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanitycell to be utilized. It is in the ER where nascent proteins are folded
into the correct shape (there are special proteins that assist in this pro-
cess) and necessary additions (such as carbohydrates) are installed. It
also serves as a “post-office” where proteins are chemically tagged with
Fig. 3.7. Diagram of energy utilization as illustrated by the metabolism of glucose.
The solid line enclosure represents a cell; the dotted line, a mitochondrion inside the
cell. One molecule of glucose (a 6-carbon molecule) that we take in from food enters
the cell and goes through a process called glycolysis (9 steps), ending up with 2 mole-
cules of pyruvate (3-carbon molecule). Pyruvate enters the mitochondrion where it is
converted to acetyl CoA after shedding 1 carbon (as CO 2 ). The acetyl group then enters
the TCA cycle. One cycle of TCA (8 steps per cycle) converts the 2-carbon acetyl group
into 2 CO 2 , while sending the electrons through the electron transport chain. During
electron transport, a proton gradient (created by hydrogen atoms missing the electron)
is produced across the inner membrane of the mitochondrion, providing energy for the
conversion of ADP (adenosine diphosphate) to ATP (adenosine triphosphate), coupled
with the formation of water by the combination of oxygen and hydrogen. The last step
is called oxidative phosphorylation. The overall event consists of the reaction of glucose
(C 6 H 12 O 6 ) and oxygen to form carbon dioxide and water, with the resulting formation of
ATP from ADP and inorganic phosphate (Pi). Starting from one molecule of glucose, a
total of 38 molecules of ATP are produced (2 from glycolysis and 36 from reactions inside
the mitochondrion).