Hi All,
Chapter 6 can be a bit confusing to understand so I thought I'd write down a short
summary here:
Glycolysis breaks down glucose and produces (net) 2 ATP and 2 NADH. The end
product is 2 pyruvates. For fermenters, the pyruvate is then reduced by the NADH (to
regenerate NAD) and often ends up being turned in to something useful to humans (like
ethanol or lactic acid).
For non-fermentors, the pyruvate then enters a transition step, where 2 more NADH are
made (because there are 2 pyruvates generated per molecule of glucose). The product
of this step, Acetyl-CoA enters into the TCA cycle where 2 more ATP, 6 more NADH, 2
FADH2 are made.
So, we have made some ATP, which is the energy currency of the cell. ATP is used to
power the synthesis of larger molecules from smaller molecules (like linking together
amino acids to form a protein, for instance). A phosphate group is cleaved off of the
ATP (adenosine triphosphate), energy is released and used by the enzyme catalyzing a
reaction and ADP (adenosine diphosphate) is formed. ADP can then be re-made into
ATP via substrate level phosphorylation during glycolysis or the TCA cycle. But the BIG
producer of ATP is cellular respiration, which depends on the energy inherent in the
electron donors NADH and FADH2.
NADH and FADH2 have, essentially, high-energy electrons which they can donate to
the electron transport chain. This is part of what we'll talk about on Thursday.
We did talk a bit about the electrons at the beginning of class. Glucose "wants" to give
up its electrons and oxygen "wants" to take electrons. By shuttling electrons from
glucose to, eventually, oxygen, via electron carriers (NADH, FADH2), energy is
released and used by the cell to create a hydrogen ion gradient across its membrane.
ATP production is driven by the energy released when the hydrogen ions move DOWN
their concentration gradient, into the cell (remember, this is the same energy that is
used to power symport/antiport in active transport).
So to follow the electrons:
Glycolysis (makes a little ATP) makes 2 electron carriers, TCA and transistion step
make 10 more electron carriers. As glucose is broken down, the potential energy in its
bonds has been transferred to either ATP directly while some energy is transferred to
the electron carriers via high energy electrons. These electron carriers then move over
to the electron transport chain where the electron slowly loses energy as it is bound to
different molecules. This energy is used to pump hydrogen ions out of the cell where it
is transformed into the potential energy inherent in a concentration gradient. This
potential energy is turned into kinetic energy as the ions move down their concentration
gradient. This energy is harvest and turned back into potential energy by creating ATP
from ADP (adding a high energy phosphate bond).
So there is a LOT of movement/transformation of energy going on.
Hopefully this summary helps a bit.