Download Mattie Knebel Kyler Salazar Jared Hansen Biology 1610 Sperry

Mattie Knebel
Kyler Salazar
Jared Hansen
Biology 1610
Sperry
March 5, 2013
Writing Assignment #2
Importance of Cellular Respiration
Animals and humans share the same characteristic of being dynamic, meaning
they are constantly at work in their bodies. A lot of these works are fueled by the
molecule ATP, which is the end product of cellular respiration along with 3 cycles. In
cellular respiration, a cell inputs glucose and outputs a total of 30-32 ATP molecules
which can be used for any actions in the cell. The three aerobic reaction cycles that
partake in cellular respiration are Glycolysis, the Citric Acid Cycle, and Oxidative
Phosphorylation. There is one anaerobic reaction cycle, anaerobic meaning the lack of
Oxygen, called fermentation.
The first cycle, Glycolysis, inputs a 6C glucose molecule, breaks it down, and
outputs two separate 3C Pyruvate. In order to achieve Glycolysis’ output, it goes
through a series of reactions. The first being Glucose converted to Glyceraldehyde-3
Phosphate. This step is an anabolic reaction, which requires 2 ATP in order to react.
Next, NAD+ comes in and picks up 2 electrons in the form of Hydrogen ions and form
NADH. The energy released from this reaction is then used to apply a phosphate group
to both of the G3P molecules, which is then rearranged to make a 3 carbon molecule.
After this, ADP is added and takes the phosphate group, leaving only the two separate
3 Carbon molecules called Pyruvate. This cycle takes place in the cytosol, located just
outside of the mitochondria. This process has a net gain of 2 ATP which is then carried
on to the next cycle. Diagram A, which can be found on our flow chart, shows this
process.
The 2nd cycle, the Citric Acid Cycle, is the production of NADH and FADH2 for
Oxidative Phosphorylation. Before this can happen, the cell must go through the linker
step. In the linker step, Coenzyme A is added to the 3C Pyruvate from Glycolysis.
Oxygen is also added in this step producing a Carbon Dioxide molecule. After this, the
Citric Acid Cycle can begin. Acetyl CoA enters into the citric acid cycle and is attached
to the 4C molecule Oxaloacetate. The CoA is then released and a 6C molecule called
citrate is left behind. After Citrate is formed, it is broken down into a 5C molecule using
Oxygen which then produces a CO2 molecule. NAD+ then comes along and takes 2
electrons producing NADH. Next, Oxygen is used to break down the 5C molecule into a
4C molecule producing another CO2 molecule. NAD+ picks up two more electrons and
produces NADH. FAD+ also uses two hydrogen ions in this step to produce FADH2.
When NAD+ is turned into NADH, it releases energy that is then used to combine a
phosphate group to an ADP molecule to produce 1 ATP molecule. After this, the 4C
Oxaloacetate can be used for the second Acetyl CoA molecule, created from Glycolysis,
and repeat the cycle to produce another ATP molecule. This process, which can be
seen in figure B of the flow chart, occurs in the mitochondrial matrix and has a net gain
of 2 ATP.
The 3rd and final cycle, Oxidative Phosphorylation, outputs the most ATP of all
the cycles (26-28) and takes place in the inner mitochondrial membrane. There are 2
main steps to this cycle, the Electron Transport Chain (ETC) and Chemiosmosis. In the
ETC, NADH gives up its electrons producing a large amount of energy. This energy that
the electrons lose is then used to pull H+ ions out of the mitochondrial matrix and into
the intermembrane layer. In the ETC, the electrons are attracted to the highly
electronegative oxygen at the end of the chain, where the electrons combine with
oxygen to produce H2O. Once the Hydrogen’s are all transported out into the
intermembrane space, Chemiosmosis can occur. In this step, H+ ions will diffuse back
into the mitochondrial matrix if ATP Synthase is present in the membrane. As the ions
diffuse back into the matrix, they release their energy. ATP Synthase utilizes this energy
to combine a phosphate group to ADP.
Our body could not go through these aerobic cycles if we did not obtain a diet full
of Carbon. Cellular respiration cannot happen without carbon. Along with carbon, these
cycles explained above also require Oxygen. Yes, the cell can still go through
Fermentation to produce Lactic acid without the presence of Oxygen; However, this
process only yields 2 ATP’s which is a very small amount compared to aerobic cycles
and the amount of ATP our cells need daily in order to properly function.
Plants utilize light energy to produce chemical energy. This process in which
CO2 and H2O are used to produce Glucose and Oxygen is referred to as
Photosynthesis. Plants use this process with the addition of cellular respiration to
produce acceptable amounts of NADH and ATP that we, humans, can later consume
into our bodies to help aid the appropriate cellular respiration in our cells.
Animals and plants are greatly codependent of each other. Animals provide
plants with CO2, which plants then use to form Oxygen and Glucose. This sugar and
oxygen is essential to humans and animals to be able to produce energy and CO2. This
recurring balanced system we participate in is what we call life.
The main misconception that was seen in my group over the course of writing
this paper was the confusion of how many ATP molecules Glycolysis produces. Yes, it
is true that 4 ATP’s are made in the Energy payoff phase, but the Energy Investment
phase of this cycle requires the use of 2 ATP’s. So although 4 ATP’s are created, 2 are
used, making Glycolysis have an overall net gain of 2 ATP’s. The only other
misconception was the question of where each of these cycles occurred. We were able
to research and conclude that Glycolysis occurs in the cytosol, the Citric Acid Cycle in
the mitochondrial matrix, and Oxidative Phosphorylation in the inner mitochondrial
membrane.