SI Worksheet 12
1. My transcription of Dr. Cusic’s notes on Glycolysis.
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Glycolysis occurs in the cytosol.
We start with a glucose molecule.
Gonna use a kinase on it (very important for the transfer of phosphates) Have to go to the bank of
ATP and borrow this. A kinase enzyme pulls off phosphates from ATP and puts them onto glucose ( and
vice versa) this addition of Phosphate makes the glucose molecule reactive, unstable, and tells it to stay
in the cell
Next, and isomerase comes in and changes the glucose w/ a phosphate into its isomer ( a fructose
with a phosphate).
The next reaction is a kinase called Phosphofructokinase. We have to go back to the bank and borrow
another ATP. PFK is essential because it is a CONTROL ENZYME. It takes a phosphate off of an ATP and
puts it on the Fructose with a phosphate.
This leaves us with a fructose with 2 phosphate groups attatched.
Magic chemistry happens which splits the 6 carbon 2 phosphate molecule into 2- 3 Carbon
molecules, each with a respective phosphate group of their own.
The 2 molecules that are formed are Dehydroxyacetone phosphate (DHAP) and Glyceraldehyde 3
phosphate (G3P). We want G3P so first we pull G3P off then use an isomerase to change the DHAP
into a second molemcule of G3P.
That completes the energy INVESTMENT phase of Glycolysis
We used 2 ATPs! In other words 2 molecules of ATP were dephosphorylated into 2 molecules of
ADP.
The next phase of glycolysis is the energy payoff phase!
You start off with 2 G3Ps which are 2- 3 carbon molecules that each have one phosphate attached.
A dehydrogenase enzyme along with the coenzyme NAD+ oxidizes the G3P which is a very
exergonic reaction. This very exergonic reaction is then used to attach a phosphate group to the
oxidized G3P resulting in 2 - 3 carbon molecules with 2 phosphates attached to each. (2 NADH’s
created.)
One of the phosphates that was added to the 3 carbon molecules with 2 phosphates each is
transferred onto an ADP thus creating ATP by way of a kinase enzyme! ( 2 ATP’s created). This
reaction is an example of Substrate level phosphorylation.
Magic Chemistry… magic chemistry… magic chemistry. You end up with a 3 carbon sugar with 1
phosphate called Phosphoenol pyruvate or (PEP)
A second substrate level phosphorylation occurs via a kinase. This creates 2 more ATP’s.
You end up with a 2 molecules of 3 carbon sugars with NO phosphates…. Thus you end up with 2
molecules of Pyruvate. This is the end of Glycolysis.
GLYCOLYSIS
GROSS ATP = 4 ATP
NET ATP = 2 ATP
NADH’s made = 2 NADH
2. Explanation of Citric Acid Cycle.
We start with 2- 3 carbon molecules of Pyruvate
Brings Pyruvate in to the Mitochondria by way of a transport protein.
We do oxidative decarboxylation, which takes off a CO2
2 net NADH’s are made.
Now we attach a Coenzyme A to new 2 Carbon beast by a Sulfur which is very reactive.
This results in the creation of 2 Acetyl COAs
3. Explanation Citric Acid Cycle.
2-carbon acetyl COA gets together with a 4-carbon oxaloacetate. The COA-SH is kicked
out. This combination creates a 6-carbon oxaloacetate molecule. Do oxidative
decarboxylation, which pulls off a CO2 and creates a NADH. This leaves us with a 5
carbon Alpha ketogluterate, now do another oxidative decarboxylation which removes a
CO2 and creates a NADH. A COA-SH comes back in and reconnects with the 4 carbon
molecule making Succinyl COA… Succinyl CoA is very reactive.. An ATP is created by
substrate level phosphorylation… and the COA-SH leaves… Now we have 4 Carbon
Succinate FADH2 is created… Magic Chemistry and the creation of a third NADH turns it
back into 4-carbon Oxaloacetate….
4. Electron transport chain….
There are 4 multi-complex domains in the electron transport chain.. a drop in free
energy occurs as the electrons travel down the chain. Electron carriers reduced in the
earlier steps of cellular respiration drop their electrons off into these multi complex
domains. As a result of this electrons go in the domain and H+ proton concentration
grows outside of the domains. Each component of the chain becomes reduced as it
gains electrons from its “uphill neighbor” complex. The “uphill neighbor” complex has
a lower electron negativity than the “downhill neighbor” this is why there is a
constant flow of electrons being exchanged. (as you go down the complexes their
electronegativity increases.) Also remember as electrons travel down the chain they
are doing from higher free energy to lower free energy. Remember FADH2 drops off
its electrons at the second multi-protein complex while NADH drops is electrons off at
the first complex (this is why NADH results in more energy than FADH2). Know that
OXYGEN is the primary electron acceptor at the bottom of the chain!!! Meaning it is
most electronegative.
Chemiosmosis – because of the great build up of H+ protons outside the complexes
and the low concentration of H+ ions inside the complexes this sets up an electro
chemical gradient… The H+ that were sent outside desperately want to get to an area
with a lower H+ concentration. In oder to do this they must come back in through a
complex known as the ATP synthase… The movement of H+ through the ATP synthase
results in the creation of ATP. These ATP are made by OXIDATIVE
PHOSPHORYLATION.
5. Energy Breakdown…
SLP
Ox. Phos
Glycolysis
2 ATP Net
2 NADH
Ox of Pyruvate
0 ATP
2 NADH
Citric Cycle
2 ATP total
6 NADH & 2 FADH2
1 NADH = 2.5 ATP eq.
1 FADH2 = 1.5 ATP eq.
4 ATP from SLP
10 NADH x 2.5 ATP eq. = 25 ATP
2 FADH2 x 1.5 ATP eq. = 3 ATP
4 ATP from SLP + 28 ATP from Ox. Phos = 32 ATP