Aerobic respiration occurs within cells.
It starts with glycolysis in the cytosol of the cell.
It then goes through the link reaction moving into the matrix of the mitochondria.
It then goes through the citric acid cycle within the mitochondria matrix.
Then it goes through the electron transport chain and chemiosmosis in the inner mitochondrial
membrane producing energy in the form of ATP.
In this video we are going to look at the first process involved in Aerobic Respiration,
Glycolysis.
Glycolysis itself is an anaerobic process and can be part of the aerobic or anaerobic
pathways.
As we move through glycolysis we will keep a note of how many NADH and ATP are used or
produced.
In glycolysis we start in the cytosol of the cell with a single molecule of glucose.
There are 10 steps in Glycolysis.
The first 5 steps of glycolysis are called the investment phase, as they use energy in
the form of ATP.
The first step in glycolysis involves the phosphorylation of one glucose molecule which
is a six carbon molecule into another six carbon molecule glucose-6-phosphate using
the enzyme hexokinase and the co-factor Magnesium.
This process takes the phosphate from an ATP, and releases a hydrogen molecule.
This step uses up an ATP molecule, giving us a net total so far of negative 1 ATP.
The second step involves the conversion of glucose-6-phosphate a six carbon molecule
into yet another 6 carbon molecule fructose-6-phosphate using the enzyme Phosphoglucose Isomerase.
This reaction is able to go both ways.
The third step involves the phosphorylation of fructose-6-phosphate into another 6 carbon
molecule Fructose-1, 6-Bisphosphate using the enzyme Phosphofructokinase and the co-factor
Magnesium.
This process takes the phosphate from an ATP creating ADP and releases a hydrogen molecule.
This step uses up a second ATP molecule, giving us a net total so far of negative 2 ATP.
The fourth step involves the breaking of Fructose-1, 6-bisphosphate into two 3 carbon molecules;
Dihydroxyacetone Phosphate and Glyceraldehyde-3-phosphate using the enzyme Aldolase.
This is a reversible reaction.
The fifth step involves the conversion of Dihydroxyacetone Phosphate into a second Glyceraldehyde-3-phosphate
using the enzyme Triosephosphate Isomerase.
This is also a reversible reaction.
This leaves us with two Glyceraldehyde-3-phosphate molecules that both move though the remainder
of the steps.
This also ends the investment phase.
The next 5 steps of Glycolysis are called the payoff phase, as glycolysis starts to
produce energy in the form of ATP as well as NADH which is used to produce ATP later
on in cellular respiration.
The sixth step involves the conversion of Glyceraldehyde-3-phosphate into 1,3-Bisphosphoglycerate,
another 3 carbon molecule, using the enzyme Glyceraldehyde-3-phosphate dehydrogenase and
the co-factor Magnesium.
This process involves using an inorganic phosphate and reducing NAD+ into NADH as well as releasing
another hydrogen.
This is a reversible reaction.
This step occurs twice, once for each Glyceraldehyde-3-phosphate.
This step produces an NADH, as it occurs twice, 2 NADH are produced in total for one molecule
of glucose.
So far we now have a net total of 2 NADH and negative 2 ATP.
The seventh step involves the conversion of 1,3-Bisphosphoglycerate into 3-Phosphoglycerate,
using the enzyme Phosphoglycerate Kinase and the co-factor Magnesium.
This process involves the phosphorylation of ADP into ATP, taking the phosphate group
from 1,3-Bisphosphoglycerate and giving it to the ADP.
This reaction is also reversible.
This step occurs twice, once for each 1,3-Bisphosphoglycerate.
This step creates an ATP, since it occurs twice, 2 ATP are produced.
We now have a net total of 2 NADH, and zero ATP, as these 2 ATP make up for the 2 ATP
used up earlier in glycolysis.
The eighth step involves the conversion of 3-Phosphoglycerate into 2-Phosphoglycerate
using the enzyme Phosphoglycerate Mutase.
This process involves shifting the phosphate group from one carbon to another.
This reaction is also reversible.
The ninth step involves the conversion of 2-Phosphoglycerate into Phosphoenol Pyruvate
(or PEP for short) using the enzyme Enolase and the cofactor Magnesium.
This process involves releasing a water molecule each time.
This reaction is also reversible.
The tenth and final step in glycolysis involves the dephosphorylation of Phosphoenol Pyruvate
into a final 3 carbon pyruvate molecule using the enzyme Pyruvate Kinase and the co-factor
Magnesium.
This process involves a Hydrogen molecule and taking a phosphate group from Phosphoenol
Pyruvate and attaching it to ADP to form ATP.
This step creates an ATP, since it occurs twice, 2 ATP are produced for one molecule
of glucose.
This takes our net total for one molecule of glucose, to a total of 2 NADH and 2 ATP
at the end of Glycolysis.
The overall reaction of glycolysis is: One Glucose molecule, 2 NAD+’s, 2 ADP’s
and 2 inorganic phosphates Gives us 2 pyruvate molecules, 2 NADH’s,
2 Hydrogens, 2 ATP’s and 2 water molecules.
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