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Cellular Respiration
Cellular Respiration is
how we derive energy
from the food we eat
(specifically glucose)
Overview
Sugar combines with oxygen to produce carbon dioxide plus water
and energy (in the form of ATP)
FIRST, we need to know why we want ATPs
ATP is needed to use energy. Here’s how it works:
Adenosine triphosphate is made up of a nitrogenous base
called adenine with a sugar called ribose and three
phosphate groups attached to it (do not like to be in a row like
that)
ATP shoots off one of the phosphate groups off the end. Now
it’s ADP (adenosine diphosphate) and when this happens
energy is released.
Through cellular respiration, one molecule of glucose can
yield a bit of heat and 38 molecules of ATP.
3 stages of Cellular Respiration
1. Glycolysis
2. Kreb’s Cycle
3. Electron Transport Chain
Stage 1: Glycolysis
Glycolysis Overview
Breaks up of glucose’s 6 carbon ring into two 3-carbon
molecules called pyruvic acids or pyruvate molecules
FUN FACT:
GLYCOLYSIS DOES NOT NEED OXYGEN.
This is called an anaerobic process. If there is not oxygen
for the next step, it goes to fermentation.
Fun facts: Fermenation
Fermentation uses more NAD+ and creates interesting
byproducts:
Yeast – ethyl alcohol
Our muscles don’t make alcohol, they make lactic acid which
is what makes you feel sore after a workout (the muscles ran
out of oxygen and kick into anaerobic respiration)
Stage 2: Kreb’s Cycle
Steps of Kreb’s Cycle
1. One of the pyruvates is oxidized (means it’s combined
with oxygen). One of the carbons off the three-carbon
chain bonds with an oxygen and leaves the cell as CO2
What’s left? Two carbon compound called acetyl coenzyme A
2. Then 2 NAD+ comes along and each pick up a hydrogen
and becomes 2 NADHs (to use later)
(remember: glycolysis made 2 NADHs and now there are 2
more, which means we now have 4)
3. Enzymes bring together a phosphate with ADP to create
another ATP molecule for each pyruvate.
(remember, we had 2 ATPs from glycolysis and now we have
2 more, we now have 4)
4. Enzymes also help join the acetyl CoA and a 4 carbon
molecule (called oxaloacetic acid) to form a 6-carbon
molecule called citric acid
5. The citric acid is oxidized (oxygen comes in and bonds with
a bunch of carbons.
The carbons left over in the form of CO2 which are pushed
out of the cell and out of our mouths, etc (that’s why we
breathe out CO2!)
This gets us back to oxaloacetic acid (that is why it’s called a
6. Each pyruvate makes 3 NADHs and 1 FADH2. Since there
are two pyruvates, that means 6 NADHs and 2 FADH2s
Let’s see what we have so far:
From the beginning of cellular respiration, we now have:
1.
2.
3.
4.
5.
10 NADHs (4 from glycolysis and 6 from Kreb’s Cycle)
2 FADH2s (From the Kreb’s Cycle)
4 ATPs (2 from Glycolysis and 2 from Kreb’s Cycle)
Carbon Dioxide byproducts
Water byproducts
Stage 3: Electron Transport Chain
All of the electrons in the NADHs and FADH2s are going to
provide the energy that will work as a pump along a chain of
channel proteins across the inner membrane of the
mitochondria.
1.These proteins swap the electrons to send hydrogen
protons from inside the center of the mitochondria. So they go
from the inner membrane to the outer compartment of the
mitochondria.
2. Once they are out, the protons want to get back in because
there are too many protons in the outer compartment and
nature always wants to seek a balance
3. So they are allowed back in through a protein called ATP
synthase.
The energy of this proton drives a spinning mechanism that
puts together some ADP and phosphates together to form
ATPs.
That makes a lot of ATPs!
spins
Final count:
38 ATPs!
Now those ATPs can be used to
make energy