Photosynthesis
and Respiration
Photosynthesis:
REVIEW
Previously, we learned that photosynthesis
takes place in the chloroplasts
In the ‘light reactions’, solar energy is captured
by photosystems on the thylakoid membrane and
used to attach phosphate groups to
energy-carrying molecules like ATP.
Photosynthesis:
REVIEW
This completes the equation for photosynthesis:
6 CO2 + 6 H20
C6H12O6 + 6 O2
In the CALVIN CYCLE, the ATP and NADPH
made in the light reactions are used to power
the assembly of sugars in the stroma, the fluidfilled interior of the chloroplasts.
Photosynthesis:
REVIEW
This completes the equation for photosynthesis:
6 CO2 + 6 H20
C6H12O6 + 6 O2
So now we have energy stored in the form of
sugars. Very nice, but what if plants (or, for that
matter, people) want to release that energy?
THEY MUST USE A DIFFERENT PATH…..!
CELLULAR RESPIRATION !
FIRST, WE REVERSE THE EQUATION:
6 CO2 + 6 H20
C6H12O6 + 6 O2
Next, we’ll need another organelle to do these
reactions in! Not chloroplasts this time, but
instead another organelle with its own DNA….
Mitochondria:
Mitochondria:
• have complex folded inner membranes
(cristae), increasing their surface area
Mitochondria:
• have complex folded inner membranes
(cristae), increasing their surface area
• have a fluid-filled interior (the matrix)
Mitochondria:
• have complex folded inner membranes
(cristae), increasing their surface area
• have a fluid-filled interior (the matrix)
• act like combustion chambers in an engine,
a ‘safe’ place to ‘burn’ fuel with oxygen
A Combustion Chamber?
A Combustion Chamber?
LET’S COMPARE!
A gasoline engine . . . .
and a mitochondria,
in cross-section.
Before combustion can
occur, however, we have to
get some “fuel” !
For that, we will need to
break down glucose
(or other sugars) OUTSIDE
the mitochondria, in a
process called . . . .
• is the breakdown of glucose (or
other sugars)
• is the breakdown of glucose (or
other sugars)
• requires an activation energy
• is the breakdown of glucose (or
other sugars)
• requires an activation energy
• occurs in the cytoplasm
Polymers of glucose, like starch, are first
broken into individual sugars through
hydrolysis
The single sugars produced contain
stored energy in their chemical bonds,
but they are still too big to pass
through the mitochondrial membrane.
ATP provides the initial activation
energy. The 6-carbon sugar will
be broken down in a series of steps
that do not involve oxygen.
C3H3O3
There will be a net gain of 2 ATP. The
final products of glycolysis are two
3-carbon molecules of pyruvate
(pyruvic acid)
C3H3O3
Pyruvate is small enough to
be easily transported through the
mitochondrial membrane, where a
new series of chemical reactions
take place. . .
The
Krebs
Cycle
The Krebs Cycle:
• takes place in the matrix
The Krebs Cycle:
• takes place in the matrix
. . Co-enzyme A is added
C3H3O3
Pyruvate enters
the matrix. . .
“acetyl CoA”
. . .a waste product ,
CO2 , is released . . .
• begins by converting each of the 3-carbon
pyruvates into a special complex called
acetyl CoA
The Krebs Cycle:
Acetyl CoA
Acetyl CoA
begins the cycle
The Krebs Cycle:
Acetyl CoA
begins the cycle
CO2
CO2
As the cycle
proceeds, CO2
are removed
The Krebs Cycle:
There is a net
gain in ATP,
and . . .
eCO2
eATP
CO2
. . .an electron
transport chain
is charged!
Electron Transport:
• takes place in the cristae
Electron Transport:
• takes place in the cristae
Electron Transport:
Electron Transport:
• takes place in the cristae
•
will draw in H+, creating a high
concentration which can be used to
drive a proton pump
Proton Pumping:
• powers the enzyme, ATP synthase
Proton Pumping:
• powers the enzyme, ATP synthase
…which is then used to make ATP
DOING THE MATH:
Glycolysis, in cytoplasm, no O2
4 ATP
DOING THE MATH:
Glycolysis, in cytoplasm, no O2
4 ATP
Krebs Cycle, in matrix, no O2
2 ATP
DOING THE MATH:
Glycolysis, in cytoplasm, no O2
4 ATP
Krebs Cycle, in matrix, no O2
2 ATP
Electron transport chains, with O2
32 ATP
DOING THE MATH:
Glycolysis, in cytoplasm, no O2
4 ATP
Krebs Cycle, in matrix, no O2
2 ATP
Electron transport chains, with O2
32 ATP
TOTAL:
38 ATP
DOING THE MATH:
Glycolysis, in cytoplasm, no O2
4 ATP*
Krebs Cycle, in matrix, no O2
2 ATP
Electron transport chains, with O2
32 ATP
TOTAL:
38 ATP
(-2 ATP)*
---------------
(*minus 2 ATP used for activation energy in glycolysis)
DOING THE MATH:
Glycolysis, in cytoplasm, no O2
4 ATP*
Krebs Cycle, in matrix, no O2
2 ATP
Electron transport chains, with O2
32 ATP
TOTAL:
NET YIELD, 1 glucose:
38 ATP
(-2 ATP)*
--------------36 net ATP
(*minus 2 ATP used for activation energy in glycolysis)