THE CALVIN CYCLE:
CONVERTING CO2 TO SUGARS
How Life Obtains & Harvests
Chemical Energy
Part 2
6 CO 2
Calvin
Cycle
ATP and NADPH power sugar
synthesis in the Calvin cycle
– The Calvin cycle
CO 2
ATP
NADPH
Input
• occurs in the cytoplasm of
photosynthetic bacteria or the
chloroplast’s stroma
• consists of carbon fixation, reduction,
release of G3P, and regeneration of
the 5-C starting molecule
CALVIN
CYCLE
Output:
G3P
6 H2O
To make one glucose requires
6
12
PGA
12
10 G3P
6
12
12
12
6
12
G3P
2 G3P
• 18 ATP + 12
NADPH
• 1 NADPH is “equal”
to 3 ATP
• Therefore at least 54
ATPs are needed to
make one glucose
H2O
Chloroplast
CO 2
Light
NADP +
ADP
+P
LIGHT
CALVIN
REACTIONS
CYCLE
(on membrane)
ATP (in stroma)
El
ec
tro
nsNADPH
O
Sugar
glucose
(or other organiccompounds)
PHOTOSYNTHESIS REVIEWED
• Photosynthesis uses light energy to make
food molecules
H2O
Cellular respiration occurs in three main stages
• Stage 1: Glycolysis
• Stage 2: Krebs (Citric Acid) Cycle
• Stage 3: Oxidative Phosphorylation
CO 2
Chloroplast
Light
NADP +
ADP
+ P
Photosystem II
Thylakoid
membranes
The Light Reactions occur
on membranes in both
prokaryotic & eukaryotic
cells
Electron
transport
chains
Photosystem I
RUBP
CALVIN
CYCLE 3-PGA
(in stroma)
Stroma
ATP
NADPH
STAGES OF AEROBIC
CELLULAR RESPIRATION
G3P
Cellular
respiration
Cellulose
O2
LIGHT REACTIONS
Sugars
Starch
Other organic
compounds
CALVIN CYCLE
1
Stage 1: Glycolysis
– Occurs in the cytoplasm of both prokaryotic
& eukaryotic cells
– Breaks down glucose into pyruvate,
producing a small amount of ATP
– Already studied this in Anerobic
Respiration
– Similarity between parts of glycolysis and
the Calvin Cycle of photosynthesis
Stage 2: The Krebs (citric acid )
Cycle
– Takes place in the cytoplasm of prokaryotes or
in the matrix (fluid portion) of the mitochondria
– Completes the breakdown of glucose,
producing a small amount of ATP
– Supplies the third stage of cellular respiration
with electrons
• G3P, PGA, soluble enzymes
Stage 3: Oxidative
phosphorylation
– Occurs on membranes in the mitochondria or
on folded membranes in prokaryotic cells
– Uses the energy released by “falling” electrons
to pump H+ across a membrane
– Harnesses the energy of the H+ gradient
through chemiosmosis, producing ATP
An overview of Aerobic Cellular
Respiration
NADH
High-energy
electrons
carried by
NADH
GLYCOLYSIS
Glucose
Pyruvate
KREBS
CYCLE
CO 2
ATP
– In the first phase of glycolysis
• ATP is used to energize a glucose
molecule, which is then split in
two
– In the second phase of glycolysis
• ATP, NADH, and pyruvate are
formed
– Pyruvate, still rich in potential energy, is
chemically groomed for the citric acid cycle
Electron Transport
and Chemiosmosis
Mitochondrion
Cytoplasm
Substrate-level
phosphorylation
Glycolysis
NADH FADH2
and
ATP
ATP
2 CO 2
Substrate-level
phosphorylation
Oxidative
phosphorylation
The Krebs cycle
• The Krebs cycle completes the oxidation of
organic fuel, generating many NADH and
FADH2 molecules
Pyruvate
Acetyl CoA
CoA
CO 2
KREBS
CYCLE
2 CO 2
3 NAD+
FADH2
3 NADH + 3 H +
FAD
ATP
ADP +
P
2
The preliminary step & the Krebs
cycle produces 1 ATP and 4 NADHs,
and 1 FADH per pyruvate
For each turn of the cycle
–Two CO2 molecules are
released
–The energy yield is one ATP,
three NADH, and one FADH2
– How many ATP per glucose?
– How many ATPs per glucose from glycolysis?
– Total ATPs per glucose from glycolysis plus
Krebs?
– What was the minimum number of ATPs
needed to make one glucose in photosynthesis?
ATPs = 54
Where is the rest of the potential energy?
Most ATP production occurs
by oxidative phosphorylation
– In chemiosmosis, the H+ diffuses back
through the inner membrane through ATP
synthase complexes
•
Driving the synthesis of ATP
Electrons from NADH and FADH2
• Travel down the electron transport chain to oxygen,
which picks up H+ to form water
H+
Intermembrane
space
– Energy released by the redox reactions
.
H+
Electron
carrier
FADH 2
Electron
flow
NADH
Mitochondrial
matrix
H+
H+
H+
Inner
mitochondrial
membrane
• Is used to pump H + into the space between the
mitochondrial membranes
H+
H+
Protein
complex
H+
H+
ATP
synthase
FAD
NAD +
H+
1 O
+ 2 H+
2 2
H+
H+
ADP
H2 O
+
P
H+
ATP
Chemiosmosis
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
Figure 6.10
Review: Each molecule of glucose
yields many molecules of ATP
• Glycolysis, Citric Acid Cycle, & Oxidative
(or 2 FADH )
phosphorylation, using electron transport and
chemiosmosis
• Produces up to 38 ATP molecules for each glucose
molecule that enters cellular respiration
2
Cytoplasm
NADH
Electron shuttle
across membrane
Maximum per glucose: + 2 ATP
Figure 6.12
by substratelevel
phosphorylation
When they are converted to molecules that enter
glycolysis or the citric acid cycle
Food, such as
peanuts
Mitochondrion
Carbohydrates
Glucose
GLYCOLYSIS 2 Pyruvate
Carbohydrates, fats, and proteins
can all fuel cellular respiration
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
CITRIC ACID
CYCLE
+ about 34 ATP
+ 2 ATP
by substrate-level
phosphorylation
by oxidative
phosphorylation
About
38 ATP
Fats
Sugars
Glycerol
Proteins
Fatty acids
Amino acids
Amino
groups
Glucose
G3P
Pyruvate
GLYCOLYSIS
Acetyl
CoA
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
ATP
3
The fuel for respiration ultimately
comes from photosynthesis
• All organisms
– Can harvest energy from organic molecules
•Producers, but not consumers
–Can also make these molecules
from inorganic sources by the
process of photosynthesis
4