MIT Department of Biology
7.014 Introductory Biology, Spring 2005
Recitation Section 5
February 16-17, 2005
Biochemistry—Photosynthesis and Respiration
A. Photosynthesis background
1. Why do we consider O2 a booster of evolution?
2. Why was it advantageous for a cell to develop photosynthesis?
3. Photosynethesis has two phases—light and dark. What does each phase accomplish?
B. Photosynthesis—light reactions
1. Below are the schematics for cyclic and noncyclic photophosphorylation. Identify each schematic and
discuss the order of steps in each process.
H
+
ATP
H
+
ADP+ Pi
Electron acceptor
Electron acceptor
A2
ATP
synthase
Acceptor 3
PS2
PS1
H
+
H
+
H
+
H
H
+
+
H
H
+
+
H H+
+
H
+
Thylakoid
membrane
Stroma
NADPH NADP+
H
+
ATP
H
+
ADP+ Pi
Electron acceptor
Electron acceptor
A2
ATP
synthase
A2’
Acceptor 3
PS2
2e
+
H2O 2H
1⁄2 (O2)
PS1
H
+
H
+
H
H
+
+
H
H
+
+
H H+
+
H
+
Thylakoid
membrane
Stroma
2. What are the main differences between the two processes?
3. What is the ATP made in photosynthesis used for?
4. In class we learned that cyclic photophosphorylation produces S as waste product. Yet we do not see S
created anywhere in the schematic above. Where and how is S released?
5. Why do cells need to make glucose out of ATP? Why not just use the ATP produced in photosynthesis?
C. Aerobic Respiration – Oxidative Phosphorylation
Dark reactions of photosynthesis are expensive, and glycolysis only produces 2 molecules of ATP. This is very inefficient. 1. What process developed to derive energy from glucose more efficiently? Why was it not possible to develop this process before noncyclic photophosphorylation arose?
2. Why was it evolutionarily advantageous for a cell to develop aerobic respiration?
Below is a schematic of the mitochondrial membrane and surrounding compartments.
Mitochondrion
Inner
Compartment
H+
H+
Inner
Membrane
ATP Synthetase
- NADH
e
H+
H+
P + ADP
H+
H+
ATP
Channel
ATP
2H ++ 1/2 O
Electron
Transport
Chain
Molecules
H+
ATP
H+
H+
Outer Membrane
H+
H+
NAD +
Proton
Pump
H+
H+
2
H2O
H+
H+
H+
H+
H+
Outer
Compartment
Figure by MIT OCW.
3. Using the schematic, explain why an NADH is “worth” 3 ATPs.
On the way to complete oxidation, each pyruvate molecule generates 4 NADH molecules, one FADH2
molecule, and one ATP molecule. FADH2 can participate in the proton gradient mechanism as well,
but only generates 2 molecules of ATP for each molecule of FADH2.
4. In lecture it was said that 36 molecules of ATP total are derived from a glucose molecule via
glycolysis followed by aerobic respiration. Describe where these ATP molecules come from.