BIOL 111 Chapter 10

End Exam 2 Content

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Fermentation

Basically Glycolysis plus regeneration of NAD⁺ by dumping extra H atoms onto Pyruvate to produce (Ethanol + CO₂ or Lactate) + 2 ATP

Occurs in:

• Bacteria
• Fungi
• yeast

≈ 2% efficiency, but still provides energy in anaerobic environment

Photosynthesis

Review of Respiration

• Respiration is Matter → Energy through redox rxns.
• Energy is lost to heat
• Follow the Carbons and electrons
• Carbon cycle
• Electron transport chain

6H₂O + 6CO₂ + Energy (sun) → 6O₂ + C₆H₁₂O₆

Stable, small molecules are converted into larger, more unstable molecules (kinetic energy to potential energy)

Takes place in Chloroplasts (inside thylakoid membrane system)

Nature of light

• λ 380-750nm
• Particle (photon) and wave-like properties
• ${\text{Energy in light}}={\tfrac {1}{\lambda }}$ (shorter wavelengths have more energy)

Pigments

Chlorophyll molecule

Selectively absorb certain wavelengths of light:

• Chlorophyll a — 440nm, 670nm (Indigo and Red)
• Chlorophyll b — 460nm, 640 (Blue and Orange)
• Carotenoids — 450-500nm (Violet to Blue)

That's why plants are green

Chlorphyll a and b are very similar, except a has Methyl group (CH₃) and b has Carbonyl group (CHO)

What happens to absorbed light?

Photon hits the pigment, an electron is excited, then falls

Dissipation:

• Re-emit light: fluorescence
• Emit heat
• Resonance transfer; Electron is Transferred to another pigment (useful)

Light Reactions

Photosystems: Electron Transport Chains

In thylakoid membrane; forms 1 ATP and 1 NADPH

(electrons handled one at a time; this process happens twice for each water molecule)

Photosystem II (PSII): Linear Electron Flow

1. outer pigments absorb violet (high energy), inner pigments absorb red (low energy)
2. electrons in pigments start "vibrating"
3. vibrations "bump" an electron from P680 into the Reaction center complex
4. P680 rips electron from water to replace the one that it lost
5. electron acceptor takes on that electron and ...

Photosystem I (PSI): Linear Electron Flow (cont'd)

1. electron in PSII acceptor "falls down" a transport chain into the cytochrome complex
2. cytochrome complex uses electron to pump H⁺ into thylakoid space
3. electron then transferred into the P700 in PSI
4. "vibrations" from pigments in PSI "bump" electron in P700 into the Reaction center complex
5. acceptor Ferredoxin (Fd) transfers that electron to NADP⁺ to form NADPH

NADPH and ATP go to the Calvin cycle to form Glucose

Photosystem I: Cyclic Electron Flow

1. Fd from PSI can go back to cyctochrome complex instead of to NADPH and donates electron to further pump H⁺ ions into thylakoid space.

Summary

1.5 ATP produced per 4H⁺ pumped by e^– transport. This is less efficient than cellular respiration (2 ATP for FADH₂ and 3 ATP for NADH)

Thursday, October 14, 2010

(Melvin) Calvin Cycle

The Calvin Cycle

• Something is regenerated.
• Carbon goes in, and Carbon comes out.
• It is an anabolic reaction:
  • Look for production of 1 BIOL 111 Chapter 9#G3P molecule (same thing as in glycolysis)
  • 1 G3P produced in 3 turns of cycle

Phase 1: Carbon Fixation

(3×) CO₂ + 5-C RuBP → very unstable 6-C → quickly broken into 2 3-C

Entire CO₂ molecule attached to 5-C RuBP by enzyme Rubisco .

Phase 2: Reduction

• 3× Input of 2 ATP from light reactions (total of 6 ATP)
• 3× Input of 4 e^– from 2 NADPH (total of 12 e^–)
• Total Output of 1 G3P

Phase 3: Regeneration

RuBP regenerated:

• 5 3-C rearranged to form 3 5-C RuBP
• 3× 1 ATP required

Summary

• 1 cycle requires 3 ATP and 2 NADPH
• 1 G3P (3 cycles) requires 9 ATP and 6 NADPH
• 1 Glucose (2 G3P; 6 cycles) requires 18 ATP and 12 NADPH

Problem: Photorespiration

An evolutionary relic that causes problems:

• Ancient atmosphere: A lot of CO₂ with little O₂
• Rubisco binds to CO₂ and O₂ (depending on which is more abundant ):
  • RuBP + CO₂ → 2 3-C
  • RuBP + O₂ → 1 3-C + 1 2-C ...problem!

Presence of 2-C causes a series of reactions:

• releases CO₂ (no longer fixed)
• requires ATP in the process
• decreases photosynthesis output by 25-50%

Solution: Adaptations

C4 Plants

Grasses, corn, plants in hot, but not dry climates

CO₂ temporarily fixed to a PEP (3C) molecule to form oxaloacetate. This is converted to Malate (4C) and the CO₂ is released, which goes to the Calvin Cycle. Remaining compound is Pyruvate, which is converted back to PEP through use of ATP.

CAM Plants

Succulents, Cacti, Pineapple, etc.

Stomata open at night only, fixing as much CO₂ as possible into organic acids. During day, organic acids used, and calvin cycle continues as normal.