Unit 3

Cellular Energetics Importance:
- 12-16% of AP exam questions cover this topic.

Activation Energy: Energy barrier that must be overcome for reactions to occur, preventing uncontrolled energy release.
- Can be overcome by:
- Inputting energy into the reaction
- Using a catalyst
Catalysts:
- Reduce activation energy.
- Increase reaction rate without changing themselves.
Enzymes: Biological catalysts that change the conformation of interacting molecules.
- Active Site: Portion of enzyme that interacts with the substrate.
- Substrate: Molecule that binds to enzyme for a reaction.
Environmental Effects on Enzymes:
- Heat: Increases reaction speed due to increased molecular movement but can denature proteins if too high.
- pH: Alterations can affect hydrogen bond formation and enzyme efficiency, reversible if conditions normalize.
- Concentration: More substrate or enzyme increases the reaction rate due to higher contact chances.
Inhibitors: Affect enzyme activity.
- Competitive Inhibitors: Compete for active site, blocking substrate binding.
- Non-competitive Inhibitors: Bind elsewhere, altering enzyme conformation and efficiency.

Bioenergetics: Study of energy transformation in organisms.
Metabolism: All energy transformations, including photosynthesis, respiration, and movement.
- Energy input > loss to maintain system function.
Energy Storage: In forms of molecules with chemical bonds (e.g. sugars, fats).
- Anabolism: Storing energy in chemical bonds (building up).
- Catabolism: Releasing energy by breaking bonds (breaking down).
- ATP is the main energy currency for cells.
- ATP → ADP + AMP during energy release mechanisms (e.g., fermentation, respiration).
ATP Breakdown: Linked to most cellular processes, streamlining energy utilization.

Photosynthesis Reaction: Converts light energy into glucose:
$6CO2 + 6H2O + Light ightarrow C6H{12}O6 + 6O2$
Evolution: Initiated in cyanobacteria, leading to Earth's oxygenation.
Phases of Photosynthesis:
- Photolysis (Light-dependent Reaction):
- Location: Thylakoid membranes.
- Absorption: Light energy absorbed by chlorophyll, producing ATP and NADPH (electron carrier).
- Water Use: Splits water, releasing oxygen.
- Calvin Cycle (Light-independent Reaction):
- Location: Stroma of chloroplasts.
- Carbon Fixation: Uses ATP and NADPH to convert CO₂ into 3-carbon sugars, joining to form glucose.
- Importance: Provides energy and organic carbon for cellular processes.
- Removes carbon from atmosphere.
Light-dependent Reaction Mechanism:
- Photosystems: Harvest light energy (PSI and PSII).
- PSII boosts electrons using light energy, transfers them, culminating in oxygen release.
- Electron Transport Chain (ETC): Utilizes energy to create H+ gradients for ATP production via chemiosmosis.
- Photophosphorylation: Process of ADP to ATP formation using light energy.

Respiration & Fermentation: Breakdown of macromolecules (sugars, fats) to generate ATP.
Eukaryotic Cellular Respiration: Breaks down glucose into CO₂ and H₂O to produce ATP.
Steps:
1. Glycolysis: Glucose (6-C) → 2 Pyruvate (C3) + 2 ATP + 2 NADH (occurs in cytosol).
2. Pyruvate Oxidation: Converts pyruvate into acetyl CoA with NAD+ → NADH (occurs in mitochondria).
3. Krebs Cycle: Acetyl CoA → Produces NADH, FADH₂, and ATP or GTP + CO₂ (occurs in mitochondrial matrix).
4. Oxidative Phosphorylation: Utilizes NADH and FADH₂ through ETC in inner mitochondrial membrane to pump H+ and generate ATP (via chemiosmosis), where final electron acceptor is O₂, producing water.
- In Prokaryotes: Glycolysis and pyruvate oxidation occur in cytosol; oxidative phosphorylation in cell membrane.
- Fermentation: In absence of O₂, pyruvate converts to organic molecules, regenerating NAD+ from NADH, allowing glycolysis to continue.

Mechanisms in life forms to maintain ATP production, such as switching to fermentation when O₂ is lacking.
Chlorophyll Diversity: Plants possess varied chlorophyll types for harnessing different light wavelengths, aiding survival and adaptation to environments.