Biology

Bioenergetics and Photosynthesis

Definition of Photosynthesis
- Photo means light; synthesis means putting together.
- The process converts solar energy into chemical energy, specifically in the form of glucose.
- Utilizes sunlight to convert water and carbon dioxide into oxygen and high-energy sugars.
- Chemical Reaction:
- 6 CO2 + 6 H2O + light
  ightarrow C6H{12}O6 + 6 O2
Processes in Photosynthesis
1. Light Dependent Reactions
- Utilizes light energy to produce ATP and NADPH; oxygen is a byproduct.
1. Light Independent Reactions (Calvin Cycle)
- Utilizes ATP and NADPH to convert carbon dioxide into glucose.
Sites of Photosynthesis in Plants
- Leaves: Major site of photosynthesis
- Mesophyll: The inner, photosynthetic tissue of a leaf located between the upper and lower epidermis.
- Stomata: Openings on the leaf surface for gas exchange (where CO₂ enters).

Plant Pigments

Chlorophyll:
- Primary pigment responsible for the green color of leaves; essential for photosynthesis.
Carotenoids:
- Contribute to yellow, orange, and red colors in plants; also involved in photosynthesis.
Anthocyanins:
- Produce red and purple colors; play a role in photosynthesis.
Betalains:
- Red or yellow pigments that complement chlorophylls and carotenoids in function.
Xanthophylls:
- Yellow pigments that are part of the carotenoid group.

Energy Molecules

Adenosine Diphosphate (ADP):
- A molecule that stores some energy and can be converted into ATP (stores energy).
Adenosine Triphosphate (ATP):
- Main energy "currency" of cells used to power cellular activities (uses energy).
- Formed from ADP when a phosphate group is added.
Nicotinamide Adenine Dinucleotide Phosphate (NADP):
- An electron carrier that carries high-energy electrons during photosynthesis (empty carrier).
Nicotinamide Adenine Dinucleotide Phosphate, reduced form (NADPH):
- Carries high-energy electrons and hydrogen to help form sugar in the Calvin Cycle (full carrier).

Light Dependent Reactions

Requirements:
- Light must be present.
Location:
- Occurs in the grana of chloroplasts.
Process:
- Produces oxygen gas; converts ADP and NADP+ into ATP and NADPH.
- Takes place within thylakoid membranes.
- Converts light energy into chemical energy.
Step-by-Step Process:
1. Photoactivation:
- Sunlight excites chlorophyll electrons, causing them to jump to higher energy states.
- When returning to ground state, energy is released as heat and photons (fluorescence).
- Reaction:
  - ext{Chl (ground state)} + ext{light energy}
    ightarrow ext{Chl (excited)} + 2e^-
1. Photophosphorylation (ATP Synthesis):
- The excited electrons are used to bind a phosphate to ADP, forming ATP.
- Reaction:
  - ADP + P
    ightarrow ATP
1. Photolysis:
- Water is split into H+ ions and oxygen.
- Reaction:
  - 2H2 O ightarrow 4H^+ + O2 + 4e^-
1. NADP Capture:
- NADP captures H+ ions to form NADPH which provides energy for the Calvin Cycle.
- Reaction:
  - NADP^+ + 2e^- + 2H^+
    ightarrow NADPH + H^-
1. Water Splits formula:
- Equation #1: H_2 O
  ightarrow H^+ + OH^-
- Equation #2: H^+ + NADP
  ightarrow NADPH
- Equation #3: OH^-
  ightarrow H2 O + O2

Calvin Cycle

Purpose:
- Uses ATP and NADPH from light dependent reactions to produce glucose.
Location:
- Takes place in the stroma of chloroplasts.
Key Terms:
- Ribulose bisphosphate (RuBP): 5-carbon molecule that captures CO₂ starting the Calvin Cycle.
- Phosphoglycerate: 3-carbon compound formed when CO₂ combines with RuBP.
- Biphosphoglycerate: High-energy 3-carbon molecule produced from phosphoglycerate using ATP.
- Phosphoglyceraldehyde (PGAL): 3-carbon sugar made in Calvin Cycle; can be converted to glucose.
- Ribulose carboxylase (RuBisCO): Enzyme that attaches CO₂ to RuBP.
Phases of the Calvin Cycle:
1. Carbon Fixation:
- Incorporation of CO₂ with RuBP, forming a six-carbon intermediate that splits into two 3-phosphoglycerate molecules.
- Catalyzed by RuBisCO, which is the most abundant protein in chloroplasts.
1. Reduction:
- Each 3-phosphoglycerate molecule receives a phosphate from ATP, becoming 1,3-bisphosphoglycerate.
- Electrons from NADPH reduce it to G3P (PGAL).
1. Regeneration of RuBP:
- Five molecules of G3P are rearranged to form three molecules of RuBP, using three additional ATP molecules.
- RuBP is now ready to accept CO₂ again.

Cellular Respiration

Definition:
- How animal cells create energy using nutrients and oxygen, producing ATP and carbon dioxide.
Overall Reaction:
- C6H{12}O6 + 6O2
  ightarrow 6CO2 + 6H2O + ext{Energy}
- Alternate pathways:
- C6H{12}O6 ightarrow 2CO2 + ext{Ethanol} + ext{Energy}
- C6H{12}O_6
  ightarrow 2 ext{Lactic Acid} + ext{Energy}
Unlocking of Terms:
- Pyruvate: A 3-carbon molecule produced at the end of glycolysis.
- Glyceraldehyde 3-phosphate (G3P): A product formed when CO₂ combines with RuBP.
- Biphosphoglycerate: A 3-carbon sugar formed in photosynthesis and glycolysis.
- Nicotinamide adenine dinucleotide (NAD+): An electron carrier that helps release/store energy in cells.
- Flavin adenine dinucleotide (FAD+): An electron carrier involved in cellular respiration.
- Acetyl-CoA: Central molecule linking breakdown of carbohydrates, fats, proteins to energy production.
Aerobic Respiration:
- Energy release through food breakdown in the presence of oxygen.
- Overall Equation:
- C6H{12}O6 + 6O2
  ightarrow 6CO2 + 6H2O + ext{Energy}

Phases of Aerobic Respiration

Glycolysis:
- Process of splitting glucose (6-C) into two 3-C molecules (G3P). Occurs in the cytoplasm.
- Energy phases:
  - Energy Investment Phase: Initial ATP expenditure.
  - Energy Payoff Phase: ATP production and NADH formation.
- Reaction:
  - C6H{12}O_6 + 2ATP + 2NAD^+
    ightarrow 2ATP + 2NADH + 2 ext{Pyruvate}
Krebs Cycle (Citric Acid Cycle):
- Acetyl-CoA is broken down into CO₂ in energy-extracting reactions. Takes place in mitochondrial matrix.
- Citric Acid Formation: Pyruvate converted into acetyl-coenzyme A; forms NADH.
- Energy Extraction: Electrons captured by NAD+ and FAD; small energy production occurs.
- Total Products:
  - ext{6CO}2, 8NADH, 2FADH2, 2 ext{ATP}
  - Reaction:
  - ext{Pyruvic Acid} + ADP + 4NAD^+ + FAD
    ightarrow 3CO2 + 4NADH + FADH2 + ATP
Electron Transport Chain:
- Consists of a series of enzyme-controlled reactions; converts energy from electrons to ATP.
- NADH and FADH2 deliver high-energy electrons from glycolysis and Krebs cycle.
- Hydrogen ions flow through ATP synthase channel, driving ATP synthesis, producing about 32 ATP.
- Overall Reaction:
  - 6O2 + 8NADH + 4FADH2 + 32ADP
    ightarrow 8NAD^+ + 4FAD + 32 ATP + 12H_2O

Net Energy Production from Aerobic Respiration

Glycolysis: 2 ATP
Krebs Cycle: 2 ATP

- Electron Transport: 32 ATP

Total Energy: 36 ATP

Anaerobic Respiration

Definition: Energy release without oxygen.
Overall Reactions:
- C6H{12}O6 ightarrow 2C O2 + ext{Ethanol} + ext{Energy}
- C6H{12}O_6
  ightarrow 2 ext{Lactic Acid} + ext{Energy}
Dependent on Oxygen: Cells can produce ATP through fermentation in anaerobic conditions.
- Types of Fermentation:
1. Alcoholic Fermentation:
- Converts glucose into ethanol, CO₂, and ATP (e.g., yeast).
1. Lactic Acid Fermentation:
- Converts glucose into lactic acid and ATP, occurring during intense exercise in animal cells.

Examples of Fermentation Products

Aspergillus: Yeast; used in fermentation processes.
Lactobacillus: Bacteria; utilized in dairy fermentation (e.g., yogurt production).
Glucose: Common substrate for fermentation.
Pyruvate: Intermediate in both fermentation and respiration.
Saccharomyces: Yeast species; important in beer and wine production.
Product Outcomes:
- Lactic Acid: Result of fermentation in muscle cells.
- Ethanol & CO₂: Produced during alcoholic fermentation (e.g., in beer and wine).
- Food Products:
- Soy Sauce: Fermented product involving multiple fermentation types.
- Cheese, Yogurt: Produced via lactic acid fermentation.
- Beer: Product of yeast fermentation.
- Wine: Result of fermenting grapes.
- Bread: Involves CO₂ production during fermentation for leavening.