Unit 3

Importance of Energy in Biological Systems

• Energy Needs:

  • Synthesis (e.g., building biomolecules)

  • Reproduction

  • Movement

  • Active transport

  • Temperature regulation

Metabolism

• Definition of Metabolism: The totality of an organism

  • Observation: Smaller organisms generally have higher metabolic rates.

Pathways of Metabolism

Fueling the Body

• High Energy Organic Molecules: From food sources like carbohydrates, lipids, proteins, and nucleic acids.

• Digestion Process:

  • Involves catabolism to break down food into usable forms.

• Adenosine Triphosphate (ATP):

  • Definition: A modified nucleotide composed of adenine, ribose, and three inorganic phosphate groups.

  • Formation of ATP: Adding phosphates is an endergonic reaction, requiring energy.

Energy Currency of Cells

• ATP: Needed as the short-term energy carrier for cellular processes.

Enzymes and Catalysts

• Definition of Catalyst: A substance that changes the rate of a reaction without being altered in the process.

• Enzyme as Biological Catalyst:

  • Speeds up metabolic reactions by lowering activation energy (the energy required to start a reaction).

  • Note: Both Catabolic and Anabolic reactions can occur but very slowly without enzymes.

Enzyme Specificity

• Substrate and Active Site:

  • The reactant that an enzyme acts on is called the enzyme’s substrate.

  • The enzyme binds to its substrate to form an enzyme-substrate complex.

  • Active Site: The specific region on the enzyme where the substrate binds.

• Function: Enzyme adds energy, speeding up the chemical reaction to create products.

Factors Affecting Enzyme Activity

• Denaturation: A process where changes to the molecular structure lead to reduced enzymatic activity.

  • Reversibility: In some cases, denaturation can be reversed, restoring enzyme activity.

Co-factors and Enzyme Helpers

• Shape Determines Function:

  • Enzymes may require assistance to achieve the correct shape for activity.

Enzyme Inhibition

Regulation of Enzyme Activity

• Gene Regulation: Cells regulate metabolic pathways by switching on/off genes that encode specific enzymes.

• Feedback Inhibition:

  • The end product of a metabolic pathway can inhibit the pathway by binding to an allosteric site on an enzyme.

  • Purpose: Prevents waste of resources and increases cellular efficiency.

• Allosteric Regulation: Protein function is affected by the binding of a regulatory molecule at a separate site:

  • Activator: Stabilizes the active form of the enzyme.

  • Inhibitor: Stabilizes the inactive form.

  • Cooperativity: Binding of one substrate triggers a shape change in other active sites, increasing stability and catalytic activity.

Overview of Photosynthesis

• Definition: Converts light energy into the chemical energy of food.

• Producers of the Biosphere:

Photosynthesis Process

• Summary Equation: $6CO2 + 6H2O + \text{Light Energy} \rightarrow C6H{12}O6 + 6O2$

• Components of Photosynthesis:

  • Sites of Photosynthesis: Mesophyll (chloroplasts), stomata (CO2 enters/O2 exits), chlorophyll (green pigment).

• Mechanisms:

  • Photosystems: Systems of light capturing pigments.

• Light Reaction Outcomes: ATP, NADPH, and O2 are formed from light energy absorption.

• Calvin Cycle: Uses ATP and NADPH from light reactions to produce carbohydrates (G3P) from CO2.

Each Phase of Photosynthesis

Light Reactions

• Conversion of Solar Energy: To ATP and NADPH using electrons from H2O.

• Pigments Absorption:

• Nature of Light: Energy released upon electron excitation in chlorophyll by light.

Calvin Cycle

• Uses ATP and NADPH: To convert CO2 into sugar via three phases:

  1. Carbon Fixation: Incorporates CO2 into RuBP.

  2. Reduction: Utilizes ATP and NADPH to convert 3-Phosphoglycerate (3-PGA) into G3P.

  3. Regeneration of RuBP: Uses ATP to regenerate RuBP for the cycle.

• Total Input and Output of Calvin Cycle:

Photorespiration

• Definition: Metabolic pathway using O2 and producing CO2 without sugar production.

  • Occurs under low CO2 conditions when stomata close to conserve water.

• Significance: Rubisco can mistakenly bind O2 instead of CO2, which can decrease photosynthetic output.

C4 and CAM Plants Adaptations

Mitochondrial Respiration

Structure of Mitochondria

• Double Membrane: Smooth outer membrane and a highly folded inner membrane.

• Function: Location for the Electron Transport Chain (ETC) and Krebs cycle.

Respiration Equation

• Respiration Equation: $C6H{12}O6 + 6O2 \rightarrow 6H2O + 6CO2 + \text{ATP}$

• Metabolic Pathway: A catabolic pathway, breaking down glucose through several stages (Glycolysis, Pyruvate Oxidation, Krebs Cycle, and ETC).

Glycolysis

• Description: Sugar splitting process, occurring outside of mitochondria, can function with or without oxygen.

• Outputs: Net gain of $2 \text{ ATP} + 2 \text{ NADH}$.

Pyruvate Oxidation and Krebs Cycle

Pyruvate Oxidation

• Occurs in the mitochondrial matrix.

  • Net Gain: $2 \text{ ATP}, 6 \text{ NADH}, 2 \text{ FADH}_2$ due to Acetyl CoA conversion (for 2 pyruvate molecules).

Krebs Cycle/Citric Acid Cycle

• Continuation of energy extraction from Acetyl CoA.

Electron Transport Chain (ETC)

• Function: Occurs in the inner membrane of mitochondria, producing $26-28 \text{ ATP}$.

• Process: H+ ions create a gradient, facilitating ATP synthesis via ATP synthase.

Anaerobic Respiration and Fermentation

Anaerobic Respiration

• Occurs without oxygen, using different electron acceptors (e.g., sulfate, nitrate).

• Types of Cells: Obligate anaerobes (cannot survive without O2) and facultative anaerobes (can switch to fermentation).

Fermentation Overview

Types of Fermentation

• End Product: Lactate buildup not a direct cause of fatigue, contrary to earlier beliefs.

Conclusion on Energy Sources for Cellular Respiration

• Fuel Sources: Carbohydrates, fats, and proteins enter metabolic pathways at various stages.

• Overall Energy Flow: Glucose → NADH → ETC → ATP production.

• Importance of Oxygen: Essential for aerobic respiration, ensures efficient energy yield from substrates.

• **Efficiency Comparison: