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General Biology I: Cellular Respiration, Photosynthesis, and Cell Signaling – Study Guide

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Energy and Metabolism

Enzyme Inhibition

Enzymes are biological catalysts that speed up chemical reactions in cells. Their activity can be regulated by inhibitors, which are molecules that decrease enzyme activity.

  • Noncompetitive Inhibition: The inhibitor binds to an allosteric (alternative) site, not the active site, causing a conformational change in the enzyme that reduces its activity.

  • Effect: This change in shape prevents the substrate from binding efficiently to the active site, even though the active site is not directly blocked.

  • Example: Heavy metals like lead or mercury can act as noncompetitive inhibitors for some enzymes.

Introduction to Metabolism

Metabolism is the sum of all chemical reactions in an organism, divided into two main types:

  • Anabolism: Formation of complex compounds from simpler ones (e.g., protein synthesis).

  • Catabolism: Breakdown of complex compounds into simpler ones, releasing energy (e.g., cellular respiration).

Negative & Positive Feedback

Feedback inhibition is a regulatory mechanism in metabolic pathways.

  • Negative Feedback: The end product of a pathway inhibits an earlier enzyme, preventing overproduction.

  • Example: ATP inhibits phosphofructokinase in glycolysis.

Redox Reactions

Redox (reduction-oxidation) reactions involve the transfer of electrons between molecules.

  • Oxidizing Agent: Gains electrons and is reduced in the process.

  • Reducing Agent: Loses electrons and is oxidized.

Respiration

Introduction to Cellular Respiration

Cellular respiration is the process by which cells convert glucose and oxygen into energy (ATP), water, and carbon dioxide.

  • Oxygen's Role: In aerobic respiration, oxygen is converted into water at the end of the electron transport chain.

Types of Phosphorylation

  • Oxidative Phosphorylation: ATP is produced using energy derived from the transfer of electrons in the electron transport chain and the flow of protons across the mitochondrial membrane.

  • Photophosphorylation: Occurs in chloroplasts during photosynthesis.

  • Substrate-level Phosphorylation: Direct transfer of a phosphate group to ADP from a substrate.

Glycolysis

Glycolysis is the first step of cellular respiration, occurring in the cytoplasm.

  • Products: Pyruvate, ATP, and NADH.

Pyruvate Oxidation

Pyruvate produced in glycolysis is converted to acetyl CoA by the pyruvate dehydrogenase complex before entering the Krebs cycle.

  • Role: Links glycolysis to the Krebs cycle by producing acetyl CoA.

Krebs Cycle (Citric Acid Cycle)

The Krebs cycle completes the oxidation of glucose derivatives, generating NADH, FADH2, and ATP.

  • Entry Reaction: Acetyl-CoA combines with oxaloacetate to form citrate.

Electron Transport Chain (ETC) and Chemiosmosis

The ETC is a series of protein complexes in the mitochondrial membrane that transfer electrons and pump protons to create a proton gradient.

  • Final Electron Acceptor: Oxygen, which forms water.

  • ATP Synthesis: The proton gradient drives ATP synthesis via ATP synthase (chemiosmosis).

Review of Aerobic Cellular Respiration

  • ATP Production: Nearly all living organisms use glycolysis and oxidative phosphorylation to generate ATP.

Fermentation & Anaerobic Respiration

  • Anaerobic Respiration: Occurs without oxygen, produces less ATP, and results in incomplete breakdown of glucose.

  • Fermentation: Allows glycolysis to continue by regenerating NAD+ in the absence of oxygen.

Photosynthesis

Introduction to Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy.

  • Equation:

  • Photosynthesis and Respiration: The products of one process are the reactants of the other.

Leaf & Chloroplast Anatomy

  • Stomata: Openings in the leaf that allow gas exchange (CO2 in, O2 out).

Electromagnetic Spectrum

  • Photon Energy: Inversely proportional to wavelength ().

Pigments of Photosynthesis

  • Carotenoids: Accessory pigments that absorb blue and green light, reflecting yellow, orange, and red.

Stages of Photosynthesis: Calvin Cycle

  • Reactants: ATP, NADPH, and CO2 are used in the Calvin cycle to synthesize glucose.

  • Phases:

    Phase 1

    Phase 2

    Phase 3

    Carbon fixation

    Glyceraldehyde-3-phosphate synthesis

    Ribulose bisphosphate regeneration

Light Reactions of Photosynthesis

  • Purpose: Convert light energy into chemical energy (ATP and NADPH).

  • Do Not Involve: Production of glucose (which occurs in the Calvin cycle).

Photorespiration

  • Occurs: Under hot, arid conditions when Rubisco adds O2 instead of CO2 to RuBP.

  • Incorrect Statement: Photorespiration does not use CO2 and release O2.

C3, C4 & CAM Plants

  • C4 and CAM Plants: Adapted to minimize photorespiration and conserve water.

  • CAM Plants: Open stomata at night to reduce water loss.

  • PEP Carboxylase: Used for initial carbon fixation in both C4 and CAM plants.

Review of Photosynthesis

  • Light-Independent Reactions: Produce glucose using ATP and NADPH from the light-dependent reactions.

Cell Signaling

Introduction to Cell Signaling

  • Signal Transduction: The transmission and conversion of signals from outside the cell to elicit a cellular response.

Classes of Signaling Receptors

  • Tyrosine Kinase Inhibitors: Block growth signaling, stopping cell division and growth.

Types of Cell Signaling

  • Quorum Sensing: Bacterial communication mechanism based on population density, coordinating collective behaviors.

Signal Amplification

  • Protein Phosphorylation: Key mechanism in signal transduction, amplifying the signal through phosphorylation cascades.

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