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General Biology Exam 2 Study Guide: Enzymes, Cells, Transport, and Metabolism

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Enzymes and Their Regulation

How Enzymes Aid Chemical Reactions

Enzymes are biological catalysts that speed up chemical reactions in cells by lowering the activation energy required for the reaction to proceed.

  • Enzyme Function: Enzymes bind to specific substrates, forming an enzyme-substrate complex that facilitates the conversion to products.

  • Regulation: Enzyme activity can be regulated by inhibitors (competitive and noncompetitive), activators, and changes in environmental conditions such as pH and temperature.

  • Example: Amylase catalyzes the breakdown of starch into sugars in saliva.

Enzyme Specificity

Enzymes are highly specific, meaning each enzyme typically catalyzes only one type of reaction or acts on a specific substrate.

  • Active Site: The region on the enzyme where the substrate binds is called the active site, which has a unique shape complementary to the substrate.

  • Lock-and-Key Model: Illustrates how only specific substrates fit into the enzyme's active site.

Cell Structure and Function

Comparing Animal, Plant, and Bacterial Cells

Cells are the basic units of life, and their structure varies among different domains.

  • Common Features: All cells have a plasma membrane, cytoplasm, ribosomes, and genetic material (DNA).

  • Differences:

    • Animal Cells: No cell wall, have lysosomes and centrioles.

    • Plant Cells: Have a cell wall, chloroplasts, and large central vacuole.

    • Bacterial Cells: Prokaryotic, lack membrane-bound organelles, have cell wall (often peptidoglycan), and may have plasmids.

Endosymbiosis and Organelle Origins

The endosymbiotic theory explains the origin of certain organelles in eukaryotic cells.

  • Process: Early eukaryotic cells engulfed prokaryotic cells, which became symbiotic organelles.

  • Organelles: Mitochondria and chloroplasts are products of endosymbiosis.

  • Evidence: These organelles have their own DNA and double membranes.

Membrane Transport: Active vs. Passive

Cells transport substances across their membranes using active and passive mechanisms.

  • Passive Transport: Movement of substances down their concentration gradient without energy input.

    • Includes diffusion, facilitated diffusion, and osmosis.

  • Active Transport: Movement of substances against their concentration gradient, requiring energy (usually ATP).

    • Includes primary active transport (e.g., sodium-potassium pump) and secondary active transport.

Concentration Gradient: The difference in concentration of a substance across a space or membrane.

Osmosis and Water Movement

Osmosis is the diffusion of water across a selectively permeable membrane.

  • Controlled by: The concentration of solutes (osmotic pressure) on either side of the membrane.

  • Direction: Water moves from areas of low solute concentration to high solute concentration.

Major Organelles: Roles and Features

Each organelle in eukaryotic cells has a specific function essential for cell survival.

  • Nucleus: Contains genetic material (DNA); controls cell activities.

  • Mitochondria: Site of cellular respiration; produces ATP.

  • Chloroplasts: Site of photosynthesis in plant cells.

  • Endoplasmic Reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).

  • Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

  • Lysosomes: Digestive organelles; break down waste.

  • Vacuoles: Storage organelles; large central vacuole in plants stores water and nutrients.

Energy and Metabolism

Kinetic vs. Potential Energy

Energy exists in different forms within biological systems.

  • Kinetic Energy: Energy of motion (e.g., movement of molecules).

  • Potential Energy: Stored energy (e.g., chemical bonds in glucose).

Photosynthesis and Cellular Respiration: Inputs, Outputs, and Goals

Photosynthesis and cellular respiration are complementary processes in the energy cycle of living organisms.

  • Photosynthesis:

    • Inputs: Carbon dioxide (CO2), water (H2O), light energy

    • Outputs: Glucose (C6H12O6), oxygen (O2)

    • Goal: Convert light energy into chemical energy stored in glucose.

    • Equation:

  • Cellular Respiration:

    • Inputs: Glucose, oxygen

    • Outputs: Carbon dioxide, water, ATP

    • Goal: Release energy from glucose to produce ATP.

    • Equation:

Importance of Water and CO2 in Photosynthesis

Water and carbon dioxide are essential reactants in photosynthesis, providing the hydrogen and carbon needed to synthesize glucose.

  • Water: Supplies electrons and protons; oxygen is released as a byproduct.

  • CO2: Source of carbon for glucose formation.

Stages of Cellular Respiration: Glycolysis, Citric Acid Cycle (CAC), and Electron Transport Chain (ETC)

Cellular respiration occurs in three main stages, each with specific goals.

  • Glycolysis: Breaks down glucose into pyruvate; produces ATP and NADH.

  • CAC (Krebs Cycle): Oxidizes acetyl-CoA to CO2; generates NADH and FADH2.

  • ETC: Uses NADH and FADH2 to produce ATP via oxidative phosphorylation.

Role of Oxygen in Cellular Respiration

Oxygen acts as the final electron acceptor in the electron transport chain, allowing for efficient ATP production.

  • Without oxygen: The ETC cannot function, and cells switch to anaerobic pathways.

ATP Production Without Oxygen

Cells can produce ATP anaerobically through fermentation when oxygen is unavailable.

  • Result: Less ATP is produced; in animal cells, lactic acid is formed.

  • Equation (Lactic Acid Fermentation):

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