Review from Exam 1

Foundational Concepts

These concepts form the basis for understanding biological processes and will be referenced throughout the course.

• pH: pH is a measure of hydrogen ion concentration in a solution. It is defined by the equation: - Higher pH means lower concentration of ions. - Example: pH 14 ( H+) has fewer H+ than pH 7 ( H+).

• Units: - Molarity (M) = moles/Liter - Avogadro's number = about (number of molecules in a mole)

• Major Categories of Biological Macromolecules:

  1. Proteins

  2. Carbohydrates

  3. Lipids

  4. Nucleic Acids

Chapter 5: Cell Membranes and Transport

Structure and Function of Cell Membranes

Cell membranes are dynamic structures composed mainly of phospholipids and proteins, crucial for maintaining cellular integrity and regulating transport.

• Components: Phospholipids (form bilayer), proteins (integral and peripheral), cholesterol.

• Phospholipid Bilayer: Hydrophilic heads face outward, hydrophobic tails face inward, creating a semi-permeable barrier.

• Fluid Mosaic Model: Describes the membrane as a mosaic of components that move fluidly within the layer.

• Membrane Fluidity:

  • High temperature: More saturated fatty acids, less fluidity.

  • Low temperature: More unsaturated fatty acids, increased fluidity.

  • Cholesterol: At high temperatures, reduces fluidity; at low temperatures, prevents solidification.

• Membrane Proteins: Facilitate transport, act as enzymes, receptors, and anchors.

Tonicity and Transport

Tonicity describes the relative concentration of solutes in solutions separated by a membrane, affecting water movement.

• Hypertonic vs. Hypotonic: - Hypertonic: Higher solute concentration outside the cell; water moves out. - Hypotonic: Lower solute concentration outside; water moves in.

• Transport Proteins: Sodium-potassium pumps maintain ion gradients essential for cell function.

• Diffusion and Osmosis: - Diffusion: Movement of solutes from high to low concentration. - Osmosis: Movement of water across a semi-permeable membrane.

Chapter 6: Metabolism and Enzymes

Energy, Work, and Metabolic Pathways

Cells require energy to perform work, which is managed through metabolic pathways involving enzymes and chemical reactions.

• Definitions: - Energy: Capacity to do work. - Work: Movement or change in matter. - Equilibrium: State where forward and reverse reactions occur at equal rates. - Metabolism: All chemical reactions in a cell. - Anabolic Pathways: Build complex molecules (biosynthesis). - Catabolic Pathways: Break down molecules (energy release).

Enzymes: Function and Regulation

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

• Active Site: Region where substrate binds and reaction occurs.

• Enzyme Specificity: Each enzyme acts on specific substrates.

• Enzyme Regulation:

  • Inhibitors:

    • Competitive: Bind to active site, blocking substrate.

    • Noncompetitive: Bind elsewhere, changing enzyme shape.

  • Activators: Increase enzyme activity.

  • Cofactors: Non-protein helpers (e.g., metal ions, vitamins).

  • Allosteric Regulation: Regulation by binding at a site other than the active site.

• Optimal Conditions: Enzymes function best at specific temperatures and pH.

• Saturation: When all active sites are occupied, reaction rate plateaus.

Laws of Thermodynamics in Biology

Thermodynamics governs energy transformations in living organisms.

• 1st Law (Law of Energy Conservation): Energy cannot be created or destroyed, only transformed.

• 2nd Law (Law of Entropy): Every energy transfer increases the disorder (entropy) of the universe.

ATP: Cellular Energy Currency

ATP (adenosine triphosphate) stores and transports chemical energy for cellular processes.

• ATP Structure: Adenine, ribose, and three phosphate groups.

• Function: Couples exergonic (energy-releasing) and endergonic (energy-consuming) reactions.

• Hydrolysis: ATP → ADP + Pi releases energy.

Cellular Respiration

Overview and Steps

Cellular respiration is the process by which cells extract energy from glucose, producing ATP, CO2, and H2O.

• Overall Equation:

• Steps:

  1. Glycolysis

  2. Pyruvate Oxidation

  3. Citric Acid Cycle (Krebs Cycle)

  4. Oxidative Phosphorylation (Electron Transport Chain & Chemiosmosis)

• Substrate-Level Phosphorylation: Direct transfer of phosphate to ADP to form ATP.

• Electron Carriers: NADH and FADH2 transport electrons to the electron transport chain.

Inputs and Outputs of Respiration

• CO2: Produced by pyruvate oxidation and citric acid cycle.

• O2: Consumed in oxidative phosphorylation.

• H2O: Produced in electron transport chain.

Glycolysis

Occurs in the cytoplasm and consists of two phases: energy investment and energy payoff.

• Energy Investment:

• Energy Payoff:

Pyruvate Oxidation

Citric Acid Cycle

Each glucose molecule results in two turns of the cycle.

• Inputs:

• Outputs:

Electron Transport Chain and Chemiosmosis

• Electron Transport Chain: NADH and FADH2 donate electrons, which power the pumping of H+ ions to create a proton gradient.

• Oxygen: Final electron acceptor, forming water.

• ATP Synthase: Uses proton motive force to synthesize ATP from ADP and Pi.

• ATP Yield: ~28 ATP produced by oxidative phosphorylation per glucose molecule.

Fermentation

Occurs when oxygen is absent; allows glycolysis to continue by regenerating NAD+.

• Alcohol Fermentation: Produces ATP, CO2, and ethanol.

• Lactic Acid Fermentation: Produces ATP and lactic acid.

• Common Step: Both share glycolysis as the initial step.

Cellular Respiration Product Table

The following table summarizes the ATP, NADH, and FADH2 produced in each step of aerobic respiration per glucose molecule.

Photosynthesis

Overview and Key Definitions

Photosynthesis is the process by which autotrophs convert light energy into chemical energy, producing glucose and oxygen.

• Autotrophs: Organisms that produce their own food (e.g., plants).

• Heterotrophs: Organisms that consume other organisms for food.

• Key Structures: Stomata, mesophyll, chloroplasts, chlorophyll, stroma, thylakoids, grana/granum, Photosystem I and II, light-harvesting complex, pigment.

Photosynthesis Reaction and Steps

• General Equation:

• Light Reactions: Occur in thylakoid membranes; convert light energy to chemical energy (ATP and NADPH).

• Calvin Cycle: Occurs in stroma; uses ATP and NADPH to fix CO2 into glucose.

Light Reactions and Calvin Cycle

• Function of Light Reactions: Produce ATP and NADPH, release O2.

• Function of Calvin Cycle: Fix carbon, produce glucose.

• Source of ATP/NADPH: Generated in light reactions.

• Consumption of Water and CO2: Water is split in light reactions (producing O2); CO2 is fixed in Calvin Cycle.

Additional Key Points

• Primary Function of Pigment Proteins: Absorb light energy for photosynthesis.

• Oxygen Production: Produced by oxidation of water in light reactions.

• Electron Pathways: Electrons move from water through photosystems to NADP+, forming NADPH.

• Carbohydrate Transport: Sugars produced in photosynthesis are transported through the plant via phloem.

• Leaf Color: Green color indicates chlorophyll presence; other pigments may be present but masked.