Chapter 5: The Working Cell

Diffusion and Transport Mechanisms

The movement of molecules across cell membranes is essential for cellular function. Cells use various mechanisms to regulate the transport of substances.

• Diffusion: The passive movement of molecules from an area of higher concentration to an area of lower concentration.

• Active vs Passive Transport:

  • Passive transport: Does not require energy; includes diffusion and osmosis.

  • Active transport: Requires energy (usually ATP) to move substances against their concentration gradient.

• Osmosis: The diffusion of water across a selectively permeable membrane.

• Membrane Proteins: Proteins embedded in the cell membrane assist in transporting molecules that cannot diffuse freely.

Example: Sodium-potassium pumps use ATP to move Na+ and K+ ions against their gradients.

Tonicity and Cell Behavior in Solutions

Tonicity describes how the concentration of solutes in a solution affects the movement of water into or out of cells.

• Hypotonic: Solution has a lower solute concentration than the cell; water enters the cell, which may cause it to swell.

• Isotonic: Solution has the same solute concentration as the cell; no net movement of water.

• Hypertonic: Solution has a higher solute concentration than the cell; water leaves the cell, causing it to shrink.

Example: Red blood cells placed in pure water (hypotonic) will swell and may burst.

Facilitated Diffusion and Aquaporins

Some molecules require assistance to cross the membrane.

• Facilitated diffusion: Transport proteins help move substances across the membrane without energy input.

• Aquaporins: Specialized channel proteins that facilitate rapid water movement.

Example: Glucose transporters allow glucose to enter cells via facilitated diffusion.

Types of Active Transport

Active transport mechanisms move substances against their concentration gradients.

• Exocytosis: The process by which cells expel materials in vesicles to the outside.

• Endocytosis: The process by which cells engulf external substances into vesicles.

Example: White blood cells engulf bacteria by endocytosis (phagocytosis).

Kinetic and Potential Energy in Cells

Cells use energy for work, including transport and chemical reactions.

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

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

Endergonic vs Exergonic Reactions

Chemical reactions in cells can either require or release energy.

• Endergonic: Require energy input (e.g., photosynthesis).

• Exergonic: Release energy (e.g., cellular respiration).

Equation Example:

ATP Structure and Function

ATP (adenosine triphosphate) is the primary energy carrier in cells.

• Structure: Composed of adenine, ribose, and three phosphate groups.

• ATP Hydrolysis: Releases energy for cellular work.

Example: Muscle contraction uses ATP hydrolysis for movement.

Enzymes and Their Regulation

Enzymes are biological catalysts that speed up chemical reactions.

• Active Site: The region of the enzyme where substrates bind and reactions occur.

• Substrate: The molecule upon which an enzyme acts.

• Competitive inhibition: Inhibitor binds to the active site, blocking substrate.

• Noncompetitive inhibition: Inhibitor binds elsewhere, changing enzyme shape.

• Feedback inhibition: End product of a pathway inhibits an earlier step.

Example: ATP can inhibit enzymes in glycolysis via feedback inhibition.

Chapter 6: Cellular Respiration

Redox Reactions in Cellular Respiration

Cellular respiration involves a series of redox (reduction-oxidation) reactions to extract energy from glucose.

• Redox reactions: Transfer of electrons between molecules.

• LEO the lion says GER: Lose Electrons = Oxidation; Gain Electrons = Reduction.

Example: NAD+ is reduced to NADH during glycolysis and the Krebs cycle.

Mitochondrion Structure and Function

The mitochondrion is the site of most cellular respiration steps.

• Structure: Double membrane organelle with inner folds called cristae.

Example: The electron transport chain is located in the inner mitochondrial membrane.

Chemical Equation for Cellular Respiration

The overall process converts glucose and oxygen into carbon dioxide, water, and energy.

Equation:

Stages of Cellular Respiration

Cellular respiration occurs in three main stages, each with specific reactants, products, and locations.

• Stage 1: Glycolysis

  • Occurs in the cytoplasm

  • Reactant: Glucose

  • Products: Pyruvate, ATP, NADH

• Stage 2: Pyruvate Oxidation & Citric Acid Cycle (Krebs Cycle)

  • Occurs in the mitochondrial matrix

  • Reactant: Pyruvate

  • Products: Acetyl-CoA, NADH, CO2

  • Citric Acid Cycle produces: NADH, FADH2, CO2, ATP

• Stage 3: Oxidative Phosphorylation (ETC and Chemiosmosis)

  • Occurs in the inner mitochondrial membrane

  • Electron transport chain (ETC) uses electrons from NADH and FADH2

  • Final electron acceptor: Oxygen

  • ATP is produced via ATP synthase

Example: Most ATP is generated during oxidative phosphorylation.

ATP Yield and Oxygen's Role

ATP is produced at each step, with the majority generated during oxidative phosphorylation. Oxygen is essential as the final electron acceptor; absence of oxygen halts the ETC.

• Your brain uses 20 percent of the energy your body produces.

• ATP is produced during glycolysis and the citric acid cycle.

• Acid cycle by substrate level phosphorylation.

• O2 is the final electron acceptor.

Chapter 7: Photosynthesis

Autotrophs vs Heterotrophs

Organisms can be classified by how they obtain energy.

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

• Heterotrophs: Organisms that consume other organisms for energy.

Pigments in Photosynthesis

Pigments absorb light energy for photosynthesis.

• Chlorophyll a: Main pigment involved in photosynthesis and participates in the light reaction.

• Chlorophyll b: Accessory pigment.

• Carotenoids: Accessory pigments that absorb different wavelengths.

Stages of Photosynthesis

Photosynthesis consists of two main stages: the light reactions and the Calvin cycle.

• Stage 1: Light Reaction (ETC and ATP Synthesis)

  • Occurs in the thylakoid membrane

  • Reactants: Water, light energy

  • Products: ATP, NADPH, O2

  • Electrons move through the light reaction via electron transport chains

  • Electrons from water feed into photosystem II and then photosystem I

• Stage 2: Calvin Cycle

  • Occurs in the stroma

  • Reactants: CO2, ATP, NADPH

  • Products: Glucose, ADP, NADP+

  • Steps:

    1. Carbon fixation

    2. Reduction of G3P

    3. Release of G3P

    4. Regeneration of RuBP

Comparison Table: Cellular Respiration vs Photosynthesis

Below is a summary table comparing the two processes:

Additional info:

• Hand-drawn diagrams in the notes illustrate the structure of mitochondria, the electron transport chain, and the citric acid cycle. These are important for visualizing the spatial organization of cellular respiration steps.

• Some details, such as the specific number of ATP molecules produced per glucose, may vary depending on the cell type and conditions, but the general yield is about 32 ATP per glucose molecule.