05 Lecture W16 ONLINE

Chapter 5: The Working Cell

Part A: Transport across membranes

• Cell Membrane Components:

  • Lipid bilayer

  • Proteins (including channel proteins)

  • Carbohydrate chains

Membrane Function

• Key Role of the Plasma Membrane:

  • Regulates the flow of materials to and from the environment.

  • It is selectively permeable, allowing only certain molecules to pass through.

Passive Transport

• Definition: Spontaneous movement of substances across a membrane without energy input.

• Types of Passive Transport:

  1. Diffusion

  2. Facilitated Diffusion

  3. Osmosis

Diffusion

• Process: Net movement from higher to lower concentration (down the concentration gradient).

• Energy Requirement: No energy input needed; equilibrium is reached when concentrations are equal.

Facilitated Diffusion

• Definition: Movement of substances that cannot pass through membranes spontaneously.

• Mechanism: Requires transport proteins embedded within the plasma membrane which help specific substances cross the membrane without energy input.

Osmosis

• Definition: Diffusion of water across a selectively permeable membrane.

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

• Key Terms:

  • Solute: Substance being dissolved (e.g., salts/sugars).

  • Solvent: Dissolving agent (water).

Comparing Solutions in Osmosis

• Hypotonic Solution: Lower solute concentration.

• Hypertonic Solution: Higher solute concentration.

• Isotonic Solution: Equal solute concentration.

• Water Movement: Water moves from hypotonic to hypertonic solutions.

Water Balance in Cells

• Osmoregulation: Controls water balance within a cell or organism.

  • Examples:

    • Isotonic: Normal state.

    • Hypotonic: Potential for lysing (swelling).

    • Hypertonic: Cells may shrivel.

Active Transport

• Definition: Movement of molecules against the concentration gradient (from low to high concentration), requiring energy input.

• Mechanism: Utilizes a membrane transport protein.

The Flow of Energy in Living Things

• Energy Source: Captured from the sun to produce sugars (food).

• Potential Energy: Food contains chemical energy stored in bonds.

Laws of Thermodynamics

1. 1st Law: Energy can be converted from one form to another but neither created nor destroyed. Every conversion releases heat.

2. 2nd Law: Every energy conversion increases entropy.

Energy Conversions in Organisms

• Efficiency: Only 34% of energy from food is converted to usable work; 66% is released as heat.

ATP - Energy for Cellular Work

• ATP: Adenosine triphosphate, the energy currency of the cell.

• Structure: Comprises an adenine nucleotide, ribose sugar, and three phosphate groups.

• Function: Transfers energy for cellular processes by breaking high-energy phosphate bonds, converting to ADP (adenosine diphosphate).

How ATP Works

• Energy Transfer: When the bond between the second and third phosphate group is broken, energy is released.

• Phosphate Transfer: ATP can energize other molecules by transferring phosphate groups.

Enzymes and Chemical Reactions

• Metabolism: Total of all chemical reactions in an organism.

  • Reactants: Starting materials.

  • Products: End materials.

Role of Enzymes

• Function: Lower activation energy required for reactions, speeding up metabolism.

• Activation Energy: Initial energy input to start a reaction.

Enzyme Specificity

• Mechanism: Each enzyme recognizes a specific substrate and catalyzes a specific reaction using an active site.

• Induced Fit: The interaction of substrate with the active site facilitates the necessary reaction.

Enzyme Inhibitors

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

• Non-competitive inhibition: Inhibitor binds to a different site on the enzyme, altering its function.

• Importance: Enzyme inhibitors regulate metabolic reactions and are utilized in many drugs (e.g., penicillin, ibuprofen).