Chapter 5: The Working Cell

Types of Energy and Conservation of Energy

Energy is the capacity to do work. In biological systems, energy exists in various forms and follows the law of conservation, which states that energy cannot be created or destroyed, only transformed.

• Kinetic Energy: The energy of motion. Example: A moving muscle or flowing water.

• Potential Energy: Stored energy due to position or structure. Example: Chemical bonds in glucose.

• Chemical Energy: A form of potential energy stored in chemical bonds. Example: ATP, glucose.

• Heat (Thermal Energy): Energy associated with random movement of atoms or molecules. Often released during energy conversions.

• Law of Conservation of Energy: Energy can change forms but is not created or destroyed.

ATP: Energy Currency of the Cell

ATP (Adenosine Triphosphate) stores energy in its high-energy phosphate bonds. Cells use ATP to power cellular work by transferring a phosphate group to other molecules (phosphorylation).

• Structure: Adenine base, ribose sugar, and three phosphate groups.

• Energy Storage: Energy is stored in the bonds between phosphate groups, especially the terminal phosphate bond.

• ATP Cycle: ATP is converted to ADP (adenosine diphosphate) when a phosphate is removed, releasing energy.

Equation:

Enzymes and Enzyme Inhibitors

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy. They are specific to their substrates and are not consumed in the reaction.

• Active Site: The region on the enzyme where the substrate binds.

• Enzyme Inhibitors: Molecules that decrease enzyme activity. They can be competitive (bind to the active site) or noncompetitive (bind elsewhere, changing enzyme shape).

Example: Many drugs and toxins act as enzyme inhibitors.

Cell Membrane Structure and Function

The cell membrane is a selectively permeable barrier composed of a phospholipid bilayer with embedded proteins. It regulates the movement of substances into and out of the cell.

• Phospholipid Bilayer: Hydrophilic heads face outward; hydrophobic tails face inward.

• Proteins: Serve as channels, carriers, receptors, and enzymes.

Transport Across Membranes

• Diffusion: Movement of molecules from high to low concentration. No energy required. Small, nonpolar molecules (e.g., O2, CO2) cross easily.

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

• Facilitated Diffusion: Movement of molecules via transport proteins. No energy required. For larger or polar molecules (e.g., glucose).

• Active Transport: Movement against the concentration gradient using energy (ATP). Example: Sodium-potassium pump.

Bulk Transport: Endocytosis and Exocytosis

• Endocytosis: Cell engulfs materials by forming vesicles. Used for large particles or bulk substances.

• Exocytosis: Vesicles fuse with the membrane to release contents outside the cell. Used for secretion of proteins, neurotransmitters, etc.

Chapter 6: Cellular Respiration

Autotrophs vs. Heterotrophs

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

• Heterotrophs: Organisms that obtain food by consuming other organisms (e.g., animals, fungi).

Photosynthesis and Cellular Respiration: Overview and Relationship

• Photosynthesis: Converts light energy to chemical energy in glucose.

• Cellular Respiration: Breaks down glucose to release energy (ATP).

Simplified Equations:

Photosynthesis:

Cellular Respiration:

Relationship: The products of one process are the reactants of the other.

Stages of Cellular Respiration

Role of Oxygen in Cellular Respiration

• Oxygen: Final electron acceptor in the Electron Transport Chain (ETC).

• Stages Requiring Oxygen: Krebs Cycle and ETC (aerobic stages).

• Stage Not Requiring Oxygen: Glycolysis (anaerobic).

Fermentation

Fermentation is an anaerobic process that allows cells to produce ATP when oxygen is scarce. It regenerates NAD+ for glycolysis.

• Lactic Acid Fermentation: Occurs in muscle cells; produces lactic acid.

• Alcoholic Fermentation: Occurs in yeast; produces ethanol and CO2.

• Conditions: Happens when oxygen is not available.

Chapter 7: Photosynthesis

Leaf Structure and Function in Photosynthesis

• Epidermis: Protective outer layer.

• Mesophyll: Main site of photosynthesis; contains chloroplasts.

• Stomata: Pores for gas exchange (CO2 in, O2 out).

• Veins: Transport water and nutrients.

Chloroplast Structure

• Outer and Inner Membranes: Enclose the organelle.

• Stroma: Fluid-filled space; site of the Calvin Cycle.

• Thylakoids: Membranous sacs; contain chlorophyll; site of light reactions.

• Grana: Stacks of thylakoids.

Chlorophylls and Light Absorption

• Chlorophylls: Pigments that absorb light energy for photosynthesis.

• Absorption: Absorb red and blue light; reflect green (why plants appear green).

• Interaction with Light: Excite electrons, initiating the light reactions.

Role of Water and Carbon Dioxide in Photosynthesis

• Water (H2O): Split during the light reactions to provide electrons and protons; releases O2 as a byproduct.

• Carbon Dioxide (CO2): Used during the Calvin Cycle to build glucose.

Stages of Photosynthesis

Calvin Cycle: Final Product and Rounds Needed

• Final Product: G3P (glyceraldehyde-3-phosphate), which can be used to form glucose and other organic molecules.

• Rounds Needed: Three turns of the Calvin Cycle are required to produce one G3P molecule; six turns to produce one glucose molecule.