Cell Structure, Membrane Function, Metabolism, Cellular Respiration, and Photosynthesis: Study Notes

Chapter 6: A Tour of the Cell

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells lack a nucleus and membrane-bound organelles. Their DNA is located in a region called the nucleoid.

• Eukaryotic cells have a true nucleus enclosed by a nuclear envelope and possess various membrane-bound organelles.

• Similarities: Both have a plasma membrane, cytoplasm, ribosomes, and genetic material (DNA).

• Differences: Eukaryotes are generally larger, more complex, and can be unicellular or multicellular; prokaryotes are usually smaller and simpler.

Plant vs. Animal Cells

• Plant cells have a cell wall, chloroplasts, and a large central vacuole; animal cells do not.

• Animal cells contain lysosomes and centrioles, which are typically absent in plant cells.

Functions of Key Organelles

• Nucleus: Contains genetic material (DNA); controls cell activities by regulating gene expression.

• Ribosomes: Sites of protein synthesis; found free in cytoplasm or bound to rough endoplasmic reticulum (RER).

• Chloroplast: Site of photosynthesis in plant cells; contains chlorophyll.

• Mitochondria: Site of cellular respiration; generates ATP.

• Rough Endoplasmic Reticulum (RER): Studded with ribosomes; synthesizes and processes proteins.

• Smooth Endoplasmic Reticulum (SER): Lacks ribosomes; synthesizes lipids, detoxifies drugs, and stores calcium ions.

• Lysosome: Contains hydrolytic enzymes for intracellular digestion; breaks down waste and cellular debris (mainly in animal cells).

Chapter 7: Membrane Structure and Function

Phospholipid Bilayer Structure

• Phospholipids have a hydrophilic (water-loving) head and hydrophobic (water-fearing) tails.

• In the bilayer, hydrophilic heads face outward toward aqueous environments, while hydrophobic tails face inward, away from water.

Fluid Mosaic Model

• The cell membrane is described as a fluid mosaic because it is flexible (fluid) and composed of various proteins embedded in or attached to a phospholipid bilayer (mosaic).

• Proteins and lipids can move laterally within the layer, allowing for membrane flexibility and function.

Tonicity and Water Movement

• Hypertonic solution: Higher solute concentration outside the cell; water moves out, causing animal cells to shrink (crenate) and plant cells to undergo plasmolysis.

• Isotonic solution: Equal solute concentration; no net water movement; animal cells remain normal, plant cells become flaccid.

• Hypotonic solution: Lower solute concentration outside; water moves in, causing animal cells to lyse (burst) and plant cells to become turgid (normal state for plants).

Passive vs. Active Transport

• Passive diffusion: Molecules move from high to low concentration without energy input.

• Active transport: Molecules move from low to high concentration, requiring energy (usually ATP).

Recognizing Transport Types

• Passive transport includes simple diffusion, facilitated diffusion (via channel or carrier proteins), and osmosis.

• Active transport involves pumps (e.g., sodium-potassium pump) and bulk transport (endocytosis/exocytosis).

Chapter 8: An Introduction to Metabolism

Kinetic vs. Potential Energy

• Kinetic energy: Energy of motion (e.g., a moving car, flowing water).

• Potential energy: Stored energy due to position or structure (e.g., chemical bonds, a rock at the top of a hill).

Exergonic vs. Endergonic Reactions

• Exergonic reactions: Release energy; ΔG < 0; spontaneous (e.g., cellular respiration).

• Endergonic reactions: Require energy input; ΔG > 0; non-spontaneous (e.g., photosynthesis).

• Catabolic pathways: Break down molecules, releasing energy (exergonic).

• Anabolic pathways: Build complex molecules, requiring energy (endergonic).

Enzyme Function

• Enzymes are biological catalysts that speed up reactions by lowering the activation energy barrier.

• They do not change the overall ΔG of a reaction.

ATP: The Cell's Energy Currency

• ATP (adenosine triphosphate) stores and provides energy for cellular processes.

• Energy is released when the terminal phosphate bond is broken (hydrolysis), forming ADP and inorganic phosphate.

• ATP hydrolysis equation: $\mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P}_i + \text{energy}$

Chapter 9: Cellular Respiration and Fermentation

Purpose of Cellular Respiration

• To convert chemical energy in glucose into ATP, which powers cellular work.

Overall Equation and Redox

• Overall equation: $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\mathrm{O}_2 \rightarrow 6\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O} + \text{energy (ATP)}$

• Glucose is oxidized to CO2; Oxygen is reduced to H2O.

Role of Oxygen

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

Anaerobic Steps and Fermentation

• Glycolysis occurs in the cytoplasm, does not require oxygen, and produces pyruvate, ATP, and NADH.

• In the absence of oxygen, cells undergo fermentation (e.g., lactic acid or alcoholic fermentation), producing less ATP and regenerating NAD+.

Chapter 10: Photosynthesis

Relationship to Cellular Respiration

• Photosynthesis and cellular respiration are complementary processes.

• Photosynthesis stores energy in glucose; respiration releases it.

Overall Equation and Redox

• Overall equation (simplified): $6\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O} + \text{light energy} \rightarrow \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\mathrm{O}_2$

• CO2 is reduced to glucose; H2O is oxidized to O2.

Light Reactions

• Occur in the thylakoid membranes of chloroplasts.

• Convert light energy to chemical energy (ATP and NADPH); produce O2 as a byproduct.

Calvin Cycle

• Occurs in the stroma of the chloroplast.

• Uses ATP and NADPH from the light reactions to fix CO2 into glucose.

• Energy for the Calvin cycle comes from ATP and NADPH generated in the light reactions.

Why Plant Leaves Are Green

• Chlorophyll pigments absorb red and blue wavelengths of light but reflect green, making leaves appear green.