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 directing protein synthesis.

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

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

• Mitochondria: Site of cellular respiration; produces ATP.

• Rough ER: Studded with ribosomes; synthesizes and processes proteins.

• Smooth ER: Lacks ribosomes; synthesizes lipids, detoxifies drugs, and stores calcium ions.

• Lysosome: Contains digestive enzymes; breaks down macromolecules, old organelles, and foreign substances.

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 water, and 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 and lipids (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 swell and possibly burst (lyse), while plant cells become turgid (normal state for plants).

Passive Diffusion 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 Types of Transport

• Passive transport includes simple diffusion, facilitated diffusion (via channels/carriers), and osmosis.

• Active transport involves pumps (e.g., sodium-potassium pump) and requires ATP.

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).

Gibbs Free Energy Equation

• The change in free energy is given by: $\Delta G = \Delta H - T\Delta S$ where ΔG is the change in free energy, ΔH is the change in enthalpy, T is temperature in Kelvin, and ΔS is the change in entropy.

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 transfers energy within cells.

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

• The released phosphate can be transferred to other molecules (phosphorylation), driving cellular work.

Chapter 9: Cellular Respiration and Fermentation

Purpose of Cellular Respiration

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

Overall Equation and Redox

• Overall equation: $\mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} \rightarrow 6\mathrm{CO_2} + 6\mathrm{H_2O} + \text{energy (ATP)}$

• 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 Processes

• Glycolysis occurs without oxygen and outside the mitochondria (in the cytoplasm).

• Anaerobic respiration/fermentation produces less ATP and results in products like lactic acid (in animals) or ethanol and CO2 (in yeast).

Chapter 10: Photosynthesis

Relationship to Cellular Respiration

• Photosynthesis and cellular respiration are complementary processes.

• Photosynthesis stores energy in glucose; respiration releases it.

Overall Purpose and Equation

• Purpose: To convert light energy into chemical energy (glucose).

• Overall equation (simplified): $6\mathrm{CO_2} + 6\mathrm{H_2O} + \text{light energy} \rightarrow \mathrm{C_6H_{12}O_6} + 6\mathrm{O_2}$

• 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.