Chapter 6 – A Tour of the Cell

Key Concepts and Definitions

• Cell: The simplest collection of matter that can be alive. All living organisms are composed of cells.

• Unicellular: An organism consisting of a single cell (e.g., Escherichia coli).

• Multicellular: An organism composed of multiple cells (e.g., humans, plants).

• Organelle: A membrane-bound intracellular structure with a specialized function within a eukaryotic cell.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles. DNA is located in the nucleoid region. Includes organisms from the domains Bacteria and Archaea.

• Eukaryotic Cells: Have a true nucleus enclosed by a nuclear envelope and possess membrane-bound organelles. Includes organisms from the domain Eukarya (protists, fungi, plants, animals).

Cell Size and Surface Area-to-Volume Ratio

• Cells are small because a high surface area-to-volume ratio allows for efficient exchange of materials with the environment.

• As a cell increases in size, its volume grows faster than its surface area, limiting the rate of exchange.

Cell Structure Identification

• Be able to identify and label major organelles and structures in diagrams of animal and plant cells, such as the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, plasma membrane, cell wall, and chloroplasts.

• Recognize which structures are common to all cells (e.g., plasma membrane, cytoplasm, ribosomes, DNA).

Endomembrane System

• The endomembrane system includes the nuclear envelope, endoplasmic reticulum (rough and smooth), Golgi apparatus, lysosomes, vesicles, and the plasma membrane.

• Path of a secreted protein: Ribosome → Rough ER → Vesicle → Golgi apparatus → Vesicle → Plasma membrane

Structure and Function of Mitochondria and Chloroplasts

• Mitochondria: Sites of cellular respiration; convert chemical energy in food to ATP. Have a double membrane and their own DNA.

• Chloroplasts: Sites of photosynthesis in plant cells; convert solar energy to chemical energy. Also have a double membrane and their own DNA.

Cytoskeleton

• Composed of microtubules, microfilaments, and intermediate filaments.

• Microtubules: Hollow tubes that maintain cell shape, aid in cell division, and serve as tracks for organelle movement.

• Microfilaments: Thin fibers involved in cell movement and muscle contraction.

Cell Walls and Extracellular Matrix (ECM)

• Cell Wall: Rigid structure outside the plasma membrane in plants, fungi, and some protists; provides support and protection.

• ECM: Network of proteins and carbohydrates outside animal cells; provides structural support and mediates cell signaling.

Chapter 7 – Membrane Structure & Function

Phospholipids and Membrane Structure

• Phospholipid: A lipid with a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails; forms the basic structure of cell membranes.

• Membranes are fluid mosaics of lipids, proteins, and carbohydrates.

Membrane Fluidity

• Membrane fluidity is influenced by the types of fatty acids (saturated vs. unsaturated) and cholesterol content.

• Unsaturated fats increase fluidity; cholesterol can both stabilize and increase fluidity depending on temperature.

Selective Permeability and Concentration Gradients

• Selective Permeability: The membrane allows some substances to cross more easily than others.

• Concentration Gradient: A difference in the concentration of a substance across a space or membrane.

Passive and Active Transport

• Passive Transport: Movement of substances across the membrane without energy input (e.g., diffusion, osmosis, facilitated diffusion).

• Active Transport: Movement of substances against their concentration gradient, requiring energy (usually ATP).

Osmosis and Tonicity

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

• Tonicity: The ability of a surrounding solution to cause a cell to gain or lose water.

Types of Membrane Transport

Endocytosis and Exocytosis

• Exocytosis: Process by which substances are exported out of the cell via vesicles fusing with the plasma membrane.

• Endocytosis: Process by which substances are imported into the cell by engulfing them in vesicles.

• Types of endocytosis:

  • Phagocytosis: "Cell eating"; cell engulfs large particles.

  • Pinocytosis: "Cell drinking"; cell engulfs extracellular fluid.

  • Receptor-mediated endocytosis: Specific molecules are taken in after binding to receptors.

Chapter 8 – Metabolism and Energy

Metabolism and Metabolic Pathways

• Metabolism: The sum of all chemical reactions in a cell.

• Metabolic Pathway: A series of chemical reactions that either build up (anabolic) or break down (catabolic) molecules.

Anabolic vs. Catabolic Pathways

• Anabolic Pathways: Build complex molecules from simpler ones; require energy (e.g., protein synthesis).

• Catabolic Pathways: Break down complex molecules into simpler ones; release energy (e.g., cellular respiration).

ATP and Energy Coupling

• ATP (Adenosine Triphosphate): The cell's main energy currency; powers cellular work by coupling exergonic and endergonic reactions.

• Energy is released when ATP is hydrolyzed to ADP and inorganic phosphate:

Enzymes

• Enzyme: A biological catalyst that speeds up chemical reactions by lowering activation energy.

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

• Allosteric Site: A site other than the active site where molecules can bind and regulate enzyme activity.

• Feedback Inhibition: The end product of a metabolic pathway inhibits an earlier step, preventing overproduction.

Thermodynamics in Biology

• First Law: Energy cannot be created or destroyed, only transformed.

• Second Law: Every energy transfer increases the entropy (disorder) of the universe.

Exergonic vs. Endergonic Reactions

Enzyme Activity and Regulation

• Enzyme activity is affected by temperature and pH; each enzyme has optimal conditions.

• Cells regulate metabolism by controlling enzyme activity and gene expression.

Example:

• Example of feedback inhibition: In the synthesis of isoleucine from threonine, isoleucine acts as an inhibitor of the first enzyme in the pathway when its concentration is high.

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard General Biology curriculum.