Cell Fundamentals & Chemical Foundations
This introductory unit lays the entire foundation. It defines Cell and Molecular Biology, traces its remarkable history from the invention of the microscope to the discovery of DNA, and establishes the fundamental properties that all living cells share. You will compare the vastly different architectures of Prokaryotic and Eukaryotic cells, understand the elegant structure of the cell membrane, explore cellular reproduction, and review the essential chemical reactions that power all of life.
Syllabus & Topics
- 1Cell and Molecular Biology: Definitions, Theory, Basics & Applications: Cell Biology: The study of cells—their structure, function, and behavior. Molecular Biology: The study of biological processes at the molecular level (DNA, RNA, Proteins). Cell Theory (Schleiden & Schwann): (1) All living things are composed of cells. (2) The cell is the basic structural and functional unit of life. (3) All cells arise from pre-existing cells. Applications: Understanding disease mechanisms, drug targets, genetic engineering, vaccine development, and cancer biology.
- 2History and Summation: Robert Hooke (1665): First coined the term ‘Cell’ after observing cork under a primitive microscope. Antonie van Leeuwenhoek (1670s): First to observe living single-celled organisms (‘animalcules’). Watson & Crick (1953): Discovered the double-helix structure of DNA. Modern Era: Development of electron microscopy, recombinant DNA technology, PCR, CRISPR gene editing, and single-cell genomics.
- 3Properties of Cells and Cell Membrane: Properties of All Cells: Metabolism (chemical reactions for energy), Growth and Reproduction, Response to stimuli, Homeostasis (maintaining internal stability). Cell Membrane (Plasma Membrane): The Fluid Mosaic Model (Singer & Nicolson, 1972). Structure: A phospholipid bilayer with embedded integral and peripheral proteins. Functions: Selective permeability (controlling what enters/exits the cell), cell signaling via membrane receptors, and cell-cell recognition via glycoproteins.
- 4Prokaryotic versus Eukaryotic Cells: Prokaryotic (Pro = before, Karyon = nucleus): No true membrane-bound nucleus (DNA floats in the nucleoid region). No membrane-bound organelles. Single, circular chromosome. Examples: Bacteria (E. coli), Archaea. Eukaryotic (Eu = true, Karyon = nucleus): True membrane-bound nucleus containing linear chromosomes. Membrane-bound organelles (Mitochondria, ER, Golgi, Lysosomes). Much larger and more complex. Examples: Animal cells, Plant cells, Fungi.
- 5Cellular Reproduction: The fundamental process by which a cell divides to produce two or more daughter cells. Prokaryotic: Binary Fission—simple splitting of the cell into two identical copies after replicating its single circular chromosome. Eukaryotic: Mitosis (somatic cell division producing identical diploid daughters) and Meiosis (reproductive cell division producing genetically unique haploid gametes). Budding: A form of asexual reproduction seen in organisms like yeast.
- 6Chemical Foundations – Introduction and Reaction Types: All life runs on chemistry. Key Biological Reactions: Oxidation-Reduction (Redox): Transfer of electrons; powers cellular respiration (ATP production). Hydrolysis: Breaking bonds by adding water (e.g., digesting proteins into amino acids). Condensation (Dehydration Synthesis): Forming bonds by removing water (e.g., building polypeptides from amino acids). Phosphorylation: Adding a phosphate group to activate/deactivate enzymes (critical for cell signaling). Acid-Base Reactions: Proton (H⁺) transfer; maintaining cellular pH homeostasis.
Learning Objectives
Exam Prep Questions
Q1. Why is the cell membrane described as a “Fluid Mosaic”?
The term “Fluid Mosaic” describes both the structure and behavior of the cell membrane:
Fluid: The phospholipid molecules in the bilayer are not fixed in place. They move laterally, allowing the membrane to remain flexible and dynamic rather than rigid.
Mosaic: The membrane contains a diverse mix of components—proteins, cholesterol, and carbohydrates (glycoproteins and glycolipids)—embedded within the lipid bilayer. These components are arranged in a patchwork pattern, resembling a mosaic.
Together, this model explains how the membrane maintains flexibility, selective permeability, and functional diversity.
Q2. What is the biggest difference between a prokaryotic and a eukaryotic cell?
The most fundamental difference is the presence of a true nucleus:
Eukaryotic cells: Have a membrane-bound nucleus that encloses and protects genetic material (DNA).
Prokaryotic cells: Lack a nucleus; their DNA exists as a single circular molecule in a region called the nucleoid, without a surrounding membrane.
This distinction is the basis of their names:
Prokaryote = “before nucleus”
Eukaryote = “true nucleus”
Q3. Why is phosphorylation so important in biology?
Phosphorylation is a key biochemical process where a phosphate group (–PO₄) is added to a protein or molecule by enzymes called kinases.
This modification can change the structure and function of proteins, effectively turning them ON or OFF. Because of this, phosphorylation acts as a major regulatory mechanism in cells.
It controls essential processes such as:
Cell signaling pathways
Metabolism
Cell division and growth
Gene expression
Many modern drugs target phosphorylation pathways—for example, kinase inhibitors like Imatinib are used in cancer treatment.