Comprehensive Study Notes: Principles of Biology - Cell Theory, Biochemistry, and Metabolism

Cell - Fundamental unit of life

• The Foundation of Living Organisms:

• Cells represent the simplest form of living matter that can exist independently.

• All life is built upon cellular structures.

• Historical Development of Microscopy:

• Visualization of cells was linked to the invention and refinement of the microscope.

• Robert Hooke: Credited with early cell discovery.

• Antoni van Leeuwenhoek: Pioneer in microscopic observation.

• Light Microscopy (LM):

• Mechanism: Light passes through the specimen and glass lenses.

• Magnification:

  • Ratio of an object’s image size to its actual size.

• Resolution:

  • Clarity of the image; defined as minimum distance between distinguishable points.

• Contrast:

  • Difference in brightness between light and dark areas.

  • Staining may be required to enhance contrast in specimens.

• Electron Microscopy (EM):

• Mechanism: Uses a beam of electrons.

  • Provides much higher resolution than light.

• Constraint: Cannot observe live cells due to preparation process.

• Transmission Electron Microscopy (TEM):

  • Used for studying internal cell structures in 2D.

• Scanning Electron Microscopy (SEM):

  • Provides detailed study of the surface topography, yielding 3D images.

• Cell Size Scales:

• Human Height: Roughly $10 m$ to $1 m$.

• Chicken Egg: $≈ 0.1 m$.

• Frog Egg: $≈ 1 mm$.

• Human Egg: $≈ 100 μm$.

• Eukaryotic Cells (Plant and Animal): Range from $10 μm$ to $100 μm$.

• Prokaryotic Cells (Bacteria): Range from $1 μm$ to $10 μm$.

• Smallest Bacteria: $≈ 100 nm$.

• Viruses: Range from $10 nm$ to $100 nm$.

• Molecules:

  • Lipids: $≈ 1-5 nm$.

  • Proteins: $≈ 5-10 nm$.

  • Small molecules: $≈ 1 nm$.

• Atoms: Approximately $0.1 nm$.

Prokaryotic vs. Eukaryotic Cells

• Common Features:

• Both cell types share:

  • Plasma membrane

  • Cytosol (semifluid substance)

  • Chromosomes (carry genes)

  • Ribosomes (make proteins)

• Prokaryotic Cells (Bacteria and Archaea):

• Nucleus: Absent; DNA is in the nucleoid.

• Organelles: No membrane-bound organelles.

• DNA Structure: Typically a single, circular chromosome.

• Size: Generally small ($1–10 μm$).

• Ribosomes: Smaller size ($70 ext{S}$).

• Cell Division: Binary fission.

• Internal Compartmentalization: Absent.

• Flagella: Simple structure made of flagellin.

• Eukaryotic Cells (Protists, Fungi, Plants, and Animals):

• Nucleus: Present; enclosed by a nuclear membrane.

• Organelles: Presence of various membrane-bound organelles (e.g., mitochondria).

• DNA Structure: Multiple linear chromosomes in the nucleus.

• Size: Larger ($10–100 μm$).

• Ribosomes: Larger size ($80 ext{S}$).

• Cell Division: Mitosis or meiosis.

• Internal Compartmentalization: Present; specialized functions.

• Flagella: Complex structure made of microtubules in a $9+2$ arrangement.

The Endomembrane System

• Components:

• Nuclear envelope

• Endoplasmic reticulum (ER)

• Golgi apparatus

• Lysosomes

• Vesicles/vacuoles

• Plasma membrane

• Unified Function:

• Components are continuous or connected via vesicles.

• Regulate protein traffic and perform metabolic functions.

• The Nucleus:

• Function: Contains most genes.

• Nuclear Envelope: Double membrane, separates nucleus from cytoplasm.

  • Contains nuclear pores for transport.

• Chromatin: DNA and histone proteins that condense into chromosomes during division.

• Nucleolus: Site of ribosomal RNA synthesis.

• Ribosomes:

• Composition: rRNA and protein complexes.

• Free Ribosomes: Located in cytosol; synthesize proteins for within the cell.

• Bound Ribosomes: Attached to ER; synthesize proteins for membranes or secretion.

• Endoplasmic Reticulum (ER):

• Rough ER:

  • Studded with ribosomes.

  • Secretes glycoproteins, distributes transport vesicles, membrane factory.

• Smooth ER:

  • Lacks ribosomes.

  • Functions in lipid synthesis, carbohydrate metabolism, detoxification