Introduction to Cell Biology

A. The Basic Building Blocks of Life

Cells are the fundamental units of life, composed of various molecules that perform essential biological functions.

• Key Point 1: All living organisms are made up of cells, which can be prokaryotic or eukaryotic.

• Key Point 2: The main molecular building blocks include proteins, nucleic acids (DNA and RNA), lipids, and carbohydrates.

• Example: The plasma membrane is primarily composed of a lipid bilayer with embedded proteins.

B. Chemical Information (DNA, RNA, Making Proteins)

Genetic information is stored in DNA and expressed through RNA to produce proteins, which carry out most cellular functions.

• Key Point 1: DNA (deoxyribonucleic acid) encodes genetic instructions; RNA (ribonucleic acid) acts as a messenger and functional molecule.

• Key Point 2: Central Dogma: Information flows from DNA → RNA → Protein.

• Example: Transcription produces mRNA from DNA; translation synthesizes proteins from mRNA.

C. Protein Structure and Function

Proteins are complex molecules with diverse structures and functions, determined by their amino acid sequences.

• Key Point 1: Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.

• Key Point 2: Protein function depends on its three-dimensional shape, which is stabilized by various bonds and interactions.

• Example: Enzymes are proteins that catalyze biochemical reactions.

D. Regulation of Protein Function (Phosphorylation, GTPases)

Cells regulate protein activity through chemical modifications and molecular switches.

• Key Point 1: Phosphorylation is the addition of a phosphate group, often altering protein activity or localization.

• Key Point 2: GTPases are proteins that act as molecular switches, cycling between active (GTP-bound) and inactive (GDP-bound) states.

• Example: Ras is a GTPase involved in cell signaling pathways.

E. Cellular Organization and Organelles

Eukaryotic cells contain membrane-bound organelles that compartmentalize cellular functions.

• Key Point 1: Major organelles include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes.

• Key Point 2: Each organelle has specialized roles, such as energy production, protein synthesis, and waste degradation.

• Example: The mitochondrion is the site of ATP production via cellular respiration.

F. Prokaryotes, Eukaryotes, and Cellular Evolution

Cells are classified as prokaryotic or eukaryotic, reflecting differences in complexity and evolutionary history.

• Key Point 1: Prokaryotes (bacteria and archaea) lack a nucleus and membrane-bound organelles.

• Key Point 2: Eukaryotes (plants, animals, fungi, protists) have a nucleus and complex organelles.

• Example: Endosymbiotic theory explains the origin of mitochondria and chloroplasts in eukaryotes.

G. Cellular Energetics

Cells require energy to perform work, which is managed through metabolic pathways.

• Key Point 1: ATP (adenosine triphosphate) is the primary energy currency of the cell.

• Key Point 2: Major processes include glycolysis, citric acid cycle, and oxidative phosphorylation.

• Example: The overall equation for cellular respiration:

H. Experimental Methods – Studying Gene Function

Modern cell biology uses various experimental techniques to investigate gene function.

• Key Point 1: Gene knockout and RNA interference (RNAi) are used to disrupt gene expression.

• Key Point 2: Reporter genes (e.g., GFP) help visualize gene expression in living cells.

• Example: CRISPR-Cas9 is a genome editing tool for targeted gene modification.

Microscopy and Cell Manipulation

A. Fundamentals of Light Microscopy

Light microscopy is a foundational technique for visualizing cells and tissues.

• Key Point 1: Uses visible light and lenses to magnify specimens up to ~1000x.

• Key Point 2: Resolution is limited by the wavelength of light; typically ~200 nm.

• Example: Brightfield, phase-contrast, and differential interference contrast (DIC) microscopy.

B. Light Microscopy: Manipulating Light and Imaging Techniques

Advanced light microscopy techniques enhance contrast and allow for specific imaging of cellular components.

• Key Point 1: Staining and optical sectioning improve visualization of structures.

• Key Point 2: Confocal microscopy uses lasers and pinholes to obtain sharp, optical sections.

• Example: Immunofluorescence labeling to detect specific proteins.

C. Fluorescence Microscopy

Fluorescence microscopy uses fluorescent dyes or proteins to visualize specific molecules within cells.

• Key Point 1: Fluorophores absorb light at one wavelength and emit at another, allowing for specific labeling.

• Key Point 2: Enables multi-color imaging and tracking of dynamic processes.

• Example: GFP-tagged proteins in live cell imaging.

D. Fluorescence Labelling of Cell Samples

Fluorescent labeling techniques are used to tag cellular components for visualization.

• Key Point 1: Immunofluorescence uses antibodies conjugated to fluorophores to detect specific proteins.

• Key Point 2: In situ hybridization labels nucleic acids with fluorescent probes.

• Example: DAPI staining for DNA in cell nuclei.

E. Fluorescence Microscopy of Living Cells and Super-Resolution Imaging

Live-cell fluorescence microscopy and super-resolution techniques allow for high-resolution, dynamic studies of cellular processes.

• Key Point 1: Live-cell imaging tracks protein movement and interactions in real time.

• Key Point 2: Super-resolution microscopy (e.g., STED, PALM, STORM) surpasses the diffraction limit of light, achieving resolutions below 50 nm.

• Example: Tracking vesicle transport in neurons using live-cell imaging.

F. Electron Microscopy

Electron microscopy provides much higher resolution than light microscopy, allowing visualization of ultrastructural details.

• Key Point 1: Transmission electron microscopy (TEM) images thin sections of cells at nanometer resolution.

• Key Point 2: Scanning electron microscopy (SEM) provides detailed surface images.

• Example: Visualizing ribosomes and organelle membranes with TEM.

G. Experimental Methods: Introducing Material into Cells

Various techniques are used to introduce DNA, RNA, proteins, or other materials into cells for experimental purposes.

• Key Point 1: Transfection introduces nucleic acids using chemical, physical, or viral methods.

• Key Point 2: Microinjection and electroporation are physical methods for delivering materials into cells.

• Example: Using lipofection to deliver plasmid DNA into cultured mammalian cells.

Summary Table: Core Topics in Cell Biology