Cell Biology: Discovery and Diversity

• This course is the fundamental science needed for future studies in Biochemistry, Microbiology, Pharmacology, and Pharmacognosy.
• Cell Biology is crucial for understanding cell function and behavior in healthy and diseased states.
• Cell Biology covers topics like the actions of drugs on cells and how antibiotics target bacterial cells.
• This course is divided into Biochemistry and Microbiology.
• The Biochemistry part of the course covers the structure, function, and behavior of eukaryotic cells.

Cell Discovery

• The discovery of cells was linked to the development of the microscope in the seventeenth century.
• Hooke was the first to observe and record cells, describing cella (open spaces) in plant tissues.
• The cell theory was proposed by botanist Schleiden and zoologist Schwann.
• The cell theory states that all living organisms are composed of cells.

Cell Diversity

• Cell size is measured in micrometers (µm), where 1 µm = 10⁻⁶ m.
• Organisms can be unicellular (e.g., bacteria) or multicellular (e.g., humans, animals, plants, fungi).
• Cells have different shapes that correlate with their specific functions include round biconcave, amoeboid, long and narrow, branched and long and kidney shaped.
• Cell functions include food digestion, detoxification, movement, reproduction, support, defending against pathogens, thinking, feeling, and consciousness.

Cell Classification

• The presence or absence of a nucleus is used to classify all living things.
• Prokaryotes are organisms with cells lacking a nucleus; "pro" means "before" and "karyon" means "nucleus."
• Eukaryotes are organisms with cells that have a nucleus.
• The term "eu" means "truly," and "karyon" means "nucleus".

Biological Membranes

• Cell membranes are selectively-permeable, dividing cells from each and creating intracellular compartments.
• Membrane composition differs between the inside and outside of the cell, and inside different cell organelles.
• Biomembranes are composed of carbohydrates, lipids, and proteins.
• Carbohydrates make up a small proportion of the membrane, existing as glycolipids or glycoproteins only in the outer leaflet.
• The protein to lipid ratio differs in each membrane depending on its function.
• Most plasma membranes consist of 50% protein and 50% lipid.
• Inner mitochondrial membranes contain 75% protein and 25% lipid due to their extensive biological functions.
• The myelin sheath in the nervous system consists of of 20% protein and 80% lipid, providing a thick permeability barrier for ions to insulate the axon.

Membrane Lipids

• Phosphoglycerides have glycerol as the alcohol backbone.
• Examples of phosphoglycerides include phosphatidyl-ethanolamine, choline, serine, glycerol, or inositol.
• Sphingomyelins have sphingosine as the alcohol backbone.
• Fatty acids are hydrophobic.
• PO₄⁻³ and alcohol are hydrophilic.
• Membrane lipids containing sugar e.g. cerebrosides & gangliosides are termed sugar-containing lipids.
• Glycosphingolipids contain sphingosine as the alcohol backbone.
• Cholesterol intercalates among the phospholipids of the membrane.
• Plasma membranes form a sheet with hydrophobic fatty acid regions protected from the environments, while hydrophilic regions (PO₄⁻³ & alcohol) are immersed in water.

Membrane Fluidity

• Membrane fluidity is determined by the relative movement of lipids within the membrane.
• Movement depends on the strength of intermolecular interactions between the lipids.
• Stronger interactions lead to a rigid membrane, while weaker interactions result in a fluid membrane.
• Longer fatty acid chains decrease fluidity.
• Increased unsaturation decreases the compactness of side chain packing, increasing fluidity.
• As temperature decreases, lipids tend to cluster together but cholesterol fill in between the phospholipids disrupting the phospholipids interactions thus increasing fluidity.
• As temperature increases, lipids separate, cholesterol pulls phospholipids together, decreasing fluidity.

Membrane Proteins

• Membrane proteins attach to the lipid bilayer.
• Plasma membrane proteins function as selective transport channels, enzymes, cell surface receptors, identity markers, adhesion molecules, and attachments to the cytoskeleton.

Cell Adhesion

• Cell adhesion is the process by which cells interact and attach to neighboring cells, mediated by cell adhesion molecules.
• Direct contact is an immediate connection with a neighboring cell, such as cell-cell adhesion (e.g., cadherin/Ca⁺²⁺ dependent adhesion).
• Indirect contact via the extracellular matrix, such as cell-matrix adhesion (e.g., integrin).

Explore the fundamental science of cell biology, crucial for understanding cell function in health and disease. Learn about cell structure, actions of drugs on cells, and antibiotic targeting in bacterial cells. Discover the history of cell discovery, from Hooke's observations to the cell theory.