Cell Biology Lecture 2: Cell Structures

Cell Biology Lecture 2

• Cells are the basic structural and functional units of all tissues and life.
• Eukaryotic cells: have a nuclear envelope and membrane-bound organelles; found in animals and plants.
• Prokaryotic cells: lack a nuclear envelope and membrane-bound organelles; found in bacteria.
• Cell components include cytoplasm, nucleus, cytosol, organelles, cytoskeleton, and cell membrane.
• Cell membrane separates cytoplasm from the external environment.

Membranous Organelles

• Mitochondria: Powerhouses of the cell producing ATP through cellular respiration. Contain their own DNA and regulate the cell cycle.
• Endoplasmic Reticulum (ER):
  • Rough ER: Has ribosomes for protein synthesis.
  • Smooth ER: Involved in lipid synthesis and calcium storage.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids; forms vesicles to transport materials to target locations.
• Lysosomes: Contain digestive enzymes breaking down unwanted materials; play a role in cellular recycling.
• Vesicles: Transport materials within or outside the cell; include secretory and endocytic vesicles.
• Peroxisomes: Contain enzymes breaking down fatty acids and detoxifying harmful substances; play a role in cellular metabolism.

Cell Membrane

• The cell membrane (plasma membrane/plasmalemma) is a thin structure surrounding the cell.
• Composition: Lipid bilayer (50%), proteins, and carbohydrates.
• Functions:
  • Regulation of transport: Acts as a barrier regulating ion and solute passage through channels and transport proteins.
  • Cell signaling: Contains receptors for proteins and hormones allowing interaction with the surrounding environment.
  • Cell adhesion: Contributes to cell adhesion to each other and the extracellular matrix, promoting tissue formation.

The Lipid Component

• Phospholipids form a bilayer: polar heads face outwards and hydrophobic tails inwards creating a barrier.
• Cholesterol (about 2% of membrane lipids) is found in inner/outer layers. Reduces membrane fluidity and increases mechanical stability, affecting processes like exocytosis and endocytosis.
• The lipid component provides a basic structure for the membrane acting as a barrier, protecting the cell and contributing to the regulated movement of materials.

The Protein Component

• Integral proteins: Embedded within the lipid layer, extending across the membrane, interacting with internal/external environments; involved in transporting ions and substances, acting as channels/carriers.
• Peripheral proteins: Located on the inner/outer surface; easily removed and play roles in cell signaling, recognition, and adhesion to the extracellular matrix.

The Carbohydrate Component

• Glycolipids: Sugars attached to lipid molecules (phospholipids).
• Glycoproteins: Sugars attached to proteins, playing roles in many cellular functions.
• Functions: Form the "cell envelope" (glycocalyx) contributing to cellular recognition; help cells adhere to the extracellular matrix. Also protect cells from injury and facilitate communication.

Explore the fundamentals of cell biology in this lecture, focusing on both eukaryotic and prokaryotic cells. Learn about key cellular components and the functions of membranous organelles like mitochondria, endoplasmic reticulum, and Golgi apparatus. This quiz will test your understanding of the basic units of life.