Cell Biology Lecture 2: Cell Structures

Study Notes

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.

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.

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.

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.

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.

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.