Lecture Notes: Eukaryotic Cell Structures and Functions

Introduction

• Focus on understanding how a cell functions by integrating genetic machinery and decision-making processes.
• Typical eukaryotic cell diagram, often seen from an early age, is a simplified depiction of cell structures.
• Real cells vary greatly in structure and do not look exactly like the diagram.
• Diagrammatic representation emphasizes organelles, which are membrane-bound structures performing specific functions.

Key Characteristics of Animal Cells

• Animal cells lack a cell wall; have a plasma membrane.
• Mitochondrion: Known as the powerhouse of the cell; transforms energy into metabolically useful forms.
• Endoplasmic Reticulum (ER):
  • Rough ER: Studded with ribosomes; site for protein synthesis.
  • Smooth ER: More tubular; involved in lipid synthesis and detoxification.
• Golgi Apparatus: Processes and packages proteins.
• Other organelles include lysosomes, peroxisomes, and cytoskeleton.

Organelles and Cell Functions

• True organelles are membrane-bound.
• Not all cells possess every organelle (e.g., some lack mitochondria; muscle cells are rich in cytoskeleton).
• Nucleus: Contains DNA; nucleolus within produces ribosomal parts.
• Endomembrane System: Includes nuclear membrane, ER, and Golgi; integral for protein processing.

Membrane Structure and Function

• Cell Membrane: Most energetically active structure, using about half of resting energy.
• Composed of amphipathic molecules (e.g., phospholipids).
• Membrane is a phospholipid bilayer with hydrophilic heads and hydrophobic tails.
• Integral for cell function, acting as a barrier and organizing cell components.

Proteins and Cholesterol in Membranes

• Membrane proteins are integral (spanning membrane) or peripheral.
• Proteins such as ion channels and receptors facilitate function and communication.
• Membranes include cholesterol, affecting membrane fluidity and stability.
• Fluid Mosaic Model: Describes dynamic nature of membranes; proteins and lipids move laterally.

Membrane Dynamics

• Lipids and proteins move quickly, driven by thermal energy.
• Cholesterol modulates membrane fluidity and rigidity.
• Living membranes are complex, containing multiple molecules for stability and function.

Conclusion

• Understanding membranes is key to understanding cellular function.
• Membranes facilitate selective permeability, communication, and structural integrity.