Cell Structure and Membrane Proteins: Anatomy & Physiology Study Notes

Cell Structure

Overview of Eukaryotic Cell Components

The eukaryotic cell contains various organelles, each with specialized functions essential for cellular activity and homeostasis. Understanding the structure and function of these organelles is fundamental in Anatomy & Physiology.

• Nucleus: The control center of the cell, containing genetic material (DNA) and surrounded by the nuclear envelope.

• Plasma Membrane: A fragile barrier that defines the cell's outer boundary, regulating the movement of substances in and out of the cell.

• Cytoplasm: The region between the plasma membrane and nucleus, packed with organelles that perform specific functions.

• Lysosome: Organelle containing digestive enzymes for breaking down waste materials and cellular debris.

• Mitochondria: The powerhouse of the cell, responsible for producing ATP through cellular respiration.

• Centrioles: Structures involved in cell division and organization of microtubules.

• Rough Endoplasmic Reticulum (Rough ER): Studded with ribosomes, involved in protein synthesis and modification.

• Ribosomes: Sites of protein synthesis, found free in cytoplasm or attached to rough ER.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Peroxisome: Contains enzymes for breaking down fatty acids and detoxifying harmful substances.

• Cytoskeletal Elements: Network of protein filaments providing structural support, shape, and movement.

Example: The mitochondria generate ATP, which is used by other organelles such as the ribosomes for protein synthesis.

Plasma Membrane Structure and Function

Plasma Membrane

The plasma membrane is a selectively permeable barrier that separates the cell from its external environment. It is composed primarily of a phospholipid bilayer with embedded proteins.

• Fragile Barrier: Maintains cellular integrity and controls exchange of materials.

• Outer Boundary: Defines the limits of the cell.

Cytoplasm

The cytoplasm is the site of most cellular activities and contains the cytosol, organelles, and inclusions.

• Packed with Organelles: Organelles within the cytoplasm perform specialized functions such as energy production, protein synthesis, and waste disposal.

Nucleus

The nucleus acts as the control center of the cell, regulating gene expression and cell division.

• Surrounded by Cytoplasm: The nucleus is centrally located and encased by the cytoplasm.

Membrane Proteins

Types of Membrane Proteins

Membrane proteins are essential for various cellular processes, including transport, signaling, and structural support. They are classified based on their association with the lipid bilayer.

• Integral Proteins: Firmly inserted into the lipid bilayer, often spanning the entire membrane. These proteins protrude from both sides of the bilayer and are also called transmembrane proteins.

• Function: Integral proteins can act as transport channels, allowing small molecules or ions to move through the lipid bilayer, or serve as carriers.

• Peripheral Proteins: Not embedded in the lipid bilayer; instead, they loosely attach to integral proteins or membrane lipids. Peripheral proteins often play roles in signaling or maintaining the cell's shape.

Example: Sodium-potassium pumps are integral proteins that actively transport ions across the plasma membrane, maintaining cellular electrochemical gradients.

Comparison of Integral and Peripheral Proteins

Feature	Integral Proteins	Peripheral Proteins
Location	Embedded in lipid bilayer	Attached to membrane surface
Function	Transport, channels, carriers	Signaling, structural support
Mobility	May span entire membrane	Loosely associated, easily removed

Key Terms:

• Transmembrane Proteins: Integral proteins that span the entire membrane.

• Transport Channels: Pathways for molecules and ions to cross the membrane.

Additional info: The fluid mosaic model describes the plasma membrane as a dynamic structure with proteins floating in or on the fluid lipid bilayer.