Membrane Structure and Function: Study Notes (Chapter 7)

Membrane Structure and Function

Learning Objectives

This chapter focuses on the structure and function of biological membranes, emphasizing the fluid mosaic model, selective permeability, and various transport mechanisms. By the end of this section, students should be able to:

• Identify the lipids and proteins of the fluid mosaic model

• Describe types of selective permeability

• Distinguish types of passive transport

• Elucidate active transport in cells

• Describe the types of bulk transport

Mosaic of Lipids & Proteins

Overview of Membrane Composition

Biological membranes are primarily composed of lipids, proteins, and a small amount of carbohydrates. This composition allows membranes to perform a variety of essential cellular functions.

• Lipids: Form the main structural fabric of the membrane

• Proteins: Embedded within or attached to the lipid bilayer, responsible for most membrane functions

• Carbohydrates: Present in small amounts, often attached to proteins or lipids, involved in cell recognition

Fluid Mosaic Model

The fluid mosaic model describes the structure of cell membranes as a mosaic of diverse protein molecules embedded in a fluid bilayer of phospholipids. This model highlights both the variety of components and their dynamic movement within the membrane.

• Mosaic: Refers to the presence of different types of molecules (lipids, proteins, carbohydrates)

• Fluid: Indicates that the lipid and protein molecules can move laterally within the layer

Membrane Proteins

Membrane proteins are crucial for the function of biological membranes. They can be classified based on their association with the membrane:

• Hydrophilic Portion: Oriented towards the extracellular or cytoplasmic side

• Hydrophobic Portion: Embedded within the membrane's hydrophobic core

Types of membrane proteins include:

• Integral proteins: Span the membrane or are deeply embedded

• Peripheral proteins: Loosely bound to the surface of the membrane

Phospholipids

Phospholipids are the primary lipid component of membranes. They are amphipathic, meaning they have both hydrophobic and hydrophilic regions:

• Hydrophilic head: Attracted to water, faces the aqueous environment

• Hydrophobic tail: Repelled by water, faces inward, away from water

This arrangement forms a bilayer that separates two aqueous environments (inside and outside the cell).

Additional info:

• Amphipathic molecules: Molecules with both hydrophilic and hydrophobic regions, crucial for membrane formation

• Fluidity: The lateral movement of lipids and proteins within the membrane is essential for membrane function, including cell signaling and transport