Especializações de membrana - Aula 19 - Módulo 1: Biologia Celular - Prof. Guilherme

Introduction to Cell Membrane Specializations

In this section, the instructor introduces the concept of cell membrane specializations and their importance in cellular functions.

Understanding Cell Membrane Functions

• The cell membrane serves the basic functions of delineating cellular space and enabling selective permeability.

• Specialized functions of the cell membrane go beyond its basic roles, requiring specific adaptations for different tasks.

• When the cell membrane performs functions other than basic ones like delimiting space or selective permeability, it is considered to have a specialized function that necessitates unique adaptations.

Types of Cell Membrane Specializations

This section explores three main types of cell membrane specializations: junctional complexes, hemidesmosomes, and cellular border specializations.

Junctional Complexes

• Cells join through junctional complexes to facilitate communication and coordination.

• Hemidesmosomes are specialized junctions that connect cells to the extracellular matrix rather than other cells directly.

Cellular Border Specializations

• Border deformities or alterations indicate cellular border specializations.

• Zona de oclusão (occlusion zone) acts as a barrier preventing unwanted substances from passing between cells.

Adhesive Junctions and Desmosomes

Adhesive junctions play a crucial role in cell adhesion and coordinated movement. Desmosomes are prominent among various types of membrane specializations.

Adhesive Junction Functionality

• Adhesive junctions involve proteins like actin and myosin for cellular contraction.

• Proteins such as actin and myosin aid in cellular contraction by connecting cells through adhesive junction proteins.

Desmosome Structure

• Desmosomes serve as buttons connecting membranes on both sides with keratin filaments providing structural support.

Plasma Membrane Structures and Functions

In this section, the speaker discusses various structures and functions related to the plasma membrane.

Plasma Membrane Components

• The junction of Hebe, also known as gap junction or communicating junction, plays a crucial role in cell support. It is referred to as plasmodesmata in plant cells.

• Gap junctions are large protein channels that allow substances to pass freely between cells for immediate and intense exchange.

Hemidesmosomes and Desmosomes

• Hemidesmosomes are half-desmosomes, providing partial adhesion between cells and the basal lamina. They ensure skin integrity by anchoring epithelial cells to the basal lamina.

• Desmosomes consist of two plaques with keratin filaments on both sides, connecting adjacent cells. This structure contributes to tissue stability in various epithelial tissues.

Cellular Junction Specializations

This section explores specialized structures at cellular junctions enhancing cell interactions.

Cellular Adhesions

• Hemidesmosomes act as half-desmosomes linking cells to the basal lamina, ensuring tissue cohesion like skin adherence due to interaction with dermis layers.

• Specialized cell-to-basal lamina connections facilitate cellular adhesion through hemidesmosomes, securing tissue integrity and preventing detachment.

Microvilli and Intercellular Interactions

The discussion focuses on microvilli's role in absorption enhancement and intercellular interactions.

Microvilli Functionality

• Microvilli increase cell surface area for nutrient absorption significantly, particularly vital in intestinal cells for efficient nutrient uptake through enhanced contact surfaces.