Cell Membranes and Their Functions

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Questions and Answers

What is the primary characteristic of tight junctions?

Forms a selective barrier between adjacent cells (correct)

Generates electrical charges across membranes

Involves extensive communication between cells

Allows for high permeability of substances

Which proteins are primarily involved in the adhesion of tight junctions?

Caveolins

Cadherins

Intrinsic membrane proteins (correct)

Integrins

What type of junction is found near the apical pole of epithelial cells?

Gap junction

Tight junction (correct)

Desmosome

Adherens junction

During which stage of development do junctions typically form?

Embryonic development Signup and view all the answers

Which of the following junction types is characterized by a filamentous structure anchoring cells together?

Intermediate junction Signup and view all the answers

What is the main function of junctions in epithelial tissues?

Providing adhesion and communication between cells Signup and view all the answers

Caveolae, a specialized type of lipid raft, play a role in which cellular process?

Endocytosis Signup and view all the answers

What is a consequence of compromised junction types in tissues?

Dissociation of tissue cells Signup and view all the answers

What is the primary function of intermediate junctions in tissues?

Adhesion of cells Signup and view all the answers

What is another name for intermediate junctions?

Belt desmosomes Signup and view all the answers

Which unique structural feature differentiates spot desmosomes from intermediate junctions?

Spot desmosomes create button-like attachment points Signup and view all the answers

What is the role of cadherins in intermediate junctions?

To mediate adhesion between neighboring cells Signup and view all the answers

What is the intercellular space between the plasma membranes in intermediate junctions?

20 to 35 nm Signup and view all the answers

Which statement about cadherin interaction is true?

Cadherins interact through their extracellular domains. Signup and view all the answers

What component connects cadherins to actin filaments in the cytoplasmic face of intermediate junctions?

Catenins Signup and view all the answers

In what type of tissues are intermediate junctions particularly prevalent?

Epithelial tissues Signup and view all the answers

What role do tight junctions play in the epithelium of the intestine?

They act as a barrier to the flow of materials between cells. Signup and view all the answers

What serves as the main structural component of tight junctions?

Occludin Signup and view all the answers

How do tight junctions contribute to cell shape determination?

Via their association with actin filaments. Signup and view all the answers

What is the primary function of the belt formed by tight junctions?

Creating a barrier to the intercellular space. Signup and view all the answers

In which tissues can tight junctions be primarily found?

Epithelial tissues, including the intestine and blood capillaries. Signup and view all the answers

What is a characteristic feature of the arrangement of tight junctions?

They have interconnecting, zipper-like structures. Signup and view all the answers

What must nutrients do to be absorbed by epithelia, considering tight junctions' role?

Cross the apical membrane surface of the epithelial cells. Signup and view all the answers

What is one of the critical controlling factors of tight junction formation?

Cellular signaling mechanisms. Signup and view all the answers

Study Notes

Plasma Membranes and Other Cell Membranes

Membranes are found in all cells, including the plasma membrane, nuclear membranes, endoplasmic reticulum membranes, Golgi apparatus membranes, vacuole membranes, plastid membranes, and mitochondrial membranes.
These membranes (called cytomembranes) form compartments within the cell, separating them from their surroundings.
Prokaryotic cells have simpler membranes than eukaryotic cells, which have more complex compartmentalization.
The plasma membrane, also called the plasmalemma or cytoplasmic membrane, is crucial for cell integrity by separating the cytoplasm from the surrounding environment.
Damage to the plasma membrane can lead to cell death.
Cell membranes are involved in many biochemical reactions, such as signal transduction, phosphorylation, and cell respiration (in prokaryotes).
They also facilitate communication and interaction between neighboring cells.
Cell membranes have selective permeability, regulating the passage of substances between compartments.
Some molecules readily pass through the lipid bilayer (hydrophobic), while others need channels or transporters (hydrophilic).
Passage can be active or passive.

The Lipid Bilayer

Cell membranes primarily consist of a phospholipid bilayer.
Phospholipids are amphipathic, meaning they have both polar (hydrophilic) heads and nonpolar (hydrophobic) tails.
They arrange in a bilayer to minimize contact between hydrophobic tails and water.
Proteins and carbohydrates are also components of cell membranes.
The proportions of these components vary between different cell types.
Different proteins have different functions, including transport, signaling, and structure.

The Fluid-Mosaic Model

The fluid-mosaic model describes the structure of cell membranes.
The model depicts a phospholipid bilayer with embedded proteins.
Protein types include peripheral (extrinsic) proteins, loosely bound to the membrane's surface, and integral (intrinsic) proteins, firmly embedded within the bilayer.
Integral proteins can span the membrane entirely (transmembrane) or only partly.
Carbohydrates are typically attached to proteins (glycoproteins) or lipids (glycolipids) on the outer surface.

Membrane Asymmetry

Proteins and lipids are not distributed evenly across the membrane layers (inner and outer leaflets).
Different types of lipids and proteins are more prevalent in one leaflet than the other.
This asymmetry is crucial for the function of the cell membrane.

Membrane Fluidity

Membranes are dynamic, their components are in constant motion within the bilayer.
Factors influencing fluidity include temperature, fatty acid saturation, and the presence of cholesterol.
Cholesterol acts as a regulator, decreasing fluidity at high temperatures and increasing it at low temperatures.
Membrane fluidity is essential for proper function.

Membrane Specializations

Cell membranes exhibit specialized domains, with variations in protein and lipid compositions.
Junctions like tight junctions, intermediate junctions (desmosomes), and gap junctions facilitate cell-cell interactions.
Gap junctions allow communication and the movement of molecules between cells.
Microvilli and stereocilia increase surface area for absorption or secretion.
Infolds of the basal membrane enhance absorption or secretion (e.g., in kidney cells).

Specialization of the plasma membrane

Junctions facilitate cell-cell adhesion, communication, and transport.
Junctions include tight, gap, and desmosomes, all with unique functions.

Transport of Macromolecules

Larger molecules use bulk transport (endocytosis and exocytosis) which is a process involving vesicles.
Endocytosis (inward movement) includes phagocytosis (for large particles) and other types of endocytosis for other molecules.
Exocytosis (outward movement) releases molecules out of the cell.
Both processes are essential for maintaining the integrity and function of the membrane.

Plant Cell Walls and Plasmodesmata

Plant cells have cell walls, aiding structural support and protection.
Plasmodesmata are channels in the cell wall permitting communication between neighboring cells.
This structure differs from the animal cell counterparts in having a rigid cell wall.
The channels enable the transport of water, ions, and small molecules between cells.

Microvilli

Microvilli increase surface area in parts of cells where absorption or secretion need enhancing.
The structure includes bundles of actin filaments providing support and possibly movement.

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Description

Explore the diverse types of cell membranes, focusing on their structure and function. Learn about the critical role of the plasma membrane, as well as how membranes in prokaryotic and eukaryotic cells differ. This quiz covers essential concepts regarding membrane permeability and cellular communication.