Membrane Proteins Functions Quiz

Functions of Membrane Proteins

• Membrane proteins serve six major functions: transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to cytoskeleton/extracellular matrix (ECM).

Membrane Carbohydrates in Cell Recognition

• Cells recognize each other through binding to surface molecules, primarily carbohydrates, on the extracellular membrane.
• Membrane carbohydrates can form glycolipids (bonded to lipids) or glycoproteins (bonded to proteins).
• The composition of carbohydrates on the plasma membrane varies across species, individuals, and even among cell types.

HIV and Cell Infection

• HIV can only infect cells expressing the CCR5 co-receptor alongside CD4 receptor.
• Individuals lacking the CCR5 receptor are resistant to HIV infection.

Membrane Synthesis and Asymmetry

• Membranes possess distinct inside and outside faces, leading to asymmetrical distribution of proteins, lipids, and carbohydrates.
• This asymmetry is established during membrane formation in the endoplasmic reticulum (ER) and Golgi apparatus.

Selective Permeability of Membranes

• Plasma membranes regulate molecular traffic, exhibiting selective permeability to exchange materials.
• Nonpolar molecules (e.g., hydrocarbons) can pass through rapidly, while polar molecules (e.g., sugars) struggle to cross.

Transport Proteins

• Transport proteins facilitate the passage of hydrophilic substances across the membrane.
• Channel proteins create hydrophilic channels for specific molecules or ions (e.g., aquaporins for water).
• Carrier proteins bind solutes and change shape to transport them across the membrane.

Water Balance in Cells with Walls

• In hypotonic solutions, plant cells become turgid from water uptake until the cell wall resists further expansion.
• Isotonic solutions result in flaccid cells, while hypertonic solutions can lead to plasmolysis where membranes separate from the cell wall.

Facilitated Diffusion

• Facilitated diffusion employs transport proteins to expedite the passive movement of substances across the plasma membrane.
• Includes both channel proteins for solute corridors and carrier proteins that change shapes to shuttle solutes.

Active Transport Mechanisms

• Active transport utilizes energy to move solutes against concentration gradients.
• Electrochemical gradients drive ion diffusion through a combination of chemical and electrical forces.

Electrogenic Pumps

• Electrogenic pumps generate voltage across membranes; the sodium-potassium pump is key in animal cells, while proton pumps serve in plants, fungi, and bacteria.
• These pumps help store energy for cellular work.

Cotransport Mechanism

• Cotransport enables the active transport of one solute to indirectly facilitate the transport of others.
• Plant cells often use the gradient of hydrogen ions generated by proton pumps to transport nutrients actively.

Bulk Transport via Exocytosis and Endocytosis

• Small molecules and water can pass through membranes directly or via transport proteins, while larger molecules use bulk transport via vesicles.
• Exocytosis involves vesicles fusing with the membrane to release contents; common in secretory cells.

Types of Endocytosis

• Endocytosis enables cells to intake macromolecules through membrane vesicle formation.
• Involves three forms:
  • Phagocytosis (cellular eating)
  • Pinocytosis (cellular drinking)
  • Receptor-mediated endocytosis (specific molecule uptake).
• In phagocytosis, cells engulf particles in vacuoles that fuse with lysosomes for digestion. In pinocytosis, extracellular fluid is engulfed into vesicles.

Test your knowledge on the six major functions of membrane proteins, including transport, enzymatic activity, signal transduction, and more. This quiz will challenge your understanding of cell membranes and their components.