Cellular Biology of Vesicular Transport (DLA)

This set of flashcards covers key vocabulary and concepts related to the cellular biology of vesicular transport, including endocytosis and exocytosis mechanisms, types of transport, and the roles of specific proteins in these processes.

What is membrane transport?

Membrane transport refers to the process by which substances move across cell membranes.

What is simple diffusion in membrane transport?

the process where substances cross the membrane down their concentration gradient without the use of energy or membrane proteins.

Which substances can cross the membrane by simple diffusion?

Small, hydrophobic, non-polar, uncharged molecules and gases such as O2 and CO2 can cross the membrane by simple diffusion.

Do all molecules require energy for membrane transport?

No, only certain molecules, particularly larger or charged ones, require energy or membrane transport proteins. Small non-polar molecules can diffuse without energy.

What are carrier proteins?

membrane proteins that bind to specific molecules and undergo conformational changes to transport these molecules across the membrane, which may be either active or passive.

What distinguishes active transport from passive transport in carriers?

Active transport requires energy to move substances against their concentration gradient, while passive transport does not require energy and moves substances down their concentration gradient.

What are channel proteins?

transmembrane proteins that create ion-selective channels, allowing small water-soluble molecules to pass through the membrane.

What are the different regulatory mechanisms for channel proteins?

Channel proteins can be regulated in various ways, including being voltage-gated, ligand-gated, or mechanically gated.

What types of molecules typically require membrane transport proteins?

All molecules that are larger, charged, or water-soluble typically require membrane transport proteins.

What is Vesicular Transport?

The mechanism by which large molecules enter, leave, and move within the cell through vesicle formation.

What are the examples of vesicular transport between organelles?

Movement between the endoplasmic reticulum (ER) and Golgi apparatus is an example of vesicular transport.

What is Endocytosis?

The process by which substances enter the cell via vesicles; includes mechanisms like pinocytosis, phagocytosis, and receptor-mediated endocytosis.

What are some functions of endocytosis?

Endocytosis is involved in nutrient uptake, cell signaling, and shape changes of the cell.

What is Exocytosis?

The process by which substances exit the cell, wherein vesicles fuse with the plasma membrane to release their contents.

What are the two pathways of exocytosis?

The two pathways of exocytosis are constitutive (continuous) and regulated (signal-dependent).

How are exocytosis and endocytosis related?

Exocytosis and endocytosis are coupled; if exocytosis is abolished, no endocytosis takes place.

What are the main classifications of endocytosis?

Endocytosis can be classified as clathrin-dependent or clathrin-independent.

What is clathrin?

a protein that plays a crucial role in the process of endocytosis by forming coated vesicles, which help in the transport of molecules into the cell.

What are the three major mechanisms of endocytosis?

phagocytosis, pinocytosis, and receptor-mediated endocytosis

What is Pinocytosis?

A form of endocytosis involving the non-specific ingestion of fluids and small solute molecules.

What are the characteristics of pinocytosis?

Non-specific and Clathrin-independent

What is Phagocytosis?

A type of endocytosis where large particles, such as microorganisms and cellular debris, are engulfed by specialized cells.

What are the characteristics of phagocytosis?

Clathrin-independent and Actin-dependent

Receptor-Mediated Endocytosis

A selective form of endocytosis where specific molecules bind to receptors on the cell membrane and are internalized in vesicles.

What are the characteristics of receptor-mediated endocytosis?

Cargo-specific and Clathrin-dependent

What is micropinocytosis?

the non-specific ingestion of fluid and small protein molecules via small vesicles, occurring in almost all cells as a continuous (constitutive pathway) process. Vesicle formation is associated with caveolin and flotillin proteins and is clathrin-independent.

What is macropinocytosis?

the non-specific uptake of extracellular fluids, solutes, nutrients, and antigens. It is regulated, clathrin-independent, and requires rearrangement of the actin cytoskeleton, creating surface membrane ruffles that trap fluid.These are specifically employed by immune cells to sample their environment.

How are particles recognized in phagocytosis?

Phagocytosis is receptor-mediated through the recognition of pathogen-associated molecular patterns (PAMPs); particles bind to plasma membrane receptors, such as antibodies.

What is the role of pseudopods in phagocytosis?

During phagocytosis, there is an extension of pseudopods, which are actin-dependent. This process is dependent on actin microfilament polymerization and is clathrin-independent.

What role do cargo receptors play in receptor-mediated endocytosis?

Cargo receptors accumulate in well-defined regions of the cell membrane, known as lipid rafts, to facilitate the uptake of specific molecules.

What are coated pits in receptor-mediated endocytosis?

Coated pits are areas on the cytoplasmic surface of the membrane where aggregation of clathrin molecules occurs, which helps to recognize and bind to specific molecules.

How does clathrin function in receptor-mediated endocytosis?

Clathrin assembles into a basket-like cage during receptor-mediated endocytosis, changing the shape of the membrane and pulling the cargo into the lumen of a forming vesicle.

What is the role of dynamin in receptor-mediated endocytosis?

Dynamin is a mechanoenzyme that mediates the pinching off of the vesicle from the plasma membrane, resulting in a coated vesicle during clathrin-dependent endocytosis.

What are the two pathways of exocytosis?

Constitutive Exocytosis and Regulated Secretory Pathway

Constitutive Exocytosis

A continuous process where certain proteins are secreted from the cell immediately after synthesis. (antibodies by plasma cells and procollagen by fibroblasts)

Regulated Exocytosis

A pathway where secretory proteins are concentrated and temporarily stored in vesicles until a regulatory signal prompts their release. (Endocrine, exocrine cells and neurons)

Vesicular transport requires careful regulation by

proteins and adhesion molecules

Endosomes

Membrane-bound compartments that play a key role in sorting and delivering internalized materials within the cell.

Ligand-Receptor Complex

A complex formed when a ligand binds to its specific receptor on the cell membrane.

Cargo Receptors

Proteins that specifically bind to ligands in receptor-mediated endocytosis, accumulating in coated pits.

Caveolin and Flotillin

Proteins associated with micropinocytosis that are involved in the formation of small vesicles.

Cell Signaling

The process by which cells communicate and respond to their external environment, often facilitated by vesicular transport.