Endomembrane Pathway Overview

A complex network of internal membranes within eukaryotic cells used for the synthesis, modification, packaging, and transport of biomolecules.

Small membrane-bound sacs within eukaryotic cells that transport molecules between organelles.

Organelle responsible for the synthesis of proteins, particularly those destined for secretion or other cellular compartments.

Organelle responsible for the synthesis of lipids, including steroids and phospholipids.

Organelle responsible for further processing, sorting, and packaging of proteins and lipids received from the ER.

The process of releasing substances from a cell by fusion of a vesicle with the plasma membrane.

The pathway where proteins are synthesized in the rough ER, modified in the Golgi, packaged into vesicles, and secreted outside the cell.

The pathway where proteins synthesized in the rough ER, modified in the Golgi, are packaged into vesicles and incorporated into the plasma membrane .

The process by which proteins are assembled on ribosomes attached to the RER.

A network of flattened sacs called cisternae, with ribosomes attached to its membrane. These ribosomes distinguish it from the smooth ER.

Proteins destined for the cell membrane, other organelles, or secretion outside the cell are synthesized here.

After being synthesized on ribosomes, proteins are transported into the ER lumen where they undergo folding, modifications like glycosylation, and quality control checks.

Proteins destined for the cytoplasm are synthesized by cytoplasmic ribosomes, not by the RER.

The rough ER is continuous with the outer nuclear membrane, forming a interconnected network of membranes.

Clathrin coat proteins form vesicles that transport materials from the Golgi apparatus for release outside the cell (exocytosis) or for internalization into the cell (endocytosis).

COPI coat proteins are involved in the movement of vesicles between different compartments of the Golgi apparatus and in the retrieval of proteins from the Golgi back to the ER.

COPII coat proteins play a crucial role in transporting vesicles from the endoplasmic reticulum (ER) to the Golgi apparatus.

Kinesin and Dynein motor proteins attach to vesicles and move them along microtubule tracks within the cell.

Vesicles bud off from one compartment (e.g., ER, Golgi) and carry their contents to another compartment.

Vesicles fuse with the membrane of their target compartment, delivering their contents.

The process of vesicle budding, transport, and fusion with a target membrane, allowing for the movement of materials within a cell.

The Golgi apparatus is a stack of flattened sacs called cisternae, which are divided into three compartments: cis, medial, and trans. Proteins travel through these compartments, undergoing modifications as they progress.

The most common function of the Golgi is glycosylation, adding sugar chains to proteins to create glycoproteins. It can also perform other modifications like phosphorylation and sulfation.

The Golgi tags proteins for their final destination by adding specific modifications, packing them into transport vesicles, and sending them to the correct location within the cell.

The cis face of the Golgi is located near the ER and receives proteins from the ER via transport vesicles. The medial face is the middle region where further modifications happen. The trans face is the exit point where modified proteins are packaged and shipped out.

Glycosylation is the process of adding sugar chains (glycans) to proteins, creating glycoproteins. This is the most common Golgi modification.

The Golgi modifies proteins by adding sugar chains, phosphate groups, or sulfate groups. These modifications help determine what proteins are and where they should go.

Vesicles pinch off from a donor membrane, forming small sacs carrying molecules.

Coat proteins, like COPII, COPI, and clathrin, help vesicles form and are specific to different transport routes.

Vesicles travel along microtubules within the cell using motor proteins like kinesin and dynein.

A vesicle attaches to its target membrane before fusing with it.

The vesicle membrane merges with the target membrane, releasing its contents.

Vesicles typically move from the ER to the Golgi and then to the plasma membrane or other compartments.

Some vesicles return to the ER from the Golgi to bring back proteins that were mistakenly transported.

Lysosomes are membrane-bound organelles that act as the cellular recycling center, containing enzymes capable of breaking down various materials within the cell.

Lysosomes originate from vesicles that bud off from the trans-Golgi network, the final processing stage of the Golgi apparatus.

Lysosomes contain hydrolytic enzymes, which are specialized for breaking down a variety of molecules, including proteins, nucleic acids, lipids, and carbohydrates.

Lysosomes maintain a highly acidic pH (around 4-5) within their interiors, necessary for the optimal activity of their digestive enzymes.

Lysosomes fuse with other vesicles containing materials destined for degradation, allowing the enzymes to access and break down the cargo.

A network of protein fibers that provides support, shape, and movement to eukaryotic cells.

Hollow tubes made of tubulin protein, responsible for organizing organelles, directing intracellular transport, and forming structures like cilia and flagella.

Rope-like fibers made of various proteins, providing mechanical strength and connecting cells in tissues.

Thin filaments made of actin protein, responsible for cell shape, movement, and muscle contraction.

The outer boundary of the cell, composed of a phospholipid bilayer, regulating what enters and exits the cell.

A type of intermediate filament found in epithelial cells, hair, nails, and horn, providing strength and resistance to mechanical tension.

A type of intermediate filament found in connective tissue cells, including muscle, contributing to tissue cohesion and strength.

A type of intermediate filament found in neurons, supporting the unique and complex structure of nerve cells.

A type of intermediate filament that forms a meshwork beneath the nuclear envelope, helping maintain the integrity of the nucleus.

A network of protein fibers located beneath the inner nuclear membrane, providing structural support and regulating the shape of the nucleus.

Lamins are intermediate filament proteins characterized by their strength and elasticity, playing a crucial role in maintaining the integrity of the nuclear envelope.

Mutations in lamin genes can lead to a wide range of diseases, including Hutchinson-Gilford progeria syndrome (HGPS), which causes premature aging, and Emery-Dreifuss muscular dystrophy, a muscle-weakening disorder.

A-type lamins and B-type lamins are the two types of lamins found in cells. They have both structural and regulatory roles in the nucleus.

The nuclear lamina is essential for essential nuclear activities like mitosis (cell division) and chromosome organization, ensuring proper cell function.

A type of intermediate filament found in the cytoplasm of nerve cells, providing structural support and helping maintain the neuron's unique shape.

Neurofilaments are crucial for maintaining the length and diameter of axons, helping them grow and stabilize.

If neurofilaments are disrupted, the axon loses structural integrity and may retract, leading to neuron death. This can contribute to various neurodegenerative diseases.

When neurons are damaged, neurofilaments can be released into the blood and cerebrospinal fluid (CSF), serving as a potential biomarker for neuro-axonal injury.

Mutations in lamin genes can lead to various diseases, including Hutchinson-Gilford progeria syndrome (HGPS), which causes premature aging, and Emery-Dreifuss muscular dystrophy, a muscle-weakening disorder.

They are an important component of the cytoskeleton, providing structural support and helping to maintain the shape and integrity of the cell.

Microtubules are long, hollow tubes made of tubulin proteins. They are found in eukaryotic cells and play a crucial role in various cellular processes.

The arrangement of microtubules in cilia and flagella is known as the "9+2" structure. It involves nine pairs of microtubules surrounding a central pair.

Motor proteins such as dynein move along microtubules, transporting vesicles and organelles within cells.

The centrosome is a microtubule organizing center (MTOC) located near the nucleus. During cell division, it plays a vital role in forming the spindle fibers that separate chromosomes.

Microtubules can change in length by adding or removing tubulin monomers. This dynamic process called 'polymerization' and 'depolymerization' is essential for various cellular functions, including cell division.

One of the main functions of microfilaments is in muscle contractions by interacting with myosin. The sliding filament model explains this process.

By quickly assembling and disassembling, microfilaments allow some cells to form temporary extensions called pseudopods. This enables them to move and capture prey.

Microfilaments are responsible for the movement of organelles within the cytoplasm, much like tiny tracks for transport.

During cell division, microfilaments form a band called the cleavage furrow, which pinches the cell in two, creating daughter cells.