Quiz 2/Exam 2 exocytosis and endocytosis

ligand

A molecule that binds directly to a receptor.

adherence

Binding of receptor proteins in the membrane to the substrate (molecules upon which an enzyme acts.

Explain why the lack of an LDL receptor will lead to high blood cholesterol levels.

Cholesterol will remain in the blood stream because it won't be taken in by cells via receptor-mediated endocytosis. This will result in high blood cholesterol.

There are three types of endocytosis

During phagocytosis ("cell eating"), a large item (such as an entire bacterium) is taken in by the cell. Pinocytosis ("cell drinking") occurs when a cell takes in materials dissolved in the surrounding liquid. Neither of these processes targets specific molecules. Receptor-mediated endocytosis, however, brings specific target molecules into the cell.

phagocytosis

Engulfment process by which the plasma membrane surrounds and encases large materials to be brought into the cell.does not target specific molecules. (difference b/w this and pinocytosis is the size of the ingested material)

invagination

Folds in the plasma membrane resulting in the formation of a pocket in the interior of the cell.

Secretion process?

How are materials targeted to vesicles? Some materials, such as neurotransmitters, are loaded into the vesicles from the cytoplasm. Other materials, like proteins, are built directly into vesicles. Proteins made for export are made on ribosomes linked to the rough endoplasmic reticulum (RER). The rough ER packages the proteins into vesicles and sends them to the Golgi apparatus. The Golgi apparatus "tags" the proteins and repackages them in a new vesicle. The cell uses the "tags" to send the protein to the correct location.

pseudopod

Literally "false foot." An extension of the cytoplasm usually associated with feeding or movement; found in phagocytic white blood cells and some single-celled eukaryotes. The amoeba uses pseudopodia to feed and to move. Pseudopodia form from the cytoskeleton of the cell.

Macrophages

Macrophages do not ingest pathogens for nutrients. They are part of the immune system, and their function is to protect the larger multi-celled organism. Ingesting and digesting foreign cells is their primary role, but macrophages can also signal other immune cells that pathogens are present. When a macrophage digests a foreign cell, it posts a piece of that cell on a marker protein called a major histocompatibility complex (MHC) that is present on its plasma membrane. The marker is a message to other cells that the macrophage has found a problem. Like a "wanted" poster. The piece of pathogen that is posted on the marker is called an antigen.

Microphages engulfment

Microphages engulfment. The macrophage finds the pathogen using chemotaxis. It then adheres to the pathogen and ingests it. Digestive enzymes digest the pathogen and unabsorbed materials are released via exocytosis. Chemotaxis — chemical signals attract the phagocyte to the pathogen. Adherence — receptor proteins on the phagocyte bind to the pathogen. Ingestion — the pathogen is brought into the cell inside a vesicle via endocytosis. Digestion — the phagolysosome contains enzymes that digest the pathogen. Elimination — exocytosis of unabsorbed material.

How do the vesicles move to the proper location?

Motor proteins attached to the vesicles move them along the microtubules of the cell's cytoskeleton. Microtubules are like the railroad tracks of the cell. Guided by microtubules and moved by motor proteins, vesicles involved in exocytosis move to the correct location on the plasma membrane.

chemotaxis

Movement in response to a chemical (stimulus) present in the environment.

endocytosis

Movement of materials into a cell using a vesicle. When the cell releases a vesicle by exocytosis, the membrane of the vesicle fuses with that of the cell. So in effect, the cell membrane expands. How do non-growing cells that release materials by exocytosis do so without increasing membrane area? These cells must "shrink" back down to their right size. Endocytosis achieves this and can also remove proteins from the membrane. In this way, endocytosis is a key process for managing the surface area and content of the membrane.

exocytosis

Movement of materials out of a cell using a vesicle. When the cell releases a vesicle by exocytosis, the membrane of the vesicle fuses with that of the cell. So in effect, the cell membrane expands. How do non-growing cells that release materials by exocytosis do so without increasing membrane area? These cells must "shrink" back down to their right size. Endocytosis achieves this and can also remove proteins from the membrane. In this way, endocytosis is a key process for managing the surface area and content of the membrane.

Phagocytosis

Phagocytosis is defined as taking in relatively large-sized materials such as bundles of chemicals or entire cells. Phagocytic cells are part of the body's immune response. They clean up cellular debris and protect the body from pathogens. Single-celled eukaryotes, and a few multicellular eukaryotes, use phagocytosis to feed. Phagocytosis allows a single-celled organism to bring in a large particle of food and digest it.

pinocytosis

Pinocytosis ("cell drinking") occurs when a cell takes in materials dissolved in the surrounding liquid. This so-called "cell drinking" occurs when the plasma membrane of the cell invaginates, pinches off, and "gulps" the enclosed liquid. Pinocytosis is unspecific, taking in any nearby materials dissolved in the extracellular fluid.

How isPseudopodia used for phagocytosis?

Pseudopodia used for phagocytosis extend out in the same way. Receptors on the surface of the plasma membrane bind to a food particle. The pseudopod extends out until it wraps around the particle in a process called engulfment. This leads to the food particle being brought into the cell in a vesicle called a phagosome or food vacuole.

three steps of secretion

Secretion involves three key steps: Materials are targeted to vesicles. The vesicles move to the proper location. Signals trigger the release of materials from the vesicles.

What triggers the release of materials from the vesicles?

Some cells release materials continually, such as mucus-secreting cells in the intestines. These cells don't seem to need a particular signal. Other cells need a separate signal to release the materials in their vesicles. Calcium!!!!! is often used to signal exocytosis. In neurons, an increase in calcium concentration in the cell triggers the release of neurotransmitters from the vesicle into the extracellular fluid between the neuron and a target cell.

Receptor-mediated endocytosis

Type of endocytosis; allows specific target molecules to be selectively brought into the cell by the binding of ligands to receptors on the plasma membrane. Receptors embedded in the membrane bind to a target molecule, called the ligand. Once the ligand binds to the receptor, the membrane invaginates and a vesicle forms. This removes the receptors from the plasma membrane. They must be put back onto the membrane's external surface through exocytosis, which returns phospholipids and membrane-bound proteins (like receptors) to the plasma membrane.

Explain how proteins are incorporated into the plasma membrane.

When a protein is made in the rough ER, it remains attached to the vesicle membrane. In this case, it will not be secreted when the vesicle fuses with the plasma membrane. Instead, it is incorporated into the plasma membrane when the vesicle membrane fuses with it. The outer part of the protein faces inside the vesicle so that, when the membranes fuse, it will be on the outside of the membrane.

Endocytosis Function

endocytosis is a key process for managing the surface area and content of the membrane. Cells also use endocytosis to ingest nutrients (large ones like macromolecule becuase no other channel can get it through), to receive signals and to defend against pathogens.

phagolysosome

fusion product of a phagosome and a lysosome Enzymes end up in the phagosome? These digestive enzymes could come from lysosomes that fuse with the phagosome. Lysosomes are vesicles in the cell that function specifically to digest food and unwanted particles. Digestive enzymes in lysosomes can break down a wide variety of materials. Since both phagosomes and lysosomes are membrane-bound packages, they can fuse their membranes and become one larger structure. This fusion product of a phagosome and a lysosome is called a phagolysosome.

Way which Single-celled organisms feed by engulfing their food.

the amoeba must first move towards its food source. It does this using chemotaxis, which is movement in response to a chemical stimulus. Once the amoeba is adjacent to its prey cell, receptors on its plasma membrane bind to the prey cell. This binding is called adherence, wherein receptor proteins on the amoeba's plasma membrane attach to a substrate, whether a food particle or surface. The amoeba begins to engulf the prey. First, the amoeba extends a pseudopod ("false-foot"), a long extension of cytoplasm. Ingestion occurs when the amoeba's pseudopod wraps around the pathogen and brings it into the cell within a vesicle using endocytosis.