Cellular Biology - AP Biology

Agonists activate receptors; therefore, the receptor is activated when the agonist binds to it.

Antagonists are ligands that inhibit receptors; thus, they create a receptor blockade. Some antagonists are able to bind irreversibly to the receptor by covalent bonds, blocking the receptor.

The axon hillock is the area of a neuron that connects the soma and axon. This is also the area of the of the neuron that "decides" whether an action potential would be initiated or not, depending on whether the cell has reached threshold or not.

Elastic fibers are a type of fiber within the connective tissue category. These types of fibers are made up of the protein elastin and they allow tissues and organs to recoil and oppose tearing forces.

Reticular fibers are composed of collagen and form thin mesh networks that supports cells, tissues, and organs. The reticular meshwork also acts as a scaffold for other structures to anchor into.

Cell junctions are common in epithelial tissue because they allow for communication and contact between neighboring cells.

During embryological development, epithelial tissue develops from all three germ layers (endoderm, mesoderm, and ectoderm).

The infolding of epithelial tissue forms glands that function in the exocrine and endocrine systems. Glands secrete products that are taken up by the circulatory system for delivery.

The sarcoplasm in muscle cells is comparable to the cytoplasm in other types of cells. The sarcoplasm is specialized in the high amount of myoglobin present. Its specialized regulation of calcium ion concentrations controls muscle contractions.

When secretory proteins are synthesized they localize to the endoplasmic reticulum (ER), specifically the rough ER, for modification. Following modification there, secretory proteins are then packaged in secretory vesicles which go on to interact with the Golgi body, and are then finally released from the the plasma membrane.

Glycolysis (the process of breaking down glucose) takes place in the cytoplasm, or cytosol—the aqueous portion of the cytoplasm. It is in the cytoplasm where the enzymes required for glycolysis are found.

The citric acid cycle takes place in the mitochondrial matrix, and the electron transport chain takes place along the inner mitochondrial membrane in order to pump protons into the intermembrane space.

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

A phosphatase removes a phosphate group from its ligand.

Several different types of proteins can change the structure of a ligand, such as isomerases, and ubiquitin ligases add ubiquitin to their ligands.

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

A phosphatase removes a phosphate group from its ligand.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

Several different types of proteins can change the structure of a ligand, such as isomerases, and ubiquitin ligases add ubiquitin to their ligands.

Ubiquitin ligases add ubiquitin to their ligands. The addition of ubiquitin acts as a signal that a protein has become ineffective and is ready for degradation. When multiple ubiquitin residues have been added to a protein molecule, it is transported to the lysosome in the cell to be digested.

A phosphatase removes a phosphate group from its ligand.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

Several different types of proteins can change the structure of a ligand, such as isomerases.

As the name implies, when activated and induced to undergo a conformational change by a ligand, ions are able to flow through the channel and into the cell. This allows the charge across the membrane tobe manipulated by the cell.

The binding of ligands causes the activation and conformational change in the ion channel to open it. Then, ions are able to flow into the cell. After a short time, the ligand dissociates from the ion gated channel. This causes the channel to deactivate and close.

Local cell signaling in eukaryotic cells refers to the communication between nearby cells. This is done through direct contact between cells, namely via cell junctions and cell-cell recognition. Gap junctions are intercellular connections that allow cytoplasmic transfer in animal cells. The counterpart in plant cells is the plasmodesmata, which are channels penetrating the cell walls of cells, allowing communication. Cell-cell recognition is the ligand-receptor binding between two cells that elicits receptor cell response. Methods of local cell signaling allow nearby cells to communicate with each other and coordinate cellular responses and activities.

Phagocytosis is a form of endocytosis in which a cell takes up solid material through the invagination of the plasma membrane to form intracellular vesicles. In multicellular organisms, the process of phagocytosis is utilized in nutrient uptake, immune system response, and in cell recycling. Cells perform phagocytosis to uptake solid nutrients into the cell. The immune system uses phagocytosis to consume foreign material for eventual degradation. In the continual process of cell recycling, old and dead cell material is taken up and reused by cells.

Pinocytosis is a type of endocytosis. During pinocytosis, the cell takes up extracellular fluid through plasma membrane invagination and vesicle formation. The process is energetically costly and requires many molecules of ATP. Pinocytosis is a non-specific process, meaning that materials are not selectively taken up. In other words, extracellular fluid is engulfed along with any or all particles within it. The fluid taken up by pinocytosis is already digested and degraded; therefore, the process is not accompanied by the action of lysosomes.

In clathrin-mediated endocytosis, the binding of a specific ligand to a receptor triggers intracellular protein recruitment, which includes clathrin. These proteins stabilize the invagination and allow the clathrin pit to pull away from the plasma membrane. After it has separated from the membrane, the proteins and clathrin dissociate from the vesicle, which then fuses with an endosome. The invagination and vesicle formation from the plasma membrane includes the internalization of both the receptor and ligand. Over time the uptake by clathrin-mediated endocytosis decreases as the number of receptors on the cell’s surface. In other words, particle uptake declines due to the internalization of recptors as a result of clathrin-mediated endocytosis.