The nucleolus is a subdivision of the nucleus; thus, it is only found in eukaryotes. It is the site of ribosome assembly. The nucleolus is made of RNA and proteins.

Histones are proteins found in the nucleus of eukaryotic cells. DNA wraps itself around histones to further condense. Also, depending on how tightly the DNA is wrapped around the histones, it may or may not be availible for activity (e.g. replication or transcription). Cells modify the interaction between DNA and histones around certain genes under certain conditions to make those genes available or unavailable as needed.

Vacuoles are membrane-bound structures that are found in bacterial, plant, fungal, and occasionally, animal cells. Vacuoles function in storage of water and waste and in maintenance of turgor pressure in plants. 

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.

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.

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.

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.