The addition or removal of phosphate groups from proteins is the most common chemical modification that regulates cellular processes. These modifications can affect the structure, activity, stability, and localization of proteins within cells as well as their interactions with other proteins.
During phosphorylation, protein kinases transfer the terminal phosphate group of ATP to specific amino acid side chains of substrate proteins. Serine, threonine, and tyrosine are the most commonly phosphorylated amino acids. Accordingly, protein kinases are classified as serine/threonine kinases, tyrosine kinases, or dual action kinases if they can phosphorylate all three amino acids. Conversely, protein phosphatases catalyze the removal of the phosphate group (dephosphorylation), restoring the original properties of the protein. Under physiological conditions, phosphorylation and dephosphorylation are tightly regulated to prevent prolonged changes in protein structure and function. Disruption of this balance can cause diseases, including cancer and various neurodegenerative disorders. For instance, a protein called tau is hyperphosphorylated in Alzheimer’s disease (AD). Physiologically, tau regulates the shape, structure, and development of neurons. The tau protein contains over 80 serine, threonine, and tyrosine residues, of which only a fraction is usually pho…
The organs in a multicellular organism’s body are made up of tissues formed by cells. To work together cohesively, cells must communicate. One way that cells communicate is through direct contact with other cells. The points of contact that connect adjacent cells are called intercellular junctions.
Intercellular junctions are a feature of fungal, plant, and animal cells alike. However, different types of junctions are found in different kinds of cells. Intercellular junctions found in animal cells include tight junctions, gap junctions, and desmosomes. The junctions connecting plant cells are called plasmodesmata. Of the junctions found in animal cells, gap junctions are the most similar to plasmodesmata. Plasmodesmata are passageways that connect adjacent plant cells. Just as two rooms connected by a doorway share a wall, two plant cells connected by a plasmodesma share a cell wall. The plasmodesma “doorway” creates a continuous network of cytoplasm—like air flowing between rooms. It is through this cytoplasmic network—called the symplast—that most nutrients and molecules are transferred among plant cells. A single plant cell has thousands of plasmodesmata perforating its cell wall, although the number and structure of plasmodesmata can vary across cells and change in individual cells. The continuum of …
1BVN Neustadt/Aisch, 2Faculty of Veterinary Medicine, Clinic for Obstetrics, Gynecology and Andrology of Large and Small Animals, Justus-Liebig-University Giessen, 3Reproductive Cell Biology Unit, Leibniz Institute for Farm Animal Biology, 4Reproductive Biochemistry Unit, Leibniz Institute for Farm Animal Biology