3.
What are the most common receptors for growth factors?
Growth factors are a group of proteins that play an essential role in living organisms' growth, differentiation, and tissue regeneration processes. They significantly influence cell division and tissue renewal. They activate healing and repair processes. They play a massive role in maintaining the health and good condition of the skin. They make communication possible, i.e., the transfer of impulses between the dermis and the epidermis. The growth factor acts through receptors located on the surface of target cells. Its binding to the receptor initiates the production of mediator molecules in signal transmission through the cell membrane. Receptor proteins, or receptors for short, bind to a specific other substance (ligand), such as a neurotransmitter or hormone, and initiate a cascade of signal transduction and cell reaction in response to the ligand. The most common growth factor receptors are the receptor tyrosine kinases RTKs (Goodman, 2007).
4.
What types of signaling proteins are common in animals but absent from plant cells, and vice versa?
Plant and animal cells belong to eukaryotes, but as a result of evolution, they have separated and evolved separately for over a billion years. This is evidenced by the fact that some molecules used in communication (e.g., nitric oxide, cGMP, Ca2+) and their associated mechanisms are similar in plants and animals. Other molecules used in animal communication do not occur in plants (Ras protein, JAK, STAT, Notch).
Most plant cell surface receptors are catalytic receptors. The most common catalytic receptor in animals, with tyrosine kinase activity (RTK), is very rare in plants. Plants often use receptors with serine-threonine kinase (RLK) activity (Alberts et al., 2002).
5.
How does signaling by hydrophobic molecules like steroid hormones differ from signaling by peptide hormones?
Hydrophobic steroid hormone signals include lipophilic molecules that diffuse
across the plasma membrane, bind to intracellular receptors, and modulate gene expression, resulting in slower action. Conversely, hydrophilic peptide hormones cannot cross the membrane to bind to cell surface receptors, initiating rapid intracellular signaling cascades leading to immediate responses. Despite these differences, both hormones play an essential role in physiological regulation, using specific receptors to interact with target cells in the endocrine system. Hydrophilic molecules such as steroid hormones typically use intracellular receptors to initiate signaling, whereas peptide hormones rely primarily on cell surface receptors (Molnar & Gair, 2015).
6. NO (nitric oxide) does not have a specific cellular receptor. How, then, does it act as a signalling molecule?
The endothelium is a thin layer of cells that lines the inner surface of blood vessels and plays a vital role in the production and regulation of nitric oxide (NO). Nitric oxide is produced by endothelial cells through the action of nitric oxide synthase (NOS). The release of NO from the endothelium contributes to vasodilation, helping regulate blood flow and influencing various physiological processes, as the information provided mentions (Esplugues, 2002).
