Chapter 15: Mechanisms of Cell Communication
• What are extracellular signal molecules? Give examples and explain their properties.
Extracellular
... [Show More] signal molecules are the means by which communication between cells is
mediated. Extra cellular signal molecules include proteins, small peptides, amino acids,
nucleotides, steroids, fatty acid derivatives, and even some dissolved gases such as nitric
oxide and carbon monoxide. Most of these signal molecules are released into the
extracellular space by exocytosis from the signaling cell. They are then emitted by
diffusion through the signaling cell’s plasma membrane and displayed on the external
surface of the cell and remain attached to it to provide a signal to other cells only when
they make contact. The way the target cell responds is by a receptor, which
specifically binds the signal molecules and then initiates a response in the target cell.
Extracellular signal molecules can either bind to a cell-surface receptor or to an intracellular
receptor.
If you need a professional to complete your college homework at a small fee, then reach out to
Homeworkanalyzers.com
• Compare intracellular and cell surface receptors. Give examples.
An intracellular receptor is a receptor that is inside of a cell as opposed to on the cell
surface. In this situation, the signaling molecule has to be small and hydrophobic so that
it can diffuse across the target cell’s plasma membrane and come into the cell. The
receptor protein that the signaling molecule binds to is inside the cell and is activated
after the signaling molecule enters the cell and travels to the target protein. The signaling
molecules, one inside, regulate the activity of specific intracellular proteins. An
example is nitric oxide (NO), whose function in mammals is to relax smooth muscle and
enhance blood flow through the blood vessels. On the other hand, a cell surface receptor is
a receptor that is on the plasma membrane and these receptors are transmembrane (whether
it be multi-pass or single-pass). The signaling molecule is often larger than in the case
with intracellular receptors and the signaling molecule is hydrophilic and therefore
unable to cross the target cell’s plasma membrane.
• What are the four forms of intercellular signaling?
The four forms of intercellular signaling are contact-dependent, paracrine, synaptic, and
endocrine. Contact-dependent intercellular signaling requires cells to be in direct
membrane-membrane contact and this is important during development and the immune
system. Paracrine intercellular signaling depends on signals that are released into the
extracellular space and act locally on neighboring cells. Synaptic intercellular signaling is
performed by neurons that transmit signals electrically along their axons and release
neurotransmitters at synapses. Lastly, endocrine intercellular signaling depends on
endocrine cells, which secrete hormones into the bloodstream for distribution throughout
the body and this type of signaling can travel long distances. Many of the same type of
signaling molecules are used in paracrine, synaptic, and endocrine signaling. The
differences lie in the speed and selectivity with which the signals are delivered to targets.
• Discuss the role of gap junctions in information signaling.
Gap junctions are narrow water-filled channels that directly connect the cytoplasm of
adjacent epithelial cells, as well as some other cell types. The channels allow the
exchange of inorganic ions and other small water-soluble molecules, but not of
macromolecules such as proteins or nucleic acids. Cells connected by gap junctions share [Show Less]