Concept 11.2: Reception: A signaling molecule binds to a receptor protein, causing it to change shape Flashcards
the signals emitted by an a mating type yeast cell are “heard” only by its prospective mates,
α cells.
In the case of the epinephrine circulating throughout the bloodstream of the impala in Figure 11.1, the hormone encounters many types of cells, but only certain target cells detect and react to the
epinephrine molecule.
the term for a molecule that specifically binds to another (often larger) molecule
ligand,
Ligand binding generally causes a receptor protein to undergo a change in
shape.
For many receptors, this shape change directly activates the receptor, enabling it to interact with other
cellular molecules.
For other kinds of receptors, the immediate effect of ligand binding is to cause the aggregation of
two or more receptor proteins, which leads to further molecular events inside the cell
Most signal receptors are plasma membrane proteins, but others are located inside the
cell.
The largest family of human cell-surface receptors is the
G protein-coupled receptors (GPCRs).
example is the co-receptor hijacked by
HIV to enter immune cells
Most water-soluble signaling molecules bind to specific sites on transmembrane receptor proteins that transmit information from the
extracellular environment to the inside of the cell.
We can see how cell-surface transmembrane receptors work by looking at three major types:
G protein-coupled receptors (GPCRs), receptor tyrosine kinases, and ion channel receptors.
Given the many important functions of cell-surface receptors, it is not surprising that their malfunctions are associated with many human diseases,
including cancer, heart disease, and asthma.
Although cell-surface receptors represent 30% of all human proteins, determining their structures has proved challenging: They make up only 1% of the proteins whose structures have been determined by
X-ray crystallography
For one thing, cell-surface receptors tend to be flexible and inherently unstable, thus difficult to
crystallize.
In that case, the β-adrenergic receptor was stable enough to be crystallized only while it was among membrane molecules and in the presence of a molecule mimicking its
ligand.
Abnormal functioning of receptor tyrosine kinases (RTKs) is associated with many types of
cancers.
For example, breast cancer patients have a poor prognosis if their tumor cells harbor excessive levels of a receptor tyrosine kinase called
HER2
Using molecular biological techniques, researchers have developed a protein called ____________ that binds to HER2 on cells and inhibits cell division, thus thwarting further tumor development
Herceptin
Intracellular receptor proteins are found in either the
cytoplasm or nucleus of target cells.
To reach such a receptor, a signaling molecule passes through the
target cell’s plasma membrane.
A number of important signaling molecules can do this because they are either
hydrophobic enough or small enough to cross the hydrophobic interior of the membrane
The hydrophobic signaling molecules include both
steroid hormones and thyroid hormones of animals.
Another chemical signaling molecule that possesses an intracellular receptor is
nitric oxide (NO), a gas; this very small molecule readily passes between the membrane phospholipids.
Once a hormone has entered a cell, its binding to an intracellular receptor changes the receptor into a
hormone-receptor complex that is able to cause a response—in many cases, the turning on or off of particular genes.
The behavior of aldosterone is a representative example of how .
steroid hormones work
This hormone is secreted by cells of the adrenal gland,
a gland that lies above the kidney
Aldosterone then travels through the blood and enters
cells all over the body.
In these cells, the hormone binds to and activates the
receptor protein.
With aldosterone attached, the active form of the receptor protein then enters the nucleus and turns on specific genes that control
water and sodium flow in kidney cells, ultimately affecting blood volume
recall that the genes in a cell’s DNA function by being transcribed and processed into
messenger RNA (mRNA), which leaves the nucleus and is translated into a specific protein by ribosomes in the cytoplasm
Special proteins called ____________________ control which genes are turned on—that is, which genes are transcribed into mRNA—in a particular cell at a particular time.
transcription factors
When the aldosterone receptor is activated, it acts as a transcription factor that turns on
specific genes
By acting as a transcription factor, the aldosterone receptor itself carries out the transduction part of the
signaling pathway
