Cell Signaling I and II Flashcards
Direct cell-to-cell signaling
involves a signaling molecule expressed on the surface of one cell and a receptor localized on the surface of an adjacent cell.
Endocrine signaling
the signaling molecules (hormones) are released from secretory cells into the blood and carried to distant target tissues.
Paracrine signaling
signaling molecules exert their effects locally on neighboring cells: they reach these target cells via the interstitial fluid.
-Neural communication is a form of local communication in
which neurotransmitters are released at a synaptic junction.
Autocrine signaling
signaling molecules bind to receptors in or on the cells that release them.
How do gap junctions play a role in cell signaling?
Gap junctions are narrow, water-filled channels, formed from proteins called connexins, that connect the cytoplasm of adjacent cells. Because some small intracellular chemical mediators are able to pass through gap junctions, signaling information can be shared by neighboring cells
What are two functions of receptors?
- to recognize and bind specific ligands (ex: hormones, neurotransmitters, drugs, etc.).
- to elicit a response by the target cell when the receptor is occupied by activating one or more intracellular signal transduction pathways.
What does it mean that receptors are highly specific?
means they are able to distinguish between closely related molecules. This lessens the probability that a given receptor will be activated by a variety of different compounds.
• Typically, a receptor binds a specific ligand or a few structurally related molecules
Whats it mean that a receptor will have a high affinity for a specific ligand?
means it can bind that ligand when the ligand is present at very low concentrations.
•Binding typically involves multiple weak, non-covalent interactions such as ionic and hydrogen bonding and hydrophobic interactions between complementary regions of the ligand and its receptor. The number and strength of these interactions determines the affinity of areceptor for a ligand
T or F. Is the binding of receptor to ligand a reversible reaction?
Truuuuu.
The binding of a ligand (L) to a receptor (R) is a reversible reaction that depends on the concentrations of both L and R
Are there a finite number of receptors in a target tissue?
-yes
Because there are a finite number of receptors in a target tissue, receptor binding is a saturable process.
Can a given ligand bingd to mulciple differ receptors?
A given ligand (hormone, drug, etc.) may bind multiple receptor types, each of which may be linked to a different signaling pathway
What is Kd?
Kd, the dissociation constant, is an important quantitative measure of the affinity of a receptor for a specific ligand
-The tightness of a bond between a receptor and a ligand depends on the number and strength on the non-covalent interactions that are formed. Molecules that are highly complementary have a greater affinity for each other than molecules that are less complementary because they have a greater fit and are able to form stronger and more numerous non-covalent interactions.
What is the binding kinetics relationships and what do the terms stand for?
The binding of a signaling molecule (L) to its receptor to form a L- receptor complex (L•R) is typically a reversible bimolecular reaction (See slide 8). Kinetic analysis of this interaction results in the following relationship:
Ka= [L*R]/[L][R] where [L•R] is the concentration of the occupied receptor, [R] is the concentration of unoccupied receptor binding sites, [L] is the concentration of the unbound (free) L and Ka is the association constant. The rate constant for the forward reaction is kf and the rate constant for the reverse reaction is kr. At equilibrium the rate of L•R formation is equal to the rate of L•R dissociation
(1) [L] and [L•R] can be determined experimentally by performing a binding study as described on the previous page.
(2) [R] cannot be measured directly.
T or F. R can be measured directly?
False
How is R calculated?
[R] is calculated from the following relationship:
[R] = Bmax–[L•R] where, [R] = concentration of unoccupied receptor binding sites; Bmax = total number of receptor binding sites; [LM•R] = concentration of occupied receptor binding sites
On a theoretical plot of [L*R]/[L] vs [L*R] what would the slope and x-intercept be?
Theoretically, a plot of [L•R]/[L] versus [L•R] should result in a straight line with a slope of –Ka and a x-intercept of Bmax. Again, Bmax is the maximum number of receptor binding sites and Ka is the association constant. Kd is the reciprocal of Ka.
What is Kd in relation to Ka?
