Question
The ligands in signal transduction pathways may be hydrophobic or hydrophilic.
(a) Describe where in a cell the receptors for hydrophilic ligands and
the receptors for hydrophobic ligands are located.
(b) Explain why hydrophobic ligands can cross the cell membrane
unassisted.
(c) A mutation in the gene for adenylyl cyclase renders the enzyme
ineffective. Predict the effect this would have on the cell.
(d) Justify your prediction from part (c).
▶️Answer/Explanation
Ans:
11. The ligands in signal transduction pathways may be hydrophobic or
hydrophilic.
(a) Describe where in a cell the receptors for hydrophilic ligands and
the receptors for hydrophobic ligands are located.
(b) Explain why hydrophobic ligands can cross the cell membrane
unassisted.
(c) A mutation in the gene for adenylyl cyclase renders the enzyme
ineffective. Predict the effect this would have on the cell.
(d) Justify your prediction from part (c).
Question
One hormone can often bind to many receptor subtypes. (Receptor subtypes are receptors with the same ligand-binding site but different
intracellular responses to ligand binding.)
Explain one regulatory benefit of this type of system. Provide one example and use it to support your explanation.
▶️Answer/Explanation
Ans:
Each cell in the body of a multicellular organism is programmed to
respond to specific combinations of signaling molecules. However,
different cell types can respond differently to the same signal (or signals).
Cells vary in what receptors they possess and thus what signals they will
respond to.
Two different cell types with the same receptor may bind to the same
molecule but respond differently. It is the intracellular machinery that
effects the response to the signal the cell received through its receptor.
This allows one chemical to have a multitude of effects in the body,
depending on the cells, their receptors, and the intracellular machinery that is
attached to them.
For example, acetylcholine binds to (nicotinic) acetylcholine receptors at
the neuromuscular junction. Acetylcholine binding to nicotinic receptors
opens sodium channels and promotes muscle contraction. Acetylcholine
binding to muscarinic receptors on heart muscle cells opens potassium ion
channels and slows the rate of heart muscle contraction. Adrenaline
(epinephrine) induces glycogen breakdown in muscle, and increased rate and
force of contractions of the heart. In fat cells, it promotes lipolysis.
Question
Cellular communication involves transduction signals from other cells, organisms, or the environment.
List the cellular structures required for cell-cell communication and provide a brief description of their function.
▶️Answer/Explanation
Ans:
Signal transduction is a complex process!
• Receptors capture specific chemical signals.
• Intracellular response molecules like G-proteins and protein kinases
are required to effect an intracellular response from the signal.
• In some signaling pathways, a mechanism for signal amplification is
required.
• Enzymes are needed to synthesize the signaling molecules.
• Gene sequences that code for all the necessary proteins must be
present and transcribed.
• If the signal works by activating gene transcription, the transcription
factor binds to the signaling molecule and then the response element
in the promoter of the gene that is expressed in the presence of the
signaling molecule.