PCB 3023 EXAM 4 QUESTIONS AND
ANSWERS GRADED A+ 2026
What is a Ligand? - ANS a molecule that binds to receptrors
What is an agonist? - ANS A ligand that binds to a receptor to initiate a response
What is an antagonist? - ANS A ligand that binds to a receptor to prevent a response
What are intracellular signaling molecules? Provide an example - ANS Seconds messengers.
ie. cAMP
What are effector proteins? What can they do? - ANS The target proteins in a pathway. Can
mediate cell responses
Signals can act over short range OR long range. T/F? - ANS True
Where are extracellular signaling molecules secreted? - ANS Outside of the cell. Example:
into the bloodstream
What is an endocrine cell? Provide an example - ANS A cell that produces long range
hormones and secretes them into the blood stream to affect a target cell.
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
1
,Example: insulin
What is a paracrine cell? Provide two examples - ANS A cell that releases signal molecules
that diffuse locally.
Example: Cytokines regulate local inflammation. Growth factors
What is an autocrine cell? Provide an example - ANS A cell that depends on its own signaling
molecules
Example: cancer cells
What are synaptic cells? Provide an example - ANS Cells that secrete neurotransmitters from
their axons terminal
What is a synapse? - ANS the junction of the nerve cell (neuron). Delivers chemical signal to
adjacent neuron
What is a contact-dependent cell? Provide an example - ANS A cell that does not depend on
secreted signaling molecules. The cell must make direct physical contact through ligand and
receptor, both of which are located in plasma membrane.
Example: Some signaling in embryonic development.
Some signal molecules (Ligands) can induce different responses in different target cells by
affecting different receptors OR by resulting in different products T/F? - ANS True
After acetylcholine is secreted from cells, it is long-lived, because it has to reach target cells all
over body. T/F? - ANS False. Acetylcholine would be short-lived
Where are receptors usually located? - ANS They can be at the cell surface (plasma
membrane) OR, if the ligand is small and hydrophobic, within the cell.
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
2
, Describe the steroid hormone cortisol as a ligand. - ANS Cortisol is able to diffuse through the
plasma membrane and bind with a nuclear receptor protein (which later acts a a transcription
regulator). It can then move through a nuclear pore channel and bind to the regulatory region
of a targeted gene, leading to transcription and translation.
What response does exposure to extracellular signals in an intracellular pathway produce? Does
this pathway occur fast or slow? - ANS Alteration of free-floating ribosome and protein
function. Occurs fast
What response does exposure to extracellular signals in an nuclear signaling pathway produce?
Does this pathway occur fast or slow? - ANS Alteration of DNA transcription and eventually
mRNA and protein synthesis. Occurs slowly.
Signaling molecules are amplified and integrated by multiple factors. T/F? - ANS True. Primary
transduction typically amplifies the signal.
What is the key mechanism for molecular on/off switches? Why? - ANS Phosphorylation.
Presence of a phosphate may turn a factor on or off. Common because it is reversible
What is phosphorylation? - ANS The key mechanism for turning factors on or off. Reversible
Describe a general phosphorylation mechanism - ANS If a factor is off, a signal will prompt a
protein kinase to convert ATP to ADP. The lone phosphate will bind to that factor and turn it on
to produce a secondary signal. A protein phosphatase will remove the phosphate to turn the
factor off
What purpose do GTP binding proteins serve? Provide examples - ANS Participate in signal
transduction. Similar purpose as phosphorylation
What proteins control GTP Binding proteins? - ANS GEF- Guanine nucleotide Exchange Factor
GAP- GTPase Activating Protein
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
3
ANSWERS GRADED A+ 2026
What is a Ligand? - ANS a molecule that binds to receptrors
What is an agonist? - ANS A ligand that binds to a receptor to initiate a response
What is an antagonist? - ANS A ligand that binds to a receptor to prevent a response
What are intracellular signaling molecules? Provide an example - ANS Seconds messengers.
ie. cAMP
What are effector proteins? What can they do? - ANS The target proteins in a pathway. Can
mediate cell responses
Signals can act over short range OR long range. T/F? - ANS True
Where are extracellular signaling molecules secreted? - ANS Outside of the cell. Example:
into the bloodstream
What is an endocrine cell? Provide an example - ANS A cell that produces long range
hormones and secretes them into the blood stream to affect a target cell.
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
1
,Example: insulin
What is a paracrine cell? Provide two examples - ANS A cell that releases signal molecules
that diffuse locally.
Example: Cytokines regulate local inflammation. Growth factors
What is an autocrine cell? Provide an example - ANS A cell that depends on its own signaling
molecules
Example: cancer cells
What are synaptic cells? Provide an example - ANS Cells that secrete neurotransmitters from
their axons terminal
What is a synapse? - ANS the junction of the nerve cell (neuron). Delivers chemical signal to
adjacent neuron
What is a contact-dependent cell? Provide an example - ANS A cell that does not depend on
secreted signaling molecules. The cell must make direct physical contact through ligand and
receptor, both of which are located in plasma membrane.
Example: Some signaling in embryonic development.
Some signal molecules (Ligands) can induce different responses in different target cells by
affecting different receptors OR by resulting in different products T/F? - ANS True
After acetylcholine is secreted from cells, it is long-lived, because it has to reach target cells all
over body. T/F? - ANS False. Acetylcholine would be short-lived
Where are receptors usually located? - ANS They can be at the cell surface (plasma
membrane) OR, if the ligand is small and hydrophobic, within the cell.
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
2
, Describe the steroid hormone cortisol as a ligand. - ANS Cortisol is able to diffuse through the
plasma membrane and bind with a nuclear receptor protein (which later acts a a transcription
regulator). It can then move through a nuclear pore channel and bind to the regulatory region
of a targeted gene, leading to transcription and translation.
What response does exposure to extracellular signals in an intracellular pathway produce? Does
this pathway occur fast or slow? - ANS Alteration of free-floating ribosome and protein
function. Occurs fast
What response does exposure to extracellular signals in an nuclear signaling pathway produce?
Does this pathway occur fast or slow? - ANS Alteration of DNA transcription and eventually
mRNA and protein synthesis. Occurs slowly.
Signaling molecules are amplified and integrated by multiple factors. T/F? - ANS True. Primary
transduction typically amplifies the signal.
What is the key mechanism for molecular on/off switches? Why? - ANS Phosphorylation.
Presence of a phosphate may turn a factor on or off. Common because it is reversible
What is phosphorylation? - ANS The key mechanism for turning factors on or off. Reversible
Describe a general phosphorylation mechanism - ANS If a factor is off, a signal will prompt a
protein kinase to convert ATP to ADP. The lone phosphate will bind to that factor and turn it on
to produce a secondary signal. A protein phosphatase will remove the phosphate to turn the
factor off
What purpose do GTP binding proteins serve? Provide examples - ANS Participate in signal
transduction. Similar purpose as phosphorylation
What proteins control GTP Binding proteins? - ANS GEF- Guanine nucleotide Exchange Factor
GAP- GTPase Activating Protein
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
3
