PCB 3023 Exam 4 questions and
answers graded A+ updated
What is a Ligand? - correct answer a molecule that binds to receptors
What is an agonist? - correct answer A ligand that binds to a receptor to initiate a response
What is an antagonist? - correct answer A ligand that binds to a receptor to prevent a response
What are intracellular signalling molecules? Provide an example - correct answer Seconds
messengers.
ie. cAMP
What are effector proteins? What can they do? - correct answer The target proteins in a pathway.
Can mediate cell responses
Signals can act over short range OR long range. T/F? - correct answer True
Where are extracellular signaling molecules secreted? - correct answer Outside of the cell. Example:
into the bloodstream
What is an endocrine cell? Provide an example - correct answer A cell that produces long range
hormones and secretes them into the blood stream to affect a target cell.
Example: insulin
What is a paracrine cell? Provide two examples - correct answer A cell that releases signal molecules
that diffuse locally.
Example: Cytokines regulate local inflammation. Growth factors
What is an autocrine cell? Provide an example - correct answer A cell that depends on its own
signaling molecules
Example: cancer cells
,What are synaptic cells? Provide an example - correct answer Cells that secrete neurotransmitters
from their axons terminal
What is a synapse? - correct answer the junction of the nerve cell (neuron). Delivers chemical signal
to adjacent neuron
What is a contact-dependent cell? Provide an example - correct answer 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? - correct answer True
After acetylcholine is secreted from cells, it is long-lived, because it has to reach target cells all over
body. T/F? - correct answer False. Acetylcholine would be short-lived
Where are receptors usually located? - correct answer They can be at the cell surface (plasma
membrane) OR, if the ligand is small and hydrophobic, within the cell.
Describe the steroid hormone cortisol as a ligand. - correct answer 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? - correct answer 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? - correct answer Alteration of DNA transcription and eventually
mRNA and protein synthesis. Occurs slowly.
Signaling molecules are amplified and integrated by multiple factors. T/F? - correct answer True.
Primary transduction typically amplifies the signal.
, What is the key mechanism for molecular on/off switches? Why? - correct answer Phosphorylation.
Presence of a phosphate may turn a factor on or off. Common because it is reversible
What is phosphorylation? - correct answer The key mechanism for turning factors on or off.
Reversible
Describe a general phosphorylation mechanism - correct answer 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 - correct answer Participate in signal
transduction. Similar purpose as phosphorylation
What proteins control GTP Binding proteins? - correct answer GEF- Guanine nucleotide Exchange
Factor
GAP- GTPase Activating Protein
What does GAP- GTPase Activating Protein do? - correct answer Inactivate GTPase by promoting GTP
hydrolysis
What does GEF- Guanine nucleotide Exchange Factor do? - correct answer Activates GTPase by
promoting the exchange of GDP for GTP
Describe a typical signaling by GTP binding protein mechanism - correct answer If a monomeric
GTPase is inactive, GEF will prompt the exchange of GDP for GTP, activating the monomeric GTPase.
To inactive the monomeric GTPase, GAP will remove a phosphate from GTP to yield GDP.
Describe a G-Protein Coupled Receptor (GPCR) - correct answer A polypeptide chain that traverses
the plasma membrane as seven alpha helices. It is where the signal molecules binds and where the
receptor is.
How many GPCRs does the human genome encode? Where are the majority located? - correct
answer >700. ~400 are olfactory
GPCRs are often targets for pharmaceuticals. T/F? - correct answer True
answers graded A+ updated
What is a Ligand? - correct answer a molecule that binds to receptors
What is an agonist? - correct answer A ligand that binds to a receptor to initiate a response
What is an antagonist? - correct answer A ligand that binds to a receptor to prevent a response
What are intracellular signalling molecules? Provide an example - correct answer Seconds
messengers.
ie. cAMP
What are effector proteins? What can they do? - correct answer The target proteins in a pathway.
Can mediate cell responses
Signals can act over short range OR long range. T/F? - correct answer True
Where are extracellular signaling molecules secreted? - correct answer Outside of the cell. Example:
into the bloodstream
What is an endocrine cell? Provide an example - correct answer A cell that produces long range
hormones and secretes them into the blood stream to affect a target cell.
Example: insulin
What is a paracrine cell? Provide two examples - correct answer A cell that releases signal molecules
that diffuse locally.
Example: Cytokines regulate local inflammation. Growth factors
What is an autocrine cell? Provide an example - correct answer A cell that depends on its own
signaling molecules
Example: cancer cells
,What are synaptic cells? Provide an example - correct answer Cells that secrete neurotransmitters
from their axons terminal
What is a synapse? - correct answer the junction of the nerve cell (neuron). Delivers chemical signal
to adjacent neuron
What is a contact-dependent cell? Provide an example - correct answer 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? - correct answer True
After acetylcholine is secreted from cells, it is long-lived, because it has to reach target cells all over
body. T/F? - correct answer False. Acetylcholine would be short-lived
Where are receptors usually located? - correct answer They can be at the cell surface (plasma
membrane) OR, if the ligand is small and hydrophobic, within the cell.
Describe the steroid hormone cortisol as a ligand. - correct answer 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? - correct answer 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? - correct answer Alteration of DNA transcription and eventually
mRNA and protein synthesis. Occurs slowly.
Signaling molecules are amplified and integrated by multiple factors. T/F? - correct answer True.
Primary transduction typically amplifies the signal.
, What is the key mechanism for molecular on/off switches? Why? - correct answer Phosphorylation.
Presence of a phosphate may turn a factor on or off. Common because it is reversible
What is phosphorylation? - correct answer The key mechanism for turning factors on or off.
Reversible
Describe a general phosphorylation mechanism - correct answer 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 - correct answer Participate in signal
transduction. Similar purpose as phosphorylation
What proteins control GTP Binding proteins? - correct answer GEF- Guanine nucleotide Exchange
Factor
GAP- GTPase Activating Protein
What does GAP- GTPase Activating Protein do? - correct answer Inactivate GTPase by promoting GTP
hydrolysis
What does GEF- Guanine nucleotide Exchange Factor do? - correct answer Activates GTPase by
promoting the exchange of GDP for GTP
Describe a typical signaling by GTP binding protein mechanism - correct answer If a monomeric
GTPase is inactive, GEF will prompt the exchange of GDP for GTP, activating the monomeric GTPase.
To inactive the monomeric GTPase, GAP will remove a phosphate from GTP to yield GDP.
Describe a G-Protein Coupled Receptor (GPCR) - correct answer A polypeptide chain that traverses
the plasma membrane as seven alpha helices. It is where the signal molecules binds and where the
receptor is.
How many GPCRs does the human genome encode? Where are the majority located? - correct
answer >700. ~400 are olfactory
GPCRs are often targets for pharmaceuticals. T/F? - correct answer True
