56 Questions
What type of signaling mechanism allows neighboring cells to share small molecules and respond to extracellular signals in a coordinated way?
Gap junctions
What is the purpose of the multiple extracellular signals that an animal cell requires?
To allow the cell to survive, divide, and differentiate
What happens to a cell if it is deprived of appropriate survival signals?
The cell will undergo programmed cell death, or apoptosis
What is the relationship between the receptor proteins and the intracellular signaling pathways in different cell types?
The receptor proteins are the same, but the signaling pathways are different
What type of signaling mechanism is used to transmit neurotransmitters to the postsynaptic target cell?
Chemical synapses
How do signal molecules work to regulate the behavior of a cell?
Signal molecules work in combinations to regulate the behavior of a cell
What is the main function of G-protein linked receptors in cell signaling?
They use G proteins to relay the signal into the cell
Which of the following is a characteristic of G-protein coupled receptors?
They have seven transmembrane α-helices
How do G-protein coupled receptors transduce extracellular signals into intracellular responses?
They use secondary messengers to activate intracellular signaling pathways
Which of the following is an example of a G-protein coupled receptor?
Neurotransmitter receptor
What is the role of the G protein in G-protein coupled receptor signaling?
The G protein binds to the receptor and relays the signal into the cell
How do G-protein coupled receptors differ from enzyme-linked receptors?
G-protein coupled receptors indirectly regulate the activity of another target protein, while enzyme-linked receptors directly activate an enzyme
What is the main function of the PIP-3/PKB (Akt) signaling pathway?
To regulate cell survival, proliferation, and apoptosis
What is the role of phosphatidylinositol 3-Kinase (PI-3K) in the PIP-3/PKB (Akt) signaling pathway?
PI-3K phosphorylates PIP-2 to produce PIP-3
How do membrane receptors that lack tyrosine kinase activity, such as those for growth hormones and cytokines, initiate signaling?
They interact with cytoplasmic proteins that have tyrosine kinase activity, such as Jak and Tyk2
What is the role of the Ca2+ pump in the muscle cell membrane?
It pumps Ca2+ out of the cytoplasm to lower the intracellular Ca2+ level
How does Ca2+ entering through voltage-gated channels in the depolarized muscle cell membrane affect the intracellular Ca2+ level?
It stimulates the ryanodine receptor on the ER membrane and elevates the intracellular Ca2+ level
What is the role of PIP-2 in the PIP-3/PKB (Akt) signaling pathway?
PIP-2 is phosphorylated by PI-3K to produce PIP-3, which then activates PKB (Akt)
Which of the following statements about enzyme-linked receptors is true?
They are activated through dimerization.
Which of the following is an example of a protein-tyrosine kinase receptor?
Insulin receptor
What is the mechanism of action for enzyme-linked receptors?
All of the above.
Which of the following is not a type of protein kinase receptor mentioned in the text?
Histidine kinase receptors
In the illustration, what does the symbol 'P' represent?
Phosphorylation
According to the illustration, what happens after ligand binding to the receptor tyrosine kinase?
The receptor dimerizes and becomes activated.
What is the role of GTP in the activation of G proteins?
GTP binding causes the G protein to release GDP and become active
What is the role of the $\alpha$ subunit of the G protein after it separates from the $\beta$ and $\gamma$ subunits?
The $\alpha$ subunit interacts with target proteins to elicit a response
What is the role of cAMP as a second messenger in G protein signaling?
cAMP is synthesized from ATP by adenylyl cyclase, and its concentration increases upon G protein activation
What is the primary function of G proteins in cellular signaling?
G proteins activate or inhibit target enzymes, such as adenylyl cyclase
What is the role of p53 in response to DNA damage at the G1 checkpoint?
Prevents G1 arrest
How do p53 mutations (loss of function) affect the cell's response to DNA damage at the G1 phase?
Prevent G1 arrest
What is the consequence of passing on damaged DNA to daughter cells due to the absence of G1 arrest?
Increased frequency of mutations
What type of genetic alterations are most common in human cancers?
p53 mutations
Which protein acts as a transcription factor and promotes the transcription of target proteins like p21 for cell cycle regulation?
p53
What is the primary role of cell cycle checkpoints?
To coordinate the various stages of the cell cycle
Which of the following is NOT a major checkpoint in the cell cycle?
S checkpoint
What is the significance of the G1 checkpoint?
It is the primary decision point for cell division
What determines whether a cell will continue through the cell cycle or enter the G0 phase?
Both internal and external signals
Which of the following statements about the G0 phase is correct?
Most human cells, including mature nerve and muscle cells, are in this non-dividing state
What is the role of kinases and phosphatases in the cell cycle control system?
They regulate the activity of proteins involved in cell cycle progression
What is the primary function of the Cip/Kip family of Cdk inhibitors?
Inhibiting Cdk4 and Cdk6 complexed with cyclin D, regulating the G1-S transition checkpoint
What is the primary role of the Ink4 family of Cdk inhibitors?
Inhibiting Cdk4 and Cdk6 complexed with cyclin D, regulating passage through the G1 checkpoint
What is the primary mechanism by which Cdks are activated?
Association with cyclins and formation of Cdk/cyclin complexes
What is the role of the p53 protein in the regulation of the cell cycle?
p53 senses DNA damage and induces the expression of p21, a Cdk inhibitor
What is the primary function of cell cycle checkpoints?
To ensure that incomplete or damaged chromosomes are not replicated and passed on to daughter cells
What is the primary purpose of the G2 checkpoint in the cell cycle?
To prevent initiation of mitosis until DNA damage has been repaired
What is the molecular mechanism that restricts DNA replication to once per cell cycle?
The action of MCM (mini-chromosome maintenance) proteins, which can only bind to the Origin Replication Complex (ORC) during G1 phase
What is the role of the G2 checkpoint in response to DNA damage?
It allows time for the cell to repair any DNA damage before proceeding to mitosis
What is the key function of the Origin Replication Complex (ORC) in DNA replication licensing?
It acts as a landing pad for the licensing factors Cdc6/18 and Cdt1
What is the significance of the difference in CDK activity between the G1 phase and the S/M phases of the cell cycle?
It regulates the initiation of DNA replication and the progression through mitosis
What is the role of the licensing process in the control of DNA replication during the cell cycle?
It ensures that DNA replication occurs only once per cell cycle
What is the primary role of the MCM complex during DNA replication?
It acts as a replicative helicase, unwinding the DNA double helix.
What is the role of CDK (cyclin-dependent kinase) in the licensing process?
It prevents re-licensing by inhibiting the binding of licensing factors to chromatin.
How is re-licensing of DNA prevented during S phase and M phase?
Geminin binds to Cdt1, preventing it from licensing the origins of replication.
What event allows a new round of licensing to occur?
Degradation of Geminin and inactivation of CDKs at the end of M phase.
What is the role of DDK (Dbf4-dependent kinase) in the initiation of DNA replication?
It activates the MCM complex to initiate DNA replication.
What is the significance of low CDK activity at the end of M phase?
It permits the loading of the MCM complex onto chromatin for licensing.
Test your knowledge on cell communication and signaling, including chemical synapses, neurotransmitters, and gap junctions. Learn about how cells transmit signals to neighboring cells and coordinate responses to extracellular signals.
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