49 Questions
What is the primary function of a receptor protein?
To receive chemical signals from outside the cell and activate intracellular signaling pathways
What is the main difference between hydrophilic and hydrophobic signal molecules?
Hydrophilic signal molecules bind to cell surface receptors, while hydrophobic signal molecules bind to intracellular receptors
What is the function of effector proteins in intracellular signaling pathways?
To process and distribute the signal to specific intracellular targets
What is the main characteristic of G-protein coupled receptors?
They are metabotropic receptors that activate G-proteins
What is the mechanism of action of ligand-gated ion channel receptors?
They bind to ligands, which directly open ion channels
What is the location of nuclear receptors?
In the nucleus or in the cytoplasm
What is the primary function of the cytosolic domain of a receptor tyrosine kinase?
To have intrinsic enzyme activity or associate with an enzyme
What is the result of the binding of a ligand to a receptor tyrosine kinase?
Dimerization and phosphorylation of the receptor
Which of the following growth factors acts through a receptor tyrosine kinase?
Insulin-like growth factor
What is the mechanism of activation of some receptor tyrosine kinases?
Conformational changes from the interaction between the two kinase domains
What is the purpose of phosphotyrosine docking sites in receptor tyrosine kinase signaling?
To bind to adaptor proteins and relay the signal
What is the primary function of intracellular receptors?
To bind to small hydrophobic signal molecules and regulate gene transcription
Which type of hormones bind to intracellular receptors?
Steroid hormones
What is the location of intracellular receptors in target cells?
In both the cytosol and nucleus
Which of the following drugs targets intracellular receptors?
All of the above
What is the result of binding of small hydrophobic signal molecules to intracellular receptors?
Alteration of gene transcription
What is the characteristic of lipophilic signals that allows them to enter target cells?
They are small and hydrophobic
What is the function of G-protein coupled receptors?
To mediate most responses to signals from the external world
What is the function of G-proteins?
To relay the signal into the cell interior
What is the function of the α subunit of G-proteins?
To hydrolyze GTP to GDP
What is the function of the β/γ complex of G-proteins?
To interact with targets
What is the function of second messengers?
To diffuse away from their source and spread the signal
What is the function of protein kinase A (PKA)?
To bind to and alter the behavior of selected signaling or effector proteins
Why are GPCRs important in medicine?
Because almost half of all known drugs work through GPCRs
What is the primary function of a receptor?
To receive chemical signals from outside the cell
What type of receptors are involved in rapid neurotransmission?
Ligand-gated ion channel receptors
What is the location of receptors that bind to hydrophilic signal molecules?
On the cell surface
What type of receptors are involved in regulating gene expression?
Nuclear receptors
What is the function of effector proteins in intracellular signaling pathways?
To process and distribute signals to specific targets
What type of signal molecules bind to intracellular receptors?
A and B
Which receptor type is also called ionotropic receptors?
Ligand-gated ion channel receptors
What is the primary function of G-proteins?
To relay the signal into the cell interior
What is the result of the activation of G-proteins?
The α subunit exchanges GDP for GTP
What is the function of cyclic adenosine monophosphate (cAMP)?
To act as a second messenger
What is the function of diacylglycerol (DAG)?
To act as a second messenger
What is the function of inositol 1,4,5-trisphosphate (IP3)?
To act as a second messenger
What is the result of the activation of protein kinase A (PKA)?
The behavior of selected signaling proteins is altered
What is the function of Gs (stimulatory) G-proteins?
To stimulate the cAMP signaling pathway
How many types of G-proteins are activated by the same signal?
Multiple types
What is the role of lipophilic signal molecules in target cells?
They diffuse directly across the plasma membrane and bind to intracellular receptors
Which of the following drugs targets intracellular receptors to decrease blood lipids?
Fibrate drugs
What is the outcome of the binding of small hydrophobic signal molecules to their respective intracellular receptor proteins?
The receptor protein alters its ability to control the transcription of specific genes
Which type of receptors are both receptors and intracellular effectors of the signal?
Intracellular receptors
What is the function of intracellular receptors in the regulation of gene transcription?
They alter the ability of transcription regulators to control gene transcription
What is the characteristic of intracellular receptors that allows them to function as transcription regulators?
Their ability to control the transcription of specific genes
What is the characteristic of receptor tyrosine kinases that distinguishes them from other enzymes?
They are transmembrane proteins with ligand-binding domain outside the plasma membrane
What is the result of dimerization of receptor tyrosine kinases?
Phosphorylation of tyrosine side chains
What is the role of the cytosolic domain of receptor tyrosine kinases?
To either have intrinsic enzyme activity or associate with an enzyme
What is true about the activation of some receptor tyrosine kinases?
They are activated by both phosphorylation and conformational changes
Study Notes
Cell Signaling
- A protein molecule that receives chemical signals from outside the cell is called a receptor
- Receptors can be located on the cell surface or inside the cell (cytoplasm or nucleus)
- Hydrophilic signal molecules bind to receptors on the cell surface, while hydrophobic signal molecules bind to receptors inside the cell
Cell Surface Receptors
- There are five types of cell surface receptors:
- Ligand-gated ion channel receptors (ionotropic)
- G-protein coupled receptors (metabotropic)
- Enzyme-coupled receptors
- Integrins
- TOLL-like receptors
G-Protein Coupled Receptors (GPCRs)
- GPCRs are integral membrane proteins that pass in and out of the plasma membrane multiple times
- They bind to a particular type of G protein, which relays the signal into the cell interior
- G proteins are membrane-associated trimeric proteins with three subunits: α, β, and γ
- When a ligand binds to a GPCR, the G protein dissociates and interacts with targets, such as enzymes or ion channels
Second Messengers
- Second messengers are intracellular signaling molecules generated in response to receptor activation
- They diffuse away from their source and spread the signal to other parts of the cell
- Important second messengers include:
- Diacylglycerol (DAG)
- Cyclic adenosine monophosphate (cAMP)
- Inositol 1,4,5-trisphosphate (IP3)
- Calcium (Ca2+)
GPCR Signaling Pathway
- GPCRs can activate many different G proteins, which can interact with multiple targets
- The same signal can activate many different GPCRs
- GPCRs are important in medicine, with almost half of all known drugs working through GPCRs or their signaling pathways
Receptor Tyrosine Kinase (RTK)
- RTKs are the largest class of enzyme-coupled receptors
- They are transmembrane proteins with ligand-binding domains outside the plasma membrane and cytosolic domains that have intrinsic enzyme activity or associate with an enzyme
- Growth factors, such as insulin and epidermal growth factor, act through RTKs
- RTKs dimerize and phosphorylate each other, creating phosphotyrosine docking sites for intracellular signaling proteins
Intracellular Receptors
- Intracellular receptors are transcription regulators that bind to lipophilic signal molecules
- They can be located in the cytosol or nucleus
- Examples of intracellular receptors include steroid hormones, thyroid hormones, retinoid, and vitamin D
- Some drugs use intracellular receptors as targets, such as Fibrates, glucocorticoids, and glitazones
Learn about cell signaling, including the location of receptors, types of cell surface receptors, and second messengers like cAMP. Explore how GPCRs and nuclear receptors work.
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