Signal Transduction Practice Questions

Q: A small Ca+2 binding protein that modifies the activity of many enzymes and other proteins in response to changes of Ca+2 concentration is known as:

Calmodulin. ***Calmodulin*** - **Calmodulin** is a highly conserved, small **calcium-binding protein** that acts as a central mediator of calcium signaling pathways. - It undergoes a conformational change upon binding **Ca2+**, enabling it to interact with and regulate the activity of numerous target enzymes and proteins, thereby orchestrating various cellular processes. *Cyclin* - **Cyclins** are a family of proteins that activate **cyclin-dependent kinases (CDKs)**, playing a crucial role in regulating the progression through the cell cycle. - While essential for cell division, cyclins do not primarily function as **Ca2+-binding regulatory proteins**. *Kinesin* - **Kinesin** is a motor protein that moves along **microtubules**, transporting vesicles, organelles, and other cellular components within the cell. - Its primary function is in intracellular transport and cell division, not in **Ca2+-dependent enzymatic regulation**. *Collagen* - **Collagen** is the most abundant protein in mammals, forming the main structural component of connective tissues like skin, bone, and cartilage. - It provides structural integrity and tensile strength to tissues and is not involved in **calcium-dependent enzyme modulation**.

Q: Which of the following acts via the steroid-thyroid receptor superfamily (nuclear receptors)?

Vitamin D3. ***Vitamin D3*** - **Vitamin D3** (calcitriol) is a **steroid hormone** that acts by binding to the **vitamin D receptor (VDR)**, which is a member of the **steroid-thyroid receptor superfamily** of nuclear receptors. - This binding leads to gene transcription modulation, affecting calcium and phosphate homeostasis. *GH* - **Growth Hormone (GH)** acts primarily through **tyrosine kinase-associated receptors** (specifically, the JAK/STAT pathway), not nuclear receptors. - It's a **peptide hormone** that regulates growth, metabolism, and body composition. *Enkephalins* - **Enkephalins** are **opioid peptides** that bind to **G protein-coupled receptors (GPCRs)** on the cell surface. - They are involved in pain modulation and do not act via nuclear receptors. *Insulin* - **Insulin** is a **peptide hormone** that primarily acts via **receptor tyrosine kinases (RTKs)**, not nuclear receptors. - Upon binding, it initiates a signaling cascade involving phosphorylation events, regulating glucose metabolism.

Q: One of the ways that cells communicate with each other is by secretion of various molecules. The secreted molecule is known as

A signaling molecule. ***A signaling molecule*** - Cells communicate by releasing **signaling molecules** that travel to other cells and bind to specific receptors. - These molecules transmit information, initiating a **response** in the target cell. *A receptor molecule* - A **receptor molecule** is located on the target cell's surface or inside the cell and binds to the signaling molecule, rather than being the secreted molecule itself. - Its role is to **receive** the signal, not to transmit it from the secreting cell. *An integrin* - **Integrins** are transmembrane proteins that link the cell's cytoskeleton to the extracellular matrix, facilitating cell adhesion and migration. - They are primarily involved in **cell-matrix interactions** and less directly in general cell-to-cell signaling via secretion. *A spectrin tetramer* - A **spectrin tetramer** is a component of the cytoskeleton, particularly important in maintaining the shape and structural integrity of red blood cells. - It functions as an **intracellular structural protein** and is not a secreted molecule involved in cell-to-cell communication.

Q: How many subunits are there in the insulin receptor?

4. ***4*** - The **insulin receptor** is a **tetramer** composed of two alpha (α) subunits and two beta (β) subunits. - The two α subunits are located extracellularly and are responsible for **insulin binding**, while the two β subunits span the cell membrane and possess **tyrosine kinase activity** upon insulin binding. *3* - The insulin receptor is not a trimeric protein. It contains four subunits. - There are no known isoforms of the insulin receptor that are trimeric. *2* - While it has two types of subunits (alpha and beta), the functional receptor is a tetramer. - The receptor requires both alpha and beta subunits to be present in pairs for proper function. *1* - The insulin receptor is a complex protein, not a monomer. - A single subunit would not be able to perform both insulin binding and intracellular signaling.

Q: Steroid hormone receptors have attachment site for all except:

Transcription activators. ***Transcription activators*** - **Steroid hormone receptors** bind directly to **steroid hormones** and **hormone response elements (HREs)** on DNA, as well as to **transcription repressors** in their inactive state. - They do not have a direct attachment site for **transcription activators**; rather, activated steroid receptors can *act* as transcription activators or co-activators through protein-protein interactions. *Hormone responsive element* - This is a specific **DNA sequence** in the promoter region of target genes where the **steroid hormone-receptor complex** binds to regulate gene transcription. - It defines the genomic target for the activated steroid receptor, ensuring **gene-specific responses**. *Steroid hormone* - The **steroid hormone** itself binds to its specific receptor, inducing a conformational change that allows the receptor to translocate to the nucleus and bind to DNA. - This binding is essential for the **receptor's activation** and subsequent gene regulation. *Transcription repressors* - In the absence of a steroid hormone, **transcription repressors** (e.g., heat shock proteins) are often bound to the **steroid hormone receptor**, preventing its activation and binding to DNA. - Upon hormone binding, these repressors dissociate, allowing the receptor to become active and modulate **gene expression**.

Q: cGMP is a second messenger for which of the following hormones?

Both Nitric oxide and Atrial natriuretic factor. ***Both Nitric oxide and Atrial natriuretic factor*** - Both **nitric oxide (NO)** and **atrial natriuretic factor (ANF/ANP)** utilize **cGMP as a second messenger**. - **ANF** binds to membrane-bound guanylyl cyclase receptors (GC-A/natriuretic peptide receptor A), which directly catalyze the conversion of GTP to cGMP, leading to **natriuresis, vasodilation, and decreased blood pressure**. - **Nitric oxide** activates soluble guanylyl cyclase in target cells, producing cGMP, which causes **smooth muscle relaxation and vasodilation**. - Both are classic examples of the cGMP signaling pathway in medical biochemistry. *Atrial natriuretic factor (alone)* - While ANF does use cGMP as a second messenger, this option is incomplete. - Selecting only ANF ignores the fact that **nitric oxide also uses cGMP**, making "both" the more accurate answer. *Nitric oxide (alone)* - While NO does use cGMP as a second messenger, this option is incomplete. - Selecting only NO ignores the fact that **ANF also uses cGMP**, making "both" the more accurate answer. *None of the options* - This is incorrect because both **ANF** and **NO** clearly utilize cGMP as their second messenger. - The cGMP pathway is well-established for both molecules in cardiovascular and renal physiology.

Q: Growth factors promote cell growth by acting on:

Tyrosine Kinase. ***Tyrosine Kinase*** - Growth factors typically bind to **receptor tyrosine kinases (RTKs)**, activating their enzymatic activity. - This activation leads to the **phosphorylation of tyrosine residues** on target proteins, initiating intracellular signaling cascades that promote cell growth, proliferation, and differentiation. *cAMP* - **Cyclic AMP (cAMP)** is a second messenger often associated with **G-protein-coupled receptors (GPCRs)**, not directly with growth factor signaling. - While cAMP plays a role in various cellular processes, it is not the primary direct target for growth factor-mediated cell growth. *G-protein-coupled receptor (GPCR)* - **GPCRs** are a large family of receptors that mediate responses to a wide range of extracellular signals, but they are generally not the primary receptors for **growth factors**. - Growth factors predominantly utilize **receptor tyrosine kinases** for their signaling. *cGMP* - **Cyclic GMP (cGMP)** is a second messenger involved in various signaling pathways, notably those regulated by **nitric oxide** and **natriuretic peptides**. - It is not the main signaling molecule directly activated by growth factors to promote cell growth.

Q: Which of the following binds to Tyrosine Kinase receptor?

Insulin. ***Insulin*** - **Insulin** is a classic example of a hormone that binds to and activates a **tyrosine kinase receptor**, leading to a cascade of intracellular signaling events for glucose uptake and metabolism. - The **insulin receptor** is a heterodimeric protein with intrinsic tyrosine kinase activity that phosphorylates itself and other proteins upon insulin binding. *Glucagon* - **Glucagon** primarily acts on **G protein-coupled receptors (GPCRs)**, specifically the glucagon receptor, to increase cyclic AMP (cAMP) and activate protein kinase A. - Its main roles are to stimulate **glycogenolysis** and **gluconeogenesis** in the liver. *Prolactin* - **Prolactin** binds to a receptor that is a member of the **cytokine receptor superfamily**, which lacks intrinsic enzyme activity. - Upon ligand binding, these receptors associate with and activate **Janus kinases (JAKs)**, leading to the JAK-STAT signaling pathway. *Growth Hormone* - **Growth hormone (GH)** also binds to a receptor belonging to the **cytokine receptor superfamily** (similar to prolactin), which then associates with and activates **JAKs**. - This activation subsequently initiates the **JAK-STAT signaling pathway**, mediating its diverse growth-promoting and metabolic effects.

Q: Products of Phospholipase C are -

Inositol triphosphate and Diacylglycerol. ***Inositol triphosphate and Diacylglycerol*** - **Phospholipase C (PLC)** cleaves **phosphatidylinositol 4,5-bisphosphate (PIP2)** into two important second messengers: **inositol 1,4,5-trisphosphate (IP3)** and **diacylglycerol (DAG)**. - **IP3** mobilizes intracellular **calcium**, while **DAG** activates **protein kinase C (PKC)**, both crucial for signal transduction pathways. *Lysophospholipid and fatty acid* - These are typically products of **Phospholipase A2**, which hydrolyzes a **fatty acid** from the *sn-2* position of a glycerophospholipid, leaving a **lysophospholipid**. - **Phospholipase C** acts on a different bond within the **phospholipid structure** and produces different second messengers. *Phosphatidate and IP2* - **Phosphatidate** is a precursor in lipid synthesis and is not directly produced by **PLC's primary action** on **PIP2**. - **IP2 (Inositol bisphosphate)** is a dephosphorylated product of **IP3** and not the direct initial product of **PLC** cleavage from **PIP2**. *Inositol and diacylglycerol* - **Inositol** itself is a cyclic alcohol and is part of the **inositol phosphate** structures. It is not directly released as a standalone product by **PLC** cleavage of **PIP2**. - It is **inositol trisphosphate (IP3)**, not free inositol, that is the second messenger formed alongside **diacylglycerol**.

Q: Which of the following hormone crosses the plasma membrane for its action?

Thyroxine. ***Thyroxine*** - **Thyroxine (T4)** and **triiodothyronine (T3)** are **lipid-soluble** thyroid hormones. - Due to their lipid solubility, they can freely cross the **plasma membrane** and bind to intracellular receptors. *Insulin* - **Insulin** is a **peptide hormone** and is **water-soluble**. - It binds to specific **cell-surface receptors** on the plasma membrane, initiating a signaling cascade without entering the cell. *Epinephrine* - **Epinephrine (adrenaline)** is a **catecholamine** and is **water-soluble**. - It acts on **G protein-coupled receptors** on the cell surface, triggering intracellular secondary messengers. *Glucagon* - **Glucagon** is a **peptide hormone** that is **water-soluble**. - Like insulin, it binds to specific **cell-surface receptors** (G protein-coupled receptors) to exert its effects.

Question 1

A small Ca+2 binding protein that modifies the activity of many enzymes and other proteins in response to changes of Ca+2 concentration is known as:

Accepted Answer

Calmodulin

Answer

Cyclin

Answer

Kinesin

Answer

Collagen

Question 2

Which of the following acts via the steroid-thyroid receptor superfamily (nuclear receptors)?

Accepted Answer

Vitamin D3

Answer

GH

Answer

Enkephalins

Answer

Insulin

Question 3

One of the ways that cells communicate with each other is by secretion of various molecules. The secreted molecule is known as

Accepted Answer

A signaling molecule

Answer

A receptor molecule

Answer

An integrin

Answer

A spectrin tetramer

Question 4

How many subunits are there in the insulin receptor?

Accepted Answer

4

Answer

3

Answer

2

Answer

1

Question 5

Steroid hormone receptors have attachment site for all except:

Accepted Answer

Transcription activators

Answer

Hormone responsive element

Answer

Steroid hormone

Answer

Transcription repressors

Question 6

cGMP is a second messenger for which of the following hormones?

Accepted Answer

Both Nitric oxide and Atrial natriuretic factor

Answer

Nitric oxide

Answer

Atrial natriuretic factor

Answer

None of the options

Question 7

Growth factors promote cell growth by acting on:

Accepted Answer

Tyrosine Kinase

Answer

cAMP

Answer

G-protein-coupled receptor (GPCR)

Answer

cGMP

Question 8

Which of the following binds to Tyrosine Kinase receptor?

Accepted Answer

Insulin

Answer

Glucagon

Answer

Prolactin

Answer

Growth Hormone

Question 9

Products of Phospholipase C are -

Accepted Answer

Inositol triphosphate and Diacylglycerol

Answer

Lysophospholipid and fatty acid

Answer

Phosphatidate and IP2

Answer

Inositol and diacylglycerol

Question 10

Which of the following hormone crosses the plasma membrane for its action?

Accepted Answer

Thyroxine

Answer

Insulin

Answer

Epinephrine

Answer

Glucagon

Signal Transduction — MCQs

Signal Transduction — MCQs

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