Signal Transduction Practice Questions

Q: Which of the following induces apoptosis in a cell?

Glucocorticoids. ***Glucocorticoids*** - **Glucocorticoids** are known to induce apoptosis in various cell types, particularly lymphocytes, making them useful in **lymphoid malignancies**. - They activate a complex signaling pathway that leads to the activation of pro-apoptotic proteins and the suppression of anti-apoptotic proteins, ultimately resulting in **programmed cell death**. *Isoprenoids* - **Isoprenoids** are a large class of organic compounds derived from isoprene, involved in various metabolic processes like cholesterol synthesis and protein prenylation, but do not directly induce apoptosis. - While some isoprenoid precursors or inhibitors of isoprenoid synthesis can affect cell proliferation or survival, isoprenoids themselves are not primary apoptosis inducers. *Myristic acid* - **Myristic acid** is a saturated fatty acid primarily involved in protein myristoylation, a post-translational modification essential for various cellular functions. - It is not known to be a direct inducer of apoptosis but can influence signaling pathways that may indirectly impact cell survival or death. *Oleic acid* - **Oleic acid** is a monounsaturated fatty acid that is a major component of cell membranes and is involved in energy storage and signaling. - It is generally considered cytoprotective and can even inhibit apoptosis in some contexts, rather than inducing it.

Q: cGMP is a second messenger for which hormone(s)?

Atrial natriuretic factor. ***Atrial natriuretic factor*** - **Atrial natriuretic peptide (ANP)** binds to a **particulate guanylyl cyclase receptor**, activating it to convert **GTP to cGMP**. - **cGMP** then mediates the downstream effects of ANP, such as **vasodilation** and increased **sodium excretion**. *Somatostatin (inhibits growth hormone and insulin secretion)* - Somatostatin acts primarily through **G-protein coupled receptors** that inhibit **adenylyl cyclase**, leading to a decrease in **cAMP** levels. - It does not directly utilize **cGMP** as a second messenger. *Angiotensin II (increases blood pressure via other pathways).* - Angiotensin II primarily acts through **Gq-protein coupled receptors**, leading to activation of **phospholipase C** and generation of **IP3** and **DAG**. - Its effects are mediated by **calcium** and **protein kinase C**, not **cGMP**. *Antidiuretic hormone (ADH)* - **ADH** acts through two main receptor types: **V1 receptors** (via **IP3/DAG** pathway) and **V2 receptors** (via **cAMP** pathway). - Neither of these pathways involves **cGMP** as a primary second messenger.

Q: Serpentine receptor is a:

Seven-pass transmembrane protein. ***Seven-pass transmembrane protein*** - Serpentine receptors, also known as **G protein-coupled receptors (GPCRs)**, are characterized by their structure, which threads through the cell membrane **seven times**. - This characteristic "serpentine" structure forms **three extracellular and three intracellular loops**, along with an extracellular N-terminus and an intracellular C-terminus, crucial for ligand binding and G protein activation, respectively. *Five-pass transmembrane protein* - This structural configuration is **not characteristic** of serpentine receptors or GPCRs, which consistently pass through the membrane seven times. - Receptors with five transmembrane domains would have a **different folding pattern** and functional mechanism compared to GPCRs. *Nine-pass transmembrane protein* - This is an **incorrect description** for serpentine receptors; GPCRs are specifically defined by their seven transmembrane helices. - While some transmembrane proteins can have more passes, nine passes are **not typical** for this class of receptors. *Three-pass transmembrane protein* - This describes a protein with **fewer transmembrane segments** than a serpentine receptor. - Receptors with only three transmembrane domains would be structurally and functionally **distinct** from GPCRs, which require seven passes to mediate their characteristic signaling.

Q: Which one of the following substances increases the release of Ca2+ from the endoplasmic reticulum?

Inositol triphosphate. ***Inositol triphosphate*** - **Inositol triphosphate (IP3)** is a secondary messenger that binds to specific receptors on the **endoplasmic reticulum (ER)**, triggering the release of stored **Ca2+** into the cytoplasm. - This calcium release plays a crucial role in various cellular processes, including **muscle contraction**, **neurotransmission**, and **hormone secretion**. *1,25 - dihydroxycholecalciferol* - This is the active form of **vitamin D**, primarily involved in **calcium absorption** from the gut and **calcium reabsorption** in the kidneys. - It does not directly increase Ca2+ release from the endoplasmic reticulum. *Diacylglycerol* - **Diacylglycerol (DAG)** is another secondary messenger, also produced from the cleavage of **PIP2** along with IP3. - DAG primarily activates **protein kinase C (PKC)**, which is involved in signal transduction pathways, but it does not directly trigger Ca2+ release from the ER. *Parathyroid hormone* - **Parathyroid hormone (PTH)** is a hormone that primarily regulates **extracellular calcium levels** by promoting bone resorption, increasing renal calcium reabsorption, and stimulating the synthesis of 1,25-dihydroxycholecalciferol. - While it ultimately increases blood calcium, it does not directly cause Ca2+ release from the endoplasmic reticulum.

Question 1

Which of the following induces apoptosis in a cell?

Accepted Answer

Glucocorticoids

Answer

Isoprenoids

Answer

Myristic acid

Answer

Oleic acid

Question 2

cGMP is a second messenger for which hormone(s)?

Accepted Answer

Atrial natriuretic factor

Answer

Antidiuretic hormone (ADH)

Answer

Angiotensin II

Answer

Somatostatin

Question 3

Serpentine receptor is a:

Accepted Answer

Seven-pass transmembrane protein

Answer

Five-pass transmembrane protein

Answer

Nine-pass transmembrane protein

Answer

Three-pass transmembrane protein

Question 4

Which one of the following substances increases the release of Ca2+ from the endoplasmic reticulum?

Accepted Answer

Inositol triphosphate

Answer

1,25 - dihydroxy cholecalciferol

Answer

Diacylglycerol

Answer

Parathyroid hormone

Signal Transduction — MCQs

Signal Transduction — MCQs

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