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Correct option is (a) True

For explanation I would SAY: In 1980S, it was discovered that nitric oxide, a GAS, acts as an intracellular messenger. NO is UNUSUAL because it acts both as an EXTRACELLULAR messenger driving the intracellular responses and also as a secondary messenger in the cell where it is generated.

Correct choice is (a) True

For explanation I would say: The PRIMARY MESSENGER molecules bind to the transmembrane receptors to initiate intracellular responses such as transcription, TRANSLATION, cell death (apoptosis). The second messenger molecules are then generated intracellularly to further the ELICITED response.

Right OPTION is (c) non-covalent INTERACTIONS

For explanation: The inactive conformation of the G-protein coupled receptor is stabilized by non-covalent interactions between the residues in the transmembrane alpha helices. Rotation or movements in these LOOPS cause changes in the conformation of cytoplasmic loops.

Correct answer is (b) external stimuli

For explanation I would SAY: Cytokines are SUBSTANCES including interleukin, interferon, secreted by certain immune CELLS that act as external stimulus whereas abnormalities in the DNA act as INTERNAL stimulus for apoptosis.

Right answer is (a) Ca^2+

To elaborate: The rise in cytoplasmic calcium concentration following fertilization triggers a diverse array of events. Activation of cyclin-dependent kinases that DRIVE the zygote towards FIRST MITOTIC division is ONE such EVENT.

Correct choice is (a) True

To explain I would say: Upon FERTILIZATION of the egg by a sperm, a growing concentration of calcium ions can be SEEN that spreads from the point of entry of the sperm TILL the other END of the egg CELL.

The CORRECT choice is (a) 1

To ELABORATE: The Ras proteins belong to the superfamily of G-proteins and contain one small subunit, also called monomeric G-protein. Ras is a GTPase anchored by a LIPID group on the INNER surface of a plasma MEMBRANE.

The correct choice is (a) blood glucose LEVELS

To explain I would say: EPINEPHRINE is called the “fight-or-flight” hormone produced by the adrenal GLAND in situations of stress. It CAUSES an increase in blood glucose levels to DEAL with stressful situations.

Correct answer is (a) True

Easy explanation: G-protein coupled receptors (GCPRs) are CALLED so because they INTERACT with the GTP-binding proteins – G-proteins. These are also called 7TM because they consist of 7 transmembrane helices.

Correct choice is (a) secondary messenger

To explain: The development of Viagra (SILDENAFIL) is based on the discovery of NITRIC oxide as a secondary messenger. During SEXUAL arousal, the nerve endings of penis release NO which causes relaxation of SMOOTH muscle cells in lining of penile blood vessels and engorgement of penis with blood.

Right answer is (a) muscle relaxation

For explanation: Acetylcholine has the function of PROMOTING muscle relaxation. It BINDS to surface RECEPTORS present on the endothelial CELLS leading to the production and release of an agent that diffuses through the plasma membrane and causes the MUSCLES to relax.

Right answer is (a) FLUORESCENT molecule

To explain I would say: Fura-2 is a highly sensitive, fluorescent molecule that binds to calcium ions by diffusing across the plasma membrane of a cell. This COMPOUND was developed in 1980S in the LABORATORY of Roger Tsien at the UNIVERSITY of California, San Diego.

The CORRECT choice is (b) ethylene GAS receptor

The best explanation: The Etr1 GENE in plants encodes for a receptor of the ethylene gas (C2H2). Ethylene is a plant hormone that regulates a variety of developmental processes such as seed germination and fruit ripening.

The correct choice is (a) True

The explanation is: The cytoplasmic protein-tyrosine kinases are activated indirectly by the extracellular signals. These kinases CONTROL processes such as IMMUNE response, CELL adhesion and neuronal cell MIGRATION.

The correct ANSWER is (d) third loop

Explanation: There are 3 loops of G-protein coupled receptor located on the outside of the CELL and 3 loops located on the cytoplasmic site. The G-proteins bind to the third INTRACELLULAR loop while the loops located outside the cell FORM the ligand-binding ACTIVE site.

Right answer is (B) cholesterol

The explanation: Steroids are hormones derived from cholesterol which carry messages by endocrine stimulation. Steroids regulate SEXUAL differentiation, pregnancy, carbohydrate METABOLISM, and excretion of sodium and POTASSIUM ions.

The correct choice is (a) HORMONES

To EXPLAIN: Endocrine MESSENGERS are also CALLED hormones and operate by the endocrine stimulation. In this pathway of CELL signaling the messenger molecules travel through the bloodstream before reaching cell surface receptors that are distant.

The correct choice is (d) procaspase-8

For explanation I would SAY: The last proteins that get involved in the APOPTOTIC pathway triggered by the tumor necrosis factor are procaspases-8 – the precursors of caspase proteins. Procaspases contain an extra PORTION that must be removed by catalytic action.

Correct choice is (B) cell survival

The best I can EXPLAIN: P13K is an enzyme that GETS activated by a wide range of stimuli. In ADHERENT epithelial cells P13K PROMOTES cell survival, while in an insulin-stimulated liver cell it promotes GLUT4 translocation and protein synthesis.

The CORRECT answer is (b) calmodulin

To explain: Calcium BRINGS about a vast variety of responses in the cell and these are DONE in CONJUNCTION with other proteins that bind to calcium, calmodulin is such a protein found universally in all PLANTS, animals and other eukaryotes.

Right choice is (a) trans-autophosphorylation

For explanation I would say: When TWO DOMAINS of protein-tyrosine kinases come CLOSE, it leads to trans-autophosphorylation in which activity of ONE RECEPTOR of the dimer phosphorylates the tyrosine residue of the other.

Right choice is (a) lamin

Easy explanation: Inactivation of lamins by the caspases LEADS to disassembly of nuclear lamina and shrinkage of the NUCLEUS. Lamins are a special class of PROTEINS that make up the inner LINING of the nuclear envelope.

The correct choice is (c) alkaloid

Explanation: Ryanodine is a TOXIC plant alkaloid which binds to the ryanodine receptors (RyRs). These receptors mediate the rise in calcium levels FOLLOWING an action potential in CARDIAC and SKELETAL muscle cells.

Right OPTION is (d) Calmodulin

Easiest explanation: The three types of cell SURFACE receptors – G-protein coupled receptors, receptor tyrosine kinases and integrins, all can converge to lead to the formation of phosphotyrosine docking sites for the SH2 domain of the ADAPTOR protein Grb2 in close proximity to the PLASMA membrane.

Right OPTION is (a) eicosanoids

For explanation: Eicosanoids are non-polar, 20-carbon containing molecules derived from the fatty ACID, arachidonic acid. Eicosanoids REGULATE processes like blood pressure, INFLAMMATION, blood clotting. Several over-the-counter drugs used to TREAT headaches inhibit eicosanoid synthesis.

Right option is (a) FAK

Easy explanation: The FOCAL ADHESION kinase (FAK) is INACTIVATED by the cleaving action of caspases during apoptosis. Cleavage of FAK leads to detachment of the APOPTOTIC cell from its neighboring cells.

Right answer is (C) T-lymphocytes

Easy explanation: The T-lymphocytes are IMMUNE cells that RECOGNIZE and kill the PATHOGEN infected target cells in an orderly manner (apoptosis). These cells accomplish the feat by binding to the cell surface receptors of infected/ abnormal cell.

The CORRECT choice is (a) TNFR1

To explain I would say: DEATH receptors are so called because of the presence of a death domain which is RESPONSIBLE for killing an INFECTED CELL. TNFR1 is one such example. It plays an important role in induced apoptosis.

The correct choice is (b) TUMOR necrosis FACTOR

To elaborate: Tumor necrosis factor (TNF) is an extracellular messenger for the extrinsic pathway of apoptosis. It has the ability to ablate tumor cells and is SECRETED by the cells of immune system in RESPONSE to ADVERSE conditions.

The correct choice is (b) insulin resistance

The BEST explanation: Diabetes Mellitus type II is caused due to insulin resistance that results from the elevated levels of glucose in the blood and SUBSEQUENT INCREASE in insulin (overstimulation). As a result of this, the target CELLS, those having insulin receptors stop responding to the presence of the HORMONE.

The correct OPTION is (a) gluconeogenesis

The explanation is: When the blood sugar levels are high, the uptake of GLUCOSE and synthesis of glycogen and TRIGLYCERIDES INCREASES while the gluconeogenesis is decreased. Gluconeogenesis is the PROCESS of synthesis of glucoses from non-sugar substrates such as pyruvate.

The correct answer is (a) HERPES VIRUS

The best explanation: The herpes virus, responsible for Kaposi’s sarcoma characterized by PURPLISH SKIN lesions prevalent in AIDS patients, encodes a constitutively active receptor for interleukin-8.

The CORRECT option is (a) autocrine, paracrine, endocrine

The BEST I can explain: The SIGNALING pathways in the FIGURE shown are autocrine, paracrine and endocrine signaling pathways respectively. All the three are stimulation pathways in which messenger molecules reach CELL surface receptors.

Right OPTION is (d) beta cells

For EXPLANATION I would say: The beta cells in pancreas secrete insulin when the blood GLUCOSE levels elevate while the alpha cells in the pancreas secrete glucagon when the blood glucose levels drop. Insulin acts as an EXTRACELLULAR MESSENGER molecule.

Correct ANSWER is (b) guanine

The best I can explain: The G-proteins are CALLED so because they bind only to the guanine nucleotides – GTP (guanosine TRIPHOSPHATE) and GDP (Guanosine diphosphate). The protein is heterotrimeric and CONSISTS of three different polypeptides SUBUNITS.

Right OPTION is (c) 7

The EXPLANATION: The G-protein COUPLED RECEPTORS (GPCRs) are a family of cell surface receptors that consist of 7 transmembrane alpha helices. These receptors translate the binding of extracellular MESSENGERS to the activation of intracellular GTP-binding proteins.

Correct choice is (c) cytochrome c

To elaborate: Cytochrome c is the COMPOUND involved in intrinsic pathway of apoptosis. It is also a COMPONENT of electron transport chain and MITOCHONDRION. As the process of apoptosis INITIATES, the cells lose contact with the environment.

The CORRECT option is (b) Nitroglycerine

To elaborate: Nitroglycerine is metabolized into nitric OXIDE which stimulates the relaxation of smooth muscle CELLS. Nitroglycerine is used to treat the pain of angina – chest pain caused to REDUCED blood flow to the heart.

The correct CHOICE is (c) caspases

For EXPLANATION: The CED3 gene PLAYS a crucial ROLE in the nematodes during apoptosis. The homologous family of PROTEINS – caspases in mammals are cysteine proteases (having a cysteine residue in the catalytic site).

Right CHOICE is (a) increase in cytosolic Ca^2+ concentration

To explain: Binding of ACETYLCHOLINE to the outer surface of endothelial CELLS SIGNALS an elevation of cytoplasmic concentration of calcium ions, that activates the enzyme NITRIC oxide synthase.