Q1. Source: CSIR NET NOV 20; Session I
Which of the following signaling molecules is NOT a protein or peptide?
a. Transforming Growth Factor alpha (TGF alpha)
b. Erythropoietin
c. Granulocyte Colony Stimulating Factor
d. Epinephrine
Statement Analysis
a. Transforming Growth Factor alpha (TGF alpha)
TGF-α is a peptide growth factor involved in cell proliferation and signaling through the EGFR pathway. Since it is a protein-based signaling molecule, this option is incorrect.
b. Erythropoietin
Erythropoietin (EPO) is a glycoprotein hormone responsible for stimulating red blood cell production. It is proteinaceous in nature, making this option incorrect.
c. Granulocyte Colony Stimulating Factor
G-CSF is a cytokine protein that stimulates the production of granulocytes in bone marrow. Hence, this is also a protein signaling molecule.
d. Epinephrine
Epinephrine (adrenaline) is a catecholamine hormone derived from the amino acid tyrosine. Unlike proteins or peptides, it is a small molecule signaling compound.
Correct Answer: d. Epinephrine
Exam Insight
Questions like these test your understanding of the chemical nature of signaling molecules. In exams such as CSIR NET, students often confuse peptide hormones with amino acid-derived hormones.
- Peptide/protein hormones = insulin, EPO, growth factors, cytokines
- Steroid hormones = cortisol, estrogen, testosterone
- Amino acid-derived hormones = epinephrine, thyroxine
Learning signaling molecules based on their biochemical origin can help eliminate options rapidly in the exam.
Q2. Source: CSIR NET NOV 20; Session I
Following statements were made about the characteristics of cyclin protein:
A. Synthesis of M-cyclin is dependent on the cyclin mRNA that is newly transcribed after every cycle
B. Destruction of M-cyclin toward the end of mitosis is driven by ubiquitin independent proteolytic system
C. G1 cyclins can be activated by mitogenic factors
D. Retinoblastoma (Rb) is a key target of the activated cyclin-D-Cdk 4/6 complex
E. While cyclin A1 expression is ubiquitous, cyclin A2 expression is restricted to the germ cell lineages.
Which one of the following options contains a combination of all correct statements?
a. A,B,D
b. B,C,E
c. B,D,E
d. A,C,D
Statement Analysis
- Statement A = Correct
M-cyclin synthesis depends on newly transcribed cyclin mRNA during each cell cycle. Cyclin levels oscillate cyclically, and fresh synthesis is essential for mitotic progression.
- Statement B = Incorrect
M-cyclin destruction occurs through a ubiquitin-dependent proteolytic pathway mediated by the Anaphase Promoting Complex/Cyclosome (APC/C). Therefore, the statement is incorrect because it mentions a ubiquitin-independent mechanism.
- Statement C = Correct
G1 cyclins, especially cyclin D, are activated in response to extracellular mitogenic signals such as growth factors. These signals help cells progress through the G1 phase.
- Statement D = Correct
The cyclin D–Cdk4/6 complex phosphorylates the Retinoblastoma (Rb) protein, releasing E2F transcription factors and promoting entry into the S phase.
- Statement E = Incorrect
The statement reverses the expression patterns:
- Cyclin A2 is ubiquitously expressed in proliferating cells.
- Cyclin A1 expression is mainly restricted to germ cell lineages.
Correct Answer: d. A,C,D
Exam Insight
Cell cycle regulation is one of the most repeatedly tested topics in CSIR NET Cell Biology.
A common CSIR NET trap is statement reversal, especially in expression profiles and regulatory pathways. Instead of memorizing isolated facts, focus on understanding:
- which cyclin acts in which phase,
- what activates it,
- and what targets it regulates.