GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Signal Transduction
Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology
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Example Questions
Example Question #1 : Cellular Signals And Communication
Which of the following events occur when the MAP Kinase pathway is activated?
The phosphorylated receptor facilitates the binding of GDP to Ras
The receptor is phosphorylated by G-coupled proteins
ATP is used to phosphorylate transcription factors
Ras blocks the activation of MAP kinases
ATP is used to phosphorylate transcription factors
When MAP Kinase signaling is activated, the receptors auto-phosphorylate to activate the signal transduction, which leads to the binding of GTP to Ras. Ras is activated when bound to GTP. Ras then activates downstream MAP Kinases, which lead to a phosphorylate cascade that eventually uses ATP to phosphorylate transcription factors. The phosphorylated transcription factors then go on to alter gene expression in the cell.
Therefore, the correct answer in this question is that transcription factors are phosphorylated using ATP molecules.
Example Question #1 : Help With Signal Transduction
Which of the following best describes proteins that facilitate signal transduction by binding many proteins of a signal transduction pathway into a complex?
Transcription factors
Adaptor proteins
Scaffold proteins
Ligases
Kinases
Scaffold proteins
The correct answer is scaffold proteins. By bringing signaling transduction pathway proteins into complex, scaffolds rapid promote activation (often by phosphorylation) of the pathway proteins to effect a biological output. Kinases phosphorylate substrates, ligases bind substrates, and transcription factors regulate transcription, however, these proteins do not complex signaling pathway intermediates to amplify a signal. Adaptor proteins are involved in signal transduction, however, their role is mainly in cross-talk between different pathways upon a certain stimulus or activation of a given signaling pathway.
Example Question #11 : Cellular Processes
Individual cell death can occur via an energy-dependent mechanism that involves the highly coordinated induction of caspases to induce death signaling cascades. What is this process referred to as?
Apoptosis
None of these
Paraptosis
Necrosis
Autophagy
Apoptosis
The correct answer is apoptosis. Apoptosis, commonly referred to as "programmed cell death", is an energy dependent mechanism that produces apoptotic bodies that are engulfed by the immune system. Mitochondrial leakage of cytochrome c can activate caspase pathways to proteolytically cleave host intracellular proteins. While necrosis is a mechanism for cell death, it is energy-independent and much less controlled and is characterized by organelle swelling and disintegration. Autophagy is a mechanism of cell death in which autophagosomes and autolysosomes are formed and degrade intracellular proteins. Paraptosis is a specific form of cell death that occurs by cell-surface receptors initiating cell death signals in the absence of normal ligands.
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