Gene X will be transcribed only in the heart tissue, because that is the only tissue where transcription factor A is present and remains predominantly in its phosphorylated (active) form.​​

Question restatement

The question describes gene X whose transcription is controlled by transcription factor A. Gene X is transcribed only when factor A is phosphorylated. The table (from the slide) lists, for three tissues (muscle, heart, brain): presence of factor A, activity of a specific protein kinase, and activity of a specific protein phosphatase. The task is to identify in which tissue(s) gene X will be transcribed.​

Concept background: kinase vs phosphatase and transcription factor activation

• Protein kinases add phosphate groups to target proteins (phosphorylation), often activating or modulating their function.​

• Protein phosphatases remove phosphate groups (dephosphorylation), usually reversing the effect of kinases.​

• Many transcription factors are activated only when phosphorylated; in this state they can bind DNA and recruit RNA polymerase, thereby turning on transcription of specific genes.​

For factor A to be active and drive transcription of gene X, two conditions must be met in a tissue:

1. Factor A must be present.​

2. Net phosphorylation of factor A must be high enough, which usually requires kinase activity to dominate over phosphatase activity for that factor.​

Interpreting the given table

From the slide (rephrased):

• Muscle: Factor A present (+), kinase activity present (+), phosphatase activity present (+).​

• Heart: Factor A present (+), kinase activity present (+), phosphatase activity absent or very low (−).​

• Brain: Factor A present (+), kinase activity absent or very low (−), phosphatase activity present (+).​

Phosphorylated factor A accumulates when kinase activity exceeds phosphatase activity.​

• In muscle, both kinase and phosphatase are active, so phosphorylation and dephosphorylation compete strongly; net phosphorylation may be too low for robust activation of gene X.​

• In heart, kinase is active but the specific phosphatase is absent, so factor A will remain highly phosphorylated and strongly active.​

• In brain, phosphatase is active but kinase is absent, so factor A remains dephosphorylated and inactive.​

Therefore, the only tissue satisfying “factor A present + predominantly phosphorylated” is heart.

Correct answer: Option B) Heart only.​

Option-by-option explanation

Option A: Muscle only

• Muscle does have factor A and the kinase, but it also has the matching phosphatase, which will rapidly remove phosphate from factor A.​

• Because kinase and phosphatase activities oppose each other, factor A will not stay sufficiently phosphorylated to sustain transcription of gene X at the required level, so “muscle only” is incorrect.​

Option B: Heart only (Correct)

• Heart expresses factor A and the specific protein kinase, but lacks the corresponding phosphatase activity.​

• With no significant dephosphorylation, factor A remains phosphorylated and active, so gene X is efficiently transcribed only in the heart; thus this is the correct option.​

Option C: Brain only

• Brain has factor A and the phosphatase, but not the kinase, so it cannot phosphorylate factor A effectively.​

• In the absence of kinase activity, phosphatase activity favors the dephosphorylated (inactive) state of factor A, so gene X is not transcribed; “brain only” is therefore incorrect.​

Option D: Muscle and heart but not brain

• Although heart satisfies the conditions for transcription, muscle does not, because phosphatase activity counterbalances kinase activity and prevents sufficient phosphorylation of factor A.​

• Since gene X is not transcribed in muscle or brain under these conditions, “muscle and heart but not brain” is also incorrect.​

Short SEO-friendly introduction (for article body)

Transcription of gene X is a classic CSIR NET Life Science-style example of how tissue-specific gene expression depends on the phosphorylation state of a transcription factor. In this problem, transcription factor A activates gene X only when phosphorylated, and the relative activities of a protein kinase and a protein phosphatase in muscle, heart and brain determine where gene X is actually expressed, making it a powerful model for understanding kinase–phosphatase balance in cell signalling and gene regulation.​