The correct option is 1 and 3 only.
Explanation
Adenosine Triphosphate (ATP) serves as the primary energy currency of the cell. It powers various endergonic (energy-consuming) biological processes, including mechanical work, active transport, and chemical biosynthesis. Hydrolysis of ATP releases energy required to drive these cellular activities.
Statement-wise Analysis
1. Muscle contraction - Correct
Muscle contraction relies on the sliding filament mechanism involving actin and myosin proteins. ATP binding and hydrolysis are essential for the myosin heads to detach from actin filaments and re-cock for the next power stroke. Without ATP, muscles would remain in a contracted state (rigor mortis).
2. Protein synthesis occurs without energy expenditure - Incorrect
Protein synthesis (translation) is a highly energy-intensive anabolic process. It requires significant energy input for the activation of amino acids (charging tRNA) and the formation of peptide bonds between amino acids. This energy is derived from the hydrolysis of both ATP and GTP (Guanosine Triphosphate). Therefore, the statement that it occurs without energy expenditure is factually wrong.
3. Conduction of nervous impulses - Correct
The transmission of nerve impulses depends on the maintenance of an electrochemical gradient across the neuronal membrane (resting potential). This gradient is established and maintained by the Sodium-Potassium pump ($Na^+/K^+$-ATPase), an active transport mechanism that consumes ATP to move ions against their concentration gradients.
Key Takeaway:
ATP is essential for mechanical work (muscle contraction), active transport (nerve impulse conduction via ion pumps), and chemical work (biosynthesis of macromolecules like proteins). Anabolic processes like protein synthesis always require energy input.