Question

Receptor tyrosine kinases function by

• A. Degrading ATP
• B. Phosphorylating tyrosine residues
• C. Breaking DNA
• D. Transporting ions

Hint:

Remember: \[ \boxed{\text{RTK}=\text{Receptor Tyrosine Kinase}} \] The word "Tyrosine" itself tells you that these receptors phosphorylate tyrosine amino acid residues during cell signalling.

Answer 1

The Correct Option is B

Concept: Receptor Tyrosine Kinases (RTKs) are transmembrane proteins that act as cell surface receptors. They transmit signals from growth factors and hormones into the cell by phosphorylating tyrosine residues on proteins. RTKs play a vital role in regulating cell growth, cell division, differentiation, metabolism, and survival.

Step 1: Structure of RTKs.
Each receptor contains:
• An extracellular ligand-binding domain.
• A single transmembrane region.
• An intracellular tyrosine kinase domain. When a ligand binds, two receptor molecules dimerize.

Step 2: Activation mechanism.
After dimerization, each receptor phosphorylates tyrosine residues on the other receptor. This process is called autophosphorylation. \[ \boxed{\text{Ligand} \rightarrow \text{Dimerization} \rightarrow \text{Tyrosine Phosphorylation} \rightarrow \text{Signal Transduction}} \]

Step 3: Eliminate incorrect options.

• RTKs do not degrade ATP.
• They do not break DNA.
• They are not ion transport proteins.
• Their primary function is phosphorylation of tyrosine residues. Final Answer: \[ \boxed{Option (B) is correct \]