What type of protein that regulates the cell cycle is encoded by proto-oncogenes?

• A. Cyclins
• B. Growth factors
• C. Tumor suppressors
• D. DNA repair enzymes

Answer: (B)

Verified step by step guidance

1. Understand the role of proto-oncogenes: Proto-oncogenes are genes that normally help cells grow. When a proto-oncogene mutates or is expressed at high levels, it becomes a 'bad' gene that can become permanently activated when it is not supposed to be. This can lead to uncontrolled cell division, a hallmark of cancer.
2. Identify the types of proteins involved in cell cycle regulation: The cell cycle is regulated by various proteins, including cyclins, growth factors, tumor suppressors, and DNA repair enzymes. Each of these plays a distinct role in cell cycle control.
3. Focus on growth factors: Growth factors are proteins that stimulate cell growth and division. They bind to specific receptors on the cell surface, triggering a cascade of cellular processes that lead to cell proliferation.
4. Relate growth factors to proto-oncogenes: Proto-oncogenes often encode for growth factors or their receptors. When these genes are mutated, they can lead to the continuous activation of growth signals, promoting cancerous growth.
5. Conclude the connection: Since proto-oncogenes encode proteins that promote cell growth and division, the type of protein they encode that regulates the cell cycle is growth factors.