Question

Which of the following is not good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution? (EXPLAIN YOUR RATIONAL FOR EACH ONE)

(a) A yeast cell lacking a Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle.
(b) The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cyclins in humans.
(c) The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast.
(d) Yeast cells have only one Cdk, whereas humans have many Cdks.

Answer 1

Option (d), which states that yeast cells have only one Cdk while humans have many, does not support the idea of conservation of the cell-cycle control system because it points out a difference in complexity rather than conservation or similarity between species.

Step-by-step explanation:

The question asks which of the following is not good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution.

• (a) A yeast cell lacking a Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle. This suggests conservation since the human Cdk can functionally complement the yeast Cdk, indicating that the core functions of Cdk have been conserved across species.
• (b) The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cyclins in humans. This indicates conservation of the protein sequences, suggesting that the function of cyclins has been conserved across very different organisms, supporting the idea of a conserved cell-cycle control system.
• (c) The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast. This also supports the idea of conservation as it shows that key regulatory mechanisms within the cell cycle are preserved across species.
• (d) Yeast cells have only one Cdk, whereas humans have many Cdks. This does not directly support the conservation of the cell-cycle control system as it points out a difference in the complexity of the system rather than its similarity or conservation.

Based on this analysis, option (d) is not good direct evidence for conservation of the cell-cycle control system across billions of years of divergent evolution since it highlights a difference rather than a similarity.

Answer 2

Answer: The statement that is not good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution is option (d) - "Yeast cells have only one Cdk, whereas humans have many Cdks."

Step-by-step explanation:

The cell cycle control system is a highly conserved and regulated process, and the presence of similar proteins across different species is one way to demonstrate its conservation through evolution. The other three options (a, b, and c) all provide evidence of this conservation.

Option (a) indicates that the human Cdk can substitute for a missing yeast Cdk during the cell cycle, which suggests that the two proteins share similar functions and mechanisms.

Option (b) indicates that the amino acid sequences of cyclins in plants and humans are similar, further supporting the conservation of the cell-cycle control system.

Option (c) indicates that the Cdk proteins in humans and yeast share conserved phosphorylation sites, which suggests that they have similar regulatory mechanisms.

In contrast, option (d) implies a difference between yeast and human Cdks, which is not consistent with the idea of conservation. However, it should be noted that the conservation of the cell-cycle control system does not require that all aspects of the system are identical across different species