In a cell cycle `G_(1)` phase is marked by the

Options

A. Transcription of r-RNA
B. Transcription of r-RNA, t-RNA
C. Transcription of r-RNA, m-RNA
D. Transcription of -RNA, m-RNA, t-RNA and synthesis of different proteins

Answer

To answer the question regarding what is marked by the G1 phase in the cell cycle, we can break down the information step by step.

### Step-by-Step Solution:

1. **Understanding the Cell Cycle**: The cell cycle consists of several phases: G1, S, G2, and M. The G1 phase is the first gap phase, which occurs after cell division and before DNA synthesis.

2. **Identifying the G1 Phase Characteristics**:
- The G1 phase is primarily a growth phase where the cell increases in size.
- During this phase, the cell prepares for DNA replication by synthesizing necessary components.

3. **Transcription Activities in G1 Phase**:
- In the G1 phase, the cell engages in transcription activities. This includes the synthesis of various types of RNA.
- The types of RNA synthesized include:
- rRNA (ribosomal RNA)
- mRNA (messenger RNA)
- tRNA (transfer RNA)

4. **Protein Synthesis**:
- Along with RNA transcription, the G1 phase is also marked by the synthesis of different proteins that are essential for the cell's functions and for preparing for the next phase of the cell cycle (S phase).

5. **Selecting the Correct Option**:
- Given the options:
- A: Transcription of rRNA
- B: Transcription of rRNA, tRNA
- C: Transcription of rRNA, mRNA
- D: Transcription of rRNA, mRNA, tRNA and synthesis of different proteins
- The most comprehensive option that includes all the activities occurring in the G1 phase is option D.

### Final Answer:
The G1 phase of the cell cycle is marked by the transcription of rRNA, mRNA, tRNA, and the synthesis of different proteins. Therefore, the correct option is **D**.