INTRODUCTION.
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| The CELL CYCLE |
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| Phases of Cell cycle |
The cell cycle is the process by which a cell grows, duplicates its DNA, and divides to produce two daughter cells. It ensures proper cell replication and function in living organisms. The cycle consists of several stages:
INTERPHASE:
This is the longest phase, where the cell prepares for division. It includes:
G1 Phase (Gap 1):
The cell grows and performs its normal functions.
S Phase (Synthesis):
DNA replication occurs, resulting in two identical sets of chromosomes.
G2 Phase (Gap 2):
The cell continues to grow and prepares for mitosis by producing necessary proteins and organelles.
MITOSIS
(M Phase): This is the phase where the cell's chromosomes are separated into two new nuclei. It includes:
Prophase:
Chromosomes condense and become visible. The nuclear envelope breaks down, and spindle fibers begin to form.
Metaphase:
Chromosomes line up at the cell's equatorial plane.
Anaphase:
Chromatids are pulled apart to opposite sides othe cell.
Telophase:
Chromatids arrive at the poles, and the nuclear envelope reforms around each set of chromosomes.
Cytokinesis:
This phase overlaps with telophase and involves the physical separation of the cytoplasm into two distinct daughter cells. In animal cells, this is achieved through cleavage furrow formation, while in plant cells, a cell plate forms.
Together, these stages ensure that cells divide accurately, maintaining genetic stability and proper activity.
MCQs.
Here are 20 most important frequently asked multiple-choice questions (MCQs) on the cell cycle along with their answers:
1. **Which phase of the cell cycle is characterized by DNA replication?**
- A) G1 phase
- B) S phase
- C) G2 phase
- D) M phase
- **Answer: B) S phase**
2. **What is the primary function of the G1 phase in the cell cycle?**
- A) DNA replication
- B) Preparation for mitosis
- C) Cell growth and preparation for DNA synthesis
- D) Chromosome segregation
- **Answer: C) Cell growth and preparation for DNA synthesis**
3. **Which checkpoint ensures that all chromosomes are properly attached to the spindle before anaphase begins?**
- A) G1 checkpoint
- B) G2 checkpoint
- C) M checkpoint
- D) S checkpoint
- **Answer: C) M checkpoint**
4. **Which cyclin-Cdk complex is crucial for the transition from G1 to S phase?**
- A) Cyclin D-Cdk4/6
- B) Cyclin E-Cdk2
- C) Cyclin A-Cdk2
- D) Cyclin B-Cdk1
- **Answer: B) Cyclin E-Cdk2**
5. **During which phase of the cell cycle does the nuclear envelope break down?**
- A) Prophase
- B) Metaphase
- C) Anaphase
- D) Telophase
- **Answer: A) Prophase**
6. **What is the role of the anaphase-promoting complex (APC) in mitosis?**
- A) To ensure proper chromosome alignment
- B) To degrade cyclins and securin, allowing chromosome separation
- C) To initiate DNA replication
- D) To repair DNA damage
- **Answer: B) To degrade cyclins and securin, allowing chromosome separation**
7. **Which phase of the cell cycle is associated with the synthesis of proteins necessary for mitosis?**
- A) G1 phase
- B) S phase
- C) G2 phase
- D) M phase
- **Answer: C) G2 phase**
8. **What marks the end of the M phase in the cell cycle?**
- A) Cytokinesis
- B) DNA replication
- C) Chromosome condensation
- D) Nuclear envelope reformation
- **Answer: A) Cytokinesis**
9. **Which protein complex is known as the "master regulator" of the cell cycle?**
- A) Cyclin-Cdk complex
- B) Cohesin complex
- C) Condensin complex
- D) Origin Recognition Complex (ORC)
- **Answer: A) Cyclin-Cdk complex**
10. **How is the G0 phase different from the G1 phase?**
- A) Cells in G0 are actively dividing, while cells in G1 are not.
- B) G0 is a quiescent phase where cells are not actively preparing to divide.
- C) G1 phase involves DNA replication, while G0 does not.
- D) G0 occurs only in prokaryotes, whereas G1 occurs in eukaryotes.
- **Answer: B) G0 is a quiescent phase where cells are not actively preparing to divide.**
11. **What triggers the transition from metaphase to anaphase?**
- A) Cyclin D accumulation
- B) Synthesis of DNA
- C) Activation of the anaphase-promoting complex (APC)
- D) Chromosome duplication
- **Answer: C) Activation of the anaphase-promoting complex (APC)**
12. **Which of the following is a key characteristic of the G2 phase?**
- A) Chromosome alignment
- B) DNA replication
- C) Preparation for mitosis
- D) Cytokinesis
- **Answer: C) Preparation for mitosis**
13. **What is the function of cohesin proteins during mitosis?**
- A) To separate sister chromatids
- B) To hold sister chromatids together
- C) To condense chromosomes
- D) To facilitate spindle formation
- **Answer: B) To hold sister chromatids together**
14. **In which phase does the cell cycle checkpoint monitor for DNA damage and repair before entering mitosis?**
- A) G1 phase
- B) S phase
- C) G2 phase
- D) M phase
- **Answer: C) G2 phase**
15. **What happens during cytokinesis?**
- A) DNA is replicated
- B) The cell's nucleus divides
- C) The cytoplasm of the cell divides, forming two daughter cells
- D) Chromosomes align at the metaphase plate
- **Answer: C) The cytoplasm of the cell divides, forming two daughter cells**
16. **Which protein is responsible for initiating DNA replication in the S phase?**
- A) DNA polymerase
- B) Helicase
- C) Origin Recognition Complex (ORC)
- D) Cyclin A
- **Answer: C) Origin Recognition Complex (ORC)**
17. **What is the role of mitotic spindle fibers during cell division?**
- A) To replicate DNA
- B) To separate chromosomes
- C) To synthesize cyclins
- D) To repair DNA
- **Answer: B) To separate chromosomes**
18. **Which phase follows the S phase in the cell cycle?**
- A) G1 phase
- B) G2 phase
- C) M phase
- D) Cytokinesis
- **Answer: B) G2 phase**
19. **During which phase does chromosome condensation occur?**
- A) Prophase
- B) Metaphase
- C) Anaphase
- D) Telophase
- **Answer: A) Prophase**
20. **How do tumor suppressor genes influence the cell cycle?**
- A) They promote cell division
- B) They prevent cell division and induce apoptosis
- C) They facilitate DNA replication
- D) They degrade mitotic spindle fibers
- **Answer: B) They prevent cell division and induce apoptosis**
These questions cover various aspects of the cell cycle, including checkpoints, phases, and regulatory mechanisms.
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