Phases of Cell Cycle Quiz

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Questions and Answers

What occurs during the G1 phase of the cell cycle?

The cell replicates its DNA.

The cell ensures it is ready for DNA replication. (correct)

The cell prepares for cell signaling processes.

The cell divides into two daughter cells.

What can happen to a cell that is not ready to proceed in the G1 phase?

It can enter the G0 phase temporarily. (correct)

It will immediately enter the S phase.

It will start replicating its chromosomes.

It will leave the cell cycle permanently.

What is the primary purpose of the G2 phase in the cell cycle?

To ensure DNA and other components are properly duplicated. (correct)

To replicate the centrosomes.

To begin the process of mitosis.

To synthesize proteins for cell division.

Which statement about the S phase is true?

The rate of synthesis of proteins involved in DNA synthesis increases. Signup and view all the answers

What occurs at the G1 checkpoint of the cell cycle?

Examination of cell size and nutrient availability Signup and view all the answers

What is a characteristic of the G0 phase?

Cells in G0 exit the cell cycle and enter a quiescent stage. Signup and view all the answers

Which checkpoint is responsible for ensuring that DNA replication has been completed?

G2 checkpoint Signup and view all the answers

How do cells generally respond when a chromosome is misplaced during the M phase?

Pause mitosis to allow for proper attachment Signup and view all the answers

What primarily indicates that a cell has completed the S phase?

The cell has the double the usual amount of DNA. Signup and view all the answers

Which internal factor influences the decision at the G1 checkpoint?

Growth factors from neighboring cells Signup and view all the answers

During which phase does the cell have its final chance to grow before mitosis?

G2 phase Signup and view all the answers

What happens to some cells that enter the G0 phase?

They can receive signals to re-enter G1 phase later. Signup and view all the answers

What is the primary role of checkpoint proteins during the cell cycle?

Decide whether to move forward with division Signup and view all the answers

Which checkpoint is primarily concerned with the integrity of DNA?

G2 checkpoint Signup and view all the answers

What do cells primarily look for during the M checkpoint?

Correct attachment of sister chromatids Signup and view all the answers

Which of the following is NOT a factor evaluated at the G1 checkpoint?

Chromosome alignment Signup and view all the answers

What is the role of cyclin-dependent kinases (Cdks) in the cell cycle?

They add negatively charged phosphate groups to other molecules. Signup and view all the answers

Why is the regulation of the cell cycle important?

To prevent cells from undergoing constant division. Signup and view all the answers

What happens to cyclins after the cell progresses to the next phase?

They are degraded after their activity is no longer needed. Signup and view all the answers

What triggers the increases in the concentration of cyclin proteins?

Both internal and external signals. Signup and view all the answers

What characterizes the synthesis and degradation cycle of cyclins?

Cyclins undergo a constant cycle of synthesis and degradation. Signup and view all the answers

What is a necessary condition for Cyclin-Dependent Protein Kinases (Cdks) to activate?

They require the presence of cyclins to activate. Signup and view all the answers

What consequence might occur due to a non-functioning cell cycle regulator?

It may disrupt multiple processes and be fatal to the cell. Signup and view all the answers

How are Cyclins named?

They undergo a constant cycle of synthesis and degradation. Signup and view all the answers

What is the primary function of cyclins in the cell cycle?

To activate cyclin-dependent kinases (CDKs) via phosphorylation Signup and view all the answers

How do Rb, p53, and p21 proteins primarily function in the cell cycle?

As tumor-suppressor proteins at the G1 checkpoint Signup and view all the answers

What happens to a cyclin after it has activated a CDK and triggered a cell cycle event?

It is degraded, rendering the CDK inactive Signup and view all the answers

What role does p53 play when damaged DNA is detected in a cell?

It halts the cell cycle and recruits repair enzymes Signup and view all the answers

What triggers the production of p21 in response to stress in cells?

Increased levels of p53 Signup and view all the answers

What is a consequence of malfunctioning regulatory proteins like p53 in cells?

Unchecked progression through the cell cycle Signup and view all the answers

Which of the following describes the action of p21 in the cell cycle?

It binds to and inhibits CDK/cyclin complexes Signup and view all the answers

Which phase of the cell cycle are Rb, p53, and p21 primarily involved in regulating?

G1 phase Signup and view all the answers

What role do spindle fibers play during metaphase?

They attach to kinetochores and align chromosomes. Signup and view all the answers

What occurs during anaphase?

Centromeres split and chromatids separate. Signup and view all the answers

What is the primary difference between cytokinesis in animal and plant cells?

Animal cells form a contractile ring, while plant cells form a cell plate. Signup and view all the answers

Which of the following correctly describes meiosis I?

It reduces the number of chromosomes from diploid to haploid. Signup and view all the answers

What is interkinesis?

The time between meiosis I and meiosis II without DNA replication. Signup and view all the answers

What happens during prophase I of meiosis?

Pairs of homologous chromosomes form tetrads. Signup and view all the answers

What identifies telophase in mitosis?

Chromosomes cluster at the spindle poles and nuclear envelope reforms. Signup and view all the answers

What characterizes meiosis II?

It produces four haploid daughter cells from two haploid cells. Signup and view all the answers

Study Notes

Cell Cycle Phases

Interphase: Divided into G1, S, G2, and G0 phases, where the majority of a cell's life is spent.
G1 Phase:
- Cell evaluates internal and external conditions for DNA replication.
- Cells can enter G0 phase if conditions are not suitable, potentially for extended periods.
- Major checkpoint determines if the cell is ready to proceed to S phase.
S Phase:
- DNA replication occurs, resulting in double the number of chromosomes.
- Continued cell growth and synthesis of proteins/enzyme important for DNA synthesis.
G2 Phase:
- Serves as a safety checkpoint after DNA replication and before mitosis.
- Ensures all DNA and intracellular components are duplicated correctly, allowing for final cell growth.
G0 Phase:
- Quiescent stage where cells are inactive and may remain until stimulated to re-enter the cycle.
- Some cells, like cardiac muscle and nerve cells, can remain in G0 permanently.

Checkpoints and Cell Cycle Regulation

G1 Checkpoint:
- Assesses size, nutrient availability, molecular signals, and DNA integrity.
G2 Checkpoint:
- Checks for DNA damage and completion of DNA replication.
M Checkpoint (Spindle Checkpoint):
- Ensures proper attachment of sister chromatids to spindle fibers before proceeding to anaphase.
- Prevents progression if chromosomes are misaligned or unattached.

Regulation of the Cell Cycle

Positive Regulation:
- Involves cyclins and cyclin-dependent kinases (Cdks) to promote progression through checkpoints.
- Cyclin levels fluctuate predictably; they activate Cdks, which then phosphorylate target proteins to initiate specific cell cycle events.
Negative Regulation:
- Tumor suppressor proteins like Retinoblastoma (Rb), p53, and p21 halt progression if issues are detected.
- p53 binds to damaged DNA, stops the cycle, and can trigger apoptosis if damage is irreparable.
- p21 inhibits Cdk activity in response to elevated p53 levels, preventing entry into S phase.

Mitosis Phases

Metaphase:
- Spindle fibers align chromosomes at the spindle equator.
Anaphase:
- Centromeres split, chromatids separate, moving to opposite poles.
Telophase:
- Chromosomes de-condense, nuclear envelope reforms, and nucleolus organizes.
Cytokinesis:
- In animals, a contractile ring forms to cleave the cell; in plants, a cell plate develops to divide cells.

Meiosis

Minimizes chromosome sets from diploid to haploid over two rounds of division.
The sequence mirrors mitosis: prophase, metaphase, anaphase, telophase occurs in both meiosis I and II.
Prophase I:
- Chromosomes condense and homologous chromosomes pair (synapsis) forming tetrads.
- Genetic recombination can occur through exchange of genetic material between non-sister chromatids.

Summary

Proper regulation and checkpoints throughout the cell cycle ensure organismal health and prevention of tumorigenesis.
Meiosis serves to produce gametes with genetic diversity through recombination and independent assortment.

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Description

Test your knowledge on the phases of the cell cycle, focusing specifically on Interphase and the G1 phase. Understand how cells evaluate their environment and readiness for DNA replication. This quiz explores key concepts and mechanisms that govern cell behavior during the cycle.