Phases of Cell Cycle

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Questions and Answers

What is the significance of the G1 phase in the cell cycle?

It is the final phase before the cell divides.

It is an inactive stage where the cell cannot grow.

It allows the cell to pause and enter G0 if conditions are not favorable. (correct)

It is when the cell replicates its DNA.

Which phase directly follows the G1 phase if the cell is prepared for DNA replication?

M phase

G2 phase

S phase (correct)

G0 phase

What does the cell ensure during the G2 phase of the cell cycle?

That protein synthesis is at its maximum rate.

That it is ready to enter G0.

That it immediately begins cell division.

That all intracellular components have been replicated properly. (correct)

What characterizes cells that are in the G0 phase?

They can exit and re-enter the cell cycle at any time. Signup and view all the answers

During which phase does the cell grow in preparation for DNA replication?

G1 phase Signup and view all the answers

What happens at the major checkpoint of the cell cycle in G1?

The cell ensures that conditions allow for DNA replication. Signup and view all the answers

How long can a cell remain in G0 phase?

Days, weeks, or even years. Signup and view all the answers

What occurs during the S phase of the cell cycle?

Chromosomes are replicated and the cell continues to grow. Signup and view all the answers

What role do cyclins play in the cell cycle?

They activate Cdk through phosphorylation. Signup and view all the answers

Which proteins are classified as tumor-suppressor proteins that regulate the cell cycle?

Retinoblastoma Protein (Rb), p53, and p21 Signup and view all the answers

What happens when damaged DNA is detected during the G1 phase?

p53 halts the cell cycle and initiates DNA repair. Signup and view all the answers

How does p21 function in relation to p53 in the cell cycle?

p21 inhibits the activity of CDK/cyclin complexes. Signup and view all the answers

What is the consequence of faulty regulatory proteins in the context of cell division?

Uncontrolled replication and potential cancer. Signup and view all the answers

What triggers the accumulation of p21 in the cell cycle?

Increase in stress and damage to DNA. Signup and view all the answers

What happens to cyclins after their specific cell cycle event has occurred?

They degrade, rendering the Cdk inactive. Signup and view all the answers

Which phase of the cell cycle do Rb, p53, and p21 primarily regulate?

G1 phase Signup and view all the answers

What is the role of spindle fibers during metaphase?

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

During which phase does the centromere split and chromatids separate?

Anaphase Signup and view all the answers

What event occurs during telophase?

Nuclear envelope assembles around separated chromosome clusters. Signup and view all the answers

What distinguishes meiosis from mitosis?

Meiosis reduces chromosome sets from diploid to haploid. Signup and view all the answers

What occurs during prophase I of meiosis?

Homologous chromosomes undergo synapsis and form tetrads. Signup and view all the answers

What is the period called between meiosis I and meiosis II?

Interkinesis Signup and view all the answers

What is a major outcome of cytokinesis in animal cells?

Pinching of the cell membrane by a contractile ring. Signup and view all the answers

What is a characteristic of interkinesis during meiosis?

No replication of DNA occurs. Signup and view all the answers

What is the primary function of the G1 checkpoint in the cell cycle?

To verify if cell size is adequate for division. Signup and view all the answers

During which checkpoint is DNA integrity specifically assessed for damage?

G2 checkpoint Signup and view all the answers

What happens if a chromosome is found to be in the wrong place during the M checkpoint?

The cell pauses mitosis to capture the misplaced chromosome. Signup and view all the answers

What is a key role of molecular signals during the G1 checkpoint?

To provide positive or negative cues for cell division. Signup and view all the answers

Which stage of the cell cycle does the G2 checkpoint prepare the cell for?

Preparation for mitosis. Signup and view all the answers

Which factor is NOT assessed at the G1 checkpoint?

DNA damage Signup and view all the answers

What is the significance of the M checkpoint in the context of sister chromatids?

To confirm their attachment to spindle microtubules. Signup and view all the answers

Which type of cells are likely to remain in the G0 phase permanently?

Nerve cells. Signup and view all the answers

What occurs at the chiasmata during meiosis?

The exchange of genetic material between homologous chromosomes. Signup and view all the answers

What phase of meiosis involves the separation of homologous chromosomes?

Anaphase I Signup and view all the answers

What defines the daughter cells at the end of telophase II?

They are haploid with unreplicated chromosomes. Signup and view all the answers

How does random assortment contribute to genetic variation?

By allowing chromosomes to be distributed randomly into gametes. Signup and view all the answers

What are recombinant chromatids?

Chromatids resulting from the combination of DNA from both homologous chromosomes. Signup and view all the answers

Which of the following describes the process that occurs during cytokinesis?

It separates the cytoplasm of the original cell into two daughter cells. Signup and view all the answers

What is the overall outcome of meiosis?

Four genetically distinct haploid cells are produced. Signup and view all the answers

What is an advantage of sexual reproduction?

It enhances genetic variation in the offspring. Signup and view all the answers

What happens in prophase II of meiosis?

Chromosomes condense and the spindle apparatus forms. Signup and view all the answers

The formula $2^n$ represents what in the context of meiosis?

The total number of different gametes that can be produced. Signup and view all the answers

Study Notes

Phases of the Cell Cycle

Interphase consists of G1, S, and G2 phases, crucial for cell growth and preparation for division.
G1 phase: Cell assesses its environment and growth conditions before DNA replication. Cells may enter G0 phase if conditions are not suitable, which can last for extended periods.
S phase: DNA replication occurs, doubling the chromosome count. Cell growth continues, and essential proteins for DNA synthesis are synthesized.
G2 phase: The cell checks the completeness of DNA replication and prepares for mitosis, serving as a final growth phase.

G0 Phase

Cells can exit the cell cycle and enter a quiescent G0 phase, where they are inactive and not preparing for division.
Some cells enter G0 temporarily; others, such as nerve and cardiac cells, may remain permanently.

Checkpoints and Regulation

Key checkpoints in the cell cycle ensure conditions are favorable for division:
- G1 checkpoint assesses cell size, nutrient availability, molecular signals, and DNA integrity.
- G2 checkpoint checks for DNA damage and ensures proper DNA replication.
- M checkpoint, or spindle checkpoint, verifies that sister chromatids are correctly attached to spindle fibers before anaphase.

Regulatory Molecules

Cyclins are proteins that activate cyclin-dependent kinases (CDKs) to promote progression through the cell cycle via phosphorylation.
Two classes of cyclins: mitotic cyclins and G1 cyclins.
Regulatory proteins, like Retinoblastoma protein (Rb), p53, and p21, can halt the cycle if conditions are not met, especially at the G1 checkpoint.

Meiosis

Meiosis reduces chromosome sets from diploid to haploid through two rounds of division: Meiosis I and Meiosis II.
Meiosis I results in two haploid daughter cells, while Meiosis II produces four genetically distinct haploid cells.

Meiosis Stages

Prophase I: Homologous chromosomes pair and form tetrads; crossing over occurs at chiasmata.
Metaphase I: Tetrads align at the metaphase plate; spindle fibers attach to kinetochores.
Anaphase I: Homologous chromosomes separate to opposite poles; sister chromatids remain attached.
Telophase I: Nuclei form around chromosome clusters; cytokinesis follows.

Genetic Variation in Sexual Reproduction

Crossing over in Prophase I leads to recombinant chromosomes, introducing genetic diversity.
Independent assortment during Metaphase I randomizes maternal and paternal chromosome orientation, yielding various gamete combinations.
Random fusion of different gametes produces genetically distinct zygotes, promoting variation in offspring.

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Description

This quiz focuses on the G1 phase of the cell cycle, where the cell assesses its environment and readiness for DNA replication. Learn about the processes and conditions that determine whether the cell continues to the next phase or enters a resting state. Test your understanding of interphase dynamics.

Phases of Cell Cycle - G1 Phase

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