Cell Cycle Overview

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Questions and Answers

What is the primary role of the G1 phase in the cell cycle?

To undergo cell division

To allow for RNA, protein, and organelle synthesis (correct)

To synthesize DNA

To prepare for chromatin condensation

During which phase of the cell cycle does the cell spend the most time, in a typical mammalian cell cycle of 16 hours?

M phase

S phase

G1 phase (correct)

G2 phase

What is the primary role of the centromere during cell division?

Replicating DNA before division

Forming the nuclear envelope

Binding of microtubules to chromosomes (correct)

Separation of chromatids during anaphase (correct)

Which statement accurately describes the mitotic spindle during prometaphase?

Microtubules are categorized as kinetochore, polar, and astral microtubules. Signup and view all the answers

Which checkpoint is responsible for the transition from G1 phase to S phase?

G1 checkpoint Signup and view all the answers

Which phase of the cell cycle is characterized by high ATP synthesis?

G2 phase Signup and view all the answers

What is the role of the contractile ring during cytokinesis?

To help in the formation of the cleavage furrow Signup and view all the answers

What is the main event that occurs during the S phase of the cell cycle?

DNA synthesis Signup and view all the answers

Which event occurs during anaphase of mitosis?

Centromeres split and chromatids move to opposite poles Signup and view all the answers

In which stage of mitosis does chromatin condense to form well-defined chromosomes?

Prophase Signup and view all the answers

What distinguishes meiosis from mitosis regarding DNA replication?

Meiosis has only one round of DNA replication prior to the first division. Signup and view all the answers

What happens to the chromatin during telophase?

Chromatin decondenses to form chromosomes. Signup and view all the answers

What is the correct definition of a diploid cell?

A cell with 46 chromosomes Signup and view all the answers

Which phase directly follows the S phase in the cell cycle?

G2 phase Signup and view all the answers

In which phase of cell division are cells typically arrested for karyotype analysis?

Metaphase Signup and view all the answers

During which phase does the nucleolus reappear?

Telophase Signup and view all the answers

Which composition of chromosomes in a sperm typically leads to the fertilization resulting in a genetic female?

23 autosomes plus an X chromosome Signup and view all the answers

What is the chromosome composition and DNA amount in a typical gamete?

23 chromosomes, 1N Signup and view all the answers

In comparison to a normal somatic cell, what is the chromosome composition found in a typical sperm cell?

22 autosomes and one sex chromosome Signup and view all the answers

What is the primary distinction between meiosis and mitosis?

Mitosis maintains the chromosome number, while meiosis halves it Signup and view all the answers

During which process do crossing over and random segregation occur, contributing to genetic variation?

Meiosis I Signup and view all the answers

Which process introduces genetic variability by the exchange of segments between nonsister chromatids?

Crossover Signup and view all the answers

Tetraploid cells are most commonly the result of which cellular process failure?

Cytokinesis of mitosis Signup and view all the answers

What is the primary outcome of the disjunction process in meiosis I?

Separation of homologous chromosomes Signup and view all the answers

In which phase does the reduction division occur, resulting in a decrease in chromosome number from 46 to 23?

Meiosis I Signup and view all the answers

What is the term for the pairing of duplicated chromosomes with their homologous counterparts?

Synapsis Signup and view all the answers

Which part of the cell cycle serves as a checkpoint for responding to DNA damage?

G2 checkpoint Signup and view all the answers

In meiosis II, how many single chromosomes are formed in each gamete after disjunction?

23 single chromosomes Signup and view all the answers

Which event does NOT occur during meiosis II?

Crossover Signup and view all the answers

What effect does the random distribution of maternal and paternal chromosomes have during meiosis?

Introduces genetic variability Signup and view all the answers

What is the main cause of variable number tandem repeat (VNTR) polymorphisms in the genome?

Unequal crossover during meiosis Signup and view all the answers

During what stage of meiosis does crossover specifically occur?

Prophase I Signup and view all the answers

Study Notes

Cell Cycle

Cell cycle is a series of events that lead to cell division, or a temporary resting stage (G0 phase).
Two major periods comprise the cell cycle:
- Interphase (interval between cell division)
- M phase (mitosis, the period of cell division)

Interphase

Interphase is a series of changes in a newly formed cell and its nucleus before it can divide again.
It's also known as the preparatory phase or inter-mitosis.
Interphase is divided into three phases:
- G1 Phase:
  - The gap of time between mitosis (M phase) and DNA synthesis (S-phase).
  - RNA, protein, and organelle synthesis occurs in this phase.
  - In a typical mammalian cell with a 16-hour cell cycle, the G1 phase lasts about 5 hours.
  - A G1 checkpoint (Cdk2-cyclin D and Cdk2-cyclin E) regulates the G1 to S phase transition.
- S Phase (synthesis):
  - DNA synthesis occurs.
  - In a typical mammalian cell with a 16-hour cell cycle, the S phase lasts about 7 hours.
- G2 Phase:
  - The gap of time between DNA synthesis (S phase) and mitosis (M phase).
  - High levels of ATP synthesis occur in this phase.
  - In a typical mammalian cell with a 16-hour cell cycle, the G2 phase lasts about 3 hours.
  - A G2 checkpoint (Cdk1-cyclin A and Cdk1-cyclin B) regulates the G2 to M phase transition.

Checkpoints

Checkpoints are specialized signaling mechanisms that control cell response to DNA damage and replication blockages.
If DNA damage or replication blockage exceeds the threshold, a checkpoint signal is produced, triggering a checkpoint activation.
Checkpoint activation slows down the cell cycle to allow DNA repair or recovery of blocked replication forks.
Main protein families controlling the cell cycle: cyclins and cyclin-dependent protein kinases (Cdks).
Cyclins regulate Cdk activity and undergo synthesis/degradation cycles.
Cdk-cyclin complexes phosphorylate target proteins, controlled by the specific cyclin.

Mitosis

Mitosis (M phase) is the process where a cell divides into two identical daughter cells with an identical number of chromosomes within them.
The human diploid number of chromosomes is 46.
Six stages:
- Prophase: Chromatin condenses to form well-defined chromosomes. Each chromosome has been duplicated and has a centromere for proper segregation. The centrosome complex splits. The mitotic spindle forms.
- Prometaphase: The nuclear envelope is disrupted, microtubules enter the area, and kinetochores (protein complexes) assemble on each chromosome.
- Metaphase: Chromosomes align at the metaphase plate. Cells can be arrested for karyotype analysis.
- Anaphase: Centromeres split, kinetochores separate, chromosomes move to opposite poles. Kinetochore microtubules shorten, polar microtubules lengthen.
- Telophase: Chromosomes decondense to form chromatin. Nuclear envelope reforms. Nucleolus reappears. Kinetochore microtubules disappear. Polar microtubules lengthen.
- Cytokinesis: The cytoplasm divides into two separate cells by a cleavage furrow, formed by a contractile ring of actin and myosin filaments.

Meiosis

Meiosis is a specialized cell division that produces gametes (sex cells).
Meiosis consists of two divisions: meiosis I and meiosis II.
Only one round of DNA replication.
Produces four unique haploid gametes each with 23 single chromosomes (half the number of normal chromosomes.
Meiosis I:
- Synapsis: Homologous chromosomes pair with their homologue, occurring only in meiosis, not mitosis or meiosis II.
- Crossover/Recombination: Exchange of large segments of DNA between maternal and paternal chromatids at the chiasma during prophase I (pachytene stage). This introduces genetic variability.
- Alignment: Homologous duplicated chromosomes align at the metaphase plate.
- Disjunction: Homologous pairs separate from each other creating secondary gametocytes. The centromeres do not split
- Cell division: Reduction division; the haploid number of chromosomes is formed
Meiosis II:
- Synapsis: Absent
- Crossover: Absent
- Alignment: 23 duplicated chromosomes align at the metaphase plate.
- Disjunction: Sister chromatids separate from each other creating gametes. Centromeres split
- Cell division: Gametes (23 single chromosomes) are formed
Key Differences between mitosis and meiosis:
- Mitosis produces two identical diploid daughter cells; meiosis produces four genetically diverse haploid gametes.
- Mitosis has one cell division; meiosis has two cell divisions.
- Mitosis has no crossing over or homologous chromosome pairing; meiosis involves both.
Chromosome numbers & DNA amounts:
- Gametes have 23 chromosomes and 1N DNA.
- Somatic cells have 46 chromosomes and 2N DNA.

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Description

Explore the phases of the cell cycle, including interphase and M phase. Understand the significance of the G1, S, and G2 phases, as well as the checkpoints that regulate cell division. Test your knowledge on cell division processes and their importance in biology.