Cell Cycle and Checkpoints Quiz
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Questions and Answers

What is the primary function of mitosis?

  • To synthesize proteins
  • To repair tissues only
  • To duplicate the DNA
  • To segregate chromosomes and divide the cell (correct)

Cytokinesis occurs only during the M phase of the cell cycle.

True (A)

What is the role of the kinetochore during cell division?

To attach chromatids to microtubules and assist in their movement to the poles of the cell.

The __________ phase of the cell cycle includes DNA duplication.

<p>Synthesis</p> Signup and view all the answers

Match the following stages of mitosis with their descriptions:

<p>Prophase = Chromatin condenses and the nuclear envelope disintegrates Metaphase = Chromosomes align at the equatorial plate Anaphase = Sister chromatids are pulled apart to opposite poles Cytokinesis = Division of the cytoplasm into two daughter cells</p> Signup and view all the answers

Which phase of mitosis is characterized by the breakdown of the nuclear envelope?

<p>Prophase (C)</p> Signup and view all the answers

How long does the M Phase typically last?

<p>About 1 hour.</p> Signup and view all the answers

Sister chromatids are separated during metaphase.

<p>False (B)</p> Signup and view all the answers

What happens during telophase?

<p>A nuclear envelope reappears around the chromosomes. (A)</p> Signup and view all the answers

Cytokinesis occurs after the completion of mitosis.

<p>True (A)</p> Signup and view all the answers

What is the chromosome number in gametes produced through meiosis?

<p>23 chromosomes</p> Signup and view all the answers

Gametes are described as ______ because they contain one member of each chromosome pair.

<p>haploid</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Telophase = Reconstitution of the nuclear envelope and uncoiling of chromosomes Cytokinesis = Division of the cytoplasm to form two daughter cells Meiosis = Process that results in haploid gametes Crossing-over = Exchange of chromosome segments between homologous chromosomes</p> Signup and view all the answers

Which statement accurately describes homologous chromosomes?

<p>They contain the same genes but may have different alleles. (B)</p> Signup and view all the answers

The zygote is haploid in chromosome number.

<p>False (B)</p> Signup and view all the answers

What is the primary outcome of crossing-over during meiosis?

<p>Genetic diversity</p> Signup and view all the answers

What is the end product of meiosis in males?

<p>Four identical haploid spermatids (D)</p> Signup and view all the answers

In females, the two meiotic divisions of a primary oocyte produce three functional gametes.

<p>False (B)</p> Signup and view all the answers

What type of division occurs during meiosis II?

<p>Equatorial division</p> Signup and view all the answers

The chromosome number is reduced from diploid (2n) to __________ (1n) during meiosis I.

<p>haploid</p> Signup and view all the answers

Match the phases of meiosis I with their correct descriptions.

<p>Prophase I = Chromosomes condense and homologous chromosomes pair Metaphase I = Paired chromosomes align at the equatorial plate Anaphase I = Homologous chromosomes segregate to opposite sides Telophase I = Formation of two haploid nuclei</p> Signup and view all the answers

During which stage of prophase I does crossing over occur?

<p>Pachytene (C)</p> Signup and view all the answers

No DNA replication occurs before meiosis II.

<p>True (A)</p> Signup and view all the answers

What is a chiasma?

<p>The point where homologous chromosomes are attached during crossing over.</p> Signup and view all the answers

What is the primary structural form of heterochromatin?

<p>Highly condensed structure (B)</p> Signup and view all the answers

Heterochromatin is transcriptionally active at all times.

<p>False (B)</p> Signup and view all the answers

What is a nucleosome composed of?

<p>DNA and histone proteins</p> Signup and view all the answers

The basic subunit of chromatin is known as a ______.

<p>nucleosome</p> Signup and view all the answers

Which of the following is associated with the regulation of gene expression or chromosome integrity?

<p>Heterochromatin (D)</p> Signup and view all the answers

Heterochromatin can influence the expression levels of adjacent genes.

<p>True (A)</p> Signup and view all the answers

The term for the inheritance mechanism involving heterochromatin is ______.

<p>epigenetic inheritance</p> Signup and view all the answers

What is the primary function of chromatin?

<p>To package DNA into a smaller volume (C)</p> Signup and view all the answers

Euchromatin is tightly packed and less accessible for transcription.

<p>False (B)</p> Signup and view all the answers

What are the two types of chromatin mentioned?

<p>Euchromatin and heterochromatin</p> Signup and view all the answers

Chromatin is composed of DNA and _____ proteins.

<p>histone</p> Signup and view all the answers

What percentage of the human genome is composed of euchromatin?

<p>92% (D)</p> Signup and view all the answers

During interphase, chromatin is more tightly packed to prevent transcription.

<p>False (B)</p> Signup and view all the answers

What structural change occurs to chromatin during mitosis?

<p>Chromatin condenses to form chromosomes.</p> Signup and view all the answers

Which of the following statements about euchromatin is true?

<p>Euchromatin is involved in the active transcription of DNA. (B)</p> Signup and view all the answers

Heterochromatin is only found in eukaryotes.

<p>False (B)</p> Signup and view all the answers

What are the two main types of heterochromatin?

<p>Constitutive heterochromatin and facultative heterochromatin.</p> Signup and view all the answers

The _______ chromosome is associated with facultative heterochromatin.

<p>inactive X</p> Signup and view all the answers

How does heterochromatin affect nearby genes?

<p>It can affect the expression of nearby genes through position-effect variegation. (B)</p> Signup and view all the answers

Match the type of heterochromatin with its description:

<p>Constitutive heterochromatin = Regions found throughout chromosomes and has structural functions. Facultative heterochromatin = Euchromatin that can convert based on developmental needs.</p> Signup and view all the answers

Euchromatin is more densely packed than heterochromatin.

<p>False (B)</p> Signup and view all the answers

What role does RNA-induced transcriptional silencing (RITS) play in heterochromatin?

<p>It is responsible for the continuous turnover of transcribed DNA in heterochromatin.</p> Signup and view all the answers

Flashcards

G2 Phase

A cell cycle phase where the cell prepares for mitosis by checking for DNA or other errors.

M Phase (Mitosis)

The phase of cell division that includes both karyokinesis (nuclear division) and cytokinesis (cell division).

Karyokinesis

The division of the nucleus during mitosis.

Cytokinesis

Division of the cytoplasm during mitosis, creating two daughter cells.

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Prophase

The first stage of mitosis where chromosomes condense and become visible.

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Metaphase

Stage where chromosomes align in the middle of the cell.

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Anaphase

Stage where sister chromatids separate and move to opposite poles.

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Chromatids

Duplicated halves of a chromosome, joined together at the centromere.

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Cleavage Furrow

The indentation formed in the plasma membrane during cytokinesis.

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Contractile Ring

The array of actin filaments that causes the cleavage furrow to deepen, resulting in cell division.

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Diploid (2n)

A cell containing two sets of chromosomes (one maternal, one paternal).

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Haploid (1n)

A cell containing one set of chromosomes.

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Meiosis

A two-part cell division process that produces gametes (sex cells) with half the number of chromosomes as the parent cell.

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Crossing-over

The exchange of genetic material between homologous chromosomes during meiosis, increasing genetic diversity.

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Meiosis in Males

Two meiotic divisions in a primary spermatocyte result in four identical, haploid spermatids, each capable of differentiating into a spermatozoon.

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Meiosis in Females

Two meiotic divisions in a primary oocyte produce one haploid ovum and three haploid polar bodies. The ovum receives most of the cytoplasm and becomes the functional female gamete.

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Reductional Division

The first division in meiosis (meiosis I) where the chromosome number is reduced from diploid (2n) to haploid (1n), and the amount of DNA is halved.

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Equatorial Division

The second division in meiosis (meiosis II) where the number of chromosomes does not change. However, the amount of DNA is reduced from (2d) to (1d).

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Prophase I Stages

Prophase I is the longest phase of meiosis I and consists of five stages: Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis.

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Leptotene

The first stage of prophase I where chromosomes start to condense.

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Zygotene

The second stage of prophase I where homologous chromosomes pair up (synapsis) to form bivalents (tetrads).

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Pachytene

The third stage of prophase I where crossing-over occurs between homologous chromosomes.

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Nucleosome

The fundamental unit of chromatin, formed by DNA wrapped around histone proteins, resembling beads on a string.

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Euchromatin

A loosely packed form of chromatin that is actively transcribed, meaning genes are easily accessed for protein synthesis.

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Heterochromatin

A tightly packed form of chromatin that is inactive for transcription, making genes less accessible for protein synthesis.

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What role does chromatin play during cell division (mitosis/meiosis)?

Chromatin condenses further into visible chromosomes, allowing organized separation of genetic material into daughter cells.

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How does chromatin structure affect gene expression?

The accessibility of genes within chromatin determines how active they are. Euchromatin (open) allows transcription, while heterochromatin (closed) restricts it.

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What are epigenetic modifications?

Chemical changes to the proteins associated with chromatin, such as methylation and acetylation, that influence gene expression without altering DNA sequence.

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Why is chromatin structure an active research area?

Understanding the complex interplay between chromatin and gene expression is crucial for unlocking the mechanisms of development, disease, and potential therapeutic targets.

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Constitutive Heterochromatin

Permanent, tightly packed DNA found in specific regions of chromosomes, like centromeres and telomeres.

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Facultative Heterochromatin

Condensed chromatin that can switch between active and inactive states, depending on developmental need.

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Position-Effect Variegation

A phenomenon where the expression of a gene is influenced by its proximity to heterochromatin.

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Satellite DNA

Highly repetitive, non-coding DNA sequences found in constitutive heterochromatin.

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RNAi

RNA interference, a mechanism for silencing gene expression through the use of small RNA molecules.

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piRNA

Piwi-interacting RNA, a class of small RNAs involved in silencing transposable elements and regulating gene expression.

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Position Effect Variegation (PEV)

A genetic phenomenon where the expression of a gene is influenced by its proximity to heterochromatin. The gene's activity can vary between cells, leading to a mosaic expression pattern.

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Insulator Sequences

DNA sequences that act as boundaries, preventing the spread of heterochromatin and ensuring the proper regulation of nearby genes.

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Histone Octamer

The core of a nucleosome, composed of two copies each of the histone proteins H2A, H2B, H3, and H4.

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Study Notes

Cell Cycle Checkpoints

  • Cell cycle checkpoints are control mechanisms in eukaryotic cell cycles
  • They ensure proper progression
  • Each checkpoint is a potential termination point assessing cell conditions
  • Progression to the next phase only occurs under favorable conditions
  • Key checkpoints: G1 (Start/restriction), G2/M, and metaphase-to-anaphase (spindle)
  • Progression determined by cyclin-dependent kinases (CDKs) activated by cyclins
  • Different cyclins produced at each cell cycle stage to control specific events

Phases of Cell Cycle

  • A typical eukaryotic cell cycle (e.g., human cells in culture) lasts approximately 24 hours
  • Duration varies between organisms and cell types (e.g., yeast in 90 minutes)
  • Divided into interphase and mitotic (M) phase
  • Interphase: cell growth and chromosome copying
  • Mitotic phase: mitosis and cytokinesis

Interphase

  • Consists of three phases: G1, S, and G2
  • G1 phase: Longest and most variable; cell gathers nutrients, synthesizes RNA and proteins needed for DNA replication
  • S phase: DNA synthesis; DNA contents are doubled, and new chromatids are formed (about 7.5-10 hours)
  • G2 phase: Cell growth and reorganization of cytoplasmic organelles; cell checks for DNA replication errors; cells prepare to enter the mitotic cycle

Mitosis

  • Mitosis: process of chromosome segregation and nuclear division followed by cell division. Creating daughter cells with the same DNA content.
  • Stages Include:
    • Prophase: Chromatin condense, visible chromosomes form, nuclear envelope breaks down
    • Metaphase: Chromosomes align at the metaphase plate, spindle fibers attach to chromosomes
    • Anaphase: Sister chromatids separate and move to opposite poles
    • Telophase: Chromosomes decondense, nuclear envelope reforms, cytoplasm divides (cytokinesis)

Cytokinesis

  • Cytokinesis: Cytoplasmic division that completes mitosis (formation of two daughter cells)

Meiosis

  • Meiosis: Two sequential nuclear divisions to produce gametes (sex cells) with half the chromosome number and DNA content of somatic cells
  • Important for genetic diversity and reproduction
  • Meiosis differs in males and females: 1) Males- producing unique, haploid spermatids capable of differentiation into spermatozoa 2) Females- produces one haploid ovum and three haploid polar bodies
  • Stages: Meiosis I and Meiosis II (with prophase, metaphase, anaphase and telophase phases) reducing the DNA content from (4d) to (1d)

Chromatin

  • Chromatin: Complex of DNA and proteins found in eukaryotic cells, packaging DNA into a compact form
  • Two types of chromatin: 1) Euchromatin: less compact, active transcription 2) Heterochromatin: more compact, less accessible for transcription
  • Nucleosomes: DNA wrapped around histone proteins, the fundamental subunit of chromatin
  • Importance in DNA packaging, regulation of gene expression, and maintaining chromosome integrity

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Description

Test your knowledge on the cell cycle, its checkpoints, and phases. This quiz covers key concepts such as G1, G2, and the role of cyclins and CDKs in controlling cell progression. Perfect for biology students looking to reinforce their understanding of eukaryotic cell cycles.

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