Cell Cycle and Chromosomes Overview
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Questions and Answers

How do cells arise?

Cells arise through cell division of preexisting cells.

What are the four phases of the cell cycle?

The four phases of the cell cycle are G1, S, G2, and M.

Cytokinesis refers to the division of the nucleus.

False

Mitosis produces reproductive cells called gametes.

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

Daughter cells produced by mitosis are genetically identical to the parent cell.

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

What are the three basic steps in cellular replication?

<p>The three basic steps in cellular replication are copying the DNA, separating the copies, and dividing the cytoplasm to create two complete cells.</p> Signup and view all the answers

What is a chromosome?

<p>A chromosome is a single long double helix of DNA wrapped around proteins called histones.</p> Signup and view all the answers

What is a gene?

<p>A gene is a section of DNA that codes for a specific RNA, which then codes for a specific protein.</p> Signup and view all the answers

What are sister chromatids?

<p>Sister chromatids are the two attached, double-stranded DNA copies of a replicated chromosome.</p> Signup and view all the answers

What is a centromere?

<p>A centromere is a specialized region of a chromosome where sister chromatids are most closely joined together.</p> Signup and view all the answers

What are kinetochores?

<p>Kinetochores are the structures on sister chromatids where microtubules attach.</p> Signup and view all the answers

What are the two main phases of the cell cycle?

<p>The two main phases of the cell cycle are interphase and M phase.</p> Signup and view all the answers

What happens during interphase?

<p>During interphase, chromosomes are uncoiled, cells are growing and preparing, or are fulfilling their specialized functions.</p> Signup and view all the answers

What happens during the M phase?

<p>During the M phase, chromosomes are condensed into compact structures, and cell division occurs.</p> Signup and view all the answers

What is the S phase?

<p>The S phase is when DNA replication occurs.</p> Signup and view all the answers

What is the purpose of the G1 phase?

<p>The G1 phase occurs between the M phase and the S phase, allowing the cell to grow and replicate organelles.</p> Signup and view all the answers

Chromosomes are visible during the G1 phase.

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

What are the two distinct events that comprise the M phase?

<p>The two distinct events in M phase are mitosis and cytokinesis.</p> Signup and view all the answers

Mitosis is a continuous process.

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

Which phase of mitosis is when the nuclear envelope breaks down?

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

During which phase of mitosis do replicated chromosomes line up on the metaphase plate?

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

What is the spindle apparatus and what is its role in mitosis?

<p>The spindle apparatus forms during prophase. It is composed of microtubules, which are protein filaments that form a framework for separating sister chromatids.</p> Signup and view all the answers

What are the three types of microtubules that make up the spindle apparatus?

<p>The three types of microtubules in the spindle apparatus are polar microtubules, kinetochore microtubules, and astral microtubules.</p> Signup and view all the answers

How is anaphase driven?

<p>Anaphase is driven by two forces: kinetochore microtubules shrink, pulling chromosomes apart; and motor proteins on polar microtubules push the poles of the cell apart.</p> Signup and view all the answers

What are the main events of telophase?

<p>The main events of telophase are the formation of a new nuclear envelope around each set of chromosomes, the decondensation of chromosomes, and the completion of mitosis as two daughter cells are formed.</p> Signup and view all the answers

How does cytokinesis occur in plants?

<p>In plants, cytokinesis occurs through the formation of a cell plate, which is a new cell wall that forms between the two daughter cells.</p> Signup and view all the answers

How does cytokinesis occur in animals?

<p>In animal cells, cytokinesis occurs through the formation of a cleavage furrow, which is a constriction in the cell membrane that eventually pinches off the two daughter cells</p> Signup and view all the answers

The cell cycle is regulated.

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

What is MPF, and how does it function?

<p>MPF, or M phase-promoting factor, is a regulatory protein complex that promotes mitosis in eukaryotic cells. It is composed of a protein kinase (Cdk) and a cyclin.</p> Signup and view all the answers

MPF is only active when bound to cyclin.

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

The level of cyclin in the cell remains constant throughout the cell cycle.

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

MPF is activated when a phosphate is added to the Cdk subunit.

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

How is MPF deactivated?

<p>MPF is deactivated by an enzyme complex that attaches proteins to the cyclin subunit. This marks the cyclin subunit for destruction, leading to deactivation of MPF.</p> Signup and view all the answers

What are cell cycle checkpoints?

<p>Cell cycle checkpoints are critical points in the cell cycle that are regulated by specific proteins. These checkpoints ensure that the cell is properly prepared to progress in the cell cycle and that any errors or problems are addressed before proceeding to the next stage.</p> Signup and view all the answers

The G1 checkpoint is the most important checkpoint in the cell cycle.

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

What is the p53 protein and what is its role in the G1 checkpoint?

<p>The p53 protein is a tumor suppressor that plays a crucial role in the G1 checkpoint by acting as a guardian of the genome. If DNA damage is detected, p53 activates proteins that pause the cell cycle to allow for DNA repair. If the damage is irreparable, p53 can trigger apoptosis, or programmed cell death, to prevent the propagation of damaged cells.</p> Signup and view all the answers

The G2 checkpoint occurs between the G2 phase and the S phase.

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

What are the two requirements for a cell to pass the G2 cell cycle checkpoint?

<p>The cell must have replicated its DNA successfully and MPF must be active.</p> Signup and view all the answers

M-phase checkpoints occur only at the transition point between anaphase and telophase.

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

What are the main characteristics of cancer cells?

<p>Cancer cells have two main characteristics: they grow in an uncontrolled fashion and they invade nearby tissues and spread to other parts of the body.</p> Signup and view all the answers

Cancer is a single disease.

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

Defects in cell cycle checkpoints can contribute to developing cancer.

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

What are the two types of tumors?

<p>The two types of tumors are malignant tumors and benign tumors.</p> Signup and view all the answers

How do malignant tumors spread?

<p>Malignant tumors can spread through the body via the blood or lymph, initiating secondary tumors, a process called metastasis.</p> Signup and view all the answers

Social control is a process that regulates cell division in response to growth factors.

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

What are growth factors, and how do they function?

<p>Growth factors are small proteins that stimulate cell division. They act as signaling molecules, receiving signals from other cells and triggering the expression of genes that promote cell growth and division.</p> Signup and view all the answers

Cancer cells require growth factors to divide.

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

How does the G1 checkpoint work?

<p>The G1 checkpoint relies on the interplay of growth factors, Rb protein, and E2F protein. Growth factors trigger the production of E2F, which promotes the expression of genes required for DNA replication. However, Rb protein acts as a tumor suppressor, binding to and inhibiting E2F activity. Growth factors also activate G1 cyclins that bind to Cdks, leading to the phosphorylation of Rb and its release of E2F.</p> Signup and view all the answers

What are the two main ways that cancer cells can escape the normal regulation of the cell cycle?

<p>Cancer cells can escape cell cycle regulation by either overproducing the G1 cyclin, which permanently activates Cdk and continuously phosphorylates Rb preventing binding to E2F; or by having a missing or defective Rb protein, which can no longer bind to E2F, allowing E2F to activate genes for S phase.</p> Signup and view all the answers

Cancer cells are able to escape cell cycle regulation by activating the p53 gene.

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

What is the impact of a defect in the G1 checkpoint?

<p>Defects in the G1 checkpoint can lead to the development of many types of cancer, allowing cells to bypass the critical decision point of whether to divide or not, resulting in uncontrolled cell growth and proliferation.</p> Signup and view all the answers

Binary fission is a process of cell division that is characteristic of eukaryotes.

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

Binary fission and mitosis are nearly identical processes.

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

Study Notes

Cell Cycle Overview

  • Cells replicate through cell division from pre-existing cells.
  • Embryos in plants and animals start as single cells.
  • Growth occurs through cell divisions.
  • Meiosis produces gametes (reproductive cells).
  • Mitosis produces somatic (body) cells.
  • Mitosis and meiosis are usually accompanied by cytokinesis (division of cytoplasm).
  • During mitosis, genetic material is copied and divided equally between two cells.
  • Daughter cells are genetically identical to the parent cell and to each other during mitosis.
  • Meiosis produces cells with half the amount of hereditary material as the parent cell.
  • Daughter cells are genetically different during meiosis.
  • Cell replication involves copying DNA, separating copies, and dividing the cytoplasm.
  • Humans have 46 chromosomes.

Chromosomes

  • A chromosome is a single, long DNA double helix wrapped around proteins called histones.
  • DNA encodes the cell's genetic information.
  • A gene is a section of DNA coding for a specific RNA, which in turn codes for a specific protein.
  • Before mitosis, each chromosome is replicated.
  • Each double-stranded DNA copy is called a chromatid.
  • Chromatids are initially attached along their entire length by proteins called cohesions.
  • Once mitosis begins, they are attached only at the centromere.
  • Chromatids attached at the centromere are called sister chromatids.
  • Two attached sister chromatids are still considered a single chromosome.
  • Unreplicated chromosomes consist of a single DNA double helix wrapped around proteins.
  • Replicated chromosomes consist of two copies of the same DNA double helix.
  • Condensed replicated chromosomes are 10,000 times shorter than their original length due to the condensation around proteins.

Cell Cycle Phases

  • Growing cells cycle between two phases: mitosis (M phase) and interphase.
  • M phase is the dividing phase.
  • Interphase is the nondividing phase.
  • Chromosomes condense into compact structures during mitosis.
  • Chromosomes are uncoiled during interphase.
  • Cells grow and prepare or fulfill specialized functions during interphase.
  • Cells mainly spend time in interphase.
  • Chromosome replication occurs only during interphase, specifically during the S phase (synthesis).
  • Interphase includes two gap phases (G1 and G2) where no DNA synthesis occurs.

Mitosis

  • Mitosis is a continuous process with 5 subphases (prophase, prometaphase, metaphase, anaphase, and telophase).
  • During prophase, chromosomes condense, becoming visible under a light microscope, and the spindle apparatus forms.
  • The spindle apparatus is composed of microtubules, forming from microtubule-organizing centers (MTOCs).
  • Polar microtubules extend from opposing spindle poles and overlap.
  • In animal cells, MTOCs are centrosomes containing centrioles.
  • During prometaphase, the nuclear envelope breaks down, and microtubules attach to chromosomes at kinetochores, structures at the chromosomes' centromere.
  • Kinetochore microtubules pull chromosomes to the middle of the spindle.
  • During metaphase, the mitotic spindle is complete.
  • Chromosomes align on the metaphase plate, an imaginary plane between the spindle poles.
  • Astral microtubules hold spindle poles in place.
  • During anaphase, cohesions holding sister chromatids together split.
  • Sister chromatids are pulled to opposite poles of the cell.
  • Two identical sets of daughter chromosomes are created.
  • Kinetochore microtubules shrink.
  • Motor proteins of polar microtubules push the poles apart.
  • During telophase, a new nuclear envelope forms around each set of chromosomes.
  • Chromosomes decondense.
  • Mitosis is complete.
  • Cytokinesis typically follows mitosis.
  • The cytoplasm divides to form two daughter cells.

Bacterial Cell Replication

  • Bacteria divide through binary fission.
  • A process similar to eukaryotic mitosis.
  • Bacterial chromosomes replicate.
  • Proteins attach to and separate the replicated chromosomes.
  • Proteins divide the cytoplasm.

Cell Cycle Control

  • Cell-cycle length varies among cell types, primarily due to variations in the G1 phase length.
  • Rapidly dividing cells essentially eliminate G1 phase.
  • Nondividing cells are permanently stuck in G1 phase, known as the G0 state.
  • Division rate can change based on various conditions.
  • Cell-cycle length variations suggest regulation.
  • M-phase checkpoints occur: between metaphase and anaphase, and between anaphase and telophase.
  • Cell cycle checkpoints ensure replicated chromosomes are correctly segregated into daughter cells.

Cancer

  • Cancer is a family of diseases caused by cells that grow uncontrollably, invading nearby tissues and spreading to other sites.
  • Cancer is caused by defects in checkpoints and regulation of the cell cycle.
  • Cancerous cells have two types of defects: activating proteins that should not be active, and preventing the suppression of tumor suppressor genes.
  • Malignant tumors are cancerous and invasive, spreading throughout the body.
  • Benign tumors are noncancerous and noninvasive.
  • Many cancers arise from cells with defects in the checkpoint.

Social Control

  • Cells respond to signals from other cells.
  • Cells only divide when the organism benefits.
  • Social control is based on growth factors, small proteins that stimulate cell division.
  • Cells in culture need growth factors (e.g., serum) to pass the G1 checkpoint.
  • Cancer cells divide without growth factors.

How Checkpoints Work

  • G1 checkpoint: Determines if cells continue through the cycle or enter the G0 resting state. Factors include: size, nutrient availability, social signals, and DNA damage.
  • G2 checkpoint: Checks if chromosome replication was successful and if DNA is undamaged. If so it triggers MPF activation. If not, it prevents MPF activation to stop mitosis.
  • M-phase checkpoints occur: between metaphase and anaphase, and between anaphase and telophase.
  • G1, G2, and M phase checkpoints influence cell cycle progression based on various factors, including intracellular events and external signals.

MPF (M-phase Promoting Factor)

  • MPF is present in the cytoplasm of M-phase cells and induces mitosis in eukaryotes.
  • Composed of two subunits: a protein kinase (Cdk) and a cyclin.
  • Cyclin concentration increases during interphase, peaking in M phase before decreasing again.
  • Cdk is a cyclin-dependent kinase (Cdk).
  • MPF is active only when bound to cyclin.
  • Target proteins are phosphorylated, initiating mitosis.
  • MPF deactivation illustrates negative feedback in cells.
  • An enzyme complex activated during anaphase marks cyclin for destruction, deactivating MPF.

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The Cell Cycle Lecture Presentation PDF

Description

Explore the fascinating processes of the cell cycle, including mitosis and meiosis, which are crucial for growth and reproduction. Understand the structure and function of chromosomes, and how genetic information is transferred during cell division. This quiz will test your knowledge on the fundamentals of cellular biology.

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