Biology Chapter on Cell Division and Cancer
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Questions and Answers

Which cell type is known for dividing frequently?

  • Bone cells
  • Intestinal cells (correct)
  • Blood cells
  • Neuronal cells

    • Cancerous cells have fully functional cell cycle checkpoints.

    False

    What do cells enter when they do not receive the go-ahead signal?

    G0 phase

    The cell cycle is driven by specific chemical signals present in the ______.

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

    Match the checkpoints to their corresponding phases in the cell cycle:

    <p>G1 checkpoint = Checks for cell size and DNA integrity G2 checkpoint = Checks for DNA replication completeness M checkpoint = Checks for chromosome alignment</p> Signup and view all the answers

    What is one consequence of cancer cells losing their checkpoints?

    <p>They become immortal.</p> Signup and view all the answers

    Molecular clocks are not involved in regulating the cell cycle.

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

    Who were HeLa cells named after?

    <p>Henrietta Lacks</p> Signup and view all the answers

    What type of cell division produces sperm and egg cells?

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

    Most DNA is packaged into ribosomes.

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

    What are the units of heredity made up of segments of DNA?

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

    Humans have _____ pairs of chromosomes in somatic cells.

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

    What is the primary function of cellular division in multicellular eukaryotes?

    <p>Development from a fertilized egg</p> Signup and view all the answers

    Meiosis results in identical daughter cells.

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

    What is a karyotype?

    <p>An ordered display of chromosome pairs</p> Signup and view all the answers

    What is chromatin?

    <p>A complex of DNA and protein that condenses during cell division.</p> Signup and view all the answers

    Match the terms with their correct descriptions:

    <p>Gene = Unit of heredity Gamete = Reproductive cell Locus = Specific position of a gene on a chromosome Heredity = Transmission of traits from one generation to another</p> Signup and view all the answers

    In humans, haploid cells contain _____ chromosomes.

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

    Offspring can exhibit variation in appearance due to genetic differences.

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

    Match the following phases with their major functions during the cell cycle:

    <p>Mitosis = Division of the nucleus Cytokinesis = Division of the cytoplasm Interphase = Preparation for cell division Meiosis = Production of gametes</p> Signup and view all the answers

    What is the scientific study of heredity and variation called?

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

    What happens when cellular checkpoints malfunction?

    <p>It can lead to uncontrolled cell growth.</p> Signup and view all the answers

    Plant cells undergo exactly the same process of cytokinesis as animal cells.

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

    What is the life cycle of a cell referred to as?

    <p>Cell cycle</p> Signup and view all the answers

    Eukaryotic cells typically have a characteristic number of _____ in each cell nucleus.

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

    What type of division does meiosis represent?

    <p>A special type of division producing gametes</p> Signup and view all the answers

    What are the joined copies of the original chromosome called?

    <p>Sister chromatids</p> Signup and view all the answers

    During anaphase, sister chromatids are still attached to each other.

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

    Name the phase of the cell cycle where DNA replication occurs.

    <p>S phase</p> Signup and view all the answers

    The __________ is the narrow 'waist' of a duplicated chromosome.

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

    Match the following stages of mitosis with their descriptions:

    <p>Prophase = Chromosomes become visible and mitotic spindle forms Metaphase = Chromosomes align at the metaphase plate Anaphase = Sister chromatids separate toward opposite poles Telophase = Nuclear envelope reappears and chromosomes decondense</p> Signup and view all the answers

    What structure controls chromosome movement during mitosis?

    <p>Mitotic spindle</p> Signup and view all the answers

    Cytokinesis occurs after the completion of mitosis.

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

    What is the role of kinetochore microtubules during mitosis?

    <p>They attach to the kinetochores of chromosomes to facilitate their movement.</p> Signup and view all the answers

    During __________, the nuclear envelope fragments and chromosomes become more condensed.

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

    What phase of interphase involves cell growth and preparation for DNA synthesis?

    <p>G1 phase</p> Signup and view all the answers

    In plant cells, cytokinesis occurs through the formation of a cleavage furrow.

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

    Describe what happens to chromosomes at the metaphase plate.

    <p>Chromosomes align along the metaphase plate with their centromeres lying at this imaginary plane.</p> Signup and view all the answers

    Cytokinesis in animal cells involves the formation of a __________.

    <p>cleavage furrow</p> Signup and view all the answers

    Which protein complex attaches sister chromatids?

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

    What is the primary difference between asexual and sexual reproduction?

    <p>Asexual reproduction produces genetically identical offspring while sexual reproduction results in unique combinations of genes.</p> Signup and view all the answers

    Human females have a homologous pair of X chromosomes.

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

    What are the two types of cells produced by meiosis?

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

    The fertilized egg is called a __________.

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

    What process is primarily involved in the production of gametes?

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

    Mitosis results in four daughter cells.

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

    How many pairs of chromosomes do human somatic cells typically have?

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

    A diploid cell is represented as __________.

    <p>2n</p> Signup and view all the answers

    Which type of chromosomes does a human sperm cell carry?

    <p>Either X or Y chromosomes</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Somatic Cells = Non-reproductive cells with two sets of chromosomes Gametes = Reproductive cells that are haploid Diploid = Cells containing two sets of chromosomes Haploid = Cells containing one set of chromosomes</p> Signup and view all the answers

    Aneuploidy refers to the normal number of chromosomes in a cell.

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

    What is the primary purpose of crossing over during meiosis?

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

    The union of gametes is called __________.

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

    How many daughter cells are produced in meiosis?

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

    What is the role of mitosis in the life cycle of an organism?

    <p>Growth and tissue repair</p> Signup and view all the answers

    Study Notes

    Learning Objectives

    • Understand the functions of cellular division and the organization of genetic material in chromatin/chromosomes.
    • Define key chromosomal/genetic material terminology.
    • Understand the major phases and processes occurring in the cell cycle during mitosis.
    • Explain how the mitotic spindle contributes to chromosomal movement in all phases of mitosis.
    • Understand the difference between animal and plant cell cytokinesis.
    • Understand why cellular checkpoints are important and what happens when they malfunction.
    • Explain how genetic material is passed through generations.
    • Understand chromosomal numbers in humans, haploid vs diploid cells (and examples in the body), human life cycle.
    • Describe the differences between asexual and sexual reproduction.
    • Explain the major outcomes of meiosis, major phases of meiosis I and meiosis II, how genetic diversity occurs.
    • Compare and contrast mitosis and meiosis.
    • Cellular division is crucial for organism growth and survival
    • The continuity of life is based on cell division.

    Cellular Division

    • The ability of organisms to produce more of their own kind.
    • Mitosis and meiosis are types of cell division.
    • Mitosis results in two identical daughter cells.
    • Meiosis results in four non-identical daughter cells.

    Functions of Cellular Division

    • In unicellular organisms: Division of one cell reproduces the entire organism.
    • In multicellular eukaryotes: Dependent on cell division for development from a fertilized egg, growth, and repair.

    Introducing the Cell Cycle

    • Cell division is an integral part of the cell cycle.
    • Cell cycle: The life of a cell from formation to its own division.
    • Most cell division results in two daughter cells with identical genetic information.
    • The exception is meiosis -- a special type of division that can produce sperm and egg cells (gametes).
    • Meiosis produces non-identical daughter cells.

    Cellular Organization of the Genetic Material

    • Genome: All the DNA in a cell
    • A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells).
    • DNA molecules in a cell are packaged into chromosomes.
    • Eukaryotic chromosomes consist of chromatin.
    • Chromatin: A complex of DNA and protein (histones) that condenses during cell division.
    • Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus.

    Distribution of Chromosomes During Eukaryotic Cell Division

    • In preparation for cell division, DNA is replicated, and the chromosomes condense.
    • Each duplicated chromosome has two sister chromatids.
    • Sister chromatids: Joined copies of the original chromosome, attached along their lengths by cohesins.
    • Cohesins: Protein complexes that attach sister chromatids.
    • The centromere: the narrow waist of a duplicated chromosome, where two chromatids are most closely attached.

    The Two Major Phases of the Cell Cycle

    • Interphase (G1, S, and G2): Cell growth and copying of chromosomes in preparation for cell division (about 90% of the cell cycle).
    • G1 phase (First gap): Cell growth, increases in size, gets ready for S phase.
    • S phase (Synthesis): DNA replication occurs.
    • G2 phase (Second gap): Cell continues to grow, gets ready for mitosis.
    • Mitotic phase (Mitosis and Cytokinesis): Mitosis: the division of the genetic material in the nucleus, and Cytokinesis: the division of the cytoplasm.

    Mitosis Consists of 5 Stages

    • Prophase
    • Prometaphase
    • Metaphase
    • Anaphase
    • Telophase and Cytokinesis

    G2 of Interphase

    • A nuclear envelope encloses the nucleus.
    • Two centrosomes have formed, regions that organize microtubules.
    • Chromosomes duplicated in S phase cannot be seen.

    Prophase

    • Chromatin fibers tightly coil into discrete chromosomes, becoming visible.
    • Duplicated chromosomes appear as two sister chromatids joined at centromeres.
    • Mitotic spindle begins to form.
    • Centrosomes and the microtubules extending from centrosomes.
    • Centrioles move away from each other

    Prometaphase

    • Nuclear envelope fragments, chromosomes are even more condensed.
    • Microtubules from each centrosome invade nuclear area.
    • Kinetochore: protein structure at the centromere on each sister chromatid.
    • Some microtubules become kinetochore microtubules, jerking chromosomes back and forth.
    • Any non kinetochore microtubules elongate the cell

    Metaphase

    • Centrosomes now at opposite poles of the cell.
    • Chromosomes have arrived at the metaphase plate, an imaginary plane at the middle of the cell.
    • Centromeres lie at metaphase plate.
    • Kinetochore of each sister chromatid attach to kinetochore microtubules.

    Anaphase

    • Shortest phase of mitosis.
    • Cohesins between chromatids are cleaved, allowing each pair to separate (becoming an independent chromosome).
    • Two new daughter chromosomes moving towards opposite poles.
    • Centromeres lead, because microtubules attached to kinetochore (at centromere).

    Telophase and Cytokinesis

    • Two daughter nuclei form.
    • Nuclear envelope reappears.
    • Chromosomes start to decondense.
    • Mitosis is now complete, creating two genetically identical nuclei.
    • Cytokinesis: Division of the cytoplasm.
    • Involves formation of a cleavage furrow, pinching cell in two (animal cells).
    • Cell plate forms during cytokinesis in plant cells.

    Animal Cell Mitosis (time-lapse) and Plant Cell Cytokinesis (in onion root cells)

    • Both animal and plant cells undergo mitosis and cytokinesis, but the mechanisms for cytokinesis differ.

    BioFlix Animation: Mitosis

    • Digital animation.
    • Demonstrates stages of mitosis

    The Mitotic Spindle

    • A structure made of microtubules that controls chromosome movement during mitosis.
    • In animal cells, assembly of spindle microtubules begins the centrosome (Microtubule-organizing center [MTOC])
    • The centrosome replicates during interphase and two centrosomes migrate to opposite ends of the cell during prophase and prometaphase
    • During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes, and begin to move the chromosomes.
    • Kinetochores are protein complexes associated with centromeres
    • At metaphase, the chromosomes are all lined up at the metaphase plate.
    • In anaphase, cohesins are cleaved by the enzyme separase.
    • Sister chromatids separate and move along the kinetochore microtubules toward opposite sides of the cell.
    • The microtubules shorten by depolymerizing at their kinetochore ends.
    • Non-kinetochore microtubules from opposite poles overlap and push against each other, elongating the cell.
    • Cytokinesis begins during anaphase or telophase, and the spindle eventually disassembles

    Comparing cytokinesis in animal and plant cells

    • In animal cells, cytokinesis involves a cleavage furrow.
    • A contractile ring of microfilaments forms during cytokinesis in animal cells.
    • In plant cells, a cell plate forms during cytokinesis.
    • Vesicles contain cell wall material derived from the Golgi apparatus.

    How do cells know when to divide?

    • Cell Cycle is tightly regulated.
    • Some cells divide frequently (intestinal cells) and others rarely divide (neuronal cells).
    • Cancerous cells escape the usual controls and proliferate.

    Molecular Clocks

    • The cell cycle is driven by specific chemical signals present in the cytoplasm.
    • The cell cycle is directed by a distinct cell cycle control system, which is similar to a clock.
    • The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received.

    Cellular Checkpoints

    • Changes in regulatory protein concentrations drive the cell cycle.
    • Three important checkpoints are in the G1, G2, and M phases
    • If the cell doesn’t receive the go-ahead signal, it will exit the cycle and switch to a non-dividing state (G0 phase).

    Cancer Cells

    • Lose their cell cycle checkpoints due to internal and/or external factors.
    • Become immortal and continuously divide provided they have enough nutrients
    • HeLa cells: Harvested from a woman named Henrietta Lacks (1951)

    Chapter 13: Meiosis

    • A special type of cell division that can produce sperm and egg cells (gametes).
    • Produces non-identical daughter cells.
    • Heredity is the transmission of traits from one generation to the next.
    • Variation is demonstrated by the differences in appearance that offspring show from parents and siblings.
    • Genetics is the scientific study of heredity and variation.

    Inheritance of Genetic Material

    • Offspring inherit genetic material from parents.
    • Genes are the units of heredity and are made of segments of DNA.
    • Locus (plural, loci): A gene's specific position along a chromosome.
    • Genes are passed to the next generation via reproductive cells called gametes (sperm and eggs).
    • Offspring acquire genes from parents by inheriting chromosome
    • Most DNA packaged into chromosomes.
    • Human somatic cells have 23 pairs of chromosomes (total of 46).
    • Karyotype: An ordered display of the pairs of chromosomes from a cell.

    Comparison of Asexual and Sexual Reproduction

    • In asexual reproduction, a single individual passes all of its genes to its offspring.
    • A clone is a group of genetically identical individuals from the same parent.
    • In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents.

    Cellular Organization of the Genetic Material

    • Somatic cells: Non-reproductive cells, with two sets of chromosomes (diploid).
    • Gametes: Reproductive cells (sperm and eggs), with half as many chromosomes as somatic cells (haploid). In an unfertilized egg, the sex chromosome is X, in a sperm either X or Y.

    Sets of Chromosomes in Human Cell

    • Human somatic cells have 23 pairs of chromosomes.
    • The sex chromosomes are called X and Y.
    • Human females have a homologous pair of X chromosomes (XX).
    • Human males have one X and one Y chromosome.
    • The remaining 22 pairs of chromosomes are called autosomes.
    • Aneuploidy: Abnormal number of chromosomes.

    Sets of Chromosomes in a Cell

    • The homologous chromosomes, or homologs, are the two chromosomes in each pair.
    • Chromosomes in a homologous pair are the same length and shape, and carry similar genes.
    • Each pair of homologous chromosomes includes one chromosome from each parent.
    • Nonsister chromatids are chromatids in a homologous pair, one from each parent.

    Behavior of Chromosome Sets in the Human Life Cycle

    • A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism.
    • Fertilization: The union of gametes.
    • The fertilized egg is called a zygote, which has one set of chromosomes from each parent.
    • The zygote produces somatic cells by mitosis, and develops into an adult.

    Animal Life Cycles

    • Gametes fuse to form a diploid zygote that divides by mitosis to develop into a multicellular organism.
    • Only diploid cells can undergo meiosis.
    • The halving and doubling of chromosomes contributes to genetic variation in offspring.

    Meiosis

    • Meiosis reduces the number of chromosome sets from diploid (2n) to haploid (n).
    • Meiosis is preceded by replication of chromosomes
    • Meiosis takes place in two consecutive cell divisions: meiosis I and meiosis II.
    • Meiosis I involves separation of homologous chromosomes.
    • Meiosis II involves separation of sister chromatids.
    • The two cell divisions result in four haploid daughter cells, rather than the two daughter cells in mitosis.
    • Each daughter cell has only half as many chromosomes as the parent cell.
    • Crossover allows for genetic recombination.

    Comparing Mitosis and Meiosis

    • Mitosis:
    • Conserves the number of chromosome sets.
    • Produces cells that are genetically identical to the parent cell.
    • Meiosis:
    • Reduces the number of chromosomes sets from two (diploid) to one (haploid).
    • Produces cells that differ genetically from each other and from the parent cell.

    Events Unique to Meiosis I

    • Synapsis: The pairing of homologous chromosomes followed by crossing over.
    • Crossing over: Exchange of genetic material between homologous chromosomes.
    • Homologous pairs at the metaphase plate
    • Separation of homologs during anaphase I

    Meiosis I Separates Homologues

    • Two consecutive cell divisions = four haploid daughter cells
    • Synapsis and crossing over
    • Homologous pairs at metaphase plate
    • Separation of homologs

    Meiosis II Separates Sister Chromatids

    • Very similar to mitosis.
    • Sister chromatids separate during anaphase II.
    • Four haploid daughter cells result

    Results of Meiosis

    • Chromosomes duplicate before meiosis.
    • Pairs of homologs and crossover at chiasma allows for genetic recombination.
    • The chromatids are sorted into four haploid daughter cells.

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