Bio Chapter 7 Questions

from study guides

What processes is cell division necessary for? And what do they each do?

• cell division is necessary for organism growth, tissue repair, maintenance, and reproduction (sexual and asexual)

• Mitosis: growth/development and tissue repair and maintenance

  • Binary fission

• Meiosis: sexual reproduction

  • gametes

How do asexual and sexual reproduction differ? Describe each process

• Sexual Reproduction: produces gametes (sperm and eggs) that are fused together through fertilization to produce offspring with genetic information

  • meiosis: two rounds of cell division to produce gametes

  • fertilization: fusion of two gametes produce via meiosis

  • offspring are genetically unique

• Asexual Reproduction: directly produces offspring through cell division

  • binary fission: prokaryotes- unicellular bacteria

  • genetic variation is due to mutations or changes in DNA sequence caused by environmental factors or errors in DNA replication

Describe the two processes involved in sexual reproduction. How do these work together to produce offspring?

1. Meiosis: two rounds of cell division to produce gametes (sperm and eggs)

   1. produces 4 genetically unique haploid gametes

2. Fertilization: fusion of two gametes produced via meiosis

the gametes are fused together through fertilization to produce offspring with genetic information

Describe the two forms of cell division that are used in asexual reproduction. Which groups of organisms use each

1. Binary Fission: daughter cells identical to mother cell

   1. Cell division signals: prokaryotic cells divide constantly if environment is favorable

   2. DNA replication: circular DNA passes through a replication matrix, beginning at ori site (origin) and moving toward ter site (terminus)

   3. DNA segregation: as replication proceeds, ori regions move toward opposite ends of the cell by moving along cytoskeleton filaments

   4. Cytokinesis: cytoplasm divides

• used by prokaryotes bacteria and archaea

1. Mitosis— similar to binary fission, few differences

   1. cell division signals depend on function of entire organism

   2. DNA replication starts at mutliple sites on chromosome

   3. eukaryotes have multiple chromosomes to be segregated

   4. cytokinesis is similar, but plant cells have a cell wall

Describe the general series of events that occur during cell division.

1. cell division signals: initiate cell division

2. DNA replication: create a copy of cell’s genetic info

3. DNA segregation: distribute copies of DNA into two new cells

4. Cytokinesis: division of the cytoplasm to form two new cells

Describe what happens to the: cell membrane, nuclear envelope, centrosomes, and chromosomes during cell division.

• Cell membrane: elongates and splits during cytokinesis

• Nuclear Envelope: stays the same until it is eventually degraded and then re-formed into two new ones

• Centrosomes: important for segregating the DNA

• Chromosomes: contain the genetic info

List and describe the phases and sub-phases of the eukaryotic cell cycle

1. Interphase

   1. Gap1 phase- cells carry out normal functions

   2. S phase- DNA replicated

   3. Gap2 phase- cells prepared for mitosis

2. M phase

   1. mitosis- PPMAT

   2. cytokinesis- division of cytoplasm, results in two daughter cells

Explain how meiosis and fertilization both work together to create genetically diverse offspring

Gametes are unique haploid cells that (when combined) form a genetically distinct zygote. Meiosis produces four unique cells through crossing over and independent assortment. Fertilization merges these unique gametes to form a new diploid individual.

Describe the parts and genetic makeup of a single unreplicated chromosome in contrast to a homologous pair of replicated chromosomes. How many chromosomes and chromatids are present in each?

• single, unreplicated chromosome: long strand of DNA

• replicated chromosome: after S phase (meiosis), chromosomes are now composed of two identical copies called sister chromatids

• homologous chromosomes: a pair of matching chromosomes, one inherited from each parent —> two pairs of sister chromatids

Describe the process of crossing over, and explain how it leads to genetic diversity in the gametes that are produced by meiosis.

• Crossing over occurs between homologs at chiasmata —> sections of DNA are exchanged which increases

• Crossing over can occur at any point along the length of the homologous chromosomes

• Genetic diversity —> genetic recombination: rearrangement of DNA sequences by breaking and rejoining chromosomes segments

Explain how the stages of mitosis, meiosis I, and meiosis II differ.

• Meiosis: gametes are produced

  • four genetically distinct haploid gametes

• Mitosis: somatic cells are produced

  • two identical cells

• Mitosis is done and the cell undergoes cytokinesis. Meiosis II followed cytokinesis and is nearly identical to mitosis!

Describe how the chromosomal makeup of a parent cell is different from the four daughter cells produced through meiosis. Also, how do the daughter cells compare to each other?

• Meiosis reduced the chromosomal makeuip of a parent cell by producing 4 daughter cells (gametes) that are haploid, but they contain only half of the chromosomes compared to the diploid parent cell —> the daughter cells are genetically unique, and possess new combinations of DNA

• daughter cells are genetically unique to each other and the parent cells (in meiosis)

Explain how nondisjunction results in aneuploidy. Explain the process and the results of this error in cell division.

• Nondisjunction happens when homologous chromosomes/sister chromatids fail to separate during Anaphase, which causes aneuploidy, or an abnormal number of chromosomes in the cell

  • daughter nucleus has an extra chromosome

  • daughter nucleus is missing a chromosome

• Nondisjunction in meiosis: homologous pair fails to separate in Anaphase I —> 4 gametes: two with chromosome missing, and two with extra copy

  • can also occur in Anaphase II with sister chromatids not separating

• Nondisjunction in mitosis: sister chromatids fail to separate —> one cell lacks daughter chromosome, other cell has an extra

Describe the resulting karyotype of a trisomic individual compared to a monosomic individual. Explain what type of gametes were fused to produce each.

• Trisomic zygotes: (2n+1) have an extra chromosome

  • sperm lacking copy of a chromosome fused with an egg

• Monosomic zygote: (2n-1) missing a chromosome

  • sperm with an extra copy of chromosome fused with an egg

Describe polyploidy and explain the types of errors in cell division and fertilization that can result in polyploidy.

• Polyploidy: organisms with triploid (3n), tetraploid (4n) and even higher numbered cells —> this is opposed to haploid and diploid with 1 and 2 unbound chromosomes

• this can occur due to:

  • failure of the spindle to form

  • failure of cytokinesis

  • polyspermy (more than one sperm fertilizes the egg)

• common in plants and fungi

• rarely beneficial in animals (except fish, amphibians, and leeches)

Describe why the cell cycle must be regulated in unicellular organisms and contrast that with multicellular organisms.

• Unicellular organisms: population growth and crash (overuse resources)

• Multicellular organisms: cells might not benefit the organism as a whole

  • cancer or non-functional tissues

Describe what the cell cycle checkpoints are generally regulating

Four checkpoints

1. Gap1 checkpoint: progression through the restriction point requires sufficient resources within the cell, lack DNA damage, and external signals

2. S checkpoint: requires lack of DNA damage and completed replication

3. Gap2 checkpoint: requires lack of DNA damage

4. M checkpoint: will arrest if a chromosome is not attached to microtubules from both poles

Explain the process of eukaryotic cell cycle regulation via CDKs, cyclins, and checkpoint proteins

• the four checkpoints are regulated by cyclin-dependent kinases (CDKs)

  • CDKs are protein kinases

  • CDKs are activated by binding to cyclin

    • cyclin are regulatory proteins synthesized when the cell receives signals telling it that it can pass through a checkpoint

  • CDKs phosphorylate checkpoint proteins that regulate these checkpoints

    • phosphorylate = add a phosphate group via kinases (uses ATP)

• Regulation via CDKs

  • specific cyclin produced in response to cell signals

  • Cyclin binds to CDK

  • specific proteins attach are phosphorylated

  • phosphorylated proteins then regulate cell cycle

Compare/contrast necrosis and apoptosis. Think about the situations when each would occur.

• Necrosis: cell is damaged or starved of oxygen

  • happens when an organism dies

• Apoptosis: genetically programmed cell death if cell is malfunctioning, infected, no longer needed, or reached its Hayflick limit

  • stem cells lack a Hayflick limit: develop into many new specialized cells which are important for growth and repair of tissues

  • cancer cells lack a Hayflick limit: cells divide without restraint because they do not require external signals or respond to cell cycle checkpoints

Describe the various mutations that impact cell cycle regulation that can result in unregulated cell division (which could lead to cancer).

Cell cycle regulation mutations can lead to cancer

• cells produce mutated CDKs that do not need cyclins

• cells produce cyclins w/o cell division signals

• cells lack functional checkpoint proteins

• cells lack functional apoptosis machinery