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Cell & Mole Bio - HES > Lecture 6 - Mitosis and Meiosis > Flashcards

Lecture 6 - Mitosis and Meiosis Flashcards

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Biology 101 flashcards
1
Q

Cell division is…

A

essential for life

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2
Q

Most cell division results in…

A

the distribution of identical genetic information (DNA) to two daughter cells.
-exception: meiosis

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3
Q

Four events required for cell division:

A
  1. Reproductive signals
  2. Replication of DNA
  3. Segregation: distribution of replicated DNA into two new cells
  4. Cytokineses: separation of cellular material into the two “daughter” cells
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4
Q

Prokaryotic cells reproduce by a process of cell division called…

A

binary fission

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5
Q

Prokaryotic cell division (4 steps)

A
  1. Reproductive signals: external factors such as nutrient concentration and environmental conditions.
  2. Replication: involves just one chromosome that is compact/folded and often circular.
  3. Segregation: Daughter DNAS move toward opposite ends, led by ori regions.
  4. Cytokinesis: Plasma membrane pinches in and new cell wall is synthesized.
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6
Q

Eukaryotic cell division (4 steps)

A
  1. Reproductive signals:
    - signals related to needs of entire organism
    - in multicellular organisms, many cells are specialized and do not divide.
  2. Replication:
    - Eukaryotes have >1 chromosomes, so process is more intricate.
  3. Segregation:
    - Sister chromatids are closely associated, newly replicated chromosomes.
    - Mitosis: mechanism separating sister chromatids into new nuclei; daughter cells genetically identical to parent cells.
    - Meiosis: nuclear division of cells involved in sexual reproduction; daughter cells not identical to parent.
  4. Cytokinesis:
    - Plant cells involve formation of cell wall, animal cells do not.
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7
Q

Cell Cycle (2 points)

A
  • Period from one cell division to the next.
  • Consists of…
    1. M Phase: mitosis/cytokinesis
    2. Interphase: long period of growth; duration highly variable among eukaryotic cells; three subphases (G1, S, and G2)
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8
Q

Cell Cycle - Interphase subphases (4 points)

A

G1 phase:
- chromosomes are single
- duration is minutes to years
- may exit to a resting phase (G0) with variable reversibility
- most human cells are in G0 - cardiac cells
G1-to-S transition:
- committed to DNA replication and cell division
S phase:
- DNA replicates; sister chromatids remain together
G2 phase:
- Preparation for mitosis, including synthesis of required proteins

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9
Q

Specific signals trigger cell cycle events including internal signals and external signals, such as…

A

growth factors

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10
Q

Growth factors can initiate cell cycle (3 points)

A
  • external chemical signals that stimulate cells to divide
  • activate cascade of intracellular events
  • particularly relevant for cells that divide slowly or go through G0 (eg. liver regeneration)
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11
Q

Eukaryotic chromosome duplication and distribution (3 points)

A

Before S phase:
- chromosome is single, long DNA molecule + proteins (complex = chromatin)
After replication:
- sister chromatids held together during G2 by cohesins.
At mitosis:
- cohesin is removed except for the centromere region, and condensins coat the DNA molecules to make them more compact.

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12
Q

Eukaryotic DNA is extensively packed and organized by: (2 points)

A
  • Histones: basic proteins (high amount of lysine and arginine) that attract negative phosphate groups of DNA.
  • Nucleosomes: structural units (beadlike) resulting from DNA-histone (and histone-histone) interactions.
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13
Q

Chromosomal structural differences during cell cycle (2 points)

A

Interphase DNA:
- less densely packed
- accessible to proteins involved in replication
Mitotic DNA:
- highly compact
- inaccessible to replication factors (and transcription factors)

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14
Q

Mitosis ensures accurate segregation of chromosomes to daughter cells through…

A

highly organized chromosome segregation and movement.

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15
Q

Organized chromosome separation: Key cellular structures (2 points)

A

Spindle apparatus (mitotic spindle, spindle)
- moves apart sister chromatids
- made of microtubules
- orientation determined by centrosome
Centrosomes (microtubule organizing center)
- cytoplasmic organelle near nucleus
- can consist of two centrioles: each a hollow tube made of nine microtubule triplets; at right angles to each other
- identify “poles” toward which chromosomes move

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16
Q

Spindle apparatus formation (3 points)

A
  • tubulin dimers near centrioles aggregate and extend fibers into middle of cell.
  • kinetochores develop on each chromatid: structure of proteins and chromosomal DNA at centromere
  • Spindle: microtubules form between poles and chromosomes.
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17
Q

Two types of spindle microtubules:

A
  1. Polar microtubules
    - run from one pole to the other
    - forms spindle framework
  2. Kinetochore microtubules
    - attach to kinetochores on sister chromatids and to microtubules in opposite halves of spindle
    - ensure chromatid movement to opposite poles
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18
Q

Organized chromosome separation: chromosome migration (2 points)

A

Chromatid separation

  • cohesion hydrolyzed by separase
  • after separation, chromatids are called daughter chromosomes: chromatids share centromere, chromosomes have own centromere

Chromosome movement

  • kinetochore motor proteins, kinesis and cytoplasmic dynein, move chromosomes along microtubules by energy from ATP hydrolysis
  • kinetochore microtubules shorten from poles
19
Q

Mitosis is subdivided into five phases:

A
  1. prophase
  2. prometaphas
  3. metaphase
  4. anaphase
  5. telophase
20
Q

Interphase (3 points)

A
  1. nucleus is well-defined and bound by nuclear envelope
  2. during S phase, both DNA and centrosomes are replicated
  3. individual chromosomes not discernible
21
Q

Prophase (6 points)

A
  1. chromatin condenses into discrete chromosomes
  2. two sister chromatids are visible - most of cohesin gone
  3. late prophase, kinetochores develop
  4. centrosomes move toward opposite ends of nuclear envelope
  5. spindle beings to form
  6. prepared for chromatid separation
22
Q

Prometaphase (4 points)

A
  1. nuclear envelope fragments
  2. nucleoli disappear
  3. chromosomes attach to the spindle through kinetochore microtubules
  4. kinetochores of sister chromatids are attached to microtubules coming from opposite poles
23
Q

Metaphase

A

chromosomes align on equatorial (metaphase) plate, with centromeres at the midline.

24
Q

Anaphase (2 points)

A
  1. sister chromatids separate, becoming daughter chromosomes

2. move centromere first to opposite poles

25
Q

Telophase (5 points)

A
  1. daughter chromosomes reach poles
  2. by the end, each pole has complete collection of chromosomes
  3. daughter nuclei and nucleoli form at poles
  4. spindle disappears
  5. chromatin becomes less tightly coiled
26
Q

Cytokinesis (3 points)

A
  • After nuclear division, cytokinesis divides cytoplasm
  • Animal cells
    • furrowing of plasma membrane
    • contractile ring of microfilaments (actin and myosin) pinch cell in two
  • Plant cells
    • vesicles from golgi apparatus appear along plane of cell division and fuse to form new plasma membrane
    • content of vesicles form cell plate- beginning of a new cell wall.
27
Q

Following cytokinesis, two genetically identical daughter cells result. Daughter cells do not necessarily contain the same number of…

A

organelles

28
Q

Reproduction cycles involve…

A

mitosis only (asexual reproduction) or both mitosis and meiosis (sexual reproduction)

29
Q

Asexual reproduction (4)

A
  • based on mitotic division of the nucleus
  • unicellular and multicellular organisms (yeast vs. Aspen trees)
  • Clone: offspring is genetically identical to parent
  • genetic variation (if any) from mutations in DNA
30
Q

Sexual reproduction (4)

A
  • offspring is NOT identical to parent.
  • requires GAMETES (reproductive cell) created by meiosis.
  • each parent contributes a gamete
  • meiosis generates genetic diversity and is the foundation for natural selection and evolution.
31
Q

Organisms that reproduce sexually have two types of cells:

A
  1. Somatic cells: body cells not specialized for reproduction.
    • contains homologous pairs of chromosomes
    • each parent contributes one homolog
  2. Gametes: sex cells
    • contains one set of chromosomes.
    • chromosome number is haploid.
32
Q

Fertilization (defn)

A

process during which two haploid gametes (one female egg and one male sperm) fuse together to form a diploid zygote.

33
Q

Meiosis results in daughter cells that…

A

differ genetically from parent cell.

34
Q

Meiosis basics (4)

A
  • consists of two nuclear divisions (meiosis I and meiosis II), but DNA is replicated once.
  • reduces chromosome number from 2n to n
  • each haploid has one complete set of chromosomes
  • generates genetic diversity.
35
Q

Unique features that distinguish Meiosis I from Mitosis (3)

A
  • homologous chromosomes pair up
  • homologous pairs separate but individual chromosomes (two sister chromatids) remain intact
  • results in two nuclei with half of the original chromosomes (one homolog each)
36
Q

Chromatid exchanges during Meiosis I (3)

A
  • during prophase I, homologous chromosomes pair by adhering along their lengths: synapsis
  • four chromatids of a homologous pair form a tetrad.
  • chiasmata form between nonsister chromatids.
    • crossing over is the exchange of genetic material.
  • results in recombinant chromatids and increases genetic diversity.
37
Q

What adds to genetic diversity in meiosis I products?

A

Independent assortment.

38
Q

Unique features that distinguish Meiosis II from Mitosis (4)

A
  • Not proceeded by DNA replication.
  • Due to crossing over in Meiosis I, sister chromatids are not necessarily identical.
  • chance assortment of chromatids contributes to further genetic diversity.
  • final products are four haploid daughter cells (n)
39
Q

Errors in Meiosis: Nondisjunction

A
  • in anaphase I, homologous pairs fail to separate.
  • in anaphase II, sister chromatids fail to separate.
    RESULT: ANEUPLOIDY: abnormal number of chromosomes.
40
Q

Aneuploidy (4)

A
  • may be caused by lack of cohesins that hold sister chromatids and homologous pairs together.
  • aneuploidy in gametes is generally lethal to embryo.
  • exception: eg. down syndrome
  • trisomies and monosomies are common in human zygotes and are the cause of many miscarriages.
41
Q

Other abnormal chromosomal event:

A

Translocation:

  • piece of chromosome may break and attach to another chromosome.
  • occurs with nonhomologous chromosomes and is not the same as crossing over.
  • eg. Down Syndrome.
42
Q
  • Chromosomes can be visualized (3)
A
  • possible to count and characterize chromosomes in metaphase of mitosis.
  • karyotype: number, shapes, and sizes of all the chromosomes of a cell.
  • karyotypes used to diagnose chromosomal abnormalities, branch of medicine called cytogenetics.
43
Q

Some cells have more than 2n (6)

A
  • organisms with complete extra sets of chromosomes are polyploid.
  • triploid (3n), tetraploid (4n), and higher.
  • if nondisjunction of all chromosomes during meiosis I, diploids gametes form, leading to autopolyploidy.
  • even numbered polyploid cells can undergo meiosis
  • triploids cannot undergo meiosis and are usually sterile.
  • polyploid cells tend to be larger and are favored as crop plants (bananas, triploid seedless watermelons, hexaploid wheat)

Cell & Mole Bio - HES (11 decks)

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