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Cell division Flashcards

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1
Q

What is Chromatin?

A

combination of DNA and proteins that make up chromosomes

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2
Q

What is a chromosome?

A

» In cell cycle, chromosome is a tightly coiled form
of the DNA-protein complex
» In molecular biology, “chromosome” simply
means “DNA strand and associated proteins”

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3
Q

What are Chromatids

A

Identical copies of the same chromosome (“sister chromatids”), joined by the centromere

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4
Q

What is cell division

A

How cells reproduce (ie, 1 parent cell divides into 2
daughter cells)
» In unicellular organisms (prokaryotes, some eukaryotes) cell division = reproduction
» In multicellular organisms, simple cell division enables growth (eg, to replace damaged tissue)

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5
Q

What is a daughter cell?

A

genetically identical to parent cell and each other

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6
Q

How do different cells divide?

A

Prokaryotes divide by binary fission.

Eukaryotes divide by mitosis or meiosis

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7
Q

What is Binary fission and how does it work?

A

It is the way a prokaryote divides
1. Copy genome
• From one origin of replication, replicate DNA in both
directions to produce 2 large circular chromosomes
• Tightly pack chromosomes w/ special proteins + “supercoiling”
2. Increase cell size
3. Split into two daughter cells

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8
Q

What is Mitosis?

A

Typical cell division, growth and repair

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9
Q

What is Meiosis

A

» Necessary for sexual reproduction
» Additional steps to avoid excess DNA and increase
genetic variability of offspring

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10
Q

Mitosis is only a small part of the cell cycle, what is the estimated time for the cycle?

A

» In normal human cell cycle (~24h):

interphase ~23h and mitosis <1h

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11
Q

How is DNA copied & packaged in Eukaryotic cell division?

A
  • During S phase
    » Copy all DNA (ie, multiple chromosomes) starting from many points of origin
  • In early stages of mitosis
    » Condense into tightly packed chromatin fibres wrapped around special proteins called “histones”
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12
Q

When was the first record of mitosis?

A

1882: Flemming records process of mitosis

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13
Q

What happens in the interphase?

A

» G1: cell growth, normal gene expression
» S: copy DNA
» G2: cell growth, duplicate organelles

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14
Q

What happens in Mitosis?

A

PPMAT

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15
Q

What happens in Cytokinesis?

A

2 new cells divide

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16
Q

What does the first P in PPMAT stand for?

A

P - prophase is where the chromosomes become visible as paired chromatids and the nuclear envelope disappears.

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17
Q

What does the second P in PPMAT stand for?

A

P - prometaphase is the process that separates the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells

18
Q

What does the M stand for in PPMAT?

A

M - metaphase is where the chromosomes become attached to the spindle fibres.

19
Q

What does the A stand for in PPMAT?

A

A - anaphase is where the chromosomes move away from one another to opposite poles of the spindle.

20
Q

What does the T stand for in PPMAT?

A

T - telophase is where the chromatids or chromosomes move to opposite ends of the cell and two nuclei are formed.

21
Q

What is Cytokinesis?

A

The cytoplasmic division of a cell at the end of mitosis or meiosis, bringing about the separation into two daughter cells.

22
Q

How does Cytokinesis work?

A
  • Actin microfilaments form a ring on inside of cell membrane, in middle of dividing cells (at location of metaphase plate) → forms a narrow groove (“cleavage furrow”)
  • Filaments are drawn together, pinching the cell membrane together → separates cytoplasm into 2 identical daughter cells
23
Q

What happens if there are errors in the cell cycle?

A
  • Errors in cell cycle can lead to uncontrolled cell growth, which can
    lead to cancer
  • Essentially, cancer is a disease of mitosis
24
Q

How many sets of chromasomes do most eukaryotes have?

A

Most eukaryotes have two sets of homologous chromosomes
» Referred to as “diploid (2n)”
» eg, humans have 46 chromosomes, but in fact
23 pairs (n = 23, 2n = 46)

25
Q

What are organisms with only one set of chromosomes called?

A

Organisms that have only 1 set of chromosomes (1n) are called “haploid”

26
Q

what is sexual reproduction

A

Fusion of two cells from different individuals

27
Q

How many chromosomes are needed for sexual reproduction to be possible?

A

For sexual reproduction to be possible, organisms need to produce cells with half the number of chromosomes as the parental cell = “gametes”

28
Q

What does mitosis produce?

A
  • Mitosis

» Produces 2 genetically identical diploid cells (ie, each has 2n chromosomes)

29
Q

What does Meiosis produce?

A
  • Meiosis

» Produces 4 haploid cells with half the number of chromosomes as parent cell (ie, each has 1n chromosome)

30
Q

What are the three types of sexual life cycles?

A
  • Animals
  • plants and some algea
  • Most fungi and some protists
31
Q

What is the first main stage of meiosis?

A 
- Meiosis I: separate homologous chromosomes and reduce number by half (ie, 2n → n)
» Prophase I and Prometaphase I
» Metaphase I
» Anaphase I
» Telophase I and cytokinesis
- No DNA replication
32
Q

What is the second main stage of meiosis?

A 
Meiosis II: separate sister chromatids (≈ mitosis)
» Prophase II and Prometaphase II
» Metaphase II
» Anaphase II
» Telophase II and cytokinesis
33
Q

Meiosis stages diagram

A 
1 diploid cell
2n chromosomes
(each w/ 2 chromatids)
          |
2 haploid cells
1n chromosome
(each w/ 2 chromatids)
          |
4 haploid cells
1n chromosome
(each w/ 1 chromatid)
34
Q

What are the two special events in Meiosis?

A
  • Synapsis (during prophase I)
    » Homologous pairs of chromosomes bind together (forming “tetrads”)
  • Crossing over
    » Large sections of chromosomes are exchanged during synapsis
35
Q

What is Asexual reproduction?

A

Asexual reproduction (by mitosis)
» Produces 2 identical daughter cells (clones)
» Allows reproduction from a single cell

36
Q

which form of reproducion is Meiosis?

A

Sexual reproduction (by meiosis)
» Produces 4 haploid daughter cells (“gametes”), genetically different from parent and from each other
» Requires 2 organisms, each providing 1 haploid (male provides sperm, female provides egg)

37
Q

What is the advantage of Meiosis?

A

Meiosis produces much greater genetic diversity than mitosis
» Independent assortment → new combinations
» Crossing over → mixing chromosomes

38
Q

What are the advantages of genetic variability?

A

Genetic diversity provides greater flexibility to adapt to changes in the environment
» Asexual reproduction creates exact clones. Good if species is well adapted to its environment but if environment changes it takes time to adapt
» Sexual reproduction creates different “versions”. Some may be better adapted to various environments, so if environment changes, there are already well-suited “versions”

39
Q

How do mitochondria and chloroplasts divide?

A

mitochondria (and chloroplasts) have their own DNA,

and divide by binary fission

40
Q

Where are the mitochondria inherited from?

A

In sexual reproduction, mitochondria are inherited exclusively from the mother (mitochondria in sperm are destroyed by egg after fertilisation)
» Analysis of mitochondrial DNA (mtDNA) can help establishing maternal ancestry (and evolutionary history)

Biology (27 decks)

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