Cell Division Flashcards

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1
Q

What are the 3 phases within interphase?

A
  • first growth - the cell grows and proteins from which cell organelles are produced are synthesised
  • synthesis - when DNA replicates (not the same as DNA replication - period when this happens)
  • second growth - when organelles e.g. mitochondria grow and divide and energy stores are increased, the cell increases further in size
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2
Q

What is interphase?

A
  • the cell is engaged in metabolic activity in preparation for cell division
  • chromosomes are not visible under a light microscope
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3
Q

What are the stages of the cell cycle?

A
  • interphase
  • nuclear division
  • cytokenesis
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4
Q

What is nuclear division?

A
  • division of the nucleus, either by mitosis or meiosis
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5
Q

What is cytokenisis?

A
  • the process by which the whole cell divides, resulting in an even distribution of organelles and cytoplasm into each daughter cell
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6
Q

How long is the cell cycle?

A
  • varies between organisms
  • typically a mammalian cell takes 24 hours to complete a cell cycle
  • of which 90% is interphase
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7
Q

What is the definition of mitosis?

A
  • the division of the nucleus of a cell that results in each of the 2 daughter cells having an exact copy of the DNA of the parent cell
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8
Q

Are daughter cells genetically identical in mitosis?

A
  • the daughter cells are genetically identical to the parent cells and each other
  • may not be identical due to mutations
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9
Q

Describe interphase

A
  • DNA widely dispersed in the nucleus
  • each molecule replicated to produce a genetically identical molecule
  • metabolic activity to prepare for mitosis (second growth)
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10
Q

Describe prophase

A
  • DNA condenses to form visible chromosomes
  • centrioles migrate to opposite poles of the cell and spindle fibres are formed
  • the nuclear envelope disintegrates
  • chromosomes are randomly arranged
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11
Q

Describe metaphase

A
  • spindle fibres develop fully to form spindle apparatus
  • spindle apparatus stretches from pole to pole
  • chromosomes line up along the EQUATOR of the cell, attaching to spindle fibres by their CENTROMERES
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12
Q

Describe anaphase

A
  • centromeres divide into 2
  • the spindle fibres contract, pulling the chromatids to opposite poles
  • mitochondria gather near the spindle to supply the energy needed
  • (can now be referred to as chromosomes)
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13
Q

Describe telophase

A
  • chromosomes reach opposite ends of the cell and disperse
  • the chromosomes are no longer visible
  • nuclear envelope reforms and the spindle disintegrates
  • new membranes form around daughter nuclei
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14
Q

Describe cytokenesis

A
  • cell divides into 2, producing 2 genetically identical daughter cells
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15
Q

What is the key difference between telophase and cytokenesis?

A
  • telophase - 2 daughter nuclei
  • cytokenesis - 2 daughter cells
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16
Q

What is the definition of meiosis?

A
  • nuclear division that results in the production of 4 daughter cells which all contain half the chromosome number of the parent cell
17
Q

When does meiosis occur?

A
  • during the formation of gametes in the sex organs
  • ovary/testes/stamens/carpel
18
Q

Why is meiosis necessary?

A
  • in sexual reproduction, 2 gametes fuse to give rise to a new offspring
  • require 2 haploid cells to join together to make 1 diploid cell
  • to maintain the number of chromosomes in adults, chromosomes need to be halved in meiosis
19
Q

What does n mean when looking at life cycles?

A
  • n is the number of chromosomes
  • 2n is the full set
  • meiosis happens when 2n halves to n
20
Q

Why is meiosis important?

A
  • produces haploid gametes (egg, sperm, pollen and ovule)
  • introduces genetic variation
21
Q

Describe the first meiotic division (meiosis 1)

A
  • homologous chromosomes pair up and their chromatids wrap around each other
  • equivalent portions of these chromatids may be exchanged in a process called crossing over
  • by the end of this stage, homologous pairs have separated with one chromosome from each pair going at random into one of the 2 daughter cells
  • this is known as independent segregation
22
Q

Describe the second meiotic division (mitosis 2)

A
  • the chromatids move apart
  • by the end of meiosis 2, 4 cells have been formed each containing 23 chromatids (now called chromosomes)
23
Q

How does independent segregation increase genetic diversity?

A
  • during meiosis 1 each chromosome lines up alongside its homologous partner
  • they line up randomly
  • one of each pair will pass into the daughter cell
  • which one goes into which depends on how the homologous pairs line up on the equator/spindle
  • since pairs line up at random, combination of chromosomes that go into daughter cells in meiosis1 are random
24
Q

How does crossing over increase genetic variation?

A
  • during meiosis 1, the homologous pairs of chromosomes associate with each other and line up
  • their chromatids wrap around each other crossing over many times
  • tensions are created and portions of the chromatids break off, these broken portions recombine with the chromatids of the homologous partner
  • homologous pair have effectively swapped portions of their DNA
  • new genetic combinations of paternal and maternal alleles
  • process is known as recombination and happens as a result of crossing over