1.6 Cell Division Flashcards

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1
Q

Cell Cycle

A

is a series of events that take place in a cell leading to its division and duplication
it includes both mitosis and cell growth
the stages are:
G1 - period of cell growth before DNA is replicated
S - period when DNA is duplicated
G2 - period after DNA is duplicated, cell prepares for cell division
(these three stages are all part of interphase)
Prophase, Metaphase, Anaphase, Telophase and Cytokinesis

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2
Q

Role of Cyclins

A

cyclins are chemicals that undergo periods of chemical synthesis and breakdown as they interact with the cell cycle and the environment to signal the beginning and end of different stages

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3
Q

Why does Mitosis occur?

A

development and growth: number of cells in an organism increases due to mitosis
cell replacement: in some parts of body cells are constantly needing to be replaced
Asexual reproduction: some organisms produce genetically similar offspring by mitosis

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4
Q

What is mitosis?

A

it is the division of the nucleus into two genetically identical daughter nuclei

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5
Q

Interphase

A
  • DNA is present as uncondensed chromatin (not visible under microscope)
  • DNA is contained within a clearly defined nucleus
  • Centrosomes and other organelles have been duplicated
  • Cell is enlarged in preparation for division
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6
Q

Prophase

A
  • DNA supercoils and chromosomes condense (becoming visible under microscope)
  • Chromosomes are comprised of genetically identical sister chromatids (joined at a centromere)
  • Paired centrosomes move to the opposite poles of the cell and form microtubule spindle fibres
  • The nuclear membrane breaks down and the nucleus dissolves
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7
Q

Metaphase

A
  • Microtubule spindle fibres from both centrosomes connect to the centromere of each chromosome
  • Microtubule depolymerisation causes spindle fibres to shorten in length and contract
  • This causes chromosomes to align along the centre of the cell (equatorial plane or metaphase plate)
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8
Q

Anaphase

A
  • Continued contraction of the spindle fibres causes genetically identical sister chromatids to separate
  • Once the chromatids separate, they are each considered an individual chromosome in their own right
  • The genetically identical chromosomes move to the opposite poles of the cell
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9
Q

Telophase

A
  • Once the two chromosome sets arrive at the poles, spindle fibres dissolve
  • Chromosomes decondense (no longer visible under light microscope)
  • Nuclear membranes reform around each chromosome set
  • Cytokinesis occurs concurrently, splitting the cell into two
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10
Q

Cytokinesis differences in Animal and Plant Cells

A

animals lack a cell wall, while plant cells have a cell wall
so in plants a cell plate beings to grow which will become the new cell wall
in animals the cell membranes on opposite sides of the cell become pinched, forming a cleavage furrow until the two sides are touching

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11
Q

Calculating mitotic index

A

is the % of cells undergoing mitosis
mitotic index = (number of cells in mitosis)/(total number of cells) x 100

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12
Q

When do cells become cancerous?

A

when they lose their ability to stop dividing, to attach to other cells, to stay where they belong and to die at the proper time

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13
Q

benign tumours

A

non cancerous

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14
Q

malignant tumours

A

cancerous

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15
Q

Metastasize

A

ability for cells to spread to other parts of the body

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16
Q

Tumour Suppressor Genes

A

are genes that act as the brakes on uncontrolled cell growth
cancer occurs when both copies of the tumour suppressor genes fail to work properly