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Biology SL > 1.6 Cell Division > Flashcards

1.6 Cell Division Flashcards

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1
Q

what is interphase?

A

the stage in the development of a cell between 2 successive divisions
an active period in the cell cycle when many metabolic reactions occur

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2
Q

what are the 3 stages of interphase?

A

G1 - first intermediated gap stage in which the cell grows and prepares for DNA replication
S - synthesis stage in which DNA is replicated
G2 - second intermediate gap stage in which the cell finishes growing and prepares for cell division

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3
Q

what is M phase?

A

the period of the cell cycle in which the cell and contents divide to create 2 genetically identical daughter cells

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4
Q

what are the two broad stages of cell M phase?

A

mitosis - nuclear division whereby DNA is separated into 2 identical nuclei
cytokinesis - cytoplasmic division, whereby cellular contents are segregated and the cell splits into 2

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5
Q

what events need to occur in interphase to prepare the cell for successful division? (6)

A

DNA replication - DNA is copied during S phase
Organelle duplication - organelle must be duplicated for twin daughter cells
Cell growth - cytoplasmic volume must increase prior to division
Transcription/translation - key proteins and enzymes must be synthesised
Obtain nutrients - vital cellular materials must be present before division
Respiration (cellular) - ATP production is needed to drive the division process

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6
Q

what are the characteristics of chromatin? (3)

A
  • DNA is loosely packed within the nucleus as unravelled chromatin
  • this unravelled form, DNA is accessible to transcriptional machinery and so genetic information can be translated
  • DNA is organised as chromatin in all non-dividing cells and throughout the process of interphase
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7
Q

what are the characteristics of chromosomes? (3)

A
  • DNA is temporarily packaged into a tightly wound and condensed chromosome prior to divisions (via supercoiling)
  • in the condensed form, the DNA is able to be easily segregated however, is inaccessible to transcriptional machinery
  • DNA is organised as chromosomes during the process of mitosis (condensed in prophase, decondensed in telophase)
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8
Q

what are the differences and similarities between chromosomes and chromatins? (4)

A
  • chromosome is condensed form of DNA which is visible during mitosis (via microscopy)
  • as the DNA is replicated during the S phase of interphase, the chromosome will initially contain 2 identical DNA strands
  • these genetically identical strands are called sister chromatids and are held together by a central region called centromere
  • when these chromatids separate during mitosis, they become independent chromosomes each made of a single DNA strand
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9
Q

what is mitosis and the stages?

A

the process of nuclear division whereby duplicated DNA molecules are arranged into 2 separate nuclei
prophase, metaphase, anaphase, telophase

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10
Q

what occurs in interphase? (4)

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 division is enlarged in preparation for division
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11
Q

what occurs in prophase? (4)

A
  • DNA supercoils and chromosomes condense (visible under microscope)
  • chromosomes are comprised of genetically identical sister chromatids (joined at a centromere)
  • paired centrosomes move to the opposite poled of the ell and form microtubule spindle fibres
  • the nuclear membrane breaks down and the nucleus dissolves
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12
Q

what occurs in metaphase? (3)

A
  • the microtubule spindle fibres from both centrosomes connect to the centromere of each chromosome
  • microtubules depolymerization 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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13
Q

what occurs in anaphase? (3)

A
  • continued contraction of the spindle fibres causes genetically identical sister chromatids to separate
  • once the chromatids separate, they are considered an individual chromosome
  • the genetically identical chromosomes move to the opposite poles of the cell
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14
Q

what occurs in telophase? (4)

A
  • once the two chromosome sets arrive at the poles, spindle fibres dissolve
  • chromosomes decondense (no longer visible under light microscope)
  • nuclear membrane reform around each chromosome set
  • cytokinesis occurs concurrently, splitting the cell into 2
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15
Q

what is cytokinesis? (2)

A
  • the process of cytoplasmic division, whereby the cell splits into 2 identical daughter cells
  • cytokinesis occurs concurrently with the final stages of mitosis (telophase) and is different in plant and animal cells
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16
Q

how does cytokinesis occur in animal cells? (4)

A
  • after anaphase, microtubule filaments form a concentric ring around the centre of the cell
  • the microfilaments constrict to from a cleavage furrow which deepens from the periphery towards the centre
  • when furrow meets in the centre, the cells becomes completely pinched off and two cells are formed
  • this separation occurs from the outside and move towards the centre, it is described as centripetal
17
Q

how does cytokinesis occur in plant cells? (4)

A
  • after anaphase, carbohydrate-rich vesicle form in a row at the centre of the cell (equatorial plane)
  • the vesicle fuse together and an early cell plate begins to form within the middle of the cell
  • the cell plate extends outwards and fuses with the cell wall, dividing the cell into 2 distinct daughter cells
  • because this separation originates into the centre and moves laterally, described as centrifugal
18
Q

what is mitotic index?

A

measure of the proliferation status of a cell population
- mitotic index may be elevated during processes that promote division, such as normal growth or cellular repair

19
Q

what can mitotic index be used for?

A

can function as an important prognostic tool from predicting the response of cancer cells to chemotherapy

20
Q

how can mitotic index be calculated?

A

is the ratio between the number of cells in mitosis and total number of cells
can be determined by analysing micrograph and counting the relative number of mitotic cells vs non-dividing cells

21
Q

what are cyclins?

A

a family of regulatory proteins that control the progression of the cell cycle

22
Q

what do cyclins acivate?

A

cyclin dependent kinases which control cell cycle processes through phosphorylation

23
Q

how do cyclins work? (3)

A
  • when a cyclin and CDK form a complex, the complex will bind to a target protein and modify it via phosphorylation
  • the phosphorylated target protein will trigger some specific event within the cell cycle
  • after the event has occurred, the cyclin is degraded the CDK is rendered inactive again
24
Q

how are cyclin concentrations tightly regulated in order to ensure that the cell cycle professes in a proper sequence? (2)

A
  • different cyclins specifically bind to, and activate different classes of cyclin dependent kinases
  • cyclin levels will peak when their target protein is required for function and remain at lower levels at all other times
25
Q

what are tumours (or cancers)?

A

abnormal cell growths resulting from uncontrolled cell divisions and can occur in any tissue organ

26
Q

what are mutagens?

A

mutagen is an agent that changes the genetic material of an organism

27
Q

what three things can mutagens be in origin?

A

physical - sources of radiation including X-rays (ionising), ultraviolet (UV) and radioactive decay
chemical - DNA interactive substances including reactive oxygen species (RPS) and metals
biological - viruses, certain bacteria and mobile genetic elements

28
Q

what are mutagens that lead to the formation of cancer called?

A

carcinogens

29
Q

what are oncogenes?

A

a gene that has the potential to cause cancer

30
Q

what are the 2 basic classes of gene most cancers are caused by?

A

proto-oncogenes - code for proteins that stimulate the cell cyles and promote cell growth and proliferation
tumour suppressor genes - code for proteins that repress cell cycle progression and promote apoptosis

31
Q

how can a proto-oncogene become a cancer-causing oncogene?

A

when a proto-oncogene is mutated or subjected to increased expression

32
Q

what are tumour suppressor genes normal function?

A

prevents cancer

33
Q

what two things may tumour cells be?

A

benign - remain in original location
malignant - spread and invade neighbouring tissue

34
Q

what are secondary tumours made of?

A

made up of the same type of cell as primary tumours

35
Q

what kind of links between smoking and the incidence of cancers?

A

strong and contain 4,000 chemical compounds over 60 which are carcinogenic
- strong positive correlation between the frequency of smoking and the development of cancer
increases the risk of ver a dozen other cancers including mouth, stomach, over, pancreas and bowel

Biology SL (38 decks)

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