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alevel biology ocr > cell cycle + mitosis, meiosis , stem cells > Flashcards

cell cycle + mitosis, meiosis , stem cells Flashcards

1
Q

how much of a cell life does it spend in interphase

A

90-95%

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2
Q

how many divisions take place in mitosis

A

1 nuclear
1 cytoplasmic

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3
Q

daughter cells are what to the parent cell

A

genetically identical to the parent cell

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4
Q

in eukaryotes the cell cycle is divided into 2 major phases

A

interphase and the mitotic phase

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5
Q

is interphase an active or passive phase and what does that mean

A

active as respiration occurs

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6
Q

what are the 3 phases in interphase

A

gap/growth stage (G1)
synthesis (S)
gap/growth stage (G2)

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7
Q

what happens in G1

A

getting dna ready to replicate
cytoplasm increases in volume as it will need to be shared (so growth in cell size)
production of proteins for organelles to be replicated

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8
Q

what happens in the S phase

A

dna replication so that its ready for mitosis

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9
Q

what happens in the G2 phase

A

ATP levels increased ready for mitosis
increases in cell size due to increase in cytoplasm volume.
error checking

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10
Q

where is the centromere located

A

in the centre of a chromosome

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11
Q

in a relicated chromosome (x) what are the 2 branches called

A

sister chromatids

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12
Q

what is a pair of homologous chromosomes

A

The two chromosomes in a homologous pair are very similar to one another and have the same size and shape. Most importantly, they carry the same type of genetic information: that is, they have the same genes in the same locations. However, they don’t necessarily have the same versions of genes.

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13
Q

what is never visible in interphase

A

chromosomes

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14
Q

how long does the cell cycle take for a human cell

A

24hrs ish

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15
Q

the cell cycle in not a life cycle as it happens

A

repeatedly

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16
Q

chromatin is wrapped around

A

histone proteins

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17
Q

what is not visible in interphase

A

chromosomes, so dna is visible as chromatin

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18
Q

an x looking chromosome means that

A

the chromosomes have been replicated

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19
Q

what happens at the G1 (end) checkpoint

A

check for:
nutrients (energy)
growth factors
dna damage

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20
Q

if the G1 checkpoint fails then what will happens

A

it will enter G0

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21
Q

how can cancer cells replicate freely

A

they reproduce quickly and over produce growth factors and so can slip through the checkpoints

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22
Q

what happens at g2 checkpoint

A

check for:
cell size
dna replication (faults)

if there is a fault then the process pauses and it will be repaired, otherwise faulty dna will be passed on daughter cells

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23
Q

which stage of mitosis has a checkpoint

A

metaphase

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24
Q

what happens at the metaphase checkpoint

A

checks that all the chromosomes are attached to spindle fibres and that they are aligned

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25
Q

chromosome/dna activity in interphase

A

dna replicates but is visible as chromatin not chromosomes

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26
Q

status of the nuclear envelope in interphase

A

present and intact, complete

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27
Q

what else happens in interphase but only in animal cells

A

centrioles replicate

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28
Q

what is the chromosome activity in prophase

A

early: chromatin condenses and coils to form chromosomes, this will appear darker as it will take up more stain

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29
Q

status of the nuclear envelope in prophase

A

it breaks down but only lateron

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30
Q

what happens to the sf in prophase

A

they form from the centrioles and migrate to the poles

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31
Q

chromosome activity in metaphase

A

align at the equator on the metaphase plate which is held in place

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32
Q

status of the nuclear envelope in metaphase

A

not present

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33
Q

sf activity in metaphase

A

they attach to the centromeres of the chromosomes

34
Q

which phase of mitosis is the longest and why

A

metaphase because it has a checkpoint

35
Q

chromosome activity in anaphase

A

sister chromatids separate

36
Q

is there a nuclear envelope in anaphase

A

no

37
Q

sf activity in anaphase

A

sf contract (shorten) pulling the sister chromatids apart and towards the poles

38
Q

what shape does the sister chromatid make when it is pulled by a sf

A

a v shape

39
Q

chromosome activity in telophase

A

chromatids assemble at opposite poles

40
Q

status of nuclear envelope at telophase

A

reforms around each set of chromosomes at each pole

41
Q

what else happens in prophase

A

the nucleolus breaks down

42
Q

what else happens in telophase

A

the nucleuolus reforms

43
Q

sf activity in telophase

A

they breakdown and detatch from sister chromatids

44
Q

why is mitosis important

A

tissue repair and replacement of damaged cells

organism growth: derive new cells via mitosis

asexual reproduction

development of embryos: zygotes undergo mitosis and differentiate to become embryos

45
Q

what does the centromere do

A

keeps the 2 sister chromatids together

sf attach to the kineticore

46
Q

what is used for looking for faults in dna

A

carrier type

47
Q

do prokaryotes carry out mitosis

A

no

48
Q

how long do rbcs live for

A

120 days

49
Q

how many divisions does meiosis

A

2 nuclear
2 cytoplasmic

50
Q

what type of cells does mitosis make

A

somatic

51
Q

what type of cells does meiosis make

A

gametes

52
Q

does crossing over occur in mitosis or meiosis

A

meiosis

53
Q

reason for meiosis

A

to make gametes for sexual reproduction, without haploid gametes a diploid zygote would not be possible

54
Q

in asexual reproduction there is no ……. as the offspring are…….. of the parent. this is because they inherit the same …… as the parents.

A

variation

clones
genes

55
Q

in sexual reproduction each …… is different. therefore when…… occurs chromosomes from the father mixed with chromosomes from the mother so the offspring have a combination of ….. giving rise to variation

A

gamete
fertilisation
alleles

56
Q

gametocytes (germline cells) are what

A

eukaryotic germ cells that divide by meiosis into gametids during gametogenisis

57
Q

male gametocytes are called

A

spermatocytes

58
Q

female gametocytes are called

A

oocytes

59
Q

what happens in prophase I in meiosis

A

dna condenses and chromosomes become visible

homologous chromosomes undergo synapsis whereby they pair up to form a bivalent,

are held together at points called chiasmata.(where the crossing over occurs)

centrioles migrate to the opposite poles and the spindle is formed

the nuclear envelope breaks down and the nucleolus disintegrates

60
Q

which stage does crossing over occur in meiosis

A

prophase 1 ONLY

61
Q

how many bivalents in a human cell

A

23 (a pair of chromsomes=1)

62
Q

result of prophase 1

A

physical change of genetic material and all 4 haploid daughter cells will be genetically distinct as the sister chromatids will no longer be identical

once the chiasmata are formed the homologous chromosomes fully condense as bivalents and then are separated (later)

63
Q

what happens in metaphase 1

A

the bivalents line up along the equator (mp) of the spindle (RANDOMLY) with the sf attached to the centromeres. independent assortment occurs. nuclear membrane fully breaks down

64
Q

what is independent assortment

A

occurs during metaphase 1. the maternal and paternal pairs of chromsomes position themselves separate from the others and can end up facing either pole (orientation) so can result in many different combinations of alleles facing the poles, IA results in genetic variation

65
Q

what happens in anaphase 1

A

the homologous pairs are pulled by sf to the opposite ends of the spindle (whole chromosomes), the centromeres do not divide
v shape created

66
Q

what happens in telophase 1

A

sf start to break down
nuclear envelopes start to form around the 2 groups of chromosomes and nucleoli reform.

67
Q

what can be different about plant cells in meiosis

A

some go straight to meiosis 2 without the reformation of the nucleus in telophase 1

68
Q

cytokinesis in animals

A

cell surface membrane pinches inwards, by the cytoskeleton, creating a cleavage furrow in the middle of the cell which contracts dividing the cytoplasm in half

cleavage furrow forms around the middle of the cell and the cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle forming two cells

69
Q

cytokinesis in plants

A

plant cells have cell walls so a cleavage furrow cannot form.

vesicles from the golgi begin to assmble in the same place the metaplate was formed.

70
Q

what else generally happens in cytokinesis

A

the cell organelles also get distributed between the 2 developing cells

71
Q

there is no ……… between meiosis 1 and meiosis 2 so the dna is … ……..

A

interphase
not
replicated

72
Q

what happens in prophase 2

A

the nuclear envelope breaks down and chromosomes condense

a spindle forms at a right angle to the old one

there is no pair of chromosomes so crossing over cannot occur

73
Q

what happens in metaphase 2

A

chromosomes line up in a single file along the equator of the spindle, IA can occur

74
Q

define stem cell

A

a cell that is unspecialised and undifferentiated

75
Q

what 2 qualities of stem cells

A

self renewal and potency

76
Q

what is self renewal

A

they can continuously divide and replicate

77
Q

what is potency

A

they have the capacity to differentiate into specialised cell types

78
Q

what is the potency and source of totipotent stem cells

A

p: can form any cell type including extra embryonic tissue (total potential)

s: zygote during the first mitotic divisions (first 1-4 days)

79
Q

potency and source of pluripotent (embryonic) stem cells

A

p: can form any cell type but cannot form whole organisms

s: early embryos/blastocysts

80
Q

potency and source of multipotent (adult) stem cells

A

p: can differentiate into a number of closely related cell types within a tissue
s

81
Q

what are haemopoietic stem cells

A

multipotent, found in bone marrrow and long bones not brain or muscle

82
Q

unipotent stem cells

A

cannot differentiate but can self renew eg muscle stem cells

alevel biology ocr (19 decks)

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