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A-level biology > 2.1.6 - cell division, cell and organisation > Flashcards

2.1.6 - cell division, cell and organisation Flashcards

1
Q

what are the 4 stages of the cell cycle

A

G1, S, G2 and M (mitosis)

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2
Q

what happens in G1

A

the cell grows and inc size
transcription of DNA to mRNA
organelles duplicate
biosynthesis happens

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3
Q

what is biosynthesis

A

where the enzymes needed for the other stages are made

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4
Q

what gene controls G1

A

p53 (tumour suppressor gene) controls this phase and stops excess growth

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5
Q

what can happen if the p53 gene doesn’t control the cell growth

A

cell may grow too much and develop into a tumour which could be cancerous

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6
Q

what happens at the early G1 checkpoint

A

if the cell isn’t progressing properly, it enters G0

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7
Q

what happens at G0

A

the cell enters to be repaired or sometimes it may have to stay there permanently

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8
Q

what are the reasons that a cell may enter G0 permanently

A

if it has differentiated into a cell that doesn’t go through mitosis
if the DNA is beyond repair

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9
Q

what happens to a cell in G0 if it is beyond repair

A

apoptosis (controlled cell death)
senescence (cell ages until death)

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10
Q

what happens at the G1/S checkpoint

A

if the cell is damaged, it won’t enter the S phase

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11
Q

what happens in the S phase (replication phase)

A

the DNA duplicates

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12
Q

why is the S phase rapid

A

to reduce the chance of mutations

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13
Q

what is the order of the genes that are duplicated in the S phase

A
  1. housekeeping genes (genes switched on in all cell types)
  2. genes active in that cell type
  3. genes normally switched off in that cell type
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14
Q

what happens at the DNA synthesis checkpoint

A

checks that DNA is replicated properly before entering G2

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15
Q

what happens in G2

A

additional growth
energy stores replenished
cytoskeleton dismantled
organelles arranged in the cytoplasm

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16
Q

what happens at the G2/M checkpoint

A

final check before mitosis and special chemicals are produced to help from spindle fibres

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17
Q

what is the M phase

A

where mitosis happens

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18
Q

what happens at the M checkpoint

A

happens 1/2 way through mitosis
the cell won’t enter anaphase if chromosomes aren’t attracted to spindle fibres

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19
Q

what happens during cytokinesis

A

cell membranes and cytoplasm divide to produce 2 genetically identical daughter cells

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20
Q

what happens during prophase in mitosis

A
  • chromosomes condense
  • the nuclear envelope breaks down into vesicles
  • the spindle fibres are formed
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21
Q

what is each chromosome in prophase made of and how is it held together

A

each chromosomes is made of 2 sister chromatids which are held by a centromere

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22
Q

what makes spindle fibres

A

the centrioles make tubulin which makes up the spindle fibres

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23
Q

what happens during mitosis metaphase

A
  • chromosomes align along the equator (metaphase plate)
  • spindle fibres attach to centromeres
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24
Q

what happens in mitosis anaphase

A
  • sister chromatids pulled apart to opposite poles of the cell
  • centromere divides
  • chromatids are called chromosomes again
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25
Q

how are the sister chromatids pulled apart

A

by the motor proteins ‘walking’ along the spindle fibres

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26
Q

what happens during mitosis telophase

A

nuclear membrane reforms from vesicles
spindle fibres disappear and chromosomes uncoil

27
Q

why is the nuclear membrane kept in vesicles

A

because it saves energy rather than rebuilding from scratch

28
Q

what are the mitosis daughter cells identical to

A

the parent cell and eachother

29
Q

the parent ell of meiosis is diploid. What does that mean

A

there are 2 copies of each chromosome one each from the mother and father

30
Q

what happens in meiosis prophase 1

A

chromosomes condense
nuclear membrane breaks down into vesicles
centrioles make spindle fibres
the chromosomes are made of sister chromatids held by a centromere
recombination occurs

31
Q

what is recombination

A

non sister chromatids wrap around each other and exchange sections of DNA

32
Q

what is the bivalent

A

the 2 non sister chromatids crossing over

33
Q

what is the chiasma

A

the specific part where the 2 non sister chromatids cross over during recombination

34
Q

what happens in meiosis metaphase 1

A

homologous pairs (still crossed over) line up at the equator
spindle fibres attach to centromere
independent assortment of chromosomes and independent segregation of chromosomes

35
Q

what is independent assortment of chromosomes

A

homologous pairs align randomly at the equator and could be on either side

36
Q

what is independent segregation of chromosomes

A

how they line up on the equator which determines how they are pulled apart during anaphase

37
Q

what happens during meiosis anaphase 1

A

homologous chromosome pairs pulled to opposite poles by motor proteins
each chromosome made of 2 non sister chromatids
centromeres still holding chromatids together
crossed over section pulled apart

38
Q

what happens during meiosis telophase 1

A

2 new nuclei form from the vesicles
spindle fibres disappear
chromosomes uncoil

39
Q

what is the purpose of meiosis 1

A

halves the chromosome number

40
Q

what happens in meiosis prophase 2

A

nuclear membrane breaks down into vesicles
chromosomes condense
centrioles make spindle fibres
chromosomes still made of 2 chromatids

41
Q

are the chromatids in the chromsomes during prophase 2 sister or non sister

A

non sister due to the crossing over in prophase 1

42
Q

what happens in meiosis metaphase 2

A

chromosomes line up at the equator
spindle fibres attach to centromere
random assortment and random segregation occur

43
Q

what is random assortment of chromatids

A

chromatids are arranged randomly and either side can be facing either pole

44
Q

what is random segregation of chromatids

A

how they arrange themselves along the equator determines how they are pulled apart in anaphase 2

45
Q

what happens in anaphase 2

A

chromatids pulled to opposite poles by motor proteins walking along spindle fibres
centromere divides

46
Q

what happens during telophase 2

A

spindle fibres disappear and nuclear membrane reforms

47
Q

what is the end product of meiosis

A

4 genetically non identical daughter cells that are different to the parent and each other

48
Q

what is the purpose of meiosis 2

A

separates chromatids and each nucleus has the correct number of chromosomes and genetic material

49
Q

what is variation caused by

A

independent assortment and segregation, random assortment and segregation, random fertilisation

50
Q

where do embryonic stem cells come from

A

2-5 day old embryos

51
Q

what can embryonic stem cells differentiate into

A

any cell in the body

52
Q

where are adult stem cells from

A

from certain locations in the body - eg bone marrow

53
Q

pros of embryonic stem cells

A

can differentiate into any cell
uses ‘wasted’ embryos from IVF

54
Q

cons of embryonic stem cells

A

ethical issues
destroying embryo
expensive
immunosuppressants needed

55
Q

pros of adult stem cells

A

no rejection as own cells used
no immunosuppressants needed
no embryos involved

56
Q

cons of adult stem cells

A

only found in certain locations
can only differentiate into the type of cell where it is found
can be painful to extract

57
Q

what are stem cells

A

undifferentiated cells that can express all genes and can self renew

58
Q

what is totipotent

A

can differentiate into any cell in the body and placental cells

59
Q

what is pluripotent (embryonic)

A

any cell in the body but not placental

60
Q

what is multipotent (adult)

A

can only be limited cell types

61
Q

multipotent animal stem cell example

A

bone marrow - can only become blood cells and genes switch on/off to determine type of blood cell

62
Q

multipotent plant example

A

meristem - inner meristem is xylem and outer meristem is phloem. the level of hormones determine if it is xylem or phloem

63
Q

what are induced pluripotent stem cells

A

created by programming differentiated cells to switch on/off key genes which enables them to become undifferentiated
made from the patients own cells so no rejections so no immunosuppressants needed

A-level biology (25 decks)

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