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Sajid OCR A level biology > The cell cycle, mitosis, meiosis > Flashcards

The cell cycle, mitosis, meiosis Flashcards

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1
Q

What is the cell cycle?

A

the sequence of events that takes place in a cell

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2
Q

What are the two main phases of the cell cycle?

A

Interphase

Mitotic phase

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3
Q

What does a cell do during interphase?

A

cells carry out their major functions

  • protein synthesis
  • normal metabolic processes
  • DNA is replicated and checked for errors
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4
Q

What are the 3 stages of interphase?

A

G1
S
G2

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5
Q

What occurs in G1 of interphase?

A
  • The cell increases in size

- organelles are duplicated

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6
Q

What occurs in G2 of interphase?

A
  • the cell continues growth

- cell double checks duplicated chromosomes for error and makes any necessary repairs

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7
Q

What occurs in S of interphase?

A

Chromosomes are duplicated

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8
Q

What is G0 of the cell cycle?

A

Cells leave the cell cycle

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9
Q

Why might a cell leave the cell cycle?

A
  • age
  • terminal differentiation
  • damage
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10
Q

What occurs in the G1 checkpoint?

A
  • Checks that chemicals needed for replication are present

- checks for any damage to DNA before S phase

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11
Q

What occurs in the G2 checkpoint?

A

Checks for any errors in the DNA and repairs mistakes

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12
Q

What occurs in the spindle assembly checkpoint?

A

checks if spindle fibres are connected to chromosomes

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13
Q

What are the two parts to the mitotic stage of the cell cycle?

A

Mitosis

Cytokinesis

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14
Q

What are the two types of cell division?

A

Mitosis and Meiosis

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15
Q

When does meiosis occur?

A

The production of gametes

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16
Q

What occurs in mitosis?

A

The nucleus divides

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17
Q

What occurs in cytokinesis?

A

The cytoplasm divides and the two cells are produced

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18
Q

Why is mitosis important?

A

It ensures the two daughter cells produced are genetically identical

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19
Q

Define chromatid

A

Two identical copies of DNA (a chromosome) held together at a centromere

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20
Q

Define chromatin

A

uncondensed DNA in a complex with histones

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21
Q

Define chromosomes

A

structures of condensed and coiled DNA in the form of chromatin

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22
Q

Define sister chromatid

A

two identical strands joined by a common centromere

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23
Q

Define centromere

A

region at which two chromatids are held together

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24
Q

Define centrioles

A

component of the cytoskeleton made of microtubles, involved in the development of spindle fibres

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25
Q

Define spindle fibres

A

a protein structure that moves chromosomes

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26
Q

Define homologous pairs

A
  • a pair of chromosomes, one maternal and one paternal, -containing the same genes on the same loci
  • which do not necessarily have the same alleles
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27
Q

How is DNA packaged?

A
  • wrapped around histones
  • chromatin
  • coiled around more proteins
  • chromosome
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28
Q

When is DNA found in chromosomes?

A

only for cell division

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29
Q

Why does DNA form chromosomes for cell division?

A

Helps protect DNA from damage when it is being moved

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30
Q

Why does DNA wrap around histones?

A

Makes it more compact

Makes it easy to access

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31
Q

What are the 4 stages of mitosis in order?

A

Prophase
Metaphase
Anaphase
Telophase

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32
Q

What happens in prophase of mitosis?

A
  • chromosomes condense/become visible
  • nuclear membrane begins to break down
  • nucleolus disappears
  • microtubles form spindle fibres
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33
Q

What happens in metaphase of mitosis?

A
  • chromosomes are moved by spindle fibres

- chromosomes line up along the equatorial plate of the cell

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34
Q

What happens in anaphase of mitosis?

A
  • sister chromatids are pulled apart by spindle fibres
  • move towards the poles of the cell
  • centromere/chromosomes split
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35
Q

What happens in telophase of mitosis?

A
  • chromatids now called chromosomes
  • chromosomes unwinds and become indistinct
  • nuclear membrane reforms
36
Q

Why are centrioles important in cell division?

A

They produce spindle fibres

Spindle fibres are responsible for the movement of chromosomes within the cell

37
Q

What happens in cytokinesis of animal cells?

A
  • a cleavage furrow forms
  • microfilaments form a ring around the edge of the plasma membrane
  • pulls the membrane inwards
  • the plasma membrane fuses in the middle to form two cells
38
Q

What happens in the cytokinesis of plants?

A
  • vesicles carry cell membrane and cell wall components assemble along the plane of division
  • the cell membrane first forms as vesicles fuse
  • cell wall forms alongside
39
Q

What do single celled organisms use mitosis for?

A

-to reproduce

40
Q

What are 4 functions of mitosis?

A
  • growth of an organism
  • repair/replacement of tissues
  • asexual reproduction
  • development of embryos
41
Q

How do yeast undergo mitosis?

A
  • yeast reproduces asexually through mitosis
  • a bud forms before DNA replicates
  • one large and one small cell are produced
42
Q

What is mitosis in bacteria called?

A

Binary fission

43
Q

Define diploid

A

Normal chromosome number, two chromosomes of each type inherited from each parent

44
Q

Define haploid

A

Half the normal number of chromosomes, one chromosome of each type

45
Q

Define gametes

A

Haploid sex cell produced by meiosis in organisms that reproduce sexually

46
Q

Define meiosis

A

Form of cell division where the nucleus divides twice resulting in a halving of chromosome number and producing 4 haploid cells

47
Q

Define reduction division

A

cell division resulting in the production of haploid cells from a diploid cell

48
Q

Define zygote

A

initial diploid cell formed when 2 gametes are joined by means of sexual reproduction

49
Q

How many rounds of cell division occur in meiosis?

A

2

50
Q

What occurs in prophase 1 of meiosis?

A
  • nuclear membrane disintegrates
  • chromosomes condense
  • bivalents are formed
  • crossing over occurs at chiasmata
51
Q

What occurs in metaphase 1 of meiosis?

A

-homologous pairs of chromosomes line up along the metaphase plate

52
Q

What occurs in anaphase 1 of meiosis?

A
  • spindle fibres pull homologous chromosomes to opposite poles
  • random assortment , pairs move apart
  • chromosomes move to the poles
53
Q

What occurs in telophase 1 of meiosis?

A
  • 2 cells with unidentical chromatids are formed
  • nuclear envelope reforms
  • chromosomes unwind
54
Q

What occurs in prophase 2 of meiosis?

A
  • chromosomes recondense, still consist of 2 chromatids

- nuclear membrane disintegrates

55
Q

What occurs in metaphase 2 of meiosis?

A
  • pairs of CHROMATIDS line up along the equatorial plate

- independent assortment of CHROMATIDS

56
Q

What occurs in anaphase 2 of meiosis?

A

-CHROMATIDS pulled apart by spindle fibres

57
Q

What occurs in telophase 2 of meiosis?

A
  • 4 haploid daughter cells are produced
  • nuclear membrane reforms
  • Chromatids uncoil
58
Q

How does independent assortment occur?

A

The arrangement of bivalents

59
Q

How does independent assortment lead to variation?

A

Different alleles can face the poles e.g. the maternal or paternal chromosomes can end up at either pole

60
Q

Define bivalent

A

Homologous chromosomes associated in pairs

61
Q

Define chiasmata

A

sections of DNA which become entangled during crossing over, break and rejoin

62
Q

At what stage in meiosis are chiasmata formed?

A

Anaphase 1

63
Q

Define recombiant chromatids

A

Chromatids with a combination of DNA from both homologous chromosomes formed by crossing ver and chiasmata

64
Q

What two processes occur in meiosis to introduce genetic variation?

A

Crossing over

Independent assortment

65
Q

What is crossing over?

A

Genes are exchanged as sections of DNA on sister chromatids break off and rejoin

66
Q

How does crossing over lead to genetic variation?

A

The genes exchanged can be different alleles so the recombiant chromosomes have different sets of alleles to the original chromatids

67
Q

Besides meiosis, how can variation be introduced? (2 ways)

A

Random fertilisation

Gene mutation

68
Q

How does random fertilisation introduce variation?

A

-each gamete has a unique combination of genes and any of the numerous male gametes can fertilise the egg

69
Q

When does random fertilisation occur?

A

When two gametes fuse to form a zygote

70
Q

How does gene mutation introduce variation?

A

-bases within a gene can be altered during DNA replication

71
Q

Can mutation in the germline be inherited?

A

yes

72
Q

Can mutation in somatic cells be inherited?

A

no

73
Q

Why are different alleles within a population important?

A
  • they introduce genetic variation
  • some combinations can provide an organism with an advantageous characteristic e.g resistance to a disease
  • so if the environment alters organisms can survive
74
Q

Why is meiosis important in organisms which reproduce sexually?

A
  • makes haploid cells
  • ensures diploid number of chromosomes is restored in fertilisation
  • variation generated through crossing over and independent assortment
  • allows for a genetically different zygote to be formed through the fusion of gametes
75
Q

Give 5 differences between mitosis and meiosis

A
  • mitosis has 1 cell division but meiosis has 2
  • mitosis maintains chromosome number whilst meiosis halves chromosome number
  • mitosis produces 2 daughter cells whilst meiosis produces 4
  • daughter cells are genetically identical to the parent cell in mitosis but genetically different in meisosis
  • mitosis produces somatic cells whilst meiosis produces gametes
76
Q

Compare the genetic make up of daughter cells produced by mitosis with the original parent cell

A
  • genetically identical
  • have same number of chromosomes
  • have the same genes as the parent cell
77
Q

Why is mitosis important in the life cycle of a human?

A
  • it allows for the growth of a human
  • repairs tissues
  • genetically identical cells produced
  • throughout life maintain chromosome number
78
Q

Why is mitosis important in the repair of tissues?

A
  • cells produced in mitosis are genetically identical
  • this allows cells to carry out the same function as the parent cell
  • as the cell has the correct information to develop the same type of cell
79
Q

What is the difference between sister and non-sister chromatids?

A

they have different alleles

80
Q

When does independent assortment occur?

A

Metaphase I and Metaphase II

81
Q

Why is it important in sexual reproduction that gametes are haploid?

A
  • without gametes less variation
  • gametes fuse to form a diploid cell
  • prevents doubling number of chromosome number in each successive generation
82
Q

Why does meiosis need to have twice as many stages as mitosis?

A
  • gametes must be haploid as when they fuse a diploid cell must form
  • halve no. chromosomes from 2n to n
  • separate homologous pairs of chromosomes
83
Q

What is the difference between prophase 1 and prophase 2?

A
  • in prophase 1 chromosomes condense into homologous pairs of chromosomes
  • in prophase 1 bivalents form
84
Q

Why is it important that the genetic information is checked at the checkpoints?

A
  • otherwise mutation of a gene could occur
  • which would mean a protein necessary for a particular function might not be produced
  • a cell could end up with too many chromosomes
85
Q

Why is replication of DNA before division of the nucleus essential?

A
  • cell produced are genetically identical, both daughter cells receive a full copy of the parent cell’s DNA
  • diploid daughter cells are produced

Sajid OCR A level biology (43 decks)

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