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Biology Module 2 > 6.1, 6.2, 6.3 The Cell Cycle, Mitosis, Meiosis > Flashcards

6.1, 6.2, 6.3 The Cell Cycle, Mitosis, Meiosis Flashcards

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1
Q

What is the cell cycle?

A

An ordered sequence of events in a cell that result in a division of the cell, and the formation of two genetically identical daughter cells.

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2
Q

What stages are included in Interphase?

A

G1, Synthesis and G2.

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3
Q

How do cells divide?

A

Not continuously. They have long periods of growth, and normal working separate divisions. The periods of growth are called INTERPHASE.

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4
Q

List off the stages of the cell cycle

A

G0, G1, S, G2, Mitosis, Cytokinesis.

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5
Q

What occurs during G1 (First Growth Stage)?

A

-Size of the cell increases
-Organelles replicate
-Protein synthesis (transcription/translation)

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6
Q

What occurs during the Synthesis Stage?

A

-DNA is replicated in the nucleus
-Chromosomes are duplicated.

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7
Q

What occurs during G2 (Second Growth Stage)?

A

-Cell continues to carry out protein synthesis (transcription/translocation)
-Energy stores replaced
-Chromosomes that may have been damaged are repaired
-Size of cell continues to increase

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8
Q

What occurs during the mitotic phase?

A

Both MITOSIS and CYTOKINESIS

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9
Q

What occurs during Mitosis?

A

The nucleus divides

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10
Q

What occurs during cytokinesis?

A

The cytoplasm divides and two cells are produced

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11
Q

What is G0?

A

The phase where the cell leaves the cycle either temporarily or permanently

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12
Q

Why might a cell enter the G0 phase?

A

-DIFFERENTIATION
-DAMAGE TO DNA
-AGE RELATED DISEASES

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13
Q

Explain why differentiation would cause a cell to enter the G0 phase.

A

A cell that becomes specialised can no longer divide, so it won’t enter the cell cycle again.

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14
Q

Explain why damage to DNA would cause a cell to enter the G0 phase.

A

Damage to DNA would make the cell no longer viable. So damaged cells enter a period of permanent cell arrest. The majority of normal cells divide a limited number of times before becoming senescent

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15
Q

What is a senescent cell?

A

A cell that has stopped dividing but has not died.

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16
Q

Explain why age related disease would cause a cell to enter the G0 phase.

A

As you age, the number of senescent cells increases, which has been linked with many age-related diseases.

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17
Q

Why is it important to control the cell cycle?

A

To ensure that a cell only divides when it has grown to the right size, the DNA is error-free and the chromosomes are in their correct positions.

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18
Q

What is in the cell cycle to control it?

A

Checkpoints

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19
Q

What do checkpoints in the cell cycle do?

A

Monitor and verify that the processes at each phase of the cell cycle have been accurately completed before the cell progresses to its next phase.

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20
Q

List the checkpoints in the cell cycle.

A

G1 Checkpoint, G2 Checkpoint, Spindle Assembly Checkpoint/Metaphase Checkpoint

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21
Q

When does the G1 Checkpoint take place?

A

At the end of the G1 Phase

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22
Q

What does the G1 Checkpoint check?

A

-Cell size
-Nutrients
-Growth factors
-DNA damage

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23
Q

What happens if a cell does not meet the requirements at the end of the G1 Checkpoint?

A

The cell enters the G0 phase

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23
Q

What happens to a cell if it does not meet the requirements at the G2 Checkpoint?

A

It undergoes programmed cell death, or apoptosis.

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24
Q

What does the G2 Checkpoint check?

A

Cell size, DNA replication and DNA damage

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24
Q

When does the G2 Checkpoint take place?

A

At the end of the G2 phase.

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25
Q

When is the Spindle Assembly Checkpoint during the cell cycle?

A

During the M phase of mitosis.

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25
Q

What does the Spindle Assembly Checkpoint check for?

A

Makes sure the chromosomes are all attached to spindles.

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26
Q

What happens if the requirements aren’t met at the Spindle Assembly Checkpoint?

A

Mitosis cannot proceed.

27
Q

What is the alternate name for the Spindle Assembly Checkpoint?

A

Metaphase Checkpoint.

28
Q

What is a centromere?

A

The region of a chromosome that the spindle fibres of the centriole attach to

29
Q

What is Chromatin?

A

Uncondensed DNA in a complex with histones

30
Q

What is a diploid?

A

Normal chromosome number, two chromosomes of each type (2n) ><

31
Q

What is a haploid?

A

Single set of unpaired chromosomes (n) >

32
Q

What are the four phases of mitosis?

A

Prophase, Metaphase, Anaphase and Telophase (PMAT)

33
Q

Why is it important that DNA replication results in two exact copies of the genetic material?

A

So that each daughter cell has identical DNA, and the correct number of chromosomes

34
Q

Describe what happens during Prophase of mitosis.

A

-Nuclear membrane breaks down
-Nucleolus disappears
-Chromatin condenses so chromasomes are visible
-Centrioles migrate to poles of cell
-Spindle fibres form at poles of cell, and attach to centrosomes, beginning to move the chromosomes to the centre of the cell

35
Q

Describe what happens during Metaphase of mitosis.

A

-Chromosomes are moved by spindle fibres to the equator of the cell
-Chromosomes are lined up in a plane called the METAPHASE PLATE.

36
Q

Describe what happens during Anaphase of mitosis.

A

-Centromeres divide
-Chromatids are separated
-Spindle fibres shorten
-Chromatids are pulled to opposite poles
-Chromosomes appear “V” shaped, because the centromere is being pulled.

37
Q

Describe what happens during Telophase of mitosis.

A

-Spindle fibres break down
-Nuclear envelopes forms around chromosomes
-Centromeres reach the poles
-Chromatids are converted back to chromosomes
-Chromosomes uncoil
-Nucleolus forms
-Cytokinesis begins

38
Q

What does Mitosis refer to?

A

Nuclear division

39
Q

What is the function of mitosis?

A

Growth, repair and replacement.

40
Q

What is cytokinesis?

A

The division of the cell into two separate cells

41
Q

When does cytokinesis begin?

A

During telophase of Mitosis

42
Q

Describe cytokinesis in ANIMAL cells.

A

-A cleavage furrow forms around the middle of the cell
-Cell-surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle
-Forms 2 cells

43
Q

Why is cytokinesis different in plant cells compared to animal cells?

A

Because plants have cell walls, so a cleavage furrow cannot be formed.

44
Q

Describe cytokinesis in PLANT cells.

A

-Vesicles from the Golgi apparatus assemble where the metaphase plate was formed
-Vesicles fuse with eachother and the cell surface membrane, dividing the cell into two
-New sections of cell wall form along the new sections of membrane.

45
Q

Why do we normally see chromosomes are a double structure containing two chromatids?

A

Because they only become visible under a microscope during mitosis/meiosis, when DNA is replicated. Chromosomes consist of a pair of chromatids, which are duplicates.

46
Q

What is a homologous pair?

A

A set of one maternal chromosome and paternal chromosome that pair up with eachother in a cell during meiosis.

47
Q

When are gametes formed?

A

During meiosis.

48
Q

What is a gamete?

A

A sex cell

49
Q

What makes meiosis a reduction division?

A

In meiosis, diploids go to haploids. Each gamete contains half the chromosome number in the parent cell.

50
Q

Why is reduction division necessary in the production of gametes?

A

Because gametes are sex cells, and two sex cells must combine to produce a diploid offspring, so gametes must be haploids.

51
Q

What divisions does meiosis involve?

A

2: Meiosis I and Meiosis II.

52
Q

What happens in Meiosis I?

A

-A reduction division
-Pairs of homologous chromosomes are separated into two cells, containing only one full set of chromosomes

53
Q

What happens in Meiosis II?

A

-Similar to mitosis
-Pairs of chromatids present in each daughter cell are separated, forming 2 more cells.
-4 haploid daughters are produced.

54
Q

Describe what happens in Prophase 1 of Meiosis I.

A

-Chromosomes condense, nuclear envelope disintegrates
-Nucleolus disappears
-Spindle formation begins
-The homologous chromosomes pair up, forming BIVALENTS
-Moving chromosomes through the liquid cytoplasm to be brought together leads to chromatids entangling. (CROSSING OVER)

55
Q

Describe what happens in Metaphase 1 of Meiosis I.

A

-Homologous pairs of chromosomes assemble, and are lined up on the metaphase plate
-The orientation of each homologous pair on the metaphase plate is random and independant of any other homologous pair (maternal or paternal chromosomes can end up facing either pole), known as INDEPENDANT ASSORTMENT, resulting in many combinations of alleles facing the poles.
-Independant assortment of chromosomes in metaphase 1 results in genetic variation

56
Q

Describe independant assortment in Meiosis.

A

The orientation of each homologous pair on the metaphase plate is random and independant of any other homologous pairs. Independant assortment is what results in genetic variation.

57
Q

Describe what happens in Anaphase 1 of Meiosis I.

A

-Homologous chromosomes are pulled to opposite poles and chromatids stay joined to eachother
-Sections of DNA on “Sister” Chromatids, which become entangled during crossing over, now break off and rejoin (sometimes resulting in an exchange of DNA). The points at which the chromatids break and rejoin are called CHIASMATA.
-When exchange occurs, this forms RECOMBINANT CHROMATIDS, with genes being exchanged between chromatids. The genes being exchanged may be different alleles of the same gene, meaning the combination of alleles on the recombinant chromatids will be different from the allele combination of either of the original chromatids. Genetic variation arises from this new combination of alleles because the sister chromatids are no longer identical

58
Q

What are recombinant chromatids?

A

Chromatids that have been created through the process of crossing over during Anaphase 1 of Meiosis I

59
Q

Describe what happens in Telophase 1 of Meiosis I

A

-Chromosomes assemble at each pole, and the nuclear membrane reforms
-Nucleolus reappears
-Chromosomes uncoil
-Cell undergoes cytokinesis and divides into two cells
-Chromosome number reduces from diploid to haploid

60
Q

Describe what happens in Prophase 2 of Meiosis II

A

-Nuclear membrane breaks down
-Centrioles produce spindle fibres and migrate to poles. Spindle fibres form at poles of the cell
-Nucleolus disappears, chromosomes condense and become visible
-Spindle fibres attach to centromeres
-Chromatids move to centre of cell

61
Q

Describe what happens in Metaphase 2 of Meiosis II

A

-Individual chromosomes assemble on the metaphase plate
-Independant assortment takes place again, so more genetic variation produced

62
Q

Describe what happens in Anaphase 2 of Meiosis II

A

-Chromatids of individual chromosomes are pulled to opposite poles are division of the centromeres
-Spindle fibres shorten, V shape of the chromatid is caused by the centromere being pulled.

63
Q

Describe what happens in Telophase 2 of Meiosis II

A

-Chromatids assemble at the poles
-Chromosomes uncoil and form chromatin
-Nuclear envelope reforms, nucleolus reappears
-Cytokinesis results in the division of cells, forming 4 daughter cells in total
-Cells will be haploids due to reduction division
-Cells will also be genetically different from eachother and from the parent cell due to crossing over and independant assortment.

64
Q

What is an allele?

A

Different version sof the same gene. Different alleles of a gene will all have the same position on a particular chromosome.

65
Q

What is the same in homologous chromosomes?

A

-Same genes in the same positions, same length and size when visible in prophase

66
Q

What is a Bivalent?

A

A pair of homologous chromosomes present during Prophase 1 of meiosis I

67
Q

What is a Chiasmata?

A

The point at which crossing over takes place during Anaphase I of Meiosis

68
Q

What is cross-over?

A

The exchange of genetic material between homologous chromosomes.

Biology Module 2 (9 decks)

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