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A-level Biology > Cell Cycle And Division > Flashcards

Cell Cycle And Division Flashcards

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1
Q

What hold two chromatids together?

A

Centromere

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2
Q

Gamete: what is the Ploidy level, number of sets of chromosomes and number of chromosomes?

For a human

A

Ploidy level: haploid
Sets of chromosomes: 1
Number of chromosomes: 23

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3
Q

Body cell: what is the Ploidy level, number of sets of chromosomes and number of chromosomes?

A

Ploidy level: diploid
Sets of chromosomes: 2
Number of chromosomes : 46

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4
Q

What are the three stages of the cell cycle?

A

Interphase
Mitosis
Cytokinesis

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5
Q

What are the three sub-stages of interphase

A

G1, s phase and G2

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6
Q

What happens in the phase G1?

A

Growth and normal metabolic processes

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7
Q

What happens in the S phase of interphase?

A

DNA replication.

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8
Q

What happens in the G2 stage of interphase?

A

Growth and preparation for mitosis by replication organelles

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9
Q

What is interphase?

A

A period of synthesis and growth

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10
Q

What is mitosis?

A

The formation of two genetically identical daughter nuclei.

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11
Q

What are the stages of mitosis?

A 
PMAT
Prophase
Metaphase
Anaphase
Telophase
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12
Q

What is the final stage of the cell cycle

A

Cytokinesis where the cytoplasm splits to form two new daughter diploid cells.

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13
Q

Why does the total cell mass increase during the cell cycle and then decrease again?

A

Because during the s phase in interphase dna is replicated so mass increases then during cytokinesis the cytoplasm splits to it returns the two lots of the initial mass

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14
Q

Describe interphase

A

The longer stage of the cell cycle
Cell size increases
Chromosomes not yet visible
G1, s phase, G2

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15
Q

Describe prophase (mitosis)

A

The longest stage of mitosis
Chromosomes condense by coiling up and getting shorter and fatter
The centrioles(only in animal cells) divide and move to opposite poles of the cell
Centromere holds the sister chromatids together
Nuclear envelope disintergrates
Spindle forms

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16
Q

Describe metaphase (mitosis)

A

The chromosomes line up along the equator of the cell

Spindle fibres attach to the centromere and shorten slightly to pull the sister chromatids apart

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17
Q

Describe anaphase(mitosis)

A

The centromere divides into two, separating the sister chromatids as the spindle fibres Shorten.
Each sister chromatid reaches the opposite pole of the cell

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18
Q

Describe telophase (mitosis)

A

One chromatid from each chromosome has reached each pole
Chromosomes uncoil and lengthen returning to chromatin
The spindle breaks down and the nuclear envelope reforms

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19
Q

What are the significances of mitosis?

A

Growth
Asexual reproduction
Chromosome number
Damage and disease

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20
Q

What is the significance of growth in mitosis?

A

-new cells increase cell number in organism
-growth, repair tissue, replace dead cells
-new body cells made which are genetically identical
-some tissues are worn away all the time (skin and gut lining) replaced identically
Humans = bone marrow, hair follicles, nail cuticles
Plants= root, shoot , meristem

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21
Q

What is the significance of asexual reproduction with mitosis?

A
  • genetically identical off spring to the parent
  • occurs in: bacteria, yeast, greenfly, strawberry plants & plants with runners and bulbs and tubers
  • no genetic variation between individuals so all identical
22
Q

What is the significance of chromosome number in mitosis?

A

Daughter cells has same number as each other and parent
Each chromosome is an exact replica of those in parent
Cells produced are genetically identical to parent providing genetic stability

23
Q

What is the significance of damage and disease in mitosis?

A
  • genes control length of cell cycle so mitosis occurs when and where needed.
  • if genes damaged incorrect divisions
  • gene may mutate when: radiation chemicals viruses change dna base sequence
  • gene will no longer act as a brake
  • solid tissue=tumour forms// blood= blood cancer
24
Q

What is an oncogene?

A

A gene with the potential to cause cancer

25
Q

What is a tumour suppressing gene?

A

Genes that prevent rapid replication leading to tumour formation

26
Q

What is a proto-oncogene?

A

A gene that causes cancer if it becomes mutated or a cell infected by a virus but before this they don’t cause cancer

27
Q

Where does meiosis occur?

A

In reproductive organs

28
Q

What is meiosis?

A

A two stage cell division in reproducing organisms that produces 4 genetically different haploid gametes with half the number of chromosomes than the parent

29
Q

How many divisions are there in meiosis?

A

2

30
Q

What are the stages in meiosis?

A 
Interphase (G1, S, G2)
Prophase I
Metaphase I
Anaphase I
Telophase I   + cytokinesis
Prophase II
Metaphase II
Anaphase II
telophase II + cytokinesis
31
Q

Is there interphase between the two divisions in meiosis?

A

No

32
Q

What is a terras also known as?

A

Bivalent

33
Q

Describe prophase I

A
  • Longest and most complex stage
  • Chromosomes condense
  • Synapsis= chromosomes from mum and dad pair up where homologous ones join together to form a bivalent
  • Crossing over occurs and the chiasmata where part of one chromosome swaps with the other
34
Q

What is crossing over?

A

When (during prophase I) part of the genetic material from the maternal and paternal chromosome swap. This occurs and the point called chiasmata

35
Q

What is a bivalent?

A

A pair of chromosomes or 4 chromatids. One maternal and one paternal

36
Q

Describe metaphase I

A
  • shortest phase
  • bivalent sapling either side of the equator
  • spindle fibres attach to the centromere
  • independent assortment of alignment of chromosomes along the equator.
37
Q

What is independent assortment?

A

When the chromosomes and bivalent s arrange themselves randomly at the cell equator so genetic information can be passed one either way

38
Q

What does independent assortment cause and why?

A

Variation because the orientation of the homologous chromosomes is random

39
Q

Describe anaphase I

A
  • homologous chromosomes separate and move to the poles of the cells
  • sister chromatids stay attached to the centromere
40
Q

Describe telophase I

A

Each pole now has a haploid set of chromosomes half the number of the chromosomes than the parent

41
Q

Describe cytokinesis I

A

The daughter cells are haploid and formed by the cytoplasm splitting

42
Q

Describe prophase II

A

The centrioles separate and move to the cell poles organising new spindle at right angles to the original spindle
Some nucleolus is present around the chromosomes

43
Q

Describe metaphase II

A

Chromosomes line up along the equator where the spindle fibres attach to the centromeres

Independent assortment occurs as their orientation is random

44
Q

Describe anaphase II

A

The centromeres divide in half so the sister chromatids move apart to either pole of the cell

To do this the spindle fibres shorten

45
Q

Describe telophase II

A

At the poles the chromatids lengthen and can no longer be distinguishable through a microscope
The spindle disintergrates
Nuclear envelope reforms

46
Q

Describe cytokinesis II

A

The cytoplasm splits from the inside outwards to form 4 haploid gametes

47
Q

Why is meiosis significant?

A

The chromosome number is constant from one generation to the next
Genetic variation

48
Q

How is genetic variation created during meiosis?

A
  • prophase I= crossing over at the chiasmata where genetic information is swapped
  • metaphase I &II = there is independent assortment of the chromosomes as the orientation is random
49
Q

Why is it essential to have genetic variation?

A

When new diseases come, some people will be more resistant than others and some may adapt faster to new conditions.

50
Q

What is a homologous pair?

A

Two chromosomes one maternal and one paternal which contain the same type of gene but may have different alleles.

A-level Biology (13 decks)

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