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cell division Flashcards

1
Q

How many pairs of chromosomes does a normal human have?

A

23

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2
Q

What does a gene do?

A

Code for a characteristic

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3
Q

For what 3 reasons does mitosis occur?

A

Growth, repair and asexual reproduction

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4
Q

What occurs during the G1 phase of the cell cycle?

A
  1. Proteins are synthesised 2. ATP is produced 3. Key organelles (including centrioles) grow larger, then duplicate
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5
Q

What is the G1 checkpoint known as in animals?

A

The restriction point

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6
Q

What is the G1 checkpoint known as in yeast?

A

START

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7
Q

Why is the G1 checkpoint important?

A

The cell must be checked to make sure that it is ready for division, as once the chromosomes are duplicated the process cannot be reversed

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8
Q

What factors are checked at the G1 checkpoint?

A
  1. Nutrients- are the necessary nutrients present in the cell and its environment 2. Size- is the cell large enough for division? 3. Molecular signals- Is the cell receiving positive cues (i.e. growth factors) from its neighbours? 4. Mechanical signals- Is the cell attached to a support/crowded by neighbours 5. DNA integrity- is any DNA damaged?
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9
Q

What happens if the cell is rejected at the G1 checkpoint?

A

It passes into a resting state called G0

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10
Q

What are some reasons for passing into G0?

A

Cell age/senescence, damage, lack of need for them to reproduce

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11
Q

Is G0 temporary or permanent?

A

It can be both

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12
Q

Which cells spend all of their existence in G0?

A

Neurons, although many cells spend much of their life in G0 performing functions

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13
Q

What else, apart from carrying out functions, can occur in G0?

A

Cell death

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14
Q

What happens if a cell passes the G1 checkpoint?

A

It passes into the S phase

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15
Q

What occurs during the S phase?

A

DNA is replicated in the nucleus

Each chromosome is duplicated in the nucleus

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16
Q

Which stages of the cell cycle make up interphase?

A

G1, S and G2

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17
Q

What occurs during the G2 phase of cell division?

A

cell continues to increase in size

The duplicated chromosomes are checked for damage, and repaired/replaced if possible and necessary

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18
Q

What is checked at the G2 checkpoint?

A

Cell size, DNA condition (integrity, i.e. is any damaged?, and replication, i.e. is it fully replicated?)

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19
Q

What happens if a problem is detected at the G2 checkpoint?

A

The cell will pause at the checkpoint to undergo repairs

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20
Q

What happens if any problem is fixed at the G2 checkpoint?

A

The cell re-enters the cell cycle, and proceeds with division as normal

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21
Q

What happens if damage found at the G2 checkpoint is irreparable, and why is this important?

A

The cell may undergo apoptosis, which is important in preventing cancer by stopping errors being passed to daughter cells

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22
Q

What is apoptosis?

A

Programmed cell death

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23
Q

What happens if a cell passes the G2 checkpoint without any problems?

A

It proceeds to mitosis

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24
Q

How many chromatids is a chromosome made up of?

A

Either 1, or two genetically identical ones

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25
Q

What is a chromatid?

A

A strand of DNA

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26
Q

How many chromatids does each chromosome have during G1?

A

1 chromatid

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27
Q

How many chromatids does each chromosome have from S phase to the beginning of mitosis?

A

2

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28
Q

How do chromosomes condense?

A

The DNA (in the form of chromatin fibres) is supercoiled around histone proteins

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29
Q

What are the 4 stages of Mitosis?

A

Prophase, Metaphase, Anaphase, Telophase

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30
Q

What is a chromosome?

A

A strip of tighlly coiled DNA

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31
Q

What 6 things occur during Prophase in mitosis?

A
  1. Chromatin fibres begin to coil and condense to form chromosomes. 2. Nucleolus disappears 3. Nuclear envelope begins to break down, and fully disappears by the end of Prophase 4. Microtubules begin to form spindle fibres linking the poles of the cell 5. Centrioles migrate to opposite poles of the cell 6. Spindle fibres attach to centromeres, begin to move chromosomes to cell centre
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32
Q

What is a centromere?

A

The point on a chromosome onto which a spindle fibre attaches

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33
Q

What occurs in Metaphase in mitosis?

A

Chromosomes are moved by the spindle fibres to form a plane in the cell’s centre, called the Metaphase Plate, and are then held in position

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34
Q

What occurs in Anaphase in mitosis?

A

Centromeres holding pairs of chromatids together in chromosomes divide. Sister chromosomes separated and pulled to opposite poles of the cell by shortening spindle fibres

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35
Q

What shape do chromatids tend to be in during Anaphase?

A

A ‘v’ shape because of them being pulled by the spindle fibres

36
Q

What occurs during telophase during mitosis?

A

Chromatids, which have now reached the poles of the cell, are referred to as chromosomes . Each new set of chromosomes assembles at its respective pole, nuclear envelope and nucleolus reform. Chromosomes start to uncoil.

37
Q

When does cytokinesis start in both animals and plants?

A

During telophase

38
Q

How does cytokinesis occur in animals?

A

The cytoskeleton pulls the cell surface membrane inwards, causing it to invaginate (pinch in). This causes a cleavage furrow to form, until the cell surface membrane pinches off and two new cells are formed

39
Q

What is the difference between cytokinesis in plants and animals?

A

In plants, it begins from the middle of the cell, as opposed to the outside as it does in animals

40
Q

How does cytokinesis occur in plant cells?

A

Vesicles from the Golgi Apparatus line up in the same position as the metaphase plate, then fuse with each other and the cell surface membrane to form a new cell surface membrane in the middle of the cell called the cell plate. The cell plate then has new cellulose deposited along it.

41
Q

Why can’t a new cell wall be formed along the cell plate during cytokinesis in plants before the separation of the two daughter cells?

A

Because otherwise the new cells would undergo immediate osmotic lysis

42
Q

What is osmotic lysis?

A

When a cell membrane bursts (and so, essentially, does the cell) due to the movement of water into the cell via osmosis

43
Q

What do homologous chromosomes have the same of?

A

They have the same gene loci, so they have genes which code for the same thing. They also have the same length

44
Q

What happens to homologous chromosomes before cell division?

A

They are copied

45
Q

What is a bivalent?

A

Where pairs of homologous chromosomes attach to each other at points called chaisma (singular) or chaismata (plural)

46
Q

What occurs during Prophase 1 of meiosis?

A
  1. Chromosomes condense 2. Homologous chromosomes pair up to form bivalents (resulting in crossing over of chromatids) 3. Nuclear envelope disintegrates 4. Centrioles migrate to poles of cell 5. Spindle fibres begin to form
47
Q

What is independent assortment?

A

Where pairs of homologous chromosomes line up with random alignments along the metaphase plate during metaphase in meiosis

48
Q

What occurs during Metaphase 1 during meiosis

A
  1. Homologous pairs assemble along metaphase plate with random orientations (independent assortment) 2. Spindle fibres from each centriole attach to centromeres
49
Q

What occurs during Anaphase 1 during meiosis?

A
  1. Homologous chromosomes pulled to opposite poles of cell by spindle fibres, sister chromatids stay attached. 2. Sections of DNA entangled during crossing over break off and rejoin, with recombinant chromatids being formed by this exchange of genes
50
Q

What is a recombinant chromatid?

A

One with a different genetic makeup to either the father or the mother’s chromatid due to sections of DNA entangled during crossing over being exchanged.

51
Q

What occurs during Telophase 1 during meiosis?

A
  1. Chromsomes assemble at the pole of each cell and uncoil 2. Nuclear envelope reforms 3. Centrioles move back into cytosol 4. Cell surface membrane invaginates and pinches off to form 2 daughter cells, each with the same amount of genetic information as the parent cell
52
Q

What happens during Prophase 2 during meiosis?

A
  1. Chromosomes condense and become visible again 2. Nuclear envelope disintegrates 3. Centrioles migrate to poles of cell, spindle fibres begin to form
53
Q

What happens during Metaphase 2 in meiosis?

A

“1. Individual chromosomes line up along metaphase plate, again with independent assortment 2. Spindle fibres attach to centromeres “

54
Q

What happens during Anaphase 2 in meiosis?

A

Chromatids of individual chromosomes pulled to poles of cell by shortening spindle fibres after division of centromeres

55
Q

What happens during Telophase 2 in meiosis?

A
  1. Chromosomes assemble at poles, then uncoil and form chromatin again 2. Nuclear envelope reforms 3. Each cell’s cell surface membrane invaginates and pinches off to form two new daughter cells, each with half the genetic information of the original parent cell
56
Q

Why is mitosis used in repair?

A

Old and damaged cells can be replaced by new, identical ones

57
Q

Why is mitosis used in growth?

A

Allows accelerated growth to increase the size of the organism

58
Q

What is meiosis?

A

A type of nuclear division that results in the formation of cells containing half the number of chromosomes as the parent

59
Q

Why does meiosis occur?

A

Occurs in diploid germ cells to produce haploid gametes inside organs called gonads (ovaries and testes), which are then used in reproduction

60
Q

What are homologous chromosomes?

A

Pairs of chromosomes, one maternal and one paternal, containing the same genes but different alleles of these genes

61
Q

How does meiosis produce genetic variation?

A

Crossing over during prophase 1 shuffles alleles, independent assortment of chromosomes in anaphase 1 leads to random distribution of maternal and paternal chromosomes of each pair, and independent assortment in anaphase 2 leads to further random distribution. Haploid gametes are produced which then undergo random fusion with gametes derived from another organism of the same species.

62
Q

What is the need for cell differentiation?

A

In single celles organisms, different organelles carry out different roles, and oxygen just diffuses across the plasma membrane into the cell due to the large SA:V. However in multicellular organisms, oxygen cannot reach all cells by simply diffusing through the membrane due to a smaller SA:V and so need specialised cells to carry out particular functions such as transporting oxygen.

63
Q

What does differentiation ensure?

A

The properties of the different organelles differ from those of other cells, and the shape of the cell changes, as does some of the contents of the cell, and all of this contributes to the specialisation of that cell to make it fit for its particular function.

64
Q

How is an erythrocyte specialised for its function?

A

Their function, as red blood cells, is to carry oxygen from the lungs to respiring cells. They are adapted to carry out this function because they are very small (7.5 micrometers) and biconcaved so have a large SA:V meaning oxygen can diffuse across their membrane and easily reach all regions within the cell. They are also flexible due to a well developed cytoskeleton so they can fit though small capillaries. Most of their organelles are lost in differentiation so they have no nucleus and mitochondria and very little cytoplasm - this makes space for the haemoglobin housed in erythrocytes

65
Q

How is haemoglobin synthesised if erythrocytes dont have a nucleus, ribosomes or rough ER?

A

They are synthesised in immature erythrocytes whilst they still have these organelles which are then lost in differentiation.

66
Q

How are neutrophils specialised for their function?

A

They are twice the size or erythrocytes, and each contains a multi lobed nucleus (which help them squeeze through gaps in the capillary wall). They are attracted to and travel towards infection sites by chemotaxis. Their function is to ingest bacteria and some fungi by phagocytosis, thus have lots of lysosomes to digest these pathogens

67
Q

How are spermatozoa (sperm cells) specialised for their function?

A

They have many mitochondria to provide ATP energy for the undulopodium to move and propel the cell forward, and they are small but long and thin so can move easily. Once they reach the ovum they release enzymes from the acrosome (specialised lysosome) which digest the protective cover on the ovum. The head contains the haploid gamete nucleus and very little cytoplasm

68
Q

How are palisade cells specialised for their function?

A

They are long and cylindrical so they can pack together closely but with a little space between them for air to circulate (allowing CO2 in the air to diffuse into cells), and they have a large vacuole so that the chloroplasts are positioned near the periphery of the cell (reducing diffusion distance). They contain many chloroplasts, and cytoskeleton threads and motor proteins so move the chloroplasts according to light intensity (upper surface of leaf when low, further down when high).

69
Q

How are guard cells specialised for their function?

A

Light energy is used to produce ATP which actively transports potassium ions from surrounding epidermal cells into the guard cells, lowering the water potential. This is then followed by water that moves in by osmosis, causing the guard cells to swell. The cell wall is thick in the middle but thinner at the tips so the tips bulge, causing the gap (stoma) between the guard cells to be enlarged. This means air can enter the spaces between the palisade cells and CO2 diffuses in, maintaining a steep concentration gradient

70
Q

How are root hair cells specialised for their function?

A

Epidermal cells on the outer layer of young plant roots - the hair like projections greatly increase the surface area for absorption of water and mineral ions (eg nitrates). Mineral ions are actively transported into the root hair cells lowering water potential so water follows by osmosis. They have specialised carrier proteins in plasma membrane to actively transport the mineral ions in.

71
Q

What is the definition of a tissue?

A

A group of cells that work together to perform a special function/set of functions.

72
Q

What are the four main types of tissue in the body?

A

Epithelial tissue (lining tissue), connective tissue (eg blood, bones and cartilage), muscle tissue, and nervous tissue

73
Q

What are the characteristics of epithelial tissue?

A

Made up almost entirely out of living cells, which are close together and form continuous sheets. Adjacent cells are bound together by lateral contacts such as tight junctions and desmosomes. There are no blood vessels in epithelial tissue, cells get nutrients by diffusion from tissue fluid in underlying connective tissue. They have short cell cycles and and divide up to 2-3 times a day to replace worn tissue. Functions: protection, absorption, filtration, excretion and secretion.

74
Q

What is the structure of connective tissue?

A

Consists of a non living extra cellular matrix containing proteins (collagen and elastin) and polysaccharides (eg hyaluronic acid which traps water). This matrix separates living cells within the tissue and enables it to withstand weight.

75
Q

What are examples of connective tissue?

A

Blood, bone, cartilage, tendons, ligaments and skin

76
Q

How is cartilage formed?

A

Immature cells in cartilage are called chondroblasts - they divide by mitosis and secrete the extracellular matrix. Once the matrix has been synthesised, they chondroblasts become mature, less active chondrocytes which maintain the matrix.

77
Q

What are the three type of cartilage?

A

Hyaline, fibrous and elastic

78
Q

What are the three types of muscle?

A

Skeletal, cardiac and smooth

79
Q

What is the function of skeletal muscle?

A

Packaged by connective tissue sheets, joined to bones by tendons - contract to cause movement of bones

80
Q

What is the function of cardiac muscle?

A

Makes up the walls of the heart and allows the heart to beat and pump blood

81
Q

What is the function of smooth muscle?

A

Occurs in the walls of the intestine, blood vessels, uterus and urinary tracts, and propels substances along these tracts

82
Q

What makes up plant vascular tissue and what is its function?

A

Xylem and phloem, both present in vascular bundles - xylem vessels carry water and minerals from roots to all parts of the plant, and phloem sieve tubes transfer the products of photosynthesis (mainly sucrose) in solution from leaves to parts of the plant that do not photosynthesis, eg roots, flowers and growing shoots

83
Q

What is epidermal tissue?

A

Found in plants, it is the layer of flattened cells that form a protective covering over leaves, stems and roots - some have walls impregnated with a waxy substance forming a cuticle

84
Q

What is an organ system?

A

A number of organs working together to carry out an overall life function

85
Q

What makes up the digestive system and what does it do?

A

Oesophagus, stomach, intestines, liver and pancreas - nutrition to provide ATP and materials for growth and repair

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