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Biology > 2.1.6 - Cell division > Flashcards

2.1.6 - Cell division Flashcards

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1
Q

What is the cell cycle ?

A

The sequence of events that takes place in a cell to enable growth and repair

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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 occurs in the cytoplasm
  • Organelles grow and divide in the cytoplasm
  • Normal metabolic processes (some continue throughout cell division e.g. respiration)
  • DNA is replicated and checked for errors in the nucleus
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4
Q

What are the three stages of interphase ?

A
  • G1 - growth phase 1
  • S - synthesis phase
  • G2 - growth phase 2
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5
Q

What occurs in the G1 phase of interphase ?

A
  • Proteins for organelle synthesis are produced ; helicase, polymerase and ligase enzymes are produced
  • Organelles are replicated
  • The cell increases in size
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6
Q

What occurs in the S phase of interphase ?

A

Chromosomes are duplicated in the nucleus

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7
Q

What occurs in G2 of interphase ?

A
  • Cell continues growth
  • Energy stores are increased
  • Cell double checks duplicated chromosomes for errors and makes any necessary repairs
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8
Q

What is G0 of the cell cycle ?

A
  • Phase when cells leave the cell cycle either temporarily or permanently.
  • A few types of cells that enter G0 can be stimulated to go back into the cell cycle and start dividing again
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9
Q

What can be stimulated to go back into the cell cycle after G0 ?

A

Lymphocytes in an immune response

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10
Q

Why might a cell leave the cell cycle?

A
  • The cell has differentiated
  • The DNA of the cell is damaged and therefore becomes senescent.
  • Age. The number of senescent cells increases with age and has been linked with age related diseases.
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11
Q

What is senescence ?

A

Senescence is the gradual deterioration of functional characteristics in living organisms

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12
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
  • Checks for cell size
  • Checks that the nutrients required for replication are present
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13
Q

What occurs in the G2 checkpoint ?

A
  • Checks for cell size
  • Checks for DNA replication
  • Checks for any errors in the DNA and repairs mistakes
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14
Q

What occurs in the spindle assembly checkpoint ?

A
  • Checks if spindle fibres are connected to the chromosomes properly
  • Checks that the chromosomes have aligned ready for metaphase
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15
Q

What is the spindle assembly checkpoint also known as ?

A

It is also known as the metaphase checkpoint - mitosis can not proceed until this checkpoint is passed

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16
Q

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

A
  • Mitosis - The nucleus divides

- Cytokinesis - The cytoplasm divides and two cells are provided

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17
Q

Define chromatid

A

Two identical copies of DNA (a chromosome)

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18
Q

Define sister chromatid

A

Two identical DNA molecules joined by a common centromere

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19
Q

Define chromatin

A

Uncondensed DNA which is in complex with histone proteins

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20
Q

Define chromosomes

A

Structures of condensed and coiled DNA molecules in the form of chromatin

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21
Q

Define homologous pairs

A
  • A pair of chromosomes, one maternal and one paternal

- Does not necessarily have the same alleles

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22
Q

Define centromere

A
  • Region at which two sister chromatids are held together

- Point where mitoticspindle fibresattach to pullsister chromatidsapart duringcell division.

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23
Q

Define centrioles

A

Component of the cytoskeleton made of microtubules and associated proteins, involved in the development of spindle fibres

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24
Q

What are centrosomes ?

A

Centrosomes are pairs of centrioles and they are the sub-cellular region which organise the cell’s microtubules

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25
Q

Why are centrioles important in cell division ?

A
  • During mitosis the spindle fibres start at the centrosomes

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

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26
Q

Define spindle fibres

A

A structure made of microtubules and associatedproteins that assemble from the centrosome to provide thestructure that moves chromosomes.

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27
Q

What is mitosis ?

A

Mitosis is the division of the nucleus into two genetically identical nuclei

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28
Q

What are the four stages of mitosis, in order ?

A
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

PMAT

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29
Q

Why is mitosis important ?

A
  • It ensures thetwo daughter cellsproduced are genetically identical
  • Each cell produced has anexact copy of the DNA present in the parent cell, and the same number of chromosomes
  • Growth, repair and replacementof cells in multicellular organisms
  • Asexual reproductionby Eukaryotic organisms
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30
Q

Why do single celled organisms use mitosis ?

A

To reproduce asexually

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31
Q

What is mitosis in bacteria called ?

A

Binary fission

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32
Q

How is DNA packaged ?

A
  • Wrapped around histone proteins to form chromatin

- Coiled around more proteins to form chromosomes

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33
Q

Why does DNA wrap around histones ?

A
  • Makes it more compact

- Makes it easy to access

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34
Q

What happens in prophase ?

A
  • Chromatinfibres condense into chromosomes
  • Nuclear membrane begins to break down andnucleolus disappears
  • Each duplicated chromosome appears astwo identical sister chromatids joined at their centromeresand, in some species, all along their arms by cohesins
  • Themitotic spindlebegins to formfrom centrosomes and the microtubules from them.
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35
Q

What happens in early metaphase ?

A
  • Thenuclear envelope fragments
  • Microtubules extending from each centromere can now invade the nuclear area
  • The chromosomes have become evenmore condensed
  • Each of the two chromatids of each chromosome now has akinetochore
  • Centrioles taken to opposite poles for formation of the spindle fibres
  • Some of the microtubules attach to the kinetochores
  • Non-kinetochore fibres interact with those from the opposite pole of the spindle.
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36
Q

What happens in late metaphase ?

A
  • Chromosomes are moved by spindle fibres toline up along the equatorial plateof the cell known as themetaphase plate
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37
Q

What happens in anaphase ?

A
  • Cohesin proteins are cleaved allowing the sister chromatids to be pulledapartby spindle fibres
  • Daughter chromosomes move towards the poles of the cell as their kinetochore microtubules (spindle fibres) shorten
  • Thecell elongatesas the non-kinetochore microtubules (spindle fibres) lengthen
  • Results in two poles of cell having equivalent, and complete, collections of chromosomes.
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38
Q

What happens in telophase ?

A
  • Two daughter nuclei formin the cell - nuclear membrane forms
  • Nucleolireappears
  • Chromatids are now calledchromosomes whichbecome less condensed and more distinct
  • Remaining spindle fibres are depolymerised
  • Mitosis is now complete.
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39
Q

What is cytokinesis ?

A

Cytokinesis is the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells

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40
Q

What occurs in cytokinesis ?

A
  • Thecytoplasm dividesand thetwo identical daughter cellsare produced
  • Starts in late telophase
  • Characterised by the formation of a cleavage furrow, which pinches the cell in two, in animal cells.
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41
Q

What happens in cytokinesis of animal cells ?

A
  • A cleavage furrow forms
  • Microfilaments form a ring around the edge of the plasma membrane pullingthe membrane inwards pinching the cell in two
  • The plasma membrane fuses in the middle to form two cells
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42
Q

What happens in cytokinesis of plant cells ?

A
  • Vesicles carrying cell membrane and cell wall components assemble along the plane of division
  • The cell membrane first forms as vesicles fuse
  • Cell walls form alongside
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43
Q

Define diploid

A

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

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44
Q

Define haploid

A

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

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45
Q

Define gametes

A

Haploid sex cell produced by meiosis in organisms that reproduce sexually

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46
Q

Define zygote

A

The initial diploid cell formed when the nuclei of gametes fuse during the fertilisation stage of sexual reproduction

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47
Q

Define reduction division

A
  • The first cell division in meiosis, the process by which germ cells are formed
  • Cell division resulting in the production of haploid cells from a diploid cell
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48
Q

Define meiosis

A

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

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49
Q

How many cell divisions occur in meiosis ?

A

2

50
Q

What occurs in meiosis I ?

A
  • The first division, reduction division, when the pairs of homologous chromosomes are separated into two cells
  • Cells are haploid, contain one full set of genes instead of two
51
Q

What are the stages of meiosis I ?

A
  • Prophase I
  • Metaphase I
  • Anaphase I
  • Telophase I
52
Q

What happens in prophase I ?

A
  • During prophase I the duplicated chromosomes condense, and homologous chromosomes pair up to form bivalents
  • The bivalents are connected lengthwise by proteins and crossing over can occur as chromatids entangle
  • A chiasma occurs at each point where a crossover has ocurred
  • The nuclear envelope fragments as in mitosis
53
Q

Define bivalent

A

Homologous chromosomes that are associated in pairs physically held together with at least one crossover

54
Q

Define chiasmata

A
  • An x-shaped region in a homologous pair which denotes where sections of DNA have become entangled and crossed over, break and rejoin
  • Singular chiasma
55
Q

What is crossing over ?

A

A genetic rearrangement between two non-sister chromatids involving the corresponding segments of DNA molecules.

56
Q

How does crossing over lead to genetic variation ?

A

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

57
Q

Define recombinant chromatids

A

Chromatids with a combination of DNA from both homologous chromosomes formed by crossing over at chiasmata.

58
Q

What happens in metaphase I ?

A
  • Homologous pairs line up with one chromosome in each pair facing each pole
  • Orientation of homologous pairs on the midline is random and independent of any other homologous pair
  • This is called independent assortment
59
Q

Define independent assortment

A

The random arrangement of bivalents at the metaphase plate.

60
Q

What can independent assortment lead to ?

A

Variation

61
Q

How can independent assortment lead to variation ?

A

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

62
Q

What happens in anaphase I ?

A
  • Breakdown of proteins responsible for sister chromatid cohesion along chromatid arms allows homologs to separate
  • Spindle fibres pull homologous chromosomes to opposite poles
  • Random assortmentof alleles aspairs move apart
63
Q

What happens in telophase I ?

A
  • Starts with each half of the cell having a complete haploid set of duplicated chromosomes
  • Each chromosome is composed of two sister chromatids; one or both chromatids include regions of non-sisterchromatid DNA
  • Nuclear envelope reforms
64
Q

When does cytokinesis happen ?

A

Cytokinesis occurs at the same time as telophase I forming two haploid daughter cells (which are not identical )

65
Q

What occurs in meiosis II ?

A
  • The second division
  • The pairs of chromatids present in each daughter cell are separated, forming two more cells
  • Four haploid cells are produced
66
Q

What are the stages of meiosis II ?

A
  • Prophase II
  • Metaphase II
  • Anaphase II
  • Telophase II
67
Q

What happens in prophase II ?

A
  • The chromosomes, which still consist of two chromatids, condense and become visible again
  • The nuclear envelope fragments once again, and spindle fibres form and start to move to the chromatids
68
Q

What happens in metaphase II ?

A
  • Individual chromosomes line up along the metaphase plate as in mitosis
  • Independent assortment occurs again, leading to more genetic variation following metaphase II
69
Q

What happens in anaphase II ?

A
  • It results in the chromatids of the individual chromosomes being pulled to opposite poles
  • Breakdown of the protein holding the sister chromatids together at the centromeres allows this division
70
Q

What happens in telophase II ?

A
  • Is essentially the same as in mitosis, resulting in the nuclear membrane reforming around chromosomes at each pole
  • Cytokinesis occurs simultaneously and results in the division of the cells forming genetically different haploid daughter cells in total
71
Q

What two processes occur in meiosis to introduce genetic variation ?

A
  • Crossing over

- Independent assortment

72
Q

Besides meiosis, what are the two ways in whichvariation can be introduced ?

A
  • Random fertilisation

- Gene mutation

73
Q

How does random fertilisation introduce variation ?

A
  • Each gamete has a unique combination of genes

- Any of the numerous male gametes can fertilise the egg

74
Q

When does random fertilisation occur ?

A

When two of the nuclei of two gametes fuse to form a zygote

75
Q

How does gene mutation introduce variation ?

A

Bases with a gene can be altered during DNA replication

76
Q

Define cell

A

A single repeating unit of an organism

77
Q

Define tissue

A

A collection of differentiated cells that have a common function

78
Q

Define organ

A

A group of tissues that work together to carry out a common function

79
Q

Define organ system

A

A group of organs that carry out a common function

80
Q

Define specialised

A

Having particular structure to serve a particular function

81
Q

Define differentiated

A
  • The process by which a less specialised cell develops a distinct form and function
  • A cell specialising
82
Q

Why do multicellular organisms need specialised cells ?

A
  • Complex communication in a multicellular organism
  • Specialised functions need specialised cells
  • To maximise efficiency of processes like absorbing nutrients
83
Q

What features does an erythrocyte have to suit it for its function ?

A
  • Biconcave disk, maximises SA to carry oxygen
  • No nucleus, more room for haemoglobin
  • Flexible, can squeeze through narrow capillaries
84
Q

What features does a neutrophil have to suit it for its function ?

A
  • Multi lobed nucleus, makes it easier for neutrophils to squeeze through small gaps
  • Granular cytoplasm, contains many lysosomes which contain enzymes used to attack pathogens
85
Q

What features does a sperm cell have to suit its function ?

A
  • Mitochondria, supplies the energy needed to swim
  • Tail, allows for movement to occur
  • Acrosome, contains digestive enzymes which digest protective layers around the ovum
86
Q

What features does a root hair cell have to suit its function ?

A

Root hairs, increase SA:V ratio to maximise the uptake of water/minerals from the soil

87
Q

What features does a palisade cell have to suit it for its function ?

A
  • Rectangular, packs closely to form a continuous layer
  • Chloroplasts are able to move in cytoplasm, so can absorb more light
  • Lots of chloroplasts
88
Q

What features does a guard cell have to suit it for its function ?

A
  • Cell wall thicker on inside than the outside, so cell does not change symmetrically as its volume changes
  • Gap in the centre, allows gases in and out
89
Q

What are the 4 main categories of tissues in animals ?

A
  • Nerve tissues, adapted to support the transmission of electrical analysis
  • Epithelial tissues, adapted to cover body surfaces, internal and external
  • Muscle tissues, adapted to contract
  • Connective tissues, adapted either to hold other tissues together or as a transport medium
90
Q

What features does squamous epithelium have to suit its function ?

A
  • Made up of squamous epithelial cells
  • Very thin due to the flat cells that make it up, 1 cell thin
  • Forms the lining of the lungs, allows for rapid diffusion
91
Q

What features does ciliated epithelium have to suit its function ?

A
    • Made up of ciliated epithelial cells
    • Have cilia that line the trachea causing mucus to be swept away from the lungs
    • Have goblet cells, release mucus to trap unwanted particles
92
Q

What features does cartilage have to suit its function ?

A
  • Contains elastin and collagen
  • Firm flexible tissue, composed of chondrocyte cells embedded in an extracellular matrix
  • Prevents the ends of bones from rubbing together and causing damage
93
Q

What features do muscles have to suit their function ?

A

Skeletal muscle fibres contain myofibrils which contain contractile proteins

94
Q

What are two tissues in plant cells ?

A
  • Epidermis tissue

- Vascular tissue

95
Q

What features does the epidermis have to suit its function ?

A
  • Covered by a waxy, waterproof cuticle to reduce the loss of water
  • Stomata are present, allow for the movement of CO2, O2 and water vapour
96
Q

What features does the xylem tissue have to suit its function ?

A
  • It is a vascular tissue that is responsible for transport of water and minerals throughout plants
  • Composed of elongated dead cells, the walls of these cells are strengthened with lignin, provides structural support
97
Q

What features does the phloem tissue have to suit its function ?

A
  • It is a vascular tissue that is responsible for the transport of nutrients from leaves and stems to parts of the plant where it is needed
  • Composed of columns of sieve tube cells separated by perforated walls called sieve plates
98
Q

Define undifferentiated

A

An unspecialised cell originating from mitosis or meiosis

99
Q

Define potency

A

The ability of a stem cell to differentiate into different cell types

100
Q

Define totipotent

A

A stem cell that can differentiate into any type of cell and form a whole organism

101
Q

Define pluripotent

A

A stem cell that can from all types of tissue but not a whole organism

102
Q

Define multipotent

A

Can only form a range of cells from a certain cell lineage

103
Q

What are stem cells ?

A

Undifferentiated cells with the potential to differentiate into a variety of the specialised cell types of an organism

104
Q

What are the characteristics of stem cells ?

A
  • Can repeatedly undergo cell division
  • Not adapted to a specific function
  • Can give rise to specialist cells
105
Q

What are stem cells used for in the body ?

A
  • Growth
  • Development, of an embryo
  • Tissue repair
106
Q

What happens after they differentiate ?

A

They can no longer divide and leave the cell cycle into the G0 phase

107
Q

What happens if stem cells do not divide fast enough ?

A

The tissues are not efficiently replaced, leading to ageing

108
Q

What happens if stem cells divide too fast ?

A

They can form masses of cells called tumours which can lead to the development of cancer

109
Q

Where are the sources of stem cells in animals ?

A
  • Embryonic stem cells
  • Adult stem cells
  • Umbilical cords of newborn babies
110
Q

Where are the sources of stem cells in plants ?

A

Meristematic tissues

111
Q

Where are meristematic tissues found ?

A
  • In the tips of roots and shoots

- In phloem and xylem tissues, called the vascular cambium

112
Q

How do cells become specialised ?

A
  • All the cells have the same DNA
  • Genes are switched on and off by epigenetics
  • Different proteins are produced in the cell
  • So the cell can undergo a specialised function due to these proteins in the cell
113
Q

What determines the function of the cell ?

A

The proteins within it

114
Q

Give an example of where totipotent cells can be found in a human

A

In a zygote

115
Q

Give an example of where pluripotent cells are found in a human

A

Blastocyst

116
Q

Give an example of where multipotent cells are found in a human

A

Blood stem cells

117
Q

What can totipotent cells turn into ?

A
  • A whole organism

- Extra embryonic tissues such as the amnion and the umbilicus

118
Q

What can pluripotent cells turn into ?

A

Different types of tissues within an organism

119
Q

What can multipotent cells turn into ?

A

Various types of cell from the lineage of the tissue they are from

120
Q

How long do erythrocytes live for ?

A

120 days

121
Q

How long do neutrophils live for ?

A

6 hours

122
Q

What supplies erythrocytes and neutrophils ?

A

Bone marrow

Biology (30 decks)

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