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BIO HL > D2.1 Cell and Nuclear Division > Flashcards

D2.1 Cell and Nuclear Division Flashcards

1
Q

what is cytokinesis

A

division of cytoplasm
happens in the final stage of nuclear division

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2
Q

what happens to mitochondria and chloroplasts in division

A

they are distributed evenly between the two cells

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3
Q

how does cytokinesis occur in animal cells

A

this happens with in tucking of the plasma membrane at the equator of the cell, pinching the cytoplasm in half
a ring of actin, myosin and other proteins form a contractile ring which pinches the membrane

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4
Q

how does cytokinesis occur in plant cells

A

the Golgi apparatus forms vesicles of new cell wall materials, which collect along the line of the equator ( cell plate)
vesicles then combine to form the new plasma membrane and cell walls

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5
Q

when can cytokinesis be unequal

A

in oogenesis ( egg production) a large egg is formed alongside several smaller cells.
Primary oocyte divides, one is a tiny polar body while the other is a secondary oocyte
When the secondary oocyte divides, another polar body is formed as well
the polar bodies then degenerate and their components are absorbed

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6
Q

What does the ovum require for the growing embryo

A

a large cytoplasm to provide nutrients and energy

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7
Q

why must nuclear division happen before cell division

A

to avoid production of cells with no nucleus
one will have a nucleus and the other will not

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8
Q

when does mitosis occur

A

they produce diploid cells so when
an organism grows
old cells are replaced
when an organism reproduces asexually

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9
Q

when does meiosis occur

A

produces haploid cells
occurs when sexual reproduction occurs, during the formation of gametes

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10
Q

When does DNA replication occur in the cell cycle

A

during interphase
produces double stranded chromosomes

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11
Q

what is each strand of a chromosome known as

A

chromatids, two in each chromosome

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12
Q

how are chromatids held together

A

held together by a centromere, a specialised DNA sequence that can be seen as a the constricted region of a chromosome

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13
Q

what happens to chromatids during nuclear division

A

each of the sister chromatids separate and move into different cells

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14
Q

what does each chromosome contain

A

one very long DNA molecule

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15
Q

what are the functions of the proteins in the chromosomes

A

some are enzymes involved in copying and repair reactions of DNA.
Bulk of then have a supporting and packaging role in DNA

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16
Q

what are nucleosomes

A

DNA double helix is looped around histone protein beads
Wrapped around 2 and a half times around 8 histone proteins

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17
Q

what is a chromatin

A

the nucleosomes are coiled up to form a chromatin fibre

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18
Q

what is a chromatid

A

the chromatin are coiled up again, looped around a scaffold protein and then supercoiled up again into the much condensed chromatid

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19
Q

what are histones

A

positively charged proteins containing a high concentration of amino acid molecules with additional basic functional groups

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20
Q

how are chromosomes during cell division

A

using microtubules and microtubule motors

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21
Q

what are microtubules and how do they assist in cell division

A

cytoskeletal fibres that can lengthen and shorten with polymerisation/ depolymerisation of tubulin
movement of chromosomes is achieved due to this and facilitated by motor proteins carrying them along the microtubules

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22
Q

What are the different stages of mitosis

A

Prophase
Metaphase
Anaphase
Telophase

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23
Q

steps of prophase

A

chromosomes present as long thin threads. They increasingly shorten and thicken by a process of supercoiling
In the end, chromosomes consist of two chromatids held together by a centromere
nucleolus gradually disappears

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24
Q

steps of metaphase

A

centrioles move to opposite ends of the cell
microtubules start to form a spindle, radiating out from centrioles
microtubules attach to centromeres and arrange them at the equator

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25
Q

steps of anaphase

A

centromeres divide
spindle fibres shorten and chromatids pulled by centromeres to opposite poles
Once separated. chromatids referred to as chromosomes

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26
Q

steps of telaphase

A

a nuclear membrane reforms around both groups of chromosomes at opposite ends of the cell
chromosome decondenses and becomes chromatin again
nucleolus reforms in each nucleus
follow by the division of the cytoplasm

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27
Q

features of meiosis

A

two divisions of the nucleus but only one replication of chromosomes
early in the meiosis one, homologous chromosomes pair up
no further interphase inbetween meiosis I and II

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28
Q

what is a bivalent

A

when homologous chromosomes pair up closely
members of a bivalent continue to shorten known as condensation

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29
Q

What happens during the coiling and shortening process in meiosis

A

chromatids can break. When non sister chromatids from homologous chromosomes break and rejoin, they can do so at corresponding sites, forming a cross structure known as chiasma

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30
Q

what is known as crossing over in meiosis

A

the creation of chiasmas that can happen at one or more places along the bivalent
it means genes have been exchanged between chromatids

31
Q

how meiosis one end

A

with two cells each containing a single set of chromosomes, made of two chromatids
members of bivalents become attached by their centromeres to the fibres of the spindle at the equatorial plate of the cell. Spindle fibres pull the homologous chromosomes apart to opposite poles but the individual chromatids remain attached by the centromeres

32
Q

what happens in meiosis II

A

centromeres of the chromosomes divide and the individual chromatids now move to opposite poles
leads to four cells, each with half the chromosome number of the original parent cell

33
Q

what is non disjunction

A

there is failure of homologous chromosomes or sister chromatids to separate properly during meiosis, leading to some gametes with more than and some with less than the haploid number of chromosomes

34
Q

what is the result of non disjunction

A

down syndrome where people have an extra chromosome

35
Q

what are the two reasons the haploid cells produced by meiosis differ genetically

A

crossing over of segments, resulting in new combinations of genes on the chromosome
random orientation of chromosomes which happens because the way bivalents line up at the equator is completely random

36
Q

what is the result of crossing over

A

due to formations of chiasmas, there can be new combinations of alleles on the chromosomes of the haploid cells

37
Q

What is the result of random orientation

A

generates a huge amount of variation in the coded information carried out by different gametes in the fertilisation stage
bivalents separate and move to the nearest pole after lining up randomly

38
Q

how do both animal and plants grow from a single cell

A

by repeated cell divisions to form an embryo

39
Q

what is proliferation and when does it happen

A

a rapid increase in number of cells
happens after early stage of animal embryos and plant meristem tissues

40
Q

what are meristems

A

they are a group of cells that retain the ability to divide by mitosis
they allow plants to grow at restricted points in the plant

41
Q

features of meristem cells

A

small
thin cellulose walls
dense cytoplasmic contents
vacuoles are mostly absent

42
Q

where are meristems found

A

at terminal growing points of stems and roots
or laterally

43
Q

what are apical meristems

A

occur at the tips of stems and root, responsible for primary growth
Cell division and growth leads to the formation of stem/root tissue
new cells formed by division rapidly increase in size and then cells differentiate

44
Q

what are lateral meristems

A

form from the cambium cells in the centre of vascular bundles, between the phloem and xylem tissue
it causes secondary growth leading to increased girth and length of stem

45
Q

why is proliferation required inside animals

A

cells constantly need to be replaced in a routine process

46
Q

stem cells under the skin

A

in the bottom/basal layer, stem cells remain undifferentiated and continue dividing throughout life
daughter cells differentiate and leave the basal layer
process maintained because basal cells are self renewing

47
Q

proliferation in wound healing

A

after blood clotting, inflammation causes increases blood flow to the wound, enabling WBC and fibroblasts to travel rapidly to the damaged skin
WBC remove infection, and fibroblasts produce proteins( proliferation) to help wound closure

48
Q

what are the three main phases in cell cycle

A

Interphase ( G1, S, G2)
division of nucleus by mitosis resulting in two identical cells
Division of cytoplasm and cell, Cytokinesis

49
Q

What happens in G1 of interphase

A

the first phase of growth, there is synthesis of new organelles that take place in the cytoplasm
intense biochemical activity in the cytoplasm/organelles
accumulation of energy stores before nuclear division

50
Q

what happen in S phase of interphase

A

period of synthesis of DNA, each chromosome makes a copy of itself
two identical structures are known as chromatids

51
Q

what happens in G2 of interphase

A

the second phase of growth is a continuation of the biochemical activity and increase in amount of cytoplasm

52
Q

how long does interphase take

A

longest part of the cell cycle, but time differs in mature cells and embryos. some cells never divide again

53
Q

what is interphase

A

metabolically active period and growth involves synthesis of cell components including proteins and DNA. Mitochondria and chloroplasts are increased

54
Q

what do chromosomes do during interphase

A

actively involved in protein synthesis
copies of particular genes are taken to the cytoplasm, ribosomes than synthesise proteins

55
Q

what happens to chromosomes in interphase

A

they are dispersed and are referred to as chromatins
among the chromatins there are one or more nucleoli which synthesis ribosomes which then migrate out into the cytoplasm

56
Q

cell cycle is regulated by molecular control system. What are key points of the system

A

key checkpoints where signals operate, along with stop points which have to be overridden
three checkpoints at G1, G2, mitosis

57
Q

the molecular control signal in the cytoplasm is what

A

proteins known as kinases and cyclins

58
Q

what are kinases

A

enzymes that activate/inactivate other proteins, always present in cytoplasm

59
Q

how are kinases related to cyclins

A

kinases activated by specific cyclins and referred to as Cyclin Dependent Kinases (CDK)

60
Q

what does cyclin do in the cytoplasm

A

cyclin concentration in the cytoplasm change constantly. As cyclin concentration increase, they combine with CDK molecules to form a complex that functions as a mitosis promoting factor ( MPF)

61
Q

what happens when Mitosis Promoting factor accumulates

A

triggers chromosome condensation, fragmentation of the nuclear membrane and spindle formation( starts mitosis)

62
Q

how is cyclin used as a checkpoint

A

specific level required to pass each checkpoint in the cycle

63
Q

what happens to cyclin in anaphase

A

destruction of cyclin commences

64
Q

what are proto-oncogenes

A

genes that encode proteins that stimulate cell division
mutations convert them to oncogenes, leading to increase in protein production, resulting in uncontrolled cell division, possibly leading to cancer

65
Q

what is an example of cancer from oncogenes

A

seen in Ras gene which codes for Ras proteins. Oncogene codes for permanently activated Ras protein which triggers the kinase cascade in the absence of growth factor, resulting in uncontrolled cell division
mutations results from a dominant allele

66
Q

What are tumour suppressor genes

A

encode for proteins that inhibit cell division or promote apoptosis if damaged DNA is copied
mutation of these result in lack of these proteins, resulting in uncontrolled cell division, possibly leading to cancer

67
Q

what is an example of a mutation in tumour suppressor genes

A

seen in p53 gene which promotes protein synthesis of protein that triggers cell death
no p53 protein being produced means cell with damaged DNA continue to proliferate, leading to uncontrolled cell division
mutation in a recessive allele

68
Q

what happens in all cancers

A

cells start to divide repeatedly without control or regulation
leads to rate of cell multiplication being much faster than the rate of cell death

69
Q

what is the result of cancer

A

irregular mass of cells is formed, called a tumour
some can be benign, some can be malignant

70
Q

what are malignant tumours

A

they are cancerous, secrete signals to trigger growth of blood and lymph vessels to serve tumour cells at the expense of other tissues

71
Q

what is metastasis

A

the spread of cancer cells to other locations
cells can break away from primary tumour and carried to other parts

72
Q

what is the result of cancer

A

cancerous cells ultimately take over the body at the expense of healthy cells, leading to malfunction and death

73
Q

what is mitotic index

A

measures how many cells in a sample are in mitosis compared to total number of cells
used to differentiate between benign and malignant

74
Q

what is the use of mitotic index

A

able to indicate rapidly dividing cell masses through high mitotic index, indicates tumour formation
used to investigate response to chemotherapy

BIO HL (16 decks)

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