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NUT1004 > Cell division > Flashcards

Cell division Flashcards

1
Q

Why do cells need to divide

A

For growth, reproduction and for replacement of dead cells

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2
Q

What are the two types of chromatin

A

Euchromatin and Heterochromatin

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3
Q

What is Euchromatin

A

Relatively uncondensed chromatin associated with active (expressed genes)

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4
Q

What is heterochromatin

A

Condensed chromatin associated with repetitive gene poor regions that are inactive (silenced)

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5
Q

What is a centromere

A

Region of a chromosome where two sister chromatids are held together

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6
Q

What are alpha satellites

A

Arrays of repeated sequences in centromeres of human chromosomes

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7
Q

What is the kinetocore

A

A protein structure located at the centromere that serves as an attachment point for mitotic spindles

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8
Q

How are chromosomes categorised based on centromere position

A

Metcentric (central centromere), submetacentric (centromere more towards one end), arcocentric (really short p arms/ top half of chromosome), telocentric (really long a arms/no p arms/ centromere at top)

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9
Q

What are telomeres

A

Specialised regions at the ends of chromosomes

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10
Q

What are the 2 functions of telomeres

A

1) Enable cells to distinguish a real chromosome end from an unnatural chromosome end caused by a chromosome break
2) solve the end replication problem

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11
Q

What is the end replication problem

A

During DNA replication the 3’ terminal portion of the chromosome cannot be copied resulting in a shortened chromosome and progressive shortening over successive replication cycles

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12
Q

What is the repeated sequence that makes up telomeres

A

5’- TTAGGG-3’

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13
Q

How do telomeres resolve the end replication problem

A

Uncopied region of the chromosome is recognised by the enzyme telomerase which adds multiple copies of ‘TTAGGG’ repeat (telomere sequence) to the template strand so the new DNA can be synthesised by replication machinery in its entirety

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14
Q

How many chromosomes does the human genome have

A

46 (23 pairs)

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15
Q

What are homologous chromosomes

A

Pairs of chromosomes that carry the same set of genes

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16
Q

What is a karyotype

A

Image of all chromosomes acquired through isolation and treatment of cells in anaphase

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17
Q

How are chromosomes seen in a karyotype

A

Opened and stained in anaphase to produce a banding pattern on the chromosomes, which enables homologous chromosomes to be paired (same banding)

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18
Q

What are the 4 techniques for staining DNA in karyotype

A

G banding, R banding, Q banding and C banding

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19
Q

What dye is used in G banding, R banding and C banding staining techniques

A

Giemsa

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20
Q

Describe the procedure and results of G banding

A

Mild proteolysis followed by giesma to produce dark bands AT rich

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21
Q

Describe the procedure and results of R banding

A

Heat denaturation and giesma to produce dark bands GC rich

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22
Q

Describe the procedure and results of Q banding

A

Stain with quinacrine and view under UV light to see AT and GC regions vary in brightness

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23
Q

Describe the procedure and results of C banding

A

Treat with alkali and giesma to produce dark banding at the centromeric region

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24
Q

Does gene number and chromosome number increase with genome size

A

No

25
Q

What are the two major processes in eukaryotes for transmission of genes

A

Mitosis and meiosis

26
Q

Where does mitosis occur

A

Somatic tissue

27
Q

What does mitosis result in

A

2 identical daughter cells with identical number of chromosomes to the parent cell (diploid)

28
Q

Why is mitosis necessary

A

Embryonic development, replacement of skin cells and wound healing

29
Q

What are spindle fibres

A

Formed from micro tubules and they between the poles of the cell creating an axis for chromosome separation

30
Q

What is a centriole

A

A cytoplasmic organelle composed of nine groups of micro tubules that serve as the foci for the generation of the mitotic spindle fibres

31
Q

What is the centrisome

A

A region of the cytoplasm containing a pair of centrioles

32
Q

What makes up interphase of the cell cycle

A

G1 (and checkpoint), s phase, G2 (and checkpoint)

33
Q

What occurs in G1

A

Cell grows and makes proteins required for DNA synthesis

34
Q

What occurs in s phase (synthesis phase)

A

DNA is replicated to produce chromosomes with two identical sister chromatids

35
Q

What occurs in G2

A

Production of proteins required for mitosis

36
Q

What is the importance of the G1 and G2 checkpoints

A

Ensures all proteins required for DNA replication (1) are present and DNA has been replicated accurately (2) before mitosis

37
Q

What is cytokinesis

A

Division of the cytoplasm

38
Q

What happens in prophase of mitosis

A

Chromosomes condense and the centrosomes move apart

39
Q

What happens in prometaphase of mitosis

A

Chromosomes are recognisable double structures
Centrioles reach the opposite poles
Spindle fibres form and attach to the kinetochore

40
Q

What occurs in metaphase of mitosis

A

Centromeres align on metaphase plate
Spindle assembly checkpoint to ensure all chromosomes are aligned and 1 sister chromatid is attached to each pole

41
Q

What occurs in anaphase of mitosis

A

Centromeres split and the daughter chromatids migrate to opposite poles

42
Q

What occurs in telophase of mitosis

A

Daughter chromosomes arrive at poles
Chromosomes decondense and nuclear envelope reforms
Cytokinesis

43
Q

What is meiosis

A

Cell division to produce sex cells/gametes

44
Q

What does meiosis produce

A

4 Haploid cells (n) that are not genetically identical

45
Q

How many divisions are in meiosis

A

2

46
Q

In meiosis 1, what are the 5 different stages of prophase 1

A

Leptotene, zygotene, pachytene, diplotene and diakinesis

47
Q

What occurs in prophase 1 of meiosis that does not happen in mitosis

A

Crossing over to generate genetic variability

48
Q

What happens in leptotene of prophase 1

A

Duplicated chromosomes condense

49
Q

What happens in zygotene of prophase 1

A

Bivalent forms, synaptonemal complex forms and synapsis begins

50
Q

What happens in pachytene of prophase 1

A

Synapsis and synaptonemal complex are complete, crossing over occurs

51
Q

What happens in diplotene of prophase 1

A

Chiasma is visible, exchange of lengths of DNA, synaptonemal complex disappears

52
Q

What happens in diakinesis of prophase 1

A

Nuclear envelope fragments, bivalent ready for metaphase

53
Q

What are tetrads

A

Homologous chromosomes pairs

54
Q

What is a dyad

A

1 half of each homologous chromosome pair

55
Q

What is the synaptonemal complex

A

A nucleoprotein ‘zipper’ that forms between the paired homologous chromosome that plays an important part in crossing over (chiasmata formation)

56
Q

What is a chiasma

A

A physical connection between non sister chromatids that results in genetic exchange and creates ‘mosaic’ chromosomes of the paternal and maternal chromosomes

57
Q

How do you calculate the number of variations produced in meiosis

A

2 to the power of chromosome number e.g. 23

58
Q

What is the difference between meiosis in human males and females

A

Divisions in oogenesis are not continuous like spermatogenesis as the first division in the ovary arrests in prophase 1 and only resumes many years later prior to ovulation and the second division only occurs after fertilisation

NUT1004 (14 decks)

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