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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

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25
What are the two major processes in eukaryotes for transmission of genes
Mitosis and meiosis
26
Where does mitosis occur
Somatic tissue
27
What does mitosis result in
2 identical daughter cells with identical number of chromosomes to the parent cell (diploid)
28
Why is mitosis necessary
Embryonic development, replacement of skin cells and wound healing
29
What are spindle fibres
Formed from micro tubules and they between the poles of the cell creating an axis for chromosome separation
30
What is a centriole
A cytoplasmic organelle composed of nine groups of micro tubules that serve as the foci for the generation of the mitotic spindle fibres
31
What is the centrisome
A region of the cytoplasm containing a pair of centrioles
32
What makes up interphase of the cell cycle
G1 (and checkpoint), s phase, G2 (and checkpoint)
33
What occurs in G1
Cell grows and makes proteins required for DNA synthesis
34
What occurs in s phase (synthesis phase)
DNA is replicated to produce chromosomes with two identical sister chromatids
35
What occurs in G2
Production of proteins required for mitosis
36
What is the importance of the G1 and G2 checkpoints
Ensures all proteins required for DNA replication (1) are present and DNA has been replicated accurately (2) before mitosis
37
What is cytokinesis
Division of the cytoplasm
38
What happens in prophase of mitosis
Chromosomes condense and the centrosomes move apart
39
What happens in prometaphase of mitosis
Chromosomes are recognisable double structures Centrioles reach the opposite poles Spindle fibres form and attach to the kinetochore
40
What occurs in metaphase of mitosis
Centromeres align on metaphase plate Spindle assembly checkpoint to ensure all chromosomes are aligned and 1 sister chromatid is attached to each pole
41
What occurs in anaphase of mitosis
Centromeres split and the daughter chromatids migrate to opposite poles
42
What occurs in telophase of mitosis
Daughter chromosomes arrive at poles Chromosomes decondense and nuclear envelope reforms Cytokinesis
43
What is meiosis
Cell division to produce sex cells/gametes
44
What does meiosis produce
4 Haploid cells (n) that are not genetically identical
45
How many divisions are in meiosis
2
46
In meiosis 1, what are the 5 different stages of prophase 1
Leptotene, zygotene, pachytene, diplotene and diakinesis
47
What occurs in prophase 1 of meiosis that does not happen in mitosis
Crossing over to generate genetic variability
48
What happens in leptotene of prophase 1
Duplicated chromosomes condense
49
What happens in zygotene of prophase 1
Bivalent forms, synaptonemal complex forms and synapsis begins
50
What happens in pachytene of prophase 1
Synapsis and synaptonemal complex are complete, crossing over occurs
51
What happens in diplotene of prophase 1
Chiasma is visible, exchange of lengths of DNA, synaptonemal complex disappears
52
What happens in diakinesis of prophase 1
Nuclear envelope fragments, bivalent ready for metaphase
53
What are tetrads
Homologous chromosomes pairs
54
What is a dyad
1 half of each homologous chromosome pair
55
What is the synaptonemal complex
A nucleoprotein ‘zipper’ that forms between the paired homologous chromosome that plays an important part in crossing over (chiasmata formation)
56
What is a chiasma
A physical connection between non sister chromatids that results in genetic exchange and creates ‘mosaic’ chromosomes of the paternal and maternal chromosomes
57
How do you calculate the number of variations produced in meiosis
2 to the power of chromosome number e.g. 23
58
What is the difference between meiosis in human males and females
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
59
What happens when meiosis goes wrong
Nondisjunction (Aneuploidy, polyploidy, trisomy)
60
What is aneuploidy
Increase or decrease in number of individual chromosomes
61
What is polyploidy
An increase in number of chromosomes sets
62
What is a trisomy
3 copies of a particular chromosome rather than 2
63
What are the 4 usual human autosomal trisomies
Trisomy 21, 18, 13 and 8
64
What is Trisomy 21
Down syndrome (intellectual disability, broad flat face)
65
What is trisomy 18
Edward’s syndrome (intellectual disability, deformed feet, heart problems)
66
What is trisomy 13
Patau syndrome (intellectual disability, small head, cleft lip and palate, extra fingers and toes)
67
What is trisomy 8
Warkany syndrome 2. (Intellectual disability, contracted fingers and toes, malformed ears, prominent foreheads)
68
Which human autosomal trisomy is rarest
Trisomy 8/ warkany syndrome 2
69
What determines maleness
Presence of the Y chromosome
70
What is the klinefelter karyotype
More than one X chromosomes in males
71
What is the turner karyotype
Single X chromosomes in females
72
What causes klinefelter and turner syndrome
Aneuploidy (NJ)
73
What does the Y chromosome code for
Fewer genes than X but still codes for 26 unique proteins for male fertility
74
What are the 3 regions of the Y chromosome
Pseudoautosomal regions (PARs), male specific region (MSY) and sex determining region (SRY)
75
Describe the PARs of the Y chromosome
Shares homologous with X, synapse and recombine with X during meiosis
76
Describe the MSY region
Does not synapse with X chromosome during meiosis
77
Describe the SRY region
Produces testis determining factor (TDF) which triggers undifferentiated gonadal tissue of the embryo to form testes
78
What is the advantage of sexes
Sexual reproduction results in recombinant genotypes enabling the population better adapted to changes in environment
79
What is dosage compensation
Mechanism to keep X-linked gene product dosages similar between males and females as females have 2 X chromosomes so potential to produce double the amount of gene product
80
What is a Barr body
Inactivated X chromosome which results from dosage compensation
81
How do you calculate the number of Barr bodies
Xn-1
82
How many Barr bodies does a turner female have (X)
None
83
How many Barr bodies does klinefelter male (XXXY) have
2
84
What is lyonization
It is randomised whether the maternal or paternal X chromosome is inactive (Barr body), all progeny cells have same inactivated X chromosomes and inactivation occurs early in development

NUT1004 (17 decks)

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