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BIOL4002 - Cell biology > Chromosome Structure and the Eukaryotic Cell Cycle > Flashcards

Chromosome Structure and the Eukaryotic Cell Cycle Flashcards

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1
Q

What do chromosomes contain?

A

Chromosomes contain the genetic material of an organism

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2
Q

Where are genes located within chromosomes?

A

Genes are physically located within the chromosomes

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3
Q

What are chromosomes composed of?

A

Chromosomes are composed of DNA and proteins

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4
Q

What does the DNA-protein complex make in chromosomes?

A

Chromatin

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5
Q

What is the primary function of genetic material?

A

The primary function of genetic material is to store needed information

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6
Q

What is chromosome compaction?

A

Chromosome compaction is the process by which DNA is tightly packed into the nucleus of a cell

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7
Q

What is a nucleosome?

A

A nucleosome is a repeating unit of DNA wrapped around an octamer of histone proteins

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8
Q

How does DNA wrap around histone proteins in a nucleosome?

A

DNA wraps itself around histone proteins in a nucleosome through the attraction between the negative charges of DNA and the positive charges of histones

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9
Q

How much does the length of DNA shorten when it wraps around histone proteins?

A

The length of DNA shortens about sevenfold when it wraps around histone proteins

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10
Q

What is the structure of the nucleosome units when they are further compacted?

A

The nucleosome units are organized into a more compact structure that is 30 nm in diameter

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11
Q

What is the effect of further nucleosome compaction on DNA length?

A

Further nucleosome compaction shortens the nucleosome structure another sevenfold

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12
Q

Why is the structure of the more compact nucleosome units difficult to determine?

A

Because the conformation of the DNA may be substantially altered when extracted from living cells

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13
Q

What are radial loop domains?

A

Loops of DNA that extend outwards from a central protein scaffold, forming a hierarchical structure of chromatin

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14
Q

What is the interaction between 30-nm fibers and nuclear matrix proteins?

A

The 30-nm fibers of chromatin are thought to interact with nuclear matrix proteins, providing additional stability and organisation to chromosomes.

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15
Q

How are chromosomes separated?

A

Each chromosome is located in a discrete, non-overlapping chromosome territory within the nucleus

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16
Q

Do different chromosomes become intertwined when they are not compacted?

A

No, different chromosomes are not substantially intertwined even when they are not compacted

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17
Q

Why is the level of compaction of chromosomes not uniform?

A

Different regions of chromosomes have different functions and therefore require different levels of compaction

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18
Q

What are the 2 forms of chromatin that exist?

A
  • heterochromatin
  • euchromatin
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19
Q

What is heterochromatin?

A
  • a highly compacted form of chromatin
  • transcriptionally inactive, meaning that genes are not read to produce RNA
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20
Q

What is euchromatin?

A
  • a less condensed form of chromatin
  • capable of gene transcription
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21
Q

Where is most chromosomal regions found in non-dividing cells?

A

Most chromosomal regions are found in non-dividing cells in a partially compacted form

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22
Q

When do chromosomes compact further?

A

Chromosomes compact further when the cell is preparing to divide (cell division)

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23
Q

What happens to all euchromatin during cell division?

A

All euchromatin is converted to heterochromatin during cell division

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24
Q

What happens to most transcriptional activities during cell division?

A

Most transcriptional activities cease during cell division

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25
Q

What happens to radial loops in metaphase chromosomes?

A

In metaphase chromosomes, highly compacted radial loops remain anchored to a scaffold formed from proteins

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26
Q

Do eukaryotic chromosomes occur in sets?

A

Yes

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27
Q

How many different chromosomes do humans have?

A

23 different chromosomes

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28
Q

What are sex chromosomes in humans?

A

X and Y chromosomes

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29
Q

How many chromosomes do humans have in most cell types?

A

Two sets of 23 chromosomes so 46 in total in most cells

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30
Q

What does diploid mean?

A

Diploid describes cells with a pair of each chromosome (2n, 2 sets of chromosomes)

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31
Q

What does haploid mean?

A

Haploid describes cells such as gametes which have only 1 member of each pair of chromosomes (1n)

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32
Q

What are homologous chromosomes (homologues)?

A

Members of a pair of chromosomes that are similar and nearly identical in genetic composition

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33
Q

Where do homologues come from in diploid organisms?

A
  • one pair of homologous chromosomes from the mother
  • the other pair from the father
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34
Q

What do slight differences in homologous chromosomes provide?

A

Provide variation in gene function

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35
Q

What are differences in genetic composition between homologues called?

A

Differences in genetic composition between homologues are called single nucleotide polymorphisms (SNPs)

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36
Q

Do sex chromosomes differ in size and genetic composition?

A

Yes

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37
Q

What are sister chromatids?

A

Sister chromatids are the individual, replicated copies of each chromosome that are still attached to each other

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38
Q

When do sister chromatids form?

A

Sister chromatids form when a cell replicates its chromosomes before cell division

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39
Q

Why do chromosomes often appear as X’s?

A

Because they consist of two identical sister chromatids that are joined together by a structure called the centromere

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40
Q

What is karyotype analysis?

A

Karyotype analysis is a field of genetics that involves microscopic examination of chromosomes

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41
Q

What can be seen through light microscopy in karyotype analysis?

A
  • tightly compacted chromosomes that have distinctive shapes
  • the number of chromosomes
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42
Q

What does the banding pattern in karyotype analysis enable?

A

The banding pattern, created by chemical dyes, enables the identification of similar chromosomes

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43
Q

How are chromosomes identified by structure?

A
  • size
  • location of the centromere
  • presence of bands
    after staining
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44
Q

What is the naming convention for the short and long arms of a chromosome?

A
  • short arm = p
  • long arm = q
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45
Q

Draw a pair of chromosomes and label it with p, q and the centromere

A

slide 17

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46
Q

What are the four types of chromosome structure based on centromere location?

A
  • metacentric (middle)
  • submetacentric (off-center)
  • acrocentric (near end)
  • telocentric (at the end)
    (slide 17)
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47
Q

Draw a pair of chromosomes for each of the 4 types of location of centromere and label it

A

slide 17

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48
Q

What is Giemsa staining used for in chromosome analysis?

A

To create banding patterns on chromosomes, which can be used for identification and analysis
- this technique is known as G-banding

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49
Q

What is the cell cycle?

A

A series of events that occur in a cell leading to cell growth and division into two daughter cells

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50
Q

What are the phases of the cell cycle?

A
  • G1 (first gap)
  • S (DNA synthesis)
  • G2 (second gap)
  • M (mitosis)
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51
Q

What are checkpoint proteins?

A
  • act as sensors to determine if the cell is in proper condition to divide
  • can delay cell division until problems are fixed
  • or prevent it entirely if necessary
52
Q

What can happen if there is a loss of checkpoint function in the cell cycle?

A

Can lead to mutation - e.g. cancer as cells gain the ability to divide continuously

53
Q

What is the role of cyclin and cyclin-dependent kinase in the cell cycle?

A

(cdks) are proteins responsible for advancing a cell through the phases of the cell cycle
- amount of cyclin varies throughout the cell cycle
- kinases controlling the cell cycle (e.g. cdk) must bind to a cyclin to be active

54
Q

How many critical regulatory points or checkpoints exist in eukaryotic cells?

A

3

55
Q

What are the 3 critical regulatory points or checkpoints in eukaryotic cells?

A
  • G1 checkpoint (restriction point)
  • G2 checkpoint
  • Metaphase checkpoint
56
Q

What happens during the Synthesis phase (S-phase) of the cell cycle?

A
  • DNA replication occurs resulting in the production of duplicated strands of DNA called sister chromatids
  • sister chromatids are tightly associated at the centromere until they separate during mitosis
57
Q

What is mitotic cell division?

A

Mitotis is when a cell divides to produce 2 new cells that are genetically identical to the original.

58
Q

What is the original cell called in mitotic cell division?

A

The original cell is called the mother cell

59
Q

What are the new cells called in mitotic cell division?

A

The new cells are called daughter cells

60
Q

What is cytokinesis?

A

Process of cell division that begins during anaphase and is completed after telophase

61
Q

What is the purpose of mitotic cell division?

A
  • asexual reproduction
  • for production and maintenance of multicellularity
62
Q

What are the 4 phases of mitosis?

A

(Interphase)
- prophase
(pro-metaphase)
- metaphase
- anaphase
- telophase
(Cytokinesis)

63
Q

What is the mitotic spindle?

A

Responsible for organising and sorting the chromosomes during mitosis

64
Q

What is the mitotic spindle composed of?

A

The mitotic spindle is composed of microtubules
- microtubules formed from tubulin proteins

65
Q

What are centrosomes and their role in mitosis?

A

Centrosomes are microtubule organizing centers (MTOCs)
-single centrosome duplicates at the beginning of M phase and define a cellular pole

66
Q

What is the role of centrosomes?

A

Responsible for organising & sorting chromosomes during mitosis

67
Q

What are the 3 types of microtubules in the spindle apparatus?

A
  • astral
  • polar
  • kinetochore
68
Q

What is the role of astral microtubules in mitosis?

A

Position the spindle apparatus within the cell

69
Q

What is the role of polar microtubules in mitosis?

A

Separate the two poles of the cell

70
Q

What is the role of kinetochore microtubules in mitosis?

A

Attached to the kinetochore of a chromosome at one end, and to the centrosome at its other end

71
Q

What happens during interphase?

A
  • chromosomes are maximally extended
  • found in the nucleus
  • cell not in mitosis
    i.e. G1, S, and G2 phases of the cell cycle
72
Q

What happens during prophase?

A
  • chromosomes have already replicated to produce sister chromatids
  • nuclear membrane dissociates into small vesicles
  • chromatids condense into compacted structures (readily visible by light microscopy)
73
Q

What happens during prometaphase?

A
  • mitotic spindle is completely formed
  • centrosomes move apart to separate the two poles
  • spindle fibers interact with sister chromatids
  • two kinetochores on each pair of sister chromatids are attached to kinetochore microtubules from opposite poles
74
Q

What happens during metaphase?

A
  • pairs of sister chromatids are aligned along a plane halfway between the poles called the metaphase plate
  • they are organised into a single row
  • when this alignment is complete, the cell is in metaphase
75
Q

What happens during anaphase?

A
  • connections between the pairs of sister chromatids are broken
  • each chromatid, now an individual chromosome, is linked to only one of the two poles by one or more kinetochore microtubules
  • kinetochore microtubules shorten, pulling the chromosomes toward the pole to which they are attached
  • two poles move farther away from each other as overlapping polar microtubules lengthen and push against each other
76
Q

What happens during telophase?

A
  • chromosomes have reached their respective poles and decondense
  • nuclear membranes now re-form to produce two separate nuclei
77
Q

What happens during cytokinesis in mitosis?

A

During cytokinesis in mitosis, the two nuclei are segregated into separate daughter cells.

78
Q

How does the process of cytokinesis differ between animals and plants?

A
  • animals = a cleavage furrow constricts like a drawstring to separate the cells
  • plants = a cell plate forms a cell wall between the two daughter cells
    (slide 34)
79
Q

What is meiosis?

A

Meiosis is a type of cell division that results in the formation of four haploid cells, each with half the number of chromosomes as the original diploid cell.

80
Q

What is required for sexual reproduction?

A

Sexual reproduction requires a fertilisation event in which two haploid gametes unite to create a diploid cell called a zygote.

81
Q

What are the haploid cells produced in meiosis called?

A

Called gametes, which are the sperm and egg cells

82
Q

What are the stages of meiosis I?

A
  • Prophase I
  • Prometaphase I
  • Metaphase I
  • Anaphase I
  • Telophase & cytokinesis I
83
Q

What are the stages of meiosis II?

A
  • Prophase II
  • Prometaphase II
  • Metaphase II
  • Anaphase II
  • Telophase and cytokinesis II
84
Q

How does meiosis differ from mitosis?

A

2 key differences:
1) Homologous pairs form a bivalent or tetrad at Prophase I
2) Crossing over occurs between homologous chromosome pairs to generate novel gene combinations

85
Q

When does meiosis occur in the cell cycle?

A

Like mitosis, meiosis begins after a cell has progressed through the G1, S, and G2 phases of the cell cycle

86
Q

When does crossing over occur in Meiosis?

A

Crossing over occurs during prophase I of Meiosis

87
Q

How is a bivalent or tetrad?

A

When homologous pairs of sister chromatids associate with each other, lying side by side

88
Q

What is synapsis?

A

Process by which homologous pairs of sister chromatids associate with each other
- forming a structure called the synaptonemal complex during prophase I of Meiosis

89
Q

What happens during crossing over?

A

Physical exchange of chromosome pieces between the homologous chromosomes of a bivalent during prophase I of Meiosis.

90
Q

What is a chiasma?

A

A site where the arms of the homologous chromosomes tend to separate but remain temporarily adhered at a crossover site

91
Q

What happens during Prophase I of Meiosis I?

A
  • replicated chromosomes condense
  • bivalents form as the nuclear membrane breaks down
    (slide 44)
92
Q

What happens during Prometaphase I of Meiosis I?

A
  • spindle apparatus complete
  • chromatids are attached to kinetochore microtubules
    (slide 44)
93
Q

What happens during Metaphase I of Meiosis I?

A

Bivalents organised along metaphase plate as double row
(slide 44)

94
Q

What happens during Anaphase I of Meiosis I?

A

Segregation of homologues occurs.
- connections between bivalents break, but not the connections that hold sister chromatids together
- a joined pair of chromatids migrates to one pole, while the homologous pair of chromatids moves to the opposite pole
(slide 44)

95
Q

What happens during Telophase I of Meiosis I?

A
  • sister chromatids reach their respective poles and decondense
  • nuclear membranes reform
    (slide 44)
96
Q

What is the result of Meiosis I?

A

The original diploid cell had its chromosomes in homologous pairs, while the two cells produced at the end of Meiosis I are haploid - they only have a single copy of each chromosome.

97
Q

Is there an S phase between Meiosis I and Meiosis II?

A

No, there is no S phase between Meiosis I and Meiosis II

98
Q

Are the sorting events of Meiosis II similar to those of Mitosis?

A

Yes, the sorting events of Meiosis II are similar to those of Mitosis

99
Q

What happens during Anaphase II of Meiosis II?

A

Sister chromatids are separated

100
Q

How does mitosis differ to meiosis?

A
  • mitosis produces two diploid daughter cells that are genetically identical
  • meiosis produces four haploid daughter cells
101
Q

What is a life cycle?

A

A life cycle is a sequence of events that produces another generation of an organism.

102
Q

What is the alternation that occurs in the life cycle of sexually reproducing organisms?

A

For sexually reproducing organisms, the alternation involves haploid cells or organisms and diploid cells or organisms.

103
Q

What is a diploid-dominant species?

A

An organism where the majority of cells are have 2 sets of chromosomes
- most animal species are diploid

104
Q

What is a haploid-dominant species?

A

An organism where the majority of cells are have 1 set of chromosomes
- many fungi and some protists

105
Q

What is the alternation of generations?

A

A life cycle found in plants and some algae where there is an intermediate dominance between generations.

106
Q

What is a sporophyte?

A

The multicellular diploid organism (in alternation of generations life cycle)

107
Q

What is a gametophyte?

A

The multicellular haploid organism (in the alternation of generations life cycle)

108
Q

Does the relative size of sporophyte and gametophyte vary?

A

Yes it varies between species

109
Q

List processes of chromosomal structural mutations

A
  • deletions
  • duplications
  • inversions
  • translocations
110
Q

What are deletions in chromosomal structural mutations?

A

Deletions refer to a chromosomal segment that is missing

111
Q

What are duplications in chromosomal structural mutations?

A

Duplications refer to a chromosomal segment that occurs 2 or more times in a row

112
Q

What are inversions in chromosomal structural mutations?

A

Inversions refer to a chromosomal segment that has changed direction along a chromosome

113
Q

What are translocations in chromosomal structural mutations?

A

Translocations refer to one chromosomal segment becoming attached to another chromosome
- can be simple or reciprocal

114
Q

What is euploid in changes in chromosome number?

A

Euploid refers to the chromosome number that is viewed as the normal number
- in diploid organism, 2 sets of chromosomes is normal
- a euploid human has 46 chromosomes

115
Q

What is polyploid in changes in chromosome number?

A

Polyploid refers to exactly 3 or more sets of chromosomes. Examples include triploid (3n), tetraploid (4n), and hexaploid (6n)

116
Q

What is aneuploidy in changes in chromosome number?

A

Aneuploidy refers to an alteration in the number of chromosomes that is not an exact multiple of a set but is any random number.
- monosomy & trisomy

117
Q

What is monosomy and trisomy?

A

Special cases of aneuploidy in which there is only one fewer (monosomy) or one more (trisomy) chromosome than the expected euploid number of chromosomes.

118
Q

What causes changes in chromosome numbers?

A

Non-disjunction

119
Q

What is non-disjunction in changes in chromosome number?

A

Non-disjunction occurs when chromosomes do not sort properly during mitosis or meiosis.
- during meiosis, this can produce gametes with too many or too few chromosomes

120
Q

What is interspecies breeding?

A

Interspecies breeding refers to the crossing of two different species to produce offspring.

121
Q

What are the 3 types of interspecies breeding?

A
  • alloploid
  • allopolyploidy
  • allotetraploid
122
Q

What are alloploid organisms?

A

Alloploid organisms have at least one set of chromosomes from two or more different species.

123
Q

What is allopolyploidy?

A

Allopolyploidy is the occurrence of two or more complete sets of chromosomes from two or more different species.

124
Q

What is an allotetraploid?

A

An allotetraploid has two complete sets of chromosomes from two different species, for a total of four sets.

125
Q

Do animals tolerate deviations from diploidy well?

A

No, they usually do not tolerate deviations from diploidy well and it is usually lethal.

126
Q

Do plants commonly exhibit polyploidy?

A

Yes, plants commonly exhibit polyploidy.

127
Q

What is Trisomy 21?

A

Down’s syndrome - relatively low in severity

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