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Biology 2 > Lecture 14 mitosis and meiosis > Flashcards

Lecture 14 mitosis and meiosis Flashcards

1
Q

What is chromatin?

A

A dense material made of double stranded DNA molecules and proteins

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2
Q

What are the two double stranded DNA molecules formed after DNA replicates during S phase called?

A

Sister chromatids

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3
Q

How are sister chromatids held together?

A

By a protein complex called cohesin along most of their length

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4
Q

When is chohesin removed?

A

Mitosis, most is removed, except at the centromere

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5
Q

What is the centromere?

A

The point at which sister chromatids are held together

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6
Q

After DNA replication, how is DNA further compacted?

A

Condensins coat the DNA molecule

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7
Q

What is the diameter of the nucleus?

A

5 micrometers

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8
Q

How long is the typical DNA in a human cell, end to end?

A

2m

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9
Q

What proteins are contained within chromosomes?

A

Histones

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10
Q

How many classes of histones are there?

A

5

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11
Q

What charge do histones have?

A

Positive at cellular pH levels

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12
Q

Why are histones positively charged?

A

High content of basic amino acids lysine and arginine

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13
Q

What do positive charges on histones do?

A

Attract negative phosphate groups on DNA

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14
Q

What interactions result in nucleosomes?

A

DNA- Histone interactions

Histone-histone interactions

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15
Q

What are nucleosomes like?

A

Bead like

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16
Q

How many histone molecules are their in each nucleosome?

A

Eight, 2 each of 4 of the histone classes

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17
Q

How are histones arranged within a nucleosome?

A

United to arrange a core or spool

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18
Q

How many base pairs are there in a nucleosome?

A

146

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19
Q

How many turns of base pairs are wrapped around each histone spool?

A

1.65 turns

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20
Q

What is the final component of a nucleosome?

A

Histone H1

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21
Q

What does H1 do?

A

Found on the outside of the DNA

clamps it to the histone core

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22
Q

What runs between nucleosomes?

A

A variable amount of non-nucleosomal linker DNA

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23
Q

How is DNA arranged during interphase?

A

A single DNA molecule running between chromosomes

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24
Q

What is DNA exposed to during interphase?

A

Nuclear environment

Including proteins involved in replication and regulation of expression

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25
Q

What happens to chromatin during mitosis and meiosis?

A

It becomes more tightly coiled and condensed

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26
Q

Up until what point does further coiling of chromatin take place?

A

Until chromatids begin to move apart

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27
Q

What is mitosis?

A

A single nucleus gives rise to two nuclei that are genetically identical to each other and to the parent nucleus

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28
Q

What are the subdivisions of mitosis, in order?

A 
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
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29
Q

What is the centrosome?

A

An organelle in the cytoplasm near the nucleus

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30
Q

What happens to the centrosome during S phase?

A

It doubles, forming a pair of centrosomes

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31
Q

What does a centrosome consist of?

A

A pair of centrioles- each one a hollow tube lined with nine micro tubules. The tubes are at right angles to each other.

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32
Q

When do the two centrosomes separate from each other?

A

At the G2 to M transition

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33
Q

Where do the centrosomes go after they have separated?

A

To opposite ends of the nuclear envelope

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34
Q

What does orientation of the centrosomes correlate with?

A

The plane at which the cell will divide

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35
Q

What is the consequence of determining the plane at which the cell divides?

A

It determines the spatial relationship of the two new cells to the parent cell- important for making body tissue

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36
Q

What surrounds the centrioles?

A

A high concentration of tubulin dimers

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37
Q

What do tubulin dimers do?

A

Initiate the formation of microtubules which orchestrate chromosomal movement

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38
Q

Plants lack centrosomes. How is chromosomal movement controlled?

A

A distinct microtubule organizing center at either end of the cell plays the same role

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39
Q

What does formation of microtubules lead to?

A

The formation of the spindle structures that segregate chromosomes

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40
Q

When do chromatids become visible?

A

prophase

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41
Q

When does the spindle form?

A

Prophase

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42
Q

What is visible under a light microscope during interphase?

A

Nuclear envelope
Nucleoli
Tangle oc chromatin

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43
Q

What happens during prophase to cohesin?

A

It is removed (not removed at centromere)- chromatids become visible

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44
Q

What structure develops late in prophase?

A

Specialized three-layered structures called kinetochores

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45
Q

Where do kinetochores develop?

A

In the centromere region, one on each chromatid

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46
Q

What are kinetochores important for?

A

Chromosome movement

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47
Q

What do the two centromeres act as?

A

A mitotic center, or pole, towards which the chromosomes move

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48
Q

How does the spindle form?

A

Microtubules form between each pole and the chromosomes

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49
Q

What is the purpose of the spindles?

A

A structure to which chromosomes attach and as a frame work for keeping the poles apart

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50
Q

What is the behavior of the spindles when they first form?

A

Initially unstable- they constantly form and fall apart

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51
Q

When do spindles become more stable?

A

When they contact microtubules from the other half spindle

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52
Q

What is the structure of the spindle?

A

Made up of 2 half spindles- each microtubule runs from one pole to the middle of the spindle, where it overlaps with the microtubules from the other half spindle

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53
Q

What are the two types of microtubule in the spindle?

A

Polar microtubules

Kinetochore microtubules

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54
Q

What are polar microtubules?

A

Microtubules that form the framework of the spindle

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55
Q

What is the structure of polar microtubules?

A

Abundant tubulin around centrioles

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56
Q

How are polar microtubules made up?

A

Tubulin dimers aggregate to form long fibers that extend to the middle region of the cell

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57
Q

What are kinetochore microtubules?

A

Microtubules that attach to the kinetochores on the chromosomes

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58
Q

When do kinetochore microtubules form?

A

Later than the polar microtubules

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59
Q

How do sister chromatids become attached to the kinetochore microtubules?

A

Sister chromatids in each chromosome pair become attached by their kinetochore to kinetochore microtubules in opposite halves of the spindle

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60
Q

What does the attachment of kinetochores to kinetochore microtubules ensure?

A

That one chromatid of the pair will move to one pole and the other chromatid to the opposite pole

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61
Q

What marks prometaphase?

A

The disappearance of the nuclear envelope and the nucleoli

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62
Q

What happens to the material that composes the nuclear envelope and nucleoli when it disappears during prometaphase?

A

It remains in the cytoplasm to be reassembled when daughter nuclei form

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63
Q

What begins to happen in prometaphase but is countered?

A

The movement of chromosomes towards the poles

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64
Q

What counters the movement of chromosomes towards the poles during prometaphase?

A
  • Repulsive force from the poles pushes the chromosomes towards the middle region (equatorial plate) of the cell
  • The two chromatids are still held at the centromere by cohesin
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65
Q

What is the middle region of the cell called?

A

The equatorial plate, or metaphase plate

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66
Q

What does the movement and countermovement of chromosomes during prometaphase do?

A

Makes the chromosomes appear to move aimlessly back and forth between poles and the middle as they approach the equatorial plate

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67
Q

What marks the start of metaphase?

A

When the centromeres arrive at the equatorial plate

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68
Q

When is the best time to see the sizes and shapes of the chromosomes and why?

A

Metaphase

Because they are maximally condensed

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69
Q

What happens by the end of metaphase?

A

All of the chromatid pairs separate simultaneously.

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70
Q

What marks the beginning of anaphase?

A

Separation of the chromatids

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71
Q

What happens during anaphase?

A

The sister chromatids move to opposite ends of the spindle

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72
Q

What does each chromatid contain during anaphase?

A

One double stranded DNA molecule called the daughter chromosome

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73
Q

Why does separation of the chromatids occur during anaphase?

A

One subunit of cohesin holding sister chromatids together is hydrolyzed

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74
Q

What type of molecule hydrolyzes the subunit of cohesin during anaphase?

A

A protease called separase

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75
Q

How is separase present in a cell?

A

It is present but inactive until anaphase, bound to an inhibitory subunit called securin

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76
Q

What happens to securin once all of the chromatids are connected to the spindle?

A

Securin in hydrolyzed

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77
Q

What effect does the hydrolysis of securin during anaphase have?

A

Separase catalyzes the cohesin breakdown

78
Q

What is the process of hydrolyzing securin in order for separase to break down cohesin called?

A

The spindle checkpoint

79
Q

What does the spindle checkpoint sense?

A

Whether there are any unattached kinetochores- if so, securin breakdown is blocked.

80
Q

What two things move chromosomes along?

A
  • Molecular motors

- Shortening microtubules

81
Q

What act as molecular motors?

A

Proteins at the kinetochore

82
Q

What are the names of the proteins at the kinetochore that act as molecular motors?

A

Cytoplasmic dynein

83
Q

How do cytoplasmic dynein’s work?

A

They hydrolyze ATP to ADP

This releases energy to move chromosomes along microtubules towards the poles

84
Q

What % of the force of motion do molecular motors account for?

A

75%

85
Q

What % of force does the shortening of microtubules towards the poles account for?

A

25%

86
Q

What happens to the poles during anaphase?

A

They are pushed further apart, doubling the distance between them

87
Q

Why does distance between poles increase during anaphase?

A

Overlapping polar microtubules extending from opposite ends contain motor proteins that cause them to slide past each other

88
Q

What happens to make the cell enter telophase?

A

The chromosomes stop moving at the end of anaphase

89
Q

What is the situation at the start of telophase?

A

Two sets of identical daughter chromosomes are at opposite ends of the spindle

90
Q

What happens to the spindle in telophase?

A

It starts to break down

91
Q

What happens to the chromosomes in telophase?

A

They start to uncoil and become diffuse tangle of chromatin

92
Q

What happens to the nuclear envelope and nucleoli in telophase?

A

They coalesce and re-form their respective structures

93
Q

What does mitosis only refer to? (Hint: what separates it from cytokinesis?)

A

The division of the nucleus

Division of cytoplasm is cytokinesis

94
Q

What effects how cytokinesis occurs?

A

The type of organism- for example, plants and animals are very different in their cytokinesis

95
Q

How do animal cells divide during cytokinesis?

A

By furrowing of the plasma membrane as if an invisible thread was cinching the cytoplasm between poles

96
Q

What is the invisible thread between poles that separates the cells during cytokinesis?

A

Microfilaments of actin and myosin in a contractile ring beneath the plasma membrane

97
Q

How does actin and myosin form a contractile ring?

A

They interact like they do during muscle contraction to produce contraction

98
Q

What do the microfilaments used to form the contractile ring assemble from?

A

Actin monomers that are present in the interphase cytoskeleton

99
Q

What controls the assembly of microfilaments during cytokinesis?

A

Calcium ions released from storage sites in the center of the cell

100
Q

Why do plant cells divide differently to animal cells?

A

Because of the presence of the cell wall

101
Q

What happens after the spindle breaks down in mitosis?

A

Membranous vesicles derived from the golgi apparatus appear at the equatorial plate.

102
Q

What happens after membranous vesicles appear at the equatorial plate of a plant cell during cytokinesis?

A

They are propelled along microtubules by motor protein kinesin and fuse to form new plasma membrane

103
Q

What happens to the contents of the vesicles used to form a new plasma membrane in plant cells during cytokinesis?

A

Contribute vesicle contents to the cell plate

104
Q

What is the cell plate?

A

The beginning of a new cell wall

105
Q

What is not distributed precisely during mitosis?

A

Organelles such as ribosomes, mitochondria and chloroplasts

106
Q

Why are organelles not precisely distributed?

A

Because it doesn’t matter as long as some of each is present

107
Q

Why is unequal distribution of cytoplasmic components important?

A

It can have functional significance for the two new cells

108
Q

What is the product of meiosis?

A

4 daughter cells that cannot undergo further duplications

109
Q

What type of nuclear division is involved in reproduction?

A

Mitosis and meiosis, however, they have different reproductive roles.

110
Q

What are the off spring produced in asexual reproduction called?

A

Clones- if the offspring are genetically identical

111
Q

What can cause variation among asexually produces offspring?

A

Mutations

112
Q

What is an advantage to asexual reproduction?

A

It is rapid and effective

113
Q

What is an advantage to sexual reproduction?

A

It results in genetic diversity

114
Q

How does meiosis produce some variation?

A

Gametes are different to each other and from their parent

115
Q

What are cells not specialized for reproduction called?

A

Somatic cells

116
Q

What are a set of chromosomes found in somatic cells called?

A

Homologous chromosomes

117
Q

What are the characteristics of chromosomes found in homologous pairs?

A

They are similar size and appearance (except some sex chromosomes)

118
Q

What genetic information do homologs have?

A

Similar but not usually identical genetic information

119
Q

What type of cell are gametes?

A

Haploid

120
Q

What is it called when two haploids fuse? What is the name of this process?

A

Zygote

Fertilization

121
Q

What are the three hall marks of all sexual life cycles?

A
  • Two parents, each provides chromosomes in the form of gametes produced by meiosis
  • Each gamete is haploid
  • Two gametes fuse to form a single cell (zygote) (diploid)
122
Q

What are the three types of sexual life cycle that can be observed after zygote formation?

A

Haplontic
Alternation of generations
Diplontic

123
Q

What organisms are haplontic?

A

Most protists, many fungi

124
Q

What is a haplontic organism?

A

One where the zygote is the only diploid cell in the life cycle

125
Q

What happens to the zygote in a haplontic organism?

A

It undergoes meiosis to produce haploid cells (spores)

126
Q

What do spores of haplontic organisms do?

A

Form a new organism (single or multicellular) by mitosis

127
Q

How do mature, haploid organisms produce gametes?

A

By mitosis

128
Q

What organisms have alternation of generation sexual life cycles?

A

Plants, some protists

129
Q

What does meiosis give rise to in alternation of generations?

A

Not gametes

Haploid spores

130
Q

What happens to the haploid spores formed during alternation of generations?

A

Divide by mitosis for form an alternate, haploid life stage called gametophyte

131
Q

What does the gametophyte produce?

A

Gametes, by mitosis

132
Q

What happens to the gametes produced by haploid gametophytes?

A

Fuse to form a zygote

133
Q

What happens to the zygote produced during alternation of generations?

A

It divides by mitosis to become the diploid sporophyte

134
Q

What organisms are diplontic?

A

Animals, some plants

135
Q

What are the only haploid cells in the life cycle of diplontic organisms?

A

The gametes

136
Q

How are diplontic organisms zygotes produced?

A

Meiosis

137
Q

What is able to be observed during metaphase of mitosis and hence counted and characterized?

A

Individual chromosomes

138
Q

What is made to be able to observe an entire set of chromosomes?

A

A photomicrograph

139
Q

What happens to the photomicrograph?

A

Images are arranged to reveal number, shape and sizes of the chromosomes

140
Q

What do the number, shape and sizes of the chromosomes constitute?

A

The karyotype

141
Q

What can the chromosomes of a karyotype be divided into?

A

22 pairs of autosomes

1 pair of sex chromosomes

142
Q

How many nuclear divisions are there during meiosis?

A

2

143
Q

How many times is the DNA replicated during meiosis?

A

once

144
Q

What are the names of the two mitotic divisions?

A

Meiosis 1 and meiosis 2

145
Q

What is a unique feature of meiosis 1 that separates it from mitosis?

A

Homologous chromosomes come together to pair along their entire lengths

146
Q

What happens during metaphase 1 of meiosis?

A

The homologous chromosomes separate

147
Q

When does crossing over occur?

A

Late stage prophase 1- prometaphase

148
Q

What does crossing over result in?

A

exchange of genetic material

149
Q

How is prophase 1 in meiosis 1 different?

A

It is long,

Chromosomes change markedly

150
Q

How do chromosomes change during prophase 1 in meiosis 1?

A

The homologous chromosomes adhere along their length in a process called synapsis

151
Q

When does the pairing process of synapsis start and end?

A

Starts during prophase 1

ends at the end of metaphase 1

152
Q

Where does the joining of homologous chromosomes begin?

A

At the telomeres

153
Q

How is joining of homologous chromosomes mediated?

A

Recognition of homologous DNA sequences on homologous chromosomes

154
Q

What else helps to mediate joining of homologous chromosomes during meiosis 1?

A

A special group of proteins form a scaffold called synaptonemal complex

155
Q

What is the structure of the synaptonemal complex?

A

Runs lengthwise along the homologous chromosomes ti join them together.

156
Q

What are the four chromatids of each pair of homologous chromosomes called?

A

tetrad, or bivalent

157
Q

How many chromatids are there in prophase 1 of meiosis 1 in humans?

A

96

158
Q

During meiosis 1, when homologous chromosomes seem to repel each other, how are they held together?

A

By physical attachments mediated by cohesins

different to cohesins holding sister chromatids

159
Q

What are regions of homologous chromosomes held together shaped like and called?

A

X-shaped

Chiasmata

160
Q

What does a chiasma reflect?

A

An exchange of genetic material between non-sister chromatids- called crossing over

161
Q

When do chromosomes start exchanging genetic material during meiosis 1?

A

Shortly after synapsis begins

not visible until repelling begins

162
Q

How long does it take for prophase I to occur in the human male testes? What about for the entire meiotic cycle?

A

1 week, 1 month for entire meiotic cycle

163
Q

In meiosis I, what attaches to the same half spindle?

A

The kinetochores of both chromatids, so the entire chromosome moves to the pole

164
Q

How are homolgous chromosomes sorted?

A

The member attached is random, so sorting to each pole is random

165
Q

What do the daughter nuclei at the end of meiosis I contain?

A

One set of chromosomes consisting of two chromatids

166
Q

What happens in some organisms following anaphase I of meiosis I?

A

Telophase I

167
Q

What follows telphase I of meiosis I?

A

Interphase called interkinesis

168
Q

What happens during interkinesis?

A

Chromatin is partially uncoiled,

No replication of genetic material

169
Q

What is the purpose of the second meiotic division?

A

To separate the chromatids

170
Q

What are the three major difference between mitosis and meiosis II?

A
  • DNA replicates before mitosis
  • Chromatids making up chromosome are identical in mitosis
  • Number of chromosomes on equatorial plate is 1/2 for meiosis II then mitosis
171
Q

What is the result of meiosis II?

A

4 haploid nuclei

172
Q

Why are the products of meiosis I genetically diverse?

A
  • Synapsis during prophase I creates recombinant chromatids (crossing over)
  • Independent assortment
173
Q

What is independent assortment?

A

Homologous pairs line up randomly at metaphase I, paternal chromatids and maternal chromatids assort independently of each other

174
Q

What is it called when homologous chromosomes fail to separate during meiosis I, or sister chromatids fail to separate during meiosis II?

A

Nondisjunction

175
Q

How else may a meiotic error occur?

A

when chromosomes fail to remain together

176
Q

What is the result of a meiotic error?

A

Aneuploid cells –> aneuploidy

177
Q

What is aneuploidy?

A

A condition in which one or more chromosomes are either lacking or present in excess

178
Q

What can cause aneuploidy?

A

Lack of cohesins

179
Q

Why does a lack of cohesins cause aneuploidy?

A

Without them, homologs line up randomly at metaphase I, 50% chance both will go to the same pole.

180
Q

What is a zygote with three copies of a particular chromosome called?

A

Trisomic

181
Q

What causes Down syndrome?

A

Trisomy of chromosome 21

182
Q

What are some symptoms of Down syndrome?

A

Impaired intelligence
Characteristic abnormalities of the hands, tongue, eyelids
Increased susceptibility to cardiac abnormalities and leukemia

183
Q

What is a zygote with only one copy of a chromosome called?

A

Monosomic for that chromosome

184
Q

Name another type of abnormal chromosomal event that can occur?

A

Translocation

185
Q

What is translocation?

A

A piece of chromosome breaks off and becomes attached to another chromosome

186
Q

How common are trisomies and monosomies in human zygotes?

A

10-30% of all conceptions

187
Q

What happens to most embryo’s that develop from aneuploidy zygotes?

A

Do not survive to birth, or die before age 1

188
Q

How many pregnancies are spontaneously terminated (miscarried) during the first 2 months, largely due to trisomies/monosomies?

A

1/5th

189
Q

What occurs when organisms have complete extra sets of chromosomes?

A

Polyploidy

190
Q

Why can polyploid cells still under go mitosis?

A

Because chromosomes behave independently of each other

191
Q

Why can’t polyploid cells undergo normal meiosis?

A

Homologous chromosomes cannot synapse to begin division

192
Q

Where is polyploidy common?

A

Modern agriculture:

-modern bread, wheat plants are hexaploids

Biology 2 (14 decks)

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