Theme 4: DNA Replication and Mitosis - Module 1: The Cell Cycle Flashcards
(163 cards)
1
Q
the ability of a pre-existing cell to give rise to another cell is due to what?
A
regulated process of cel division
2
Q
for prokaryotes, what is cell division also considered?
A
reproduction
3
Q
why is prokaryotic cell division also considered reproduction?
A
because cell division gives rise to a new organism (made up of one cell)
4
Q
what are founding prokaryotic cells with regards to reproduction?
A
all essential elements necessary to reproduce
5
Q
what are prokaryotic cells capable of?
A
making exact copies of their genomes and then segregating one copy of each genome to each two daughter cells
6
Q
what does the process of cell division in prokaryotes require?
A
identical genetic material distributed amongst the daughter cells
7
Q
what is the process of cell division in prokaryotes a form of?
A
asexual reproduction
8
Q
what is the asexual reproduction of prokaryotes referred to as?
A
binary fission
9
Q
when is the process of cell division in prokaryotes initiated?
A
when the DNA of the bacterial chromosome is attached by proteins to the inside of the plasma membrane
10
Q
where does DNA replication begin?
A
along an origin of replication region of the bacterial chromosome
11
Q
what occurs as the chromosome continue to replicate?
A
cell begins to elongate and newly synthesized DNA is also anchored to the plasma membrane
12
Q
how long does the cell continue to elongate for?
A
until the two DNA attachment sites are at opposite ends of the elongated cell
13
Q
when DNA replication is complete and the bacterium is around double its size what does the bacterial cell begin to do?
A
bacterial cell begins to constrict along the midpoint of the cell
14
Q
what is the constriction of the cell accompanied by?
A
the synthesis of new cell membrane and wall - leads to complete division of the two identical daughter cells
15
Q
what does the regulated process in eukaryotes refereed to as ?
A
mitosis
16
Q
what does division in eukaryotic cells allow for?
A
unicellular fertilized egg to develop into a complex multicellular organism
17
Q
what do early embryos contain?
A
stem cells
18
Q
what are stem cells?
A
unspecialized cells that can both reproduce indefinitely and under appropriate conditions
19
Q
what are stem cells able to do?
A
able to differentiate into specialized cells of one of one or more types
20
Q
what can cell division lead to after an organism is fully grown?
A
lead to continual renewal and repair of cells that make up various tissues
21
Q
are there adult stem cells?
A
yes
22
Q
what are adult stem cells not able to do?
A
not able to give rise to all cell types in the organism
23
Q
what are adult stem cells able to do?
A
replace non-responding specialized cells
24
Q
explain the property of the adult skeletal muscle
A
stable tissue with little cell turnover
25
what happens when muscle cells undergo injury
quiescent (non-dividing) satellite stem cells that are present in the basement membrane of the muscle tissue are able to become activated and begin diving again to enable muscle regeneration
26
what does the activation of the satellite cells lead to?
proliferation, differentiation, and fusion of muscle precursor cells
27
what are the muscle precursor cells called
myoblasts
28
what to the my blasts eventually become committed to forming?
the mature muscle cells that make up the muscle fibers (myofibers)
29
what happens when the myofibers are formed?
no longer able to divide
30
what is one of the main distinctions between prokaryotic and eukaryotic cell division?
- eukaryotic DNA is larger
- organized into linear chromosomes
- highly condensed into the nucleus of the cell
31
what does the process of cell division in eukaryotes require? why?
- more regulated control
| - larger cell cycle
32
how many distinct stages does the eukaryotic cell cycle consist of?
two
33
what is one of the stages?
interphase
34
what does this stage consist of?
- S phase
- 2 gap growth phases G1 and G2
- M phase
35
what occurs in the S phase?
DNA synthesis
36
what occurs in the M phase?
mitosis and cytokinesis
37
what must occur with each mitotic cell division?
the linear chromosome of eukaryotes must be replicated and then separated into daughter cells
38
what occurs in during the interphase stage?
cells prepare for cell division
39
how do cells prepare for cell division?
- replication of DNA in nucleus
| - overall increase in cell size
40
where does replication of DNA occur?
in the S (synthesis) phase
41
what do the G1 and G2 phases prepare the cell for?
DNA synthesis and mitosis
42
how long does it take for specific cells to pass through the cell cycle?
depends on the type of cells in question
43
do all cells participate in regular cell cycle that leads to regular divisions?
no
44
can cells pause in the cycle? if so, in what phase?
yes
| G0 phase
45
what happens with cells in the G0 phase?
they pause somewhere between the M and S phase
46
how long is the pause?
wide range - can be short or long (days - years)
47
what are considered non-dividing cells?
cells that enter the G0 phase permanently
48
what type of cells enter a permanent G0 phase?
- cells that make up the lenses of our eyes
- nerve cells
- mature muscle cells
49
can stem cells reproduce indefinitely?
yes
50
do stem cells have periods of quiescence and thus undergo no cell division?
yes
51
is it true that skeletal muscles have little to no cell division?
yes
52
what happens when an injury occurs?
the quiescent satellite stem cells are activated from the dormant G0 phase of the cell cycle and reenter the cell cycle
53
with the cells reentering the cell cycle what occurs as a result?
enables proliferation, differentiation and maturation of new muscle cell precursors that can fuse and repair the muscle tissue with new muscle fibres
54
what happens once the myofibers are formed?
they exit the cell cycle and enter the quiescent G0 phase
55
how many stages does mitosis consist of?
five
56
how can these stages characterized?
can be morphometrically characterized based on the distinctive changes that occur to the chromosomes that are involved in the cell division process
57
what did Walther Flemming discover?
distinct stages of mitosis could be staged based on chromosomal position and features
58
due to Flemmings work on salamander embryos, we know the five stages of mitosis, what are they?
- prophase
- prometaphase
- metaphase
anaphase
telophase
59
what must occur before entering mitosis?
chromosomes of cells must be duplicated and condensed
60
why must the chromosomes of cells be duplicated and condensed before entering mitosis?
to allow for the daughter cells to acquire the same amount of genetic information as the parent cell in a relatively short period of time
61
what form is each chromosome in during most of interphase?
a long, thin chromatin fiber
62
what occurs prior to mitosis?
exact copies of every chromosome are created
63
what phase are the copies of the exact chromosome created in? through what process?
- S phase
| - process of DNA replication
64
where are DNA sequences replicated from?
end to end of the DNA molecule
65
what are the newly synthesized molecules associated with?
histones and other chromosomal proteins that allow for tight compaction
66
is the centromere fully replicated?
yes
67
why do the paired centromeres appear fused together?
because they're so highly compact
68
when chromosomes are duplicated into two identical copies what are they referred to as?
sister chromatids
69
what allows us to have 23 distinct chromosome pairs?
since we inherit a paternal and maternal chromosome
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how many homologous chromosomes do we have?
22 (one maternal and one paternal in origin)
71
how many are sex chromosomes?
1
72
what happens as a cell transitions from G2 to the M-phase?
duplicated chromosomes begin to condense and the individual chromosomes becomes visible even with a light microscope
73
what is the first stage of mitosis?
prophase
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during prophase how will each chromosome appear?
as identical sister chromatids that are joined at their centromeres
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what are centromeres?
duplicated cellular microtubule organizing centres
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what do centromeres do in prophase?
radiate long microtubules forming a mitotic spindle
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where do centromeres become positioned?
at opposite poles of the cell
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what are the mitotic spindles crucial for?
separating the chromosomes into two daughter cells
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summarize prophase
chromosomes condensed - centrosomes radiate microtubules and migrate to opposite poles
80
what follows prophase in mitosis?
prometaphase
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what is the defining feature of pro metaphase?
fragmentation of he nuclear envelope
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what are kinetochores?
specialized protein structures that associate with each one of the two sister chromatids on either side of the centromere
83
what can occur because the nuclear envelope breaks down?
the microtubules that are extending from each centrosome as part of the mitotic spindle are able to attach to specialized region on the centromeres o the chromosome (referred to as kinetochores)
84
is it true that some microtubules that radiate from the centrosome attach directly to the kinetochore regions?
yes
85
what are the kinetochores essential for?
essential to help pull the chromosomes to the poles of the cell
86
what are other microtubules that also radiate from the centrosome as part of the mitotic spindle?
polar microtubules
87
what do polar microtubules do?
interact with each other and help push the poles of the cell away from each other
88
summarize prometaphase?
microtubules of each mitotic spindle attach to chromosomes
| - nuclear envelope starts to break down
89
what is the third stage of mitosis?
metaphase
90
what is metaphase marked by?
the alignment of chromosomes at the centre of the cell
91
when the chromosomes are aligned at the centre of the cell what is this region identified as?
the metaphase plate
92
what facilities the alignment at the metaphase plate?
the kinetochore microtubules of each chromosome are attached at the kinetochores of each sister chromatid
93
what follows metaphase?
anaphase
94
what happens to the kinetochore microtubules during anaphase?
begin to shorten
95
what happens when the kinetochore microtubules begin to shorten?
the sister chromatids separate into individual chromosomes that are pulled towards the opposite spindle poles of the cell
96
what do the polar microtubules do during anaphase?
they push against each other and help elongate the cell
97
what is present at the end of anaphase?
the two ends of the cell will have equivalent and complete sets of chromosomes
98
summarize anaphase
sister chromatids (which become individual chromosomes when the centromere splits) separate and travel to opposite poles
99
what is the final stage of mitosis?
telophase
100
what is telophase the stage of?
two new daughter nuclei form in the cell
101
why does this occur?
because the nuclear envelope reforms around the chromosomes at the opposite poles of the dividing cell
102
what happens to the chromosomes and spindle microtubules during telophase?
- chromosomes begin to decondense
| - spindle microtubules are depolymerized/broken down
103
what marks the end of mitosis?
the division of one nucleus into two genetically identical nuclei
104
what must follow the process of mitosis?
the division of the cell into two identical cells
105
summarize telophase
nuclear envelope re-forms and chromosomes decondense
106
what does the process of cytokinesis do?
division of cytoplasm and therefore the cell
107
how does cytokinesis begin in animal cells?
with the formation of a contractile ring made up of motor proteins that contract bundles of actin fibers along the midline of the cell
108
what does this lead to?
formation of a defined cleavage furrow
109
what does a cleavage furrow do?
separates the cell into two distinct and seperate daughter cells
110
are the stages of mitosis similar across all eukaryotic cell types?
yes
111
where can differences in cytokinesis be observed?
depends on the dividing cell types
112
is the process of cytokinesis distinct and different in plant and animal cells?
yes
113
why is there a difference in cytogeneses between plant and animal cells?
plant cells have a cell wall
114
what happens during cytokinesis of plant cells?
plant cells lay down a newly developed cell wall along a cell plate region in the middle of the diving cell
115
when is cytogeneses complete in plant cells?
once the forming ell wall fuses with the original cell wall
116
when is cell division important?
during developmental growth and with regards to maintenance and repair
117
what did research in the 1970s begin to shed light on?
that there could be a mitosis promoting factor
118
what would this mitosis promoting factor allow?
the transition from the G2 to M phase of the cell cycle
119
what was studied in the 1980s?
protein level changes of dividing sea urchin embryos
120
what did this research team do?
- added radioactively labelled amino acids to the sea urchin eggs
- research team was sure the radio labelled methionine would be incorporated into any newly synthesized proteins in the embryos
- good way to measure protein changes in developing embryos
121
when and how did the team observe changes?
- took samples of rapidly dividing embryos every 10 minutes
- visualized any changes in protein levels using gel electrophoresis (allows for distinct separation of different protein types)
122
what did Hunt and his research team discover?
most protein bands on the gel became darker as cell division and embryonic development progressed
123
what happened with one protein band?
oscillated in intensity
124
what was found about the oscillating protein?
protein increased then decreased with each subsequent cell division
125
what was this protein called?
cyclin (due to its cyclic nature)
126
what did Hunt and researchers suspect this protein was involved in?
playing some sort of regulatory role on cell cycle progression
127
what did follow up work by Hunt and his colleagues identify?
that the mitosis promoting factor consists of a cyclin protein and a cyclin-dependent kinase (CDK) protein - together they control progression of the cell cycle
128
what is kinases?
enzymes that activate or inactive other proteins
129
how do kinases activate or inactivate other proteins?
by phosphorylating key amino acids on the target proteins
130
is it true that many kinases that regulate the cell cycle stay at a constant convention in the cell?
yes
131
for much of the time are kinase active or inactive?
inactive
132
how do kinase become active?
activated by binding to cyclin proteins
133
how did kinase acquire the name cyclin-dependent kinases?
because the activity of the kinases is dependent on being bound to cyclins
134
what can the cyclin-cyclin dependent kinase complex trigger? how is this done specifically?
- the multitude of changes that occur during the various cell cycle events
- by phosphorylation of target proteins that promote cell division
135
what is the activity of the cyclin0dependent kinase?
it rises and falls with changes in the concentration of its activating cyclin protein
136
is it true that there are many different types of cyclin-CDK complexes that are involved in the regulation of each stage of the cell cycle?
yes
137
when is cyclin-CDK regulation important?
during three steps of the eukaryotic cell cycle
138
what is the G1/S cyclin-CDK complex needed for?
the transition from the G1 to S phase and helps to prepare the cell for DNA replication (i.e. increasing the expression of histone proteins)
139
what does the S-cyclin-CDK complex help with?
to initiate DNA synthesis
140
what does the M cyclin-CDK complex initiate?
the process of mitosis
141
what other key factors play an important role in the regulation of the cell cycle?
presence of multiple check points
142
what do cell-cycle check points serve as?
form of cellular surveillance
143
what are cell-cycle check points able to do?
block cyclin-CDK activity should something go wrong during the progression of the cell cycle
144
what can cell-cycle check points do?
pause cell division
145
how long can cell-cycle check points pause cell division?
until the preparation for the next stage of the cell cycle is complete
146
what else can a cell-cycle check point serve as ?
opportunity for damage to be repaired
147
what are the three major check point of the cell cycle?
- DNA damage checkpoint at the end of G1 phase
- DNA replication checkpoint at the end of the G2 phase
- spindle assembly checkpoint before anaphase during mitosis
148
due to cellular monitoring only what kind of DNA will be able to enter the S phase or replication due to the G1 checkpoint?
undamaged DNA
149
due to G2 checkpoint when can a cell enter the mitosis phase?
only when all DNA is replicated
150
due to the M phase checkpoint when will a cell complete mitosis?
if all chromosomes are attached to a microtubule from the mitotic spindle
151
looking at an example of the DNA damage checkpoint, are the genes that normally inhibit cell cycle progression turned on or off?
off
152
what is p53?
protein that can inhibit the cell cycle when turned on
153
what happens when damage occurs to the structure of DNA (damage that includes double-stranded breaks in the phosphodiester backbone)
specific protein kinases are able to phosphorylate p53
154
p53 protein is normally present in very high or very low levels in the nucleus? what is most of this protein doing?
- very low levels
| - most is being exported out of the nucleus degraded
155
what happens during phosphorylation?
p53 is able to accumulate within the nucleus and acts as a transcription factor to turn on genes that will inhibit the cell cycle
156
what does this lead to?
production of a CDK inhibitor protein
157
what does the inhibitor protein do? what does this give the cell?
- bind to and block the activity of the G1-S cyclin-CDK complex and thus stop/pause the cell cycle in the G1 phase
- gives cell the opportunity to repair the damaged DNA
158
spindle assembly example, as early as the pro metaphase stage of mitosis, regulatory proteins that are associated with the spindle assembly checkpoint are able to monitor what?
the degree to which the sister chromatids are attached to the microtubules of the mitotic spindle at their kinetochore regions
159
what type of signal do unattached kinetochores create?
"wait" signal
160
what does the "wait" signal lead to?
the recruitment of spindle-assembly check point proteins
161
what are these proteins activated by?
lack of tension in the centromere area
162
when is progression of metaphase and entry into anaphase allowed?
when each sister chromatid is attached to a kinetochore microtubule
163
what happens when this occurs?
spindle checkpoint proteins are removed from the centromere region and separase, a specialized enzyme, is able to break sister chromatid attachments
