The cell cycle, stem cells, cancer Flashcards
(109 cards)
1
Q
Name the four phases of the cell cycle
A
G1, S, G2, M
2
Q
What are the 5 sections the M phase of mitosis is split into?
A
Prophase, prometaphase, metaphase, anaphase, telophase
3
Q
What happens in prophase of mitosis?
A
The nuclear envelope has dissolved in G2
The chromosomes fully condense
The early mitotic spindle forms
4
Q
What happens in prometaphase?
A
The kinetochore microtubules begin connecting to the kinetochores
5
Q
Describe metaphase
A
Chromosomes align at equator along the metaphase plate
Centrosomes at spindle poles
6
Q
Describe anaphase
A
Sister chromatids separate
Spindles contract
7
Q
Describe briefly telophase and cytokinesis
A
Lamins reform
Chromosomes reach poles of cells
Nucleus envelope reforms
Spindles degrade
8
Q
What holds the chromatids together? Describe the structure
A
Cohesin
A multi subunit protein, which forms a dimer loop trapping 2 strands of DNA inside
9
Q
What are the 3 stages of chromosome packaging?
A
- Beads on a string chromatin
- Chromatin fibre of nucleosomes
- Chromosome coils to create condensed form - using condensin and cohesin
10
Q
What are chromosomes condensed by? Describe the process
A
Condensin creates dimer loops
Coordination with cohesin allows chromosomes to condense into 300nm fibres
11
Q
What are the SMC complexes?
A
Structural maintenance of chromosomes complexes
Cohesin and condensin
12
Q
How many centrioles in a centrosome
A
2
13
Q
What are the mitotic spindles made of?
A
Microtubules
14
Q
How many microtubules in a spindle?
A
3
15
Q
What protein attaches astral microtubules to the cell membrane?
A
Dynein
16
Q
What tightens the mitotic spindle?
A
Kinesin-14
17
Q
What expands the mitotic spindle?
A
Kinesin-5
18
Q
What proteins move the chromosomes to the poles of the cell?
A
Kinesin 4 and Kinesin 10
19
Q
What is the centromere?
A
Where the chromosomes are joined at a single point along their length
Dense, tightly structured DNA, much denser than the rest of the chromosome
20
Q
How does the centromere attach to the spindles?
A
The centromere has a kinetochore region, which has several proteins
DNA has low affinity for microtubules, and the centromere has no genes
21
Q
What are the 3 layers of the kinetochore? What are their function?
A
- Checkpoint - collar - attaches to spindles
- Outer - structural
- Inner - binds to DNA
22
Q
What orients chromosomes so one chromatid faces each side?
A
The kinetochore and kinesins 4, 10 enable the chromosome to walk to the ends of the spindle fibre
23
Q
What pulls the chromatids apart?
A
Separase enzyme, which is part of the anaphase promoting complex, breaks down cohesin
24
Q
How do spindles shorten? What is this mechanism called?
A
The + end is attached to the kinetochore, and tubulin begins to leave there - depolymerisation of the plus end.
Then, the force pulls the kinetochore closer to the poles.
The Pac-man flux mechanism
25
Is mitosis or meiosis the source of genetic diversity?
Meiosis
26
What are the names of the 5 phases that prophase of meiosis 1 is split into?
Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis
## Footnote
Long Zebra Penises Defeat Ducks
27
What kind of gametes does meiosis produce?
Haploid
28
When does bivalent formation occur?
Meiosis 1
29
What are the points where homologous chromosomes join called?
Chiasmata
30
What happens in leptotene?
Duplicated chromosomes start to condense
31
What happens in zygotene?
Synaptonemal complexes form, synapsis begins, joining chromosomes - maternal and paternal form a zip
32
What happens in pachytene?
Synapsis ends, crossing over begins - breakage of DNA and refusion with alternate chromatids
33
How can you tell a cell has entered diplotene?
Chiasmata are visible
Bivalents/tetrads visible under microscope
34
what happens in diplotene?
synaptotemal complex dissolves so chromatids are free, homologous chromosomes are still joined together but only by crossover junctions (chiasmata)
35
What happens in diakinesis?
The nuclear envelope fragments
Homologous chromosomes ready for metaphase
Bivalents associate with meiotic spindle
36
What is the synaptonemal complex?
A collection of proteins and chromosomal structures
Zip the chromatids together - maternal and paternal
- has lateral and central elements that bind to chromatids of homologous chromosomes
37
What is pulled apart in mitosis and meiosis?
Mitosis = chromatids
Meiosis = chromosomes, then chromatids
38
Describe the mitosis daughter cells in terms of n and C
2n
2C
39
Describe the meiosis daughter cells in terms of n and C
n
C
40
What does n mean?
Ploidy number. Number of complete sets of chromosomes in a cell - haploid = n, diploid = 2n
41
What does C mean?
DNA content in the cell - 2C = diploid
42
What forms the cleavage furrow in cytokinesis?
Actin and myosin contractile ring, forms 2 bulges (not equal in budding yeast)
43
How does cytokinesis occur in plants?
Construction of the phragmoplast/cell plate, has plasmodesmata in
- vacuole gains volume, cell wall loosens and so cell can expand and grow
44
What is a holliday junction?
Crosswise structure between 2 duplexes of DNA
45
what is a chiasma?
visible point of crossing over in a bivalent
46
what are chiasmata good for?
allowing DNA to swap so good for gene mapping and gene behaviour
47
what protein is used in crossover?
SPO1 - like scissors, creates a nick in the back bone of DNA
48
what does a larger chromosome mean?
more crossover events
49
In which organism does cytokinesis not come after cell division?
drosophila fruit flies
50
What happens in G2 of interphase?
- Cells grow more
- Synthesis of proteins for mitosis e.g. tubulin for MT
- Repair of damage from S phase
- Checkpoint
51
what is the hay flick limit?
max. number of times a cell can replicate
- about 50 in humans
52
what have condensin and cohesin evolved from?
bacterial equivalents
53
what are the three sets of Microtubules in the spindle?
Astral, kinetochore, interpolar
54
what do kinetochore microtubules do?
bind to chromosomes and centrioles/centrosome so chromatids can pull apart
55
what do inter polar microtubules do?
- provide strength
- fix other microtubules
- rigid structure that can grow/shrink to balance out
56
What is the pac-man flux? When does it happen?
- Kinetochore MT depolymerises at its + end
- As the MTs shorten, they reel in the chromatid
- This looks like pac man eating a MT
- Happens in anaphase (mitosis and meiosis)
57
What happens to the telomeres after each round of cell division?
they become shorter
58
what are the three germ layers?
endoderm, mesoderm, ectoderm
59
what does mesoderm give rise to?
middle of use
- organs, muscle, bones, blood
60
what does ectoderm give rise to?
stuff on outside of us
- skin, nervous tissue
61
what are totipotent stem cells?
turns into anything, any type of cell
62
what are omnipotent stem cells?
can do anything it wants
63
what are pluripotent stem cells?
most cells in regions of body that can turn into most other things e.g most types of mesoderm and ectoderm
- but not the placenta!!
64
what are multipotent stem cells?
can differentiate into specific related cell types
65
what are oligpotent stem cells?
can differerentiate into a few number of cell types, limited to regions and types
e.g any type of neutrophil or msuscle cell
66
what is a unipotent stem cell?
can only ever be one type of cell
67
which stem cells are normally used in research?
toti, multi or omnipotent
68
what does haemopoetic mean?
to do with blood or circulatory system
69
what is a stem cell niche?
specific locations that regulate participation in tissue regeneration, maintenance and repair
- protects stem cells and restricts over-active stem cells from proliferation
70
Name 3 types of SOMATIC stem cells/niches
- Bone marrow
- Intestinal crypts of lieberkuhn
- Hair follicle bulge
71
what are the stem cells in plants
meristem - apical root and apical shoot
vascular bundles
72
what's special about plants compared to animals for stem cells?
plants have more stem cells than humans and any part of the plant can give rise to a whole new plant using auxins and cytokinins
73
benefits of stem cells?
research e.g HeLa cells
don't have to sacrifice a whole organism
tissue engineering - can culture and grow
aborted embryos can be used
therapeutics - organ transplants
transformation - use callus - create conditions like using agrobacterium to get resistant crops
74
what stem cells are used to overcome ethical issues?
iPS (induced pluripotent stem cells)
75
How are iPS made?
Take oligopotent stem cells and dedifferentiate them, insert into mouse fibroblast (GMO) and add a pluripotent gene promoter
- select and maintain cells with active promoter
- inject into normal mouse embryos and breed
76
what is different about the cell cycle in budding yeast compared to normal fission yeast?
No G2 phase
S and M phase are overlapped
Buds off to create daughter cells rather than truly dividing
77
What are cdc mutants?
Cell division cycle mutants, most common in yeast
Cell Division Cycle (CDC) mutants refer to organisms or cells that exhibit defects in the processes of the cell cycle, leading to issues in cell division
78
How many cdcs in fission and budding yeast?
70 in fission yeast
100 in budding yeast
79
What do cdc mutants do?
They arrest the cell cycle, each one at a particular point. This causes regulation of DNA and DNA repair to change
Each mutant is defective in a single gene so each one stops at a particular point of the cell cycle
80
What are cdc mutants sensitive to?
Temperature - they all arrest earlier at a higher temperature
81
what is cdc2? Where is it found?
cell division cycle protein 2, found in fission yeast
82
What does cdc2 do?
Encodes for a protein kinase (cdk1) and governs G1 to S phase and G2 to M phase.
This is because it catalyses the phosphorylation of lamins, leading to nuclear envelope breakdown
83
what happens if cdc2 is mutated?
It stops the cell from starting DNA synthesis and stays in G1
84
what is cdk1?
cyclin-dependent kinase 1
85
what does cdk1 do?
phosphorylates and activates other proteins and initiated DNA synthesis
86
What are tumour suppressor genes?
They and limit cell division, and activate apoptosis pathways to prevent cancer
87
What happens when tumour suppressors mutate?
They enable the activation of oncogenes and encourage cell proliferation and uncontrolled cell division
88
what is P53?
A tumour suppressor gene
- stimulates other proteins related to the cell cycle
- stops cell cycle progressing too far
- induces senescence or apoptosis
89
what does P53 respond to?
DNA damage
Short telomeres
Stress, hypoxia
Hyper proliferative signals
90
Name 4 therapies for cancer
Surgery
Radiotherapy
Chemotherapy
Pharmaceuticals
91
what is radiotherapy?
killing off specific tissues to kill off rapidly dividing cells
- radio waves
92
what is chemotherapy?
chemical poison to kill and inhibit rapidly dividing cells
93
How can pharmaceuticals be used to treat cancer?
The chemical signals can be used to block receptors or pathways
94
What are the two models for how tumours may work?
Stochastic
Cancer stem cell
95
what is the stochastic model?
Every cell in a tumour in cancerous and divides uncontrollably
96
What is the cancer stem cell model? And what is it tested by?
Only a finite number of cells in the tumour are able to replicate and rest are just tissue - only the stem cells proliferate
So treatment only needs to target the active replicating cells and stem cell origin - tested using Reseeding assay
97
Are tumour more or less differentiated than normal cells?
Less differentiated but self-renewing and more resistant to apoptosis.
98
What sits between stem cells and differentiated cells in a terminal differentiation area?
Transit amplifying cells
99
What potency are HAEMOPOEITIC STEM CELLS?
Multipotent - responsible for production of all blood cell types
100
Where are amniotic stem cells found?
Free floating in amniotic fluid
101
What kind of potency are most bone marrow stem cells?
Multipotent
102
What potency is almost all plant tissue?
Totipotent
103
What are the 3 stem cell types/niches?
Embryonic
Somatic
Induced pluripotent iPS
104
Define induced pluripotent stem cells
A type of pluripotent stem cell that is generated by reprogramming adult somatic cells (such as skin or blood cells) to revert to a pluripotent state, similar to that of embryonic stem cells.
105
What is callus tissue in plants?
In plants, callus tissue refers to a mass of undifferentiated plant cells that forms in response to injury or as part of the process of tissue culture
106
What implications do cancer stem cells have for treatment?
CSCs do not divide rapidly so may be missed…leading to potential future relapse
Treatments need to target the CSCs, and perhaps the tumour will die
107
What kind of microtubules keep the centrosome in place?
Astral
108
What is at the end of a chromosome?
Telomere
109
When does crossing over occur?
Prophase 1
