Gametes - Cell Cycle Flashcards
1
Q
What is the duration of skin cell cycle
A
12-24 hours
2
Q
Describe the nature of cell cycle with liver cells
A
- Transient withdrawal from the cell cycle
- Temporarily disassemble cell cycle control system
- Retain ability to reassemble control system quickly to re-enter cycle
- Divide once every year or 2 - rapidly with liver damage
3
Q
Frequency of cell division with mature nerve & muscle cells
A
- DO NOT divide at all after maturity
- Terminally differentiated in G0 state
4
Q
What is the frequency of cell division of other cells (e.g. some lymphocytes)
A
Withdraw and re-enter cell cycle repeatedly
5
Q
Abbreviations for interphase
What is happening during interphase
How much of cell division does it account for
A
G1, S, G2
Growth & cell division
Cells spend about 90% of time interphase
6
Q
What is the abbreviation for the mitotic phase
What is happening during this phase
A
M
Cell division
7
Q
What is another name for the quiescent phase
A
Senescent (G0)
8
Q
Where is there greatest variation in cell-cycle length
A
G1 or G0
9
Q
How long does it take to go from S to M phase in mammals
Is this value constant
A
12-24 hours
relatively constant, regardless of interval from 1 division to the next
10
Q
What sort of capacity do embryonic stem cells have
What is their cell cycle characterised by
A
- Have the capacity for unlimited proliferation
- They retain the potential for differentiation
- Characterised by shotr GI phase and a high proportion of cells in S phase
11
Q
G0 phase
A
- Terminally differentiated cells withdraw from cell cycle indefinitely
- Reentry point - a cell returing from G0 enters at early G1 phase
12
Q
G1 phase
A
- RNA and protein synthesis
- No DNA synthesis
- 6-12 hours
13
Q
Restriction point after G1
A
- A cell that passes this point is committed to pass into S phase
14
Q
S phase
A
- DNA synthesis doubles the amount of DNA in the cell
- RNA and protein also synthesized
- 6-8 hours
15
Q
G2 phase
A
- No DNA synthesis
- RNA and protein synthesis continue
- 3-4 hours
16
Q
M phase
A
- Mitosis (nuclear division) and cytokinesis (cell division) yield 2 daughter cells
- 1 hr
17
Q
Differentiate mitosis from cytokinesis
A
MITOSIS = nuclear division
CYTOKINESIS = cell division
18
Q
Name the 3 phases of interphase
A
G1, S and G2
19
Q
Explain the events of the G1 phase
A
- Recovery from previous division
- Cell doubles its organelles
- Cell grows in size
- Accumulates raw materials for DNA synthesis (DNA replication)
20
Q
Explain the events of the S phase (of interphase)
A
- DNA replication
- Proteins associated with DNA are synthesised
- Chromosomes enter with 1 chromatid each
- Chromosomes leave with 2 identical chromatids each
21
Q
Explain the events of the G2 phase
A
- Between DNA replication and onset of mitosis
- Cell synthesises proteins necessary for division
22
Q
What is a chromatid
A
23
Q
Define mitosis
A
Process of nuclear division in eukaryotic cells that occurs when a parent cell divides to produce 2 identical daughter cells
24
Q
Describe PROPHASE
A
- Disappearance of nuclei
- Chromatin fibres condense into discrete chromosomes composed of 2 identical sister chromatids joined at a centromere
- Formation of mitotic spindle, composed of microtubules between the 2 centrosomes
- Centrosomes move apart
25
Describe PRO-METAPHASE
* Nuclear envelope fragments and dissolves
* Spindle fibres extend from each pole towards the cell equator
* Kinetochores form at the centromere
* Kinetochore microtubules attach to the chromosomes
26
Describe METAPHASE
* Centrosomes are at opposite poles of the cell
* Chromosomes migrate to the metaphase plate
* Centromeres of all chromosomes are aligned on metaphase plate
* Kinetochore and non-kinetochore fibres forming spindle
* Identical chromatids attached to kinetochore fibres from opposite ends
\* important that it's done correctly
27
Describe TELOPHASE
* Non-kinetochore microtubules further elongate the cell
* Daughter nuclei begin to form at the 2 poles
* Nuclear envelope forms around chromosomes
* Nucleoli reappear
* Chromatin protein uncoils and chromosomes become less distinct
28
Explain cytokinesis
Division of cytoplasm and organelles
Contractile ring of actin and myosin that cleaves the cell in 2
29
What happens during interphase (of MEIOSIS)
* Each of the chromosomes replicate
* Results in 2 identical sister chromatids
* Chromatids remain attached at centromere
* 2 centrosomes result, each containing a pair of centrioles
30
How much of the meiotic process is spent in Prophase I
What happens to the chromosomes
What structure is formed
* 90% of the meiotic process is spent in prophase I
* Chromosomes condense
* Synapsis occurs - **homologous** chromosomes come together to form a _tetrad_
* Tetrad is 2 chromosomes or 4 chromatids (sister & non-sister chromatids)
31
What is a tetrad
2 chromosomes or 4 chromatids (sister and non-sister chromatids)
\* Formed by synapsis
32
Explain SYNAPSIS of prophase I
33
What important event occurs during prophase I
Where does it take place
What does it create in the offspring
During crossing over, segments of non-sister chromatids break and reattach to the other chromatid
The chiasmata (chiasma) are the sites of crossing over
Creates variation/diversity in the offspring's traits
34
Name the 2 major occurences of meiosis
1. Crossing over
2. Non-disjunction
35
What happens to tetrameres during metaphase I
How are they attached
What sort of pairs are they in
Where are kinetochores & centromeres facing
* "Tetrads" chromosomes align on metaphase plate
* Attached by their centromeres to spindle fibres from centrioles
* Still in homologous pairs
* Kinetochores of sister chromatids face same pole
* Major difference between mitosis and meiosis
* Centromeres of homologous chromosomes face opposite poles
* INDEPENDENT ASSORTMENT OCCURS
36
Explain anaphase I
Where do the spindles move
* Spindle guides the homologous chromosomes towards the opposite poles
* Sister chromatids remain attached
* Move as a unit towards the same pole
* Contrasts mitosis
* Attachments between the homologous chromosomes breaks down
* Homologous chromosomes are separated
* Not the chromatids that separate
37
How would you describe each pole in telophase I
What event occurs
What is formed as a result
What MAY happen
* Cytokinesis occurs
* 2 daughter cells form - they are haploid with duplicated chromosomes
* Spindle may or may not break down
* May be an INTERKINESIS - time between meiosis I and II
* Nuclear envelope may reform briefly
* **No further replication of genetic material**
38
Overview of meiosis II
39
# Define non-disjunction
What does it result in
* Non-disjunction is the failure of homologous chromosomes, or sister chromatids, to separate during meiosis
* Results with the production of zygotes with abnormal chromosome numbers (an abnormal chromosome number i.e. an abnormal amount of DNA is damaging to offspring)
40
Name the 2 ways in which non-disjunction usually occurs
* Monosomy
* Trisomy
41
What does trisomy mean
* If an organism has trisomy 18 it has 3 chromosomes in the 18th set
* Trisomy 21 =\> 3 chromosomes in the 21st set
* If an organism has monosomy 23 it has only 1 chromosome in the 23rd set
42
Non-disjunction associated with Down's Syndrome
Trisomy 21
43
Non-disjunction associated with Turner's Syndrome
Monosomy 23 (X)
44
Non-disjunction associated with Kleinfelter's Syndrome
Trisomy 23 (XXY)
45
Non-disjunction associated with Edward's Syndrome
Trisomy 18
46
Name the 3 stages at which there are checkpoints
G1
G2
M
47
Name the 3 types of the cell cycle's regulatory molecules
1. Kinases
2. Cyclins
3. External signals (growth factors)
48
Kinases' role as cell cycle's signal
When does Cdk become active
* Amount doesn't fluctuate
* Cyclin dependent kinase (Cdk) - inactive until cyclin are present
49
Cyclin's role as cell cycle's signal
* Molecule conc fluctuates
* Binds with kinase and serves as a checkpoint
* Cyclin-Cdk complex promotes activities that lead to next stage of cycle
50
What does a lack of nutrients inhibit
Cell division
51
What is required for cell division
Specific growth factors
* Platelet-derived growth factor (PDGF) required for fibroblast division in healing (wound healing)
52
What are the 2 physical factors that act as regulatory signals of the cell cycle
* Density-dependent inhibition (contact inhibition)
* Anchorage-dependent inhibition
* Cells must attach to substratum (surface)
* Anchorage is signalled to cell-cycle control system by linkage between membrane proteins and elements of cytoskeleton
53
Graphic depiction of density-dependent inhibition of cell division
How do cancer cells differ
54
What substance plays a key role at the G1 checkpoint
What is its function determined by
* Retinoblastoma (Rb) protein plays a key role at G1 checkpoint
* Rb protein function is determined by its phosphorylation status
* S Phase Cyclin-CDk complexes phosphorylate Rb
55
Series of events needed to occur in order to progress to S phase
Cyclin dependent kinase CDK4 binds with cyclin D to form active complexes
This results in phosphorylation of Rb and dissociates pRb from the pRb-E2F complex
E2F binds DNA to upregulate transcription of genes required to progress to S phase
56
What does the M phase checkpoint do
* The G2/M damage checkpoint prevents the cell from entering mitosis (M phase) if the genome is damaged
* It also checks if the cell is big enough (ie has the resources to undergo mitosis
* It is almost exclusively internally controlled
57
What is the composition of the M-phase Promoting Factor (MPF)
What does it trigger
* Composed of 2 key subunits - Cdc2 (CDK1) and cyclin B
* Triggers progression to M phase by phosphorylation of a number of proteins e.g. proteins that degrade nuclear membrane
58
Where do cyclins (that activate kinases) accumulate
In G2
59
What happens to M-phase cyclins during G2
They begin to rise and form mitosis promoting factors (MPF) - M cyclin Cdk complexes
60
What does the G2 checkpoint check for
DNA damage
Then MPF initiates assembly of mitotic spindle, the breakdown of the nuclear envelope, cessation of gene transcription, and condensation of the chromosomes, and taking the cell cycle all the way to metaphase
61
Where are the chromosomes at the M checkpoint
What does MPF activate
* All chromosomes are aligned at the metaphase plate
* MPF activates the anaphase promoting complex (APC) which allows sister chromatids to separate, activating G1 cyclins and degrades M cyclins
62
In MPF regulation, what does Cdc2 form complexes with and when
Cyclin B during S and G2
63
What does CDK-activating kinase do and where
* It phosphorylates CDC2 at threonine-161
* Stabilises its association with cyclin B
* Not immediately active
* Phosphorylation of Tyrosine-15 and threonine-14 inhibitory kinases
* Final activation occurs with dephosphorylation of tyrosine-15 and threonine-14 inhibitory kinases
* MPF is switched off when cyclin B is degraded and threonine 161 is dephosphorylated
64
Metaphase/maturation promoting factor function
