Cell Cycle, Division and Production Flashcards
1
Q
What is the function of Cell Cycle?
A
to duplicate accurately the amount of DNA in chromosomes, segregate the DNA and Divide cell into genetically identical daughter cells (each cell receive complete copy of entire genome).
- Cell Duplication
- DNA segregation
- Cell Division
2
Q
What does the cell cycle duration depend on?
A
duration of cell cycle depends on factors:
1. availability of energy sources
2. the way the cell is differentiated
3 . its surroundings
4. Whether the cell passed the internal tests for readiness to divide (checkpoints).
ex: cell cycle in flies are 8 mins, mammals epithelial cells- 12 hours, frogs- 30 mins (divide synchronously) and mammal fibroblasts- 20 hours.
3
Q
What are the four phases in the cell cycle? Describe them. What is interphase?
A
G1 phase, S phase, G2 phase and M phase.
M phase (mitosis or nuclear division)- is the most intense, dynamic phase of cell cycle (a form of cell division. Cytokinesis (cytoplasmic division) also part of M phase.
S phase- Duplication of genome that occurs between two GAP (G) phases (G1 and G2). S phase- most tightly controlled and demanding process.
Interphase– a combination of G1, S and G2 phase (the entire cell cycle minus M phase).
4
Q
Which phase is the most crucial decision-making point in the cell cycle? Why is it an important decision making point in the cell?
A
G phase (G1 specifically) Staying in G1 phase allows cell to monitor the environment for stimulatory factors, make a decision whether to proceed to S phase, or pause, or enter which could be permanent (either SENESCENT or TERMINALLY DIFFERENTIATED) or temporary non-dividing QUIESCENT state called G0.
5
Q
What is the shortest phase of the cell cycle and why?
A
M phase- SHORTEST phase because the cell tends to minimize the time it spends with completely inactive (condensed) genome without the ability to transcribe it.
6
Q
What are the checkpoints for Cell cycle control system?
A
Checkpoints for Cell cycle control:
- at end of G1, checkpoint: is the environment favorable ?(to be able to enter S phase).
- Between G2 and M phase, checkpoint: Is all DNA replicated? Is all DNA Damage repaired? (to enter Mitosis)
- towards end of M phase, Checkpoint: Are all chromosomes properly attached to mitotic spindle?
7
Q
What is the duration of cell cycle stages proportional to?
A
Duration of cell cycle stages is proportional to amount of cells at certain stage in unsynchronized population.
8
Q
list the duration of cell cycle stages from longest to shortest
A
Longest to shortest duration:
G1 phase, G2 phase, S, and M phase.
9
Q
What are the two main factors that the Cell cycle control system depends on? Where did cell cycle control start from?
A
Genes responsible for cell cycle control first discovered in yeast, and includes CYCLIN (conserved protein factors) and CYCLIN-DEPENDENT PROTEIN KINASES (Cdks) that appear and disappear in cyclic manner (follow one another).
10
Q
Described the kind of system that was used to decipher cell cycle control system in mammals.
A
using frog eggs as model system, helped decipher cell cycle control system.
Process:
- extracts taken from frog egg at different stages can trigger or stop normal cell cycle added in transition.
Ex: inject cytoplasm from M phase in cell- detect spindle and OOCYTE driven into M PHASE
-inject cytoplasm from interphase cell- OOCYTE DOES NOT ENTER M phase.
11
Q
Described the kind of system that was used to decipher cell cycle control system in mammals.
A
using frog eggs as model system, helped decipher cell cycle control system for mammals.
Process:
- extracts taken from frog egg at different stages can trigger or stop normal cell cycle added in transition.
Ex: inject cytoplasm from M phase in cell- detect spindle and OOCYTE driven into M PHASE
-inject cytoplasm from interphase cell- OOCYTE DOES NOT ENTER M phase.
12
Q
What regulates each phase of the cell cycle?
A
Each phase of the cell cycle is regulated by specialized CYCLIN- Cdk protein complex that regulates a different set of target proteins
ex: G1 and S- S cyclin; G2 and M phase- M cyclin.
13
Q
Describe the major cyclins and CDKs of Vertebrates. What cyclin is used for mammals in G1 vs G1/S phase? Why is formation of G1/S complex most important?
A
G1 cyclins (Cyclins D1, D2 and D3 in mammals) form G1-Cdk complexes with Cdk4 and Cdk6 that drives cell through G1 phase. This complex manages events in phase G. The switch between G1 and S is mediated by G1/S-Cdk Complex made of Cyclin E and Cdk2. formation of the complexes is most important, as it is heavily influenced by environmental conditions, extracellular signals permit cells to divide.
14
Q
How many D cyclins are in mammals?
A
Three D cyclins (D1, D2, and D3).
15
Q
Describe what occurs during cyclic degradation?
A
Cyclins are destroyed by proteosomal pathway that drives the transition from one phase to the next. ANAPHASE- PROMOTING COMPLEX (APC) marks M-cyclin for degradation( by ubiquitylation of CYCLIN by APC/C) and takes cell out of mitosis.
The same APC complex destroys SECURIN and triggers separation of chromatids during ANAPHASE.
16
Q
Describe how inhibitory kinases help control activity of cyclin-cdk complexes. what activates and inhibits complex?
A
Cdk protein concentrations in the cells increase gradually. To trigger abrupt activation of Cdk activity, Cdk comes in inactive, phosphorylated form. In this case, M cyclin, is phosphorylated by inhibitory kinase, Wee1. Removal of phosphate by phosphatase CDc25 activates the complex
17
Q
How is activity of cyclin-Cdk complexes controlled by inhibitory signals? What kind of inhibitory signals?
A
When cyclin -cdk active, the activity of complex can be transiently delayed (paused) allowing cells to make a decision whether or not to move to next phase, for example from G1 to S.
Ex: inhbitory subunit p27 bind to cyclin-cdk complex and inactivate complex. Without subunit, and cyclin-Cdk complex it is active.
the activity of cyclin-cdk complex is controlled by both inhibitory subunits (p27) and inhbitory kinases (wee1)
18
Q
What helps control the transition between cell stages?
A
presence of Cyclin-Cdk complexes control transition between the cell cycle stages.
ex: At first checkpoint(end of G1), CDK inhibitors block entry to S phase.
-at second checkpoint (between G2 and M), inhibition of activating phosphatase (cdc25) which blocks entry to mitosis.
at third checkpoint, (M phase), the inhibition of APC/C activation delays exit from Mitosis
19
Q
what are mitogens and what are they useful for? What are other uses of mitogens? What would happen if mammalian cell has no mitogens?
A
Mitogens- external protein activator that triggers cell division.
Other uses; Mitogens serves as transcription regulators, but also TUMOR SUPPRESSORs that are normally Identified by absence in various tumors (since tumor cells tend to divide uncontrollably (devoid of those factors through selection process).
If deprived of transcription regulators called MITOGENS, mammalian cells would stay in G1.
20
Q
Describe the signaling pathway of how mitogens trigger cell divison.
A
Pathway of mitogens triggering cell division:
- mitogen bind to mitogen receptor
- activated receptor leads to activation of intracellular signaling pathway in nucleus
- activation of G1-CDK and G1/S-Cdk leads to phosphorylation of Rb protein
- When Rb protein phosphorylated it is inactivated, which leads to activation of transcription regulator
- genes are then transcribed for entry into S-phase and cell division to occur.
what happens when Rb not phosphorylated? Rb active, transcription regulator inactive, no cell division.
21
Q
What process can lead to arresting or halting cell cycle at G1 phase? How does p53 play a role in this process and what can occur if process goes wrong?
A
DNA damage can arrest the cell cycle at G1.
P53 is a major TUMOR SUPRESSOR protein that helps cells sense the DNA damage and temporarily halt the cell cycle at G1, until the DNA repair system is engaged.
Inability to repair DNA triggers p53 dependent APOPTOSIS (programmed cell death)
22
Q
What processes are cyclin concentrations regulated by?
A
Cyclin concentrations are regulated by transcription and proteolysis
23
Q
What major processes does the cell cycle control system trigger?
A
The cell cycle control system triggers division, tissue integrity and renewal.
24
Q
What does the activity of cyclin-CDK complexes depend on?
A
activity of cyclin-CDK complexes depend on phosphorylation and dephosphorylation.
25
What phase of cell cycle, can Cdks be stabily inactivated?
G1 phase.
26
What two major things can S-Cdk initiate?
S-Cdk can initiate DNA replication and block re-replication.
27
What can arrest the cycle in G2 phase?
INCOMPLETE REPLICATION can halt or arrest cell cycle in G2 phase.
28
What controls the S-phase in cell cycle and how does it control it?
When can Prereplication complex initiate replication?
How does S-cdk trigger assembly of replisome
S-CDK complex controls S-phase.
In S-phase, S-CDK initiates replication and blocks repetition of replication
The pre-replication complex cannot initiate replication at ORI unless, it is activated by S-Cdk
S-Cdk phosphorylates Helicase, which triggers assembly of functional replisome (rep fork, DNA polymerase, etc)
29
What happens when replication is incomplete in S-phase of cell cycle?
If replication is incomplete in S-phase, the cell will be halted at G2 phase.
The presence of active replication prevents CDC25 from activation, which is necessary to dephosphorylate and thus activate M-Cdk
30
What happens to CDKs at the beginning of G1 in cell cycle and why does this occur?
When do you see the rise of cdks again?
ALL CDKS are inhibited at the beginning of G1.
While ANAPHASE-promoting complex (APC) marks M-cyclin for degradation, it is also activated by M-Cdk at the same time. The lack of activator and gene expression depletes cell from eventually all cdks completely ate end of mitosis. The rise of cdks start in G1 with accumulation of G1 cyclins that trigger transition to S phase.
31
How can cells delay division for prolonged periods?
by entering specialized nondividing states (G0).
32
What complex drives cell entry into M phase and mitosis and how does this complex amplify its activity?
M-CDK drives entry of cells into M phase and mitosis.
Activated M-Cdk self regulates (amplifies) its own activity by activating Cdc25 (positive feedback) and shutting down Wee1.
33
What occurs in the M phase of the cell cycle? what two major processes does M phase consist of?
What are the 5 stages mitosis is divided into?
In M phase, the division of a cell into two daughter cells occur.
M phase consists of nuclear division called MITOSIS, and cytoplasmic division called CYTOKINESIS.
Mitosis is divided into 5 stages : Prophase, Prometaphase, Metaphase, Anaphase, Telophase and Cytokinesis (PPMAT).
34
What major events occurs during interphase of cell cycle?
What occurs before replication and what kind of karyotype is present?
What karyotype is present after S phase?
What does n represent?
During interphase:
1. Centrosomes are duplicated
2. Tubulins and other proteins are synthesized, cell also increases in size.
3. DNA is replicated but is still in decondensed state.
4.Before replication, each chromosome has homologous pair (represented by two homologous chromosomes, each came from either father or mother)
This karyotype is called DIPLOID (2n)
n is a number of non-homologous chromosomes.
After S phase, each cell becomes TETRAPLOID (4n)
interphase is a preparation to M-phase (include g1, S, G2)
35
Describe the varying karyotypes and number of chromosomes for eukaryotic mammals, yeast, plants and also prokaryotes during mitosis
In MITOSIS for EUKARYOTES:
most eukaryotes: are 2n to 4n> 2n + 2n (DIPLOID)
some eukaryotes like YEAST are n to 2n > n + n (HAPLOID)
some eukaryotes: 2Xn to 4Xn > 2Xn + 2Xn (plants)
in BINARY DIVISION for PROKARYOTES
prokaryotes: n to 2n > n + n (BACTERIA)
36
What occurs during the prophase stage of mitosis?
| What appears in the chromosomes?
Prophase is the first step of mitosis.
In prophase, the duplicated chromosome CONDENSE, outside nucleus, the MITOTIC SPINDLE forms between two centrosomes; CENTROSOMES move apart towards opposite sides and nuclear envelope is still intact.
The condensed chromosome have two sister chromatids held together by kinetochores.
37
What two cellular structures help configure duplicated chromosomes for SEGREGATION? How do these structures differ in functions and what activates these structures?
Cohesins and Condensins configure duplicated chromosomes for segregation.
Cohesin- tie together TWO SISTER CHROMATIDS and prevent them from breaking apart.
Condensin- help to COIL and thus condense EACH sister chromatid (one at a time)
Cohesins and condensin are structurally related and activated by M-Cdk.
38
what other cell division pathway are cohesions and condensins important in? what occurs when there is a defect in chromatid cohesion?
cohesions and condensins are important in MEIOSIS, which generates GAMETES.
Defects in sister chromatid cohesion leads to MISEGEREGATION and results in abnormal number of chromosomes (ANEUPLOIDY).
39
What cellular structure do microtubules form that is crucial for separation of sister chromatids and cytokinesis?
MITOTIC SPINDLE which is crucial for separation of sister chromatids and cytokinesis
40
What are the two transient cytoskeletal structures that mediate M phase in animal cells? How do microtubules attach to centromeres and what is their function?
what is the function of contractile ring?
MITOTIC SPINDLE AND CONTRACTILE RING mediate M phase.
microtubules of mitotic spindle attach to centromeres of sister chromatids through protein complex called KINTEOCHORE, and separate chromatids at beginning of ANAPHASE.
Contractile ring- composed of actin and myosin, help divide a cell into two cells, during cytokinesis.
41
Describe the structure of microtubules and how they extend and shrink. What occurs at plus end vs minus end?
Microtubules undergo constant polymerization and depolymerization (shrink) by addition and removal of tubulin alpha/beta heterodimers at PLUS end.
Plus end- is beta tubulin end (where add and remove dimers)
Minus end- "alpha end", normally remains INTACT and attached to microtubule-organizing center (CENTROSOME)
42
What are the components of centrosome?
centrosome composed of pair of centrioles, centrosome matrix, and nucleating sites (increase number of microtubules in spindle)
43
What is the driving force behind cell division? What is the function of this force?
DYNAMIC INSTABILITY is the driving force behind cell division.
Dynamic instability- the ability of microtubules to shrink and grow. It is responsible for chromosome segregation and cell polarization into two daughter cells during cell division.
44
What cellular structure stabilizes cell shape during cell division and how does it do this?
Plasma membrane CAPPING PROTEIN stabilizes shape during cell division by stabilizing plus end.
Capping protein will bind to plus end where microtubules are growing and shrinking and block the plus end (prevent addition and removal of microtubules) this stabilizes microtubules.
without, capping proteins, you will have unstable microtubule/plus end.
45
What occurs in the centrosomes during interphase and prophase? what phase does the mitotic spindle start to assemble?
Differentiate between interpolar and astral microtubules.
In interphase- centrosomes duplicate
During prophase- centrosome outgrow microtubules and forming MITOTIC SPINDLE
mitotic spindle assembles in prophase
Interpolar microtubules are perpendicular to equator. Their associated plus end push centrosomes further apart.
The remaining microtubules become ASTRAL microtubules (not connected to kinetochore)
46
What happens during prometaphase of mitosis?
| How is the nuclear envelope broken down?
Prometaphase starts abruptly with Breakdown of NUCLEAR ENVELOPE. This allows chromosomes to attach to spindle microtubules via kinetochores and undergo active movement (chromosomes start moving).
PHOSHPHORYLATION of nuclear envelope proteins (nucelar pore proteins, lamins) promotes the breakdown of nucelar envelope into separate lamella and vesicles.
M-Cdk phosphorylates nuclear envelope.
47
Explain what a kinetochore is and its role in cell division.
What is kinetochore attached to and how many microtubules does it bind in humans vs yeast?
A kinetochore is a protein complex that recognizes special DNA sequence present at centromere (it also where mitotic spindles attach to for linking chromosome to spindle)
Kinetochore is attached to KINETOCHORE MICROTUBULES.
Human kinetochores bind 20-40 microtubules
Yeast chromatid binds just one microtubule.
48
Describe the three classes of microtubules that make up the fully formed mitotic spindle.
Three classes of microtubules (that make up mitotic spindle):
1. Kinetochore microtubules- on centromere of condensed sister chromatids
2. Astral microtubules- connect to centrosome and cytosolic part
3. Interpolar microtubules- at plus end, interaction of microtubules from opposite centrosomes.
49
Describe the mitotic spindle formation and centrosome cycle. What is the centrosome cycle and when does it occur?
When does mitotic spindle start to form?
Centrosome Cycle- process of centrosome duplication and separation.
Centrosome duplicates during interphase (specifically G1/S phase), forming two centrosomes and thus two poles of mitotic spindle.
As mitosis begins, two centrosomes separate, each nucleating a radial array of microtubules called ASTER. The separation is driven by INTERPOLAR MICROTUBULES.
mitotic spindle starts to assemble in prophase.
50
What occurs in the metaphase of mitosis? what happens to kinetochore microtubules?
At metaphase, the chromosomes are aligned at the equator of spindle, midway between spindle poles. The kinetochore microtubules on each sister chromatid attach to opposite poles of spindle.
51
What structure forms during metaphase, and why is this structure important?
in metaphase, duplicated sister chromatids align half way between two spindle poles, forming METAPHASE PLATE.
This arrangement is highly important for synchronous separation and equal distribution of sister chromatids between daughter cell (mechanism still poorly understood)
52
What occurs during Anaphase of mitosis? What happens to kinetochore microtubules and spindle poles?
At anaphase, sister chromatids synchronously SEPARATE and are pulled slowly towards the spindle pole to which they are attached.
The kinetochore microtubules get shorter and spindle poles move apart, both contributing to chromosome segregation.
53
explain how chromosomes segregate during anaphase. What must first occur in anaphase? Explain how cohesion gets destroyed and what proteins must be used.
Anaphase begins with BREAKAGE of linkage that holds sister chromatids together.
The cohesion linkage is destroyed by protease called SEPARASE. Before anaphase begins, this protease in inactive state by inhibitory protein called SECURIN.
In order to destroy cohesion and start anaphase, Securin has to be removed from Separase.
54
Explain what structure destroys securin and thus allows anaphase to start.
How does this structure destroy securin?
APC complex (anaphase promoting complex) destroys securin and thus allows anaphase to start. APC also marks M cyclin for degradation.
APC Complex triggers the separation of chromatids by PROMOTING the DESTRUCTION of COHESION
through cascade of reactions.
inhibitory securin will bind and inactivate separase (protein that destroys cohesion). But once APC is active, it will ubiquilate and degrade securin, which activates separase.
separase will then cleave cohesions an allow separation of chromatids.
55
What happens to the daughter chromosomes during anaphase?
how fast do sister chromatids move and what is the driving force?
Explain the two anaphase processes that occur and how do they differ?
During anaphase, daughter chromosomes are pulled towards opposite poles, as kinetochore microtubules depolymerase.
Sister chromatids move with speed of 1 mm per minute.
The driving force is created by DISSASEMBLY of microtubules and motor proteins, KINESINS and DYNENINS.
Two processes ANAPHASE A and ANAPHASE B occur simultaneously (NOT separate phases that follow one another). These processes differ in that they involve kinetochore on one hand, and aster and interpolar microtubules on the other.
Anaphase A- kinetochore microtubules SHORTEN and drag chromosome towards their spindle pole; chromosomes are PULLED
Anaphase B- Poles PUSHED and PULLED apart. Sliding force between interpolar microtubule from opposite pole push pole apart; pulling force at cell cortex drag pole
56
What are the functions of two motor proteins Kinesin and Dynein in mitosis?
Kinesin and dynein drive cargo along microtubules.
Kinesin- move cargo from Minus end to plus end, (from the center to the periphery)
Dynenin- move cargo from plus end to minus end (opposite direction) arrow move left.
57
which motor protein provide anterograde transport? Which provides retrograde?
Kinesin- provide ANTEROGRADE transport along AXON terminal (outward transport)
Dynein- provide RETROGRADE transport of cargo (Backward transport, cell body)
58
what happens to soluble microtubules if tail domain of motor proteins attaches to immobile surface?
If tail domain of motor proteins is attached to immobile substrate (surface), soluble microtubules can be moved back and forth along substrate.
59
What occurs in isolated doublet microtubules?
In isolated doublet microtubules, Dynein produces microtubule sliding using ATP.
60
Describe what occurs with the motor proteins in Anaphase B. What is the role of kinesin and Dynein in this process?
In Anaphase B, the two spindle poles move apart by two driving forces created by Kinesin and dynein.
Kinesin- walk from minus end to plus end, which provides sliding of overlapping INTERPOLAR microtubules (pushing poles apart) (process 1)
Dyneins are immobilized by their tails at cell cortex that underlies PM. They walk from plus to minus end on ASTRAL microtubules, bringing centrosomes closer to PM and pulling poles apart (prcoess 2)
61
What structures are crucial for functioning of mitotic spindle?
Motor proteins (kinesin and dynein)
62
What occurs during telophase in mitosis? How does the division of cytoplasm begin?
During telophase, the two sets of chromosomes arrive at the poles of spindle, a new nuclear envelope reassembles around each set, completing the formation of two nuclei and marking end of mitosis.
Division of cytoplasm beings with assembly of contractile ring.
63
What are the two major processes that occur during telophase? what happens when envelope is reformed?
Two major processes in telophase are:
1. The mitotic spindle disassembles
2. nuclear envelope is reappears and is formed from nuclear membrane vesicles (nuclear pore and lamins are dephosphorylated)
Once the nuclear envelope is formed again, chromosomes decondense.
64
What assists in the assembly of mitotic spindle?
| What triggers sister chromatid separation in anaphase?
CHROMOSOMES assist in assembly of mitotic spindle (spindle starts to assemble in prophase)
Proteolysis triggers sister chromatid separation during anaphase. In anaphase, chromosomes also segregate.
65
What prevents sister chromatid separation?
An UNATTACHED chromosome will prevent sister chromatid separation.
66
What occurs during cytokinesis in animal cells?
During cytokinesis of an animal cells, the cytoplasm is divided in two by a contractile ring of actin and myosin filaments, which pinches the cell into two daughter cells, each with one nucleus.
Here you have complete nuclear envelope around decondensed chromosomes.
67
When does cytokinesis occur and when does the process end?
| What structure forms at beginning of cytokinesis?
Cytokinesis and mitosis overlap in time.
Cytokinesis starts in ANAPHASE and is not completed until TELOPHASE is over.
Cytokinesis begins with formation of CLEAVAGE FURROW, which is initiated by overlapping INTERPOLAR MICROTUBULES.
68
How is cytokinesis finally completed?
Cytokinesis is completed by CONTRACTILE RING made of ACTIN and MYOSIN Filaments.
at some point, the cytokinesis process becomes irreversible regardless of the presence of spindle.
ring will form inside cleavage furrow.
69
What happens to the shape of the cell during cytokinesis? What about after cytokinesis? How does this affect nearby cells?
During cytokinesis, cells normally round up and lose their contacts with surrounding cells.
once cytokinesis is completed, cell changes shape and expresses attachment proteins called INTEGRINS to allow them to reestablish their contacts with the substrate (neighboring cells and ECM), so that new cells can be accommodated within tissue.
70
What occurs in cytokinesis of plant cells? How does it differ from animal cells in terms of structures formed?
Cytokinesis in plant cells is guided by specialized microtubule based structure called PHRAGMOPLAST.
Cytokinesis in higher plants are different from animals cells as the plant cells are surrounded by cell walls, and have NO CLEAVAGE FURROWS.
Instead they use remnants of interpolar microtubules to arrange membrane, polysaccharides and glycoprotein filled vesicles from GOLGI in middle of dividing cells from telophase, to form PHRAGMOPLAST, and allow accumulated vesicles to fuse later and form two membranes.
71
What determines the plane of cytoplasmic cleavage?
| What occurs during cytokinesis of plant cells?
MITOTIC SPINDLE determines plane of cytoplasmic cleavage.
| Formation of new CELL WALL in plant cell cytokinesis
72
What must be distributed to daughter cell when cell divides?
Membrane enclosed organelles must be distributed to daughter cell when the cell divides.
73
What is sexual reproduction? What is fertilization?
| How does this differ from asexual reproduction? What is Meiosis?
sexual reproduction- a development of a new organism from fusion of two cells that come from two organisms, parental and maternal.
Fertilization- the fusion of parental cells
Asexual reproduction does not involve sexual partner; in many cases it creates substantial genetic variability by shuffling the organism's own genes through process of HOMOLOGOUS RECOMBINATION that occurs during MEIOSIS.
Meiosis- is a specialized cell division that reduces the number of chromosomes.
74
What two processes does sexual reproduction include?
Sexual reproduction = MEIOSIS and FERTILIZATION
75
Differentiate between somatic cells in terms of chromosome number. How are gametes produced.
Somatic cells are normally DIPLOID (2n), each chromosome has a HOMOLOGOUS PAIR that came from either father or mother.
GAMETES- (which are EGGS and SPERMS) are HAPLOID (n) cells that are produced in specialized sex organs (GONADS), called OVARIES AND TESTES. Gametes have only ONE out of two homologous chromosomes present.
76
What is a zygote? What does the zygote later develop into?
A zygote is a fertilized egg. After the first division, a zygote becomes an EMBRYO that further develops into an adult organism.
77
Where do somatic cells, gametes and organs/organ systems all develop from?
They all develop from a single cell, a fertilized egg with restored diploid number of chromosomes.
78
What are the two organisms involved sexual reproduction and what do they produce?
what kind of things does the egg carry and what is a role of sperm cell.
What is another name for sperm cell and how is it able to function?
Two different organisms of same species that are engaged in sexual reproduction are called MALES and FEMALES, and the games they produce are called SPERMS and EGGS.
Eggs- normally carry a lot of nutrients necessary for development of embryo upon fertilization.
Sperm cell or SPERMATOZOON (pl spermatozoa) are small and highly mobile.
The mobility of many animal sperm cells , like humans are due to FLAGELLUM, while many other organism's sperm may have no motility organelles at all, or like nematode spermatozoa they can have crawling cells (amoeba like)
79
Describe the sexual reproduction and fertilization in Nematode C elegance. What makes this organism unique?
The Nematode C elegance (worm) is a Hermaphroditic, as eggs and sperm are produced in the same body.
It is still a form of sexual reproduction as it involves HAPOLOID gametes and self-fertilization (similarly seen in plants)
80
Describe the unique form of sexual reproduction of fish species. How do these fish species change?
some fish are sequential hermaphrodites, as these species change their sex and types of gametes produced based on their AGE.
At younger age, fish are female, and produce eggs.
at older age, fish become male and produce sperm.
81
What scientist discovered Meiosis and how did he do it?
Thomas Boveri discovered meiosis by studying the maturation of eggs of a nematode. He noticed that as eggs matured, there was a point where chromosome numbers reduced in half.
82
compare and contrast meiosis and mitosis in terms of duplication and division.
What kind of karyotype does meiosis begin with?
When does yeast undergo meiosis?
What occurs after duplication in meiosis and what does this form?
Meiosis and Mitosis both go through ONE round of chromosome/DNA REPLICATION
However, Mitosis goes through one round of cell division (form 2 diploid nuclei), while meiosis undergoes TWO round of cell division.
In humans and other multicellular eukaryotes, meiosis begins in specialized Diploid GERM-LINE CELLS that reside in female and male gonads, ovaries (produce eggs) and testes (make sperm).
Yeast (unicellular organism) undergoes meiosis that is triggered by starvation.
83
compare and contrast meiosis and mitosis in terms of duplication and division.
What kind of karyotype does meiosis begin with?
When does yeast undergo meiosis?
What occurs after duplication in meiosis and what does this form?
Meiosis and Mitosis both go through ONE round of chromosome/DNA REPLICATION
However, Mitosis goes through one round of cell division (form 2 diploid nuclei), while meiosis undergoes TWO round of cell division.
In humans and other multicellular eukaryotes, meiosis begins in specialized Diploid GERM-LINE CELLS that reside in female and male gonads, ovaries (produce eggs) and testes (make sperm).
Yeast (unicellular organism) undergoes meiosis that is triggered by starvation.
After duplication, duplicated paternal chromosomes, align along duplicated maternal homologs. This process is called PAIRING (does NOT happen in mitosis)
PAIRING forms a BIVALENT.
84
What does pairing result in during meiosis?
| How does the bivalent form and what happens as a result of pairing and first cell division of meiosis 1?
Pairing results in formation of bivalent during meiotic metaphase.
The twin copies of each duplicated chromosome, paternal or maternal called SISTER CHROMATIDS stick together at beginning of first meiotic division (MEIOSIS 1_ forming structure called bivalent.
As a result of pairing followed by meiosis I (1st cell division), each daughter cell receives either paternal or maternal duplicated chromosomes and for each chromosome, the choice is RANDOM.
85
Describe the different number of gametes that can occur after two rounds of cell division in mitosis.
What does n represent in terms of gametes and how many possible gamete combos can humans have?
how long are the process of meiosis II and mitosis compared to how long gametes stay in meiosis I?
The independent and random distribution of paternal chromosomes among gametes result in 2^n different gametes. n is the number of chromosomes.
For humans, 2^23= 8,388,608.
While mitosis and meiosis II are usually accomplished within hours, the germline cells may stay in meiosis I for days, months or even years because of the long time they spend in prophase I (due to crossing over).
86
When does recombination of duplicated homologs occur in meiosis. How do the daughter cells in mitosis and meiosis differ?
Recombination of duplicated homologs occur in prophase I of meiosis, before the homologs line up along metaphase plate.
Daughter cells in mitosis- will create genetically identical diploid cells.
Daughter cells in meiosis- will create NON-identical Haploid cells, that are recombinated.
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What do the the non-sister chromatids do in meiosis I?
| What structures from during Homologous recombination?
During meiosis I, the NON-SISTER chromatids in each bivalent swap segments of DNA.
This process is called CROSSING-OVER, where paternal and maternal chromatids undergo HOMOLOGOUS RECOMBINATION and form multiple CHIASMATA that are stabilized and moved along DNA chains by specialized nucleoprotein complex called SYNAPTONEMAL COMPLEX.
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What does the synaptonemal complex compose of?
The synaptonemal complex is made of transverse filaments, axial cores, sister chromatids of duplicated maternal and paternal homologs, and cohesions that hold the sister chromatids together. this complex mediates recombination of homologs.
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What process in meiosis provides genetic variability in sexually reproducing species?
What happens to synaptonemal complex after prophase I has ended?
CROSSOVERS that occur during meiosis are a major source of genetic variation in sexually reproducing species.
by the time prophase ends, the synaptonemal complex has disassembled, allowing the homologs to separate along most of their length.
90
What is the role of chiasmata in mitotic division?
What are bivalents stabilized by?
Chiasmata help to properly segregate duplicated homologs during first mitotic division
Before anaphase, I the few remaining chiasmata resist pulling, thus helping to position and stabilize all bivalents together at metaphase plate.
The bivalents (similar to mitosis) are stabilized by COHESIN proteins along their entire length that is eventually degraded by proteolysis to start anaphase I.
At the centromeres, they still hold chromatids together.
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What happens with the sister chromatids in metaphase of meiosis I vs Anaphase of meiosis?
in metaphase- chiasmata is helping the sister chromatid from from maternal and paternal to to be glued to each other.
During anaphase, the arms of sister chromatids become unglued, allowing the duplicated homologs to separate
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What occurs during second round of meiotic division and what is produced?
Are these cells identical?
The second round of meiotic division (meiosis II) occurs without any further DNA replication and simply separates each pair of duplicated chromatids into separate gametes.
formation of HAPLOID daughter cells.
All haploid cells are NOT IDENTICAL.
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What are two ways of genetic assortment that can generate new chromosome combinations?
Two kinds of genetic assortment:
1. Independent and random distribution of paternal and maternal chromosomes (homologs) between gametes
2. Exchange of segments between maternal and paternal chromosomes through homologous recombination during cross over.
94
Describe the process of oogenesis in humans. How many primary oocytes are arrested in meiosis I at birth?
how do you compare oogenesis and spermatogenesis time period.
When can meiosis be completed in human oocytes?
Oogenesis (growth of primary oocyte into mature ovum) about 20,000 primary oocytes are arrested at meiosis I during at birth.
oogenesis is an asymmetrical and intermittent (from birth) process, while SPERMATOGENESIS starts in puberty and each cycle is completed from start to finish in 74 days.
meiosis in human oocytes can only be completed if fertilization has occurs (sperm penetrate egg)
95
Explain how meiosis is flawed and prone to errors?
What kind of errors may be seen? What issue is largely responsible for miscarriages in females?
What abnormality leads to Down Syndrome?
The frequency of chromosome MIS-SEGREGATION during GAMETOGENESIS is pretty high.
In Females, NONDISJUNCTION during MEIOSIS occurs in 10% of human oocytes and is largely responsible for high rate of miscarriages
nondisjunction- failure of homologs or sister chromatids to separate properly- aneuploidy
In some cases, for example, for CHROMOSOME 21, the abnormal EMBRYOS survive an results in DOWN SYNDROME trisomy 21, extra chromosome)
96
Explain how fertilization is a tightly controlled process in mammals.
what is zona pellucida and what is it's role?
Fertilization is a restoration of diploid set of chromosomes through fusion between an EGG and SPERM, resulting in formation of a fertilized egg called ZYGOTE.
The Zygote is capable of dividing and developing into an EMBRYO and further into an adult organism.
Zona Pellucida- protective layer surrounding egg that has to be digested by Sperm proteases.
this ingestion happens very fast and triggers the influx of Calcium into the cell and resulting in massive exocytosis that lifts the zona pellucida off the egg PM and hardens it, preventing entry of additional sperm.
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What does fertilization reconstitute or provide?
Fertilization restores a complete DIPLOID genome
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What are the two benefits of sexual reproduction?
The two benefits of sexual reproduction is that:
1. generates Genetic DIVERSITY
2. gives organisms COMPETITIVE advantage in CHANGING environment.
Reproduction includes both diploid and haploid cells.
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What processes ensures proper segregation of homologs?
Chromosome pairing and crossing over ensure proper segregation of homologs
100
Describe how some animals reproduce through simple cell division and other forms of asexual reproduction.
What kind of processes do prokaryotes or plants undergo?
What organisms reproduce through buds?
Reproduce through fragmentation?
Prokaryotes reproduce through SIMPLE BINARY CELL DIVISION (dna replicates, and cell divide into two separate cells)
Some animals and plants, besides being able to reproduce sexually, may also produce ASEXUALLY forming OFFSHOOTS (BUDS) that detach and give rise to new independent organisms
Ex: hydrazoa like HYDRA and other POLYPS (corals) asexually produce like this.
Even more complex organisms like BLACKWORMS can reproduce by FRAGMENTATION.
importantly such organisms are genetically identical to their parents
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How does asexual reproduction introduce genetic variation?
What is parthogenesis?
How do hermaphroditic species reproduce?
What two major processes introduce genetic variation and how do they do that?
a
102
How do egg and sperm cells relate and differ?
| What process do sex chromosomes undergo?
a
103
Explain what occurs in animals that go through sex dimorphism and provide examples.
How is sex determined in some animal species?
a
104
What makes yeast so special? How do they reproduce?
| What does sexual reproduction always involve?
a
105
What are the benefits of sexual reproduction?
a
