Mitosis and Meiosis Flashcards
What is the longest phase of the cell cycle?
G1
Describe the role of cyclins and CDKs in G1 Phase:
in the early G1 phase, cyclin D binds to CDK4 or CDK6 to form complexes. This cyclin D-CDK4/6 complex helps initiate the transition from G1 to the S phase, passing a restriction point by phosphorylating and inactivating the retinoblastoma protein (Rb), which in turn releases E2F transcription factors, leading to the expression of genes necessary for DNA replication.
Describe the role of cyclins and CDKs in S Phase:
During the S phase, cyclin E binds to CDK2 to form a complex. This cyclin E-CDK2 complex further phosphorylates Rb, promoting the progression of the cell cycle by allowing DNA replication to occur.
Describe the role of cyclins and CDKs in G2 Phase:
In the G2 phase, cyclin A binds to CDK1 to form a complex. This cyclin A-CDK1 complex regulates the transition from G 2 to M phase by phosphorylating various target proteins involved in mitosis preparation, such as proteins that regulate microtubule organization and chromosome condensation.
Describe the role of cyclins and CDKs in mitosis:
As cells enter mitosis, cyclin B binds to CDK1, forming a complex known as
mitosis-promoting factor (MPF). Cyclin B-CDK1 is essential for initiating and coordinating the events of mitosis, including nuclear envelope breakdown, chromosome condensation, spindle formation, and the onset of anaphase.
How can dysregulation of cycline-CDK complexes clinically manifest?
Dysregulation of cyclin-CDK complexes can lead to various diseases, including cancer, where aberrant cell cycle progression is a hallmark feature
What is the “C-value?”
The “C value” typically refers to the amount of DNA in the haploid genome of
a species, often measured in picograms (pg). This value varies among different species and is not specific to individual chromosomes but rather represents the total amount of DNA in a cell’s nucleus. For humans C = 3.5 pg DNA. Mature gametes are 1C. Somatic cells in G1 are 2C.
What are the three classes of microtubules in cell division?
- Polar Microtubules extend from each centrosome toward the center of the cell during cell division. They overlap with microtubules from the opposite spindle pole and contribute to the elongation of the spindle apparatus. Polar microtubules are involved in the separation of chromosomes during cell division, ensuring that each daughter cell receives the correct number of
chromosomes. - Astral Microtubules are shorter microtubules that radiate outward from the centrosomes toward the cell periphery. They help to position the spindle apparatus within the cell and are involved in orienting the spindle poles. Astral microtubules also play a role in cell signaling and positioning the cell during cell division, particularly in asymmetric cell divisions.
- Kinetochore Microtubules are the primary microtubules that attach to the kinetochores of chromosomes. These microtubules extend from each centrosome toward the chromosomes, forming a physical connection between the centrosomes and the chromosomes. Kinetochore microtubules play a critical role in the movement of chromosomes during cell division,
facilitating their alignment at the metaphase plate and their subsequent segregation to opposite poles during anaphase.
What is the restriction point in cell division?
G1 Checkpoint: also known as the restriction point (as mentioned above), occurs toward the end of the G1 phase. At this checkpoint, the cell evaluates external signals, nutrient availability, and the integrity of the DNA before committing to DNA replication and cell division. Factors such as cell size, availability of growth factors, and DNA damage are assessed. If conditions are favorable and DNA is undamaged, the cell proceeds to the S phase to initiate DNA replication.
What is the G2 /M Checkpoint?
G2 /M Checkpoint: occurs at the boundary between the G2 phase and the mitotic (M) phase. At this checkpoint, the cell ensures that DNA replication is complete, DNA is undamaged, and the cell size is adequate before entering mitosis. Factors such as DNA integrity and repair, replication completion,
and cell size are assessed. If conditions are favorable, the cell proceeds to enter mitosis.
What is the SAC?
Cell division
Spindle Assembly Checkpoint (SAC): operates during metaphase, ensuring proper attachment of spindle fibers to kinetochores and alignment of chromosomes at the metaphase plate before the onset of anaphase. The SAC prevents premature segregation of chromosomes and ensures that each daughter cell receives the correct number of chromosomes. It monitors tension exerted on kinetochores by microtubules and delays anaphase onset until all chromosomes are properly aligned and attached to the spindle.
What can occur when a faulty cell passes SAC?
Non-disjunction is an obvious example of failure of a chromosome segregation checkpoint that should be acave before the cell passes from metaphase into anaphase.
When a checkpoint fails to provide a safe gaurd in the cell cycle, what can occur in somatic cells?
When checkpoints fail in somaac cells the result can be dysplasia and eventually neoplasia or cancer.
When a checkpoint fails to provide a safe gaurd in the cell cycle, what can occur in somatic cells during early development of in gametes?
When checkpoints fail in gametes or in somaac cells during early development the results can lead to congenital abnormaliaes. Females with Turner syndrome (45X) result from non-disjunction
How is the DNA content and chromosome number represented for a somatic cell after the S phase?
2N4C
What is the reduction division?
The first meiotic division
When are chiasma formed?
During the early stages of prophase I
What are the stages of meiosis?
When does meiosis begin in females?
What difference in meiosis, compared to mitosis, contributes to genetic diversity?
