HomeWork | Cell Division & Cell Cycle Flashcards
Differences between mitosis and meiosis
Mitosis and meiosis are both types of cell division, but they differ in several ways, including:
Purpose
Mitosis is used to create new body cells, while meiosis is used to create egg and sperm cells for sexual reproduction.
Number of daughter cells
Mitosis produces two daughter cells, while meiosis produces four.
Genetic makeup
Mitosis produces genetically identical daughter cells, while meiosis produces genetically unique daughter cells.
Number of chromosomes
Mitosis produces daughter cells with the same number of chromosomes as the parent cell, while meiosis produces daughter cells with half the number of chromosomes as the parent cell.
Cell type
Mitosis occurs in somatic cells, or non-reproductive cells, while meiosis occurs in germ cells, or cells that participate in sexual reproduction.
Number of cell divisions
Mitosis involves one cell division, while meiosis involves two successive cell divisions.
Mitosis is a fundamental process for life, and is responsible for the growth of embryos and babies, as well as the repair and replacement of cells throughout life. When mitosis is not regulated correctly, it can lead to health problems such as cancer
Mitosis is the process by which a cell replicates its chromosomes and then segregates them, producing two identical nuclei in preparation for cell division.
Meiosis is a type of cell division that produces gametes, or sperm and egg cells, in sexually reproducing organisms.
The concept: cell cycle, mitotic apparatus, synapsis, MPF
Cell Cycle
In cell biology, the “cell cycle” refers to a series of ordered events a cell undergoes as it grows, replicates its DNA, and prepares for division, ultimately resulting in the creation of two new daughter cells, each with a complete copy of the original cell’s genetic material; this process involves distinct phases like interphase (growth and DNA replication) and the mitotic phase (cell division) where the replicated DNA is separated into two new cells.
Key points about the cell cycle:
Stages:
The cell cycle is typically divided into interphase (G1, S, and G2 phases) and the mitotic phase (M phase) which includes mitosis (nuclear division) and cytokinesis (cytoplasm division).
Interphase:
During interphase, the cell grows, synthesizes proteins, and replicates its DNA.
Mitosis:
During mitosis, the replicated chromosomes are precisely separated and distributed into two new nuclei.
Cytokinesis:
Following mitosis, cytokinesis occurs where the cell cytoplasm divides, creating two distinct daughter cells.
Regulation:
The cell cycle is tightly regulated by checkpoints to ensure proper DNA replication and prevent errors that could lead to mutations or cancer.
Mitotic Apparatus
In cell biology, the “mitotic apparatus” refers to a complex, temporary structure made primarily of microtubules that forms during cell division (mitosis) and is responsible for accurately separating and distributing replicated chromosomes to the two daughter cells, ensuring each receives a complete set of genetic material; essentially, it’s a highly organized system that orchestrates chromosome movement during mitosis.
Key points about the mitotic apparatus:
Components:
The mitotic apparatus consists of the spindle fibers (microtubules), which extend from the poles of the cell, and the asters, which are star-shaped structures at each pole where microtubules radiate outwards.
Function:
The spindle fibers attach to the centromeres of chromosomes via specialized protein complexes called kinetochores, allowing the apparatus to pull the sister chromatids apart and move them to opposite poles of the cell during anaphase.
Dynamic nature:
The mitotic apparatus is a dynamic structure, with microtubules constantly assembling and disassembling to facilitate chromosome movement.
Importance:
Proper functioning of the mitotic apparatus is crucial for accurate chromosome segregation, preventing errors in cell division that could lead to genetic abnormalities
Synapsis
In cell biology, “synapsis” refers to the process where two homologous chromosomes pair up lengthwise during the prophase I stage of meiosis, allowing for the potential exchange of genetic material through crossing over; essentially, it’s the close alignment of matching chromosomes to facilitate genetic recombination before they separate during cell division.
Key points about synapsis:
Occurs during meiosis:
Synapsis is a crucial step in meiosis, specifically during the pachytene phase of prophase I.
Homologous chromosome pairing:
During synapsis, homologous chromosomes (one from each parent) come together and align along their entire length.
Synaptonemal complex:
A protein structure called the synaptonemal complex forms between the paired chromosomes, holding them together and facilitating the process of synapsis.
Crossing over:
Once synapsis is established, the paired chromosomes can undergo crossing over, where genetic material is exchanged between non-sister chromatids.
MPF
In cell biology, MPF, which stands for “Maturation Promoting Factor,” refers to a protein complex that acts as a key regulator of the cell cycle, specifically triggering the transition from the G2 phase to the M phase (mitosis) by phosphorylating various proteins necessary for cell division to occur; essentially, it acts as the “go-ahead” signal to initiate mitosis.
Key points about MPF:
Composition:
MPF is composed of two main components: a cyclin B protein and a cyclin-dependent kinase (CDK) called Cdk1 (also known as p34cdc2).
Activation:
The activity of MPF is tightly regulated; as cyclin B levels rise during the G2 phase, it binds to Cdk1, forming the active MPF complex.
Function:
Once activated, MPF phosphorylates various target proteins, leading to crucial events like nuclear envelope breakdown, chromosome condensation, and spindle formation, which are necessary for mitosis to proceed.
The features of different phases in a mitotic cell cycle
The mitotic cell cycle consists of several phases, including interphase (G1, S, and G2 stages), prophase, prometaphase, metaphase, anaphase, and telophase, where the key feature is theprecise separation and distribution of replicated chromosomes into two identical daughter cells, with each phase having distinct characteristics involved in chromosome condensation, spindle fiber attachment, and movement to opposite poles of the cell.
Interphase (G1, S, and G2):
G1 phase:Cell grows and prepares for DNA replication, synthesizing proteins and organelles.
S phase:DNA replication occurs, resulting in duplicated chromosomes.
G2 phase:Further cell growth and protein synthesis, preparing for mitosis.
Mitosis (Prophase, Prometaphase, Metaphase, Anaphase, Telophase):
Prophase:
Chromatin condenses into visible chromosomes.
Nuclear envelope begins to break down.
Centrioles move to opposite poles of the cell.
Prometaphase:
Nuclear envelope completely breaks down.
Spindle fibers attach to the kinetochores of chromosomes.
Chromosomes start to move towards the cell equator.
Metaphase:
Chromosomes align at the metaphase plate (center of the cell).
Spindle fibers are fully attached to the chromosomes, ensuring proper alignment.
Anaphase:
Sister chromatids separate and are pulled apart by spindle fibers towards opposite poles of the cell.
Telophase:
Nuclear membrane reforms around each set of chromosomes at opposite poles.
Chromosomes begin to decondense.
Cytokinesis (cell division) usually begins during late telophase.
Key points to remember:
Mitosis ensures that each daughter cell receives an exact copy of the parent cell’s genetic material.
The spindle fibers play a crucial role in separating the chromosomes during anaphase.
Checkpoints exist during the cell cycle to monitor proper DNA replication and prevent errors before proceeding to the next phase.
MPF and its molecular mechanism in cell cycle regulation.
MPF (Maturation Promoting Factor), also known as M-phase promoting factor, is a protein complex that plays a crucial role in regulating the cell cycle bytriggering the transition from the G2 phase to the M phase (mitosis) through phosphorylation of target proteins, essentially acting as a key regulator for entry into mitosis;it consists of a cyclin B protein bound to a cyclin-dependent kinase (CDK1), where the activity of CDK1 is controlled by the level of cyclin B throughout the cell cycle.
Key points about MPF and its mechanism:
Components:
MPF is composed of two proteins: cyclin B, which acts as a regulatory subunit, and CDK1 (cyclin-dependent kinase 1), which is the catalytic subunit responsible for phosphorylation.
Cyclin B regulation:
The level of cyclin B fluctuates during the cell cycle, rising significantly in the G2 phase and peaking at the G2/M transition, which is critical for MPF activation.
Activation mechanism:
Phosphorylation and dephosphorylation:To become active, CDK1 needs to be dephosphorylated at specific sites by phosphatases like CDC25, while inhibitory phosphorylation by kinases like Wee1 needs to be removed.
Cyclin B binding:When cyclin B levels rise and bind to CDK1, the complex becomes activated, allowing it to phosphorylate target proteins that initiate mitosis.
Target proteins:
Once activated, MPF phosphorylates various proteins involved in key mitotic events like nuclear envelope breakdown, chromosome condensation, and spindle formation.
Negative feedback loop:
As mitosis progresses, a negative feedback loop is triggered where the activated MPF complex triggers the degradation of cyclin B, leading to its inactivation and allowing the cell to exit mitosis.
Important aspects of MPF regulation:
Cell cycle checkpoints:
MPF activity is tightly regulated by various cell cycle checkpoints that ensure proper DNA replication and damage repair before allowing the cell to enter mitosis.
Protein kinases and phosphatases:
Several protein kinases (like Wee1) and phosphatases (like CDC25) play crucial roles in regulating MPF activity by phosphorylating and dephosphorylating CDK1 at specific sites.
Cancer implications:
Dysregulation of MPF activity, often due to mutations in the cyclin B or CDK1 genes, can lead to uncontrolled cell proliferation and contribute to cancer development.
