Lecture 4

The first stage of Prophase I in meiosis, where chromosomes condense and become visible, each consisting of two sister chromatids. Cell organelles migrate to the cell's periphery.

The second stage of Prophase I, where homologous chromosomes, one from the mother and one from the father, pair up to form a bivalent (tetrad) of four chromatids. The synaptonemal complex connects the homologous chromosomes.

The third stage of Prophase I, where chromosomes continue to condense and further coil. Histones are synthesized at this stage.

The fourth stage of Prophase I, where the homologous chromosomes start to separate, but they remain connected at points called chiasmata. This is where genetic material is exchanged.

The final stage of Prophase I, where the chromosomes continue to separate, and chiasmata become more obvious. The nuclear envelope breaks down and the spindle fibers form.

The protein structure that holds homologous chromosomes together during synapsis, forming a ladder-like structure.

The exchange of genetic material between non-sister chromatids during Prophase I. This results in offspring inheriting a unique mix of parental genes.

Points of contact between non-sister chromatids in a bivalent, where crossing-over occurs. These are visible as X-shaped structures.

A family of proteins that bind to and inactivate cyclin-dependent kinases (CDKs), essential enzymes that regulate cell cycle progression. They act as brakes to prevent uncontrolled cell growth.

A type of CDKI that binds to and inhibits the activity of CDK1, CDK2, CDK4, and CDK6, which are crucial for cell cycle transitions.

A member of the CIP/KIP family of CDKIs that plays a key role in controlling cell cycle entry, blocking cells from progressing into the S phase if DNA damage is detected.

A natural process of programmed cell death that involves the orderly dismantling of cellular components. It is crucial for development, tissue homeostasis, and eliminating damaged or harmful cells.

An uncontrolled, chaotic form of cell death that occurs due to external factors such as injury or infection. It leads to cell swelling, membrane rupture, and inflammation.

A protein complex that promotes the degradation of proteins during mitosis, particularly during the transition from metaphase to anaphase. It accomplishes this by attaching ubiquitin tags to target proteins, marking them for destruction by the proteasome.

A protein complex essential for initiating the separation of sister chromatids during anaphase. It is activated by the MPF complex and triggers the breakdown of cohesins, proteins that hold sister chromatids together.

During the G1 and S phases of the cell cycle, the centrosome duplicates, creating two centrosomes.

In the G2 phase of the cell cycle, the two centrosomes mature and connect to each other.

During M-phase, the two daughter centrosomes separate, leading to the formation of the aster, a star-shaped structure at each pole of the mitotic spindle.

A specialized protein complex that helps condense chromosomes during prophase, making them shorter and thicker.

Microtubules radiating outward from the centrosomes that form the mitotic spindle, attaching to chromosomes during cell division.

The specialized region on a chromosome where microtubules attach during cell division, ensuring proper separation.

The stage of mitosis where the nuclear membrane breaks down, allowing microtubules from the spindle to attach to the kinetochores of the chromosomes.

The stage of mitosis where chromosomes are lined up in the middle of the cell, forming the metaphase plate, ensuring that they are properly aligned for separation.

The stage of mitosis where sister chromatids are pulled apart by the mitotic spindle, moving to opposite poles of the cell.

The final stage of mitosis characterized by the reformation of the nuclear envelope, decondensation of chromosomes, and the formation of the contractile ring that leads to cytokinesis.

The stage in meiosis II where chromosomes condense, the nuclear envelope breaks down, and the spindle fibers form, similar to prophase in mitosis but with half the number of chromosomes.

The stage in meiosis II where the chromosomes line up along the middle of the cell, with spindle fibers attached to each sister chromatid.

The stage in meiosis II where the centromeres of the sister chromatids separate, and the chromatids move to opposite poles of the cell, creating four haploid daughter cells.

The stage in meiosis II where the nuclear envelope reforms around the chromosomes, the chromosomes decondense, and the cytoplasm divides, resulting in four haploid daughter cells.

A point in the cell cycle where the cell checks internal and external conditions to ensure proper progression of the cycle.

Checkpoint occurring between G1 and S phase, ensuring that the cell is ready for DNA replication.

Checkpoint occurring between G2 and M phase, ensuring that the cell has successfully replicated its DNA and is ready for mitosis.

A small protein or peptide that triggers a cell to begin cell division or accelerates the rate of division.

Mitogens attach to receptors on the cell membrane, initiating a chain reaction that transmits the signal to the nucleus.

A key player in the cell cycle, it acts as a 'brake' on the process, preventing transition into S phase unless conditions are favorable.

Internal regulators that control key phases of the cell cycle, their levels fluctuate throughout the cycle.

A family of protein kinases that work together with cyclins to drive the cell cycle forward. Their activity is dependent on cyclin association.

The complex formed by the combination of a cyclin and a Cdk, which becomes active at specific stages of the cell cycle. The complex can cause phosphorylation of various substrates.

A type of cyclin that peaks during the S phase, driving the replication of DNA. Its associated Cdk complex is S-Cdk.

A family of internal control proteins that can inhibit the activity of cyclin-Cdk complexes, slowing down or stopping the cell cycle when necessary.

The inactivation of S-Cdk and M-Cdk complexes allows the cell to exit the G1 phase and enter the S phase, where DNA replication occurs.

The concentration of these cyclins rises during the G1 phase, activating G1-Cdk complexes which phosphorylate Rb protein, leading to the production of E-cyclins and forming a G1/S-Cdk complex.

A protein complex that triggers the start of mitosis, also known as M-phase Promoting Factor (MPF). It is formed by the binding of cyclin B to Cdk1.

This phase is crucial for the preparation for mitosis. The cell completes the replication of its DNA and prepares the necessary proteins and organelles for cell division.

The process where the levels of cyclin B increase and bind to Cdk1, forming the MPF complex. This complex activates proteins that initiate the disintegration of the nuclear envelope and chromosome condensation.

A positive feedback loop that amplifies the activity of MPF. Activated MPF complexes indirectly activate more MPF complexes, ensuring a robust and efficient transition into mitosis.

This phase is marked by the breakdown of the nuclear envelope, condensation of chromosomes, and spindle formation, preparing the cell for the separation of chromosomes.

The process of cell division that creates two daughter cells from a single parent cell. It consists of four main stages - prophase, metaphase, anaphase, and telophase.

The second division of meiosis, which occurs immediately after meiosis I and is similar to mitosis but with only one set of chromosomes in each cell.

The cell cycle is a series of events that lead to cell division in eukaryotic cells. It includes stages of growth, DNA replication, and nuclear and cytoplasmic division, ensuring that each daughter cell receives a complete copy of the genome.

Interphase is the longest phase of the cell cycle when the cell grows, copies its DNA, and prepares for division. It consists of three sub-phases: G1, S, and G2.

Mitosis is a type of cell division that produces two genetically identical daughter cells. It involves four main stages: prophase, metaphase, anaphase, and telophase, each with a specific function in separating chromosomes.

Cytokinesis is the division of the cytoplasm, which occurs after mitosis. It results in the physical separation of the two daughter cells, completing the cell division process.

A checkpoint is a control point during the cell cycle where the cell checks whether certain conditions are met before proceeding to the next phase. There are checkpoints during the G1, G2, and M phases.

The G0 phase is a resting phase where cells exit the cell cycle and do not divide. Some cells remain in this phase permanently, while others can re-enter the cell cycle.

The cell cycle is regulated through a complex interplay of internal and external signals. Internal regulators include cyclins and cyclin-dependent kinases (CDKs), while external regulators include growth factors and mitogens.