Mitose et Méiose

Mitose et Méiose

• Mitose: Somatique cell division, producing two genetically identical daughter cells from a single parent cell. This process converts a diploid cell (2n) into two diploid cells (each with 2n). A key part of this process is the replication of a double K chromosome.
• Méiose: Germline cell division. A process consisting of two successive cell divisions that result in four haploid (n) cells from an initial diploid (2n) cell. Produces gametes (sex cells). This entails the separation of homologous chromosomes (first division) and then chromatids (second division) in each resulting haploid cell.

Cycle Cellulaire Régulation

• Phase G0: A resting phase outside the cell cycle. The cell is neither growing nor dividing.
• Phase G1 (Growth and Preparation): The cell grows and prepares for DNA replication.
• Phase S (DNA Synthesis): DNA replicates, doubling the chromosome number. Each chromosome becomes composed of two sister chromatids.
• Phase G2 (Preparation for Mitosis): The cell finishes growing and checks for DNA integrity before mitosis.
• Phase M (Mitosis): The actual cell division. The parent cell divides into two daughter cells, each with the identical genetic material. Cycle consists of 3 phases (G1, S, G2) to prepare and transition to mitosis phase. Control point to prevent going back, once entering G1 or G2.

Cyclins and Cdks

• Cyclins and Cyclin-dependent kinases (Cdks): Protein complexes that regulate transitions between cell cycle phases.
  • Cyclins D and Cdk 4/6: regulates G1 to S transition.
  • Cyclins E and Cdk 2: regulates S phase.
  • Cyclins A and Cdk 2: regulates S to G2 transition.
  • Cyclins A/B and Cdk 1: regulates entry into mitosis (M phase).

ADN Replication

• DNA Replication: An essential process occurring during the S phase of the cell cycle. It ensures each daughter cell receives a complete set of genetic material identical to the parent cell.
• Decompaction: DNA needs to be unwound (decondensed) for access in replication.
• Semi-conservative: Each new DNA molecule consists of one old strand and one newly synthesized strand in replication.

Mitose phases

• Prophase: Chromosomes condense, nuclear membrane disintegrates, and the mitotic spindle forms.
• Metaphase: Chromosomes align at the metaphase plate.
• Anaphase: Sister chromatids separate and move to opposite poles.
• Telophase: Chromosomes decondense, nuclear membranes reform, and cytokinesis begins.

Kinétochores

• Kinétochores: Protein complexes located at centromeres. Essential for chromosome attachment to microtubules of the mitotic spindle. Crucial for chromosome separation. Aurora protein stabilises the centromere.

ADN quantity

• Before replications: Each cell contains 46 chromosomes (n ADN).
• After replications: Each cell contains 46 chromosomes with 2 chromatids (2n ADN).
• After Mitosis: Each daughter cell contains 46 chromosomes with one chromatid (n ADN). This ensures a stable genetic make-up across cell divisions.