Cell Cycle and Its Regulation

Overview of the Cell Cycle

The cell cycle is a series of events that cells undergo to grow and divide. It consists of interphase (G1, S, G2) and the mitotic (M) phase, which includes mitosis and cytokinesis. - Interphase: The cell grows, replicates its DNA, and prepares for division. - Mitotic Phase (M phase): The cell divides its chromosomes and cytoplasm to produce two daughter cells.

Cell Cycle Checkpoints

Cell cycle checkpoints are regulatory mechanisms that ensure the fidelity of cell division. They prevent cells with damaged DNA or incomplete processes from proceeding. - G1 checkpoint: Checks for DNA damage before DNA replication. If damage is detected, the cell may undergo apoptosis or repair the DNA. - G2 checkpoint: Ensures DNA has been replicated properly before mitosis. - M checkpoint: Ensures chromosomes are properly aligned before cell division proceeds.

DNA Replication

Mechanism and Importance

DNA replication is the process by which a cell copies its entire genome before cell division. This ensures that each daughter cell receives a complete set of genetic instructions. - Semiconservative replication: Each new DNA molecule consists of one old (parental) strand and one new (daughter) strand. - Origins of replication: Multiple sites where DNA replication begins in eukaryotic chromosomes. - Replication fork: The area where the DNA double helix is unwound and new strands are synthesized.

Transmission of Genetic Information

DNA replication allows genetic information to be inherited from parent to daughter cells. Each gene is a unit of hereditary information, and accurate replication is essential for growth and reproduction.

Eukaryotic Chromosome Structure

Chromosomes and Chromatids

Chromosomes are long, linear DNA molecules wrapped around proteins (histones). After DNA replication, each chromosome consists of two identical sister chromatids joined at the centromere. - Sister chromatids: Genetically identical copies formed during S phase. - Centromere: Region where chromatids are joined and spindle fibers attach during mitosis.

Mitosis: Process and Phases

Purpose and Outcomes

Mitosis is the process by which a eukaryotic cell divides its nucleus and chromosomes, resulting in two genetically identical daughter cells. It is essential for growth, cell replacement, and asexual reproduction.

Phases of Mitosis

Mitosis consists of several distinct phases: - Prophase: Chromosomes condense, spindle apparatus forms, and centrosomes migrate to opposite poles. - Prometaphase: Nuclear envelope breaks down, spindle fibers attach to chromosomes at the centromere. - Metaphase: Chromosomes align at the metaphase plate (center of the cell). - Anaphase: Sister chromatids separate and are pulled to opposite poles. - Telophase: Nuclear envelope re-forms, chromosomes decondense. - Cytokinesis: Division of the cytoplasm, resulting in two daughter cells.

Microscopic View of Mitosis

Mitosis can be observed under a microscope, where dividing cells show condensed chromosomes and distinct phases.

Genetic Concepts: Ploidy and Chromosome Number

Ploidy and Karyotype

- Ploidy (n): The number of unique sets of chromosomes in a cell. Most somatic cells are diploid (2n), containing one set from each parent. - Karyotype: The complete set of chromosomes in an individual, including autosomes and sex chromosomes.

Homologous Chromosomes vs. Sister Chromatids

Summary Table: Cell Cycle Phases and Key Events

Additional info:

- The cell cycle is tightly regulated to prevent uncontrolled cell division, which can lead to cancer. - DNA replication is semiconservative, ensuring genetic continuity. - Mitosis maintains chromosome number and genetic identity in daughter cells.