Cell cycle
Overview of Cell Division and Cell Cycle
Cell Division: A critical process that includes mitosis (for somatic cells) and meiosis (for reproductive cells).
Cell Cycle: A series of stages that cells go through as they grow and divide, maintaining homeostasis.
The kinetochore is the center of each chromatid.
telomeres protect the ends of the chromosome (Cap) for aging
Stages of the Cell Cycle
Interphase: The longest phase of the cell cycle, where the cell grows and prepares for division.
G1 Phase (Gap 1): Cell grows and synthesizes proteins; organelles duplicate, significant RNA and protein synthesis occurs.
S Phase (Synthesis): DNA replication occurs, resulting in the duplication of chromosomes.
quality control checks to enter G2
G2 Phase (Gap 2): Further growth and preparation for mitosis; additional organelles and proteins are synthesized.
G0 Phase: A resting state where cells are not actively dividing; some cells can remain here for extended periods (like neurons).
M Phase (Mitosis): The phase where the cell divides its copied DNA into two identical daughter cells.
Prophase: Chromatin condenses into chromosomes; the nuclear membrane begins to break down.
asters extend from the centrioles, helping to organize the mitotic spindle
Metaphase: Chromosomes align at the cell equator; spindle fibers attach to kinetochores at the centromere.
polar microtubules form each aster forming interconnections
metaphase plate is formed
Anaphase: Sister chromatids are pulled apart to opposite sides of the cell.
shortening of the kinetochore
the non-kinetochore is elongated and pushed to separate parts of the cell.
Telophase: New nuclear membranes form around the separated chromatids; the cell prepares for cytokinesis.
Cytokinesis: The process that follows mitosis, where the cytoplasm divides to form two daughter cells.
spindle breaks down
nuclear envelop forms
Nucleoli are reconstructed
In animal cells, a contractile ring of myosin proteins pinches the cell, while in plant cells, a cell plate forms.
Chromatin and Chromosomes
Chromatin: The relaxed form of DNA when the cell is not dividing. It condenses to form chromosomes during mitosis.
Chromosome Structure: Each chromosome consists of two sister chromatids held together at the centromere.
Kinetochore: A protein complex that assembles at the centromere and is crucial for the attachment of spindle fibers during cell division.
Telomeres and Aging
Telomeres: Repetitive sequences at the ends of chromosomes that protect them from deterioration. They shorten with each cell division, contributing to aging and the Hayflick limit (the maximum number of times a cell can divide).
Checkpoints in the Cell Cycle
G1/S Checkpoint: Assess the cell's size, DNA integrity, and whether conditions are favorable for division; regulated by proteins like p53 (tumor suppressor).
G2/M Checkpoint: Ensures all DNA is replicated accurately before mitosis begins.
M Checkpoint: Ensures that all chromosomes are properly attached to spindle fibers before separation.
cyclins are regulatory proteins that control the progression of the cell cycle by activating cyclin-dependent kinases (CDKs), which then phosphorylate target proteins to drive the cell through each phase.
Importance of Checkpoints in Cancer Biology
Unregulated cell division can lead to cancer; dysfunctions in checkpoint proteins or DNA damage can result in uncontrolled proliferation (tumorigenesis).
High levels of certain proteins (like cyclins) regulate transitions between phases of the cell cycle; imbalances can lead to cancerous growth.
Summary of Key Concepts
The cell cycle consists of phases that prepare for cell division.
Mitosis is crucial for growth and repair, while meiosis is responsible for creating gametes.
DNA structure and checkpoint mechanisms are essential for maintaining genetic integrity and preventing cancer.
Understanding these processes has implications for biomedicine, particularly in cancer treatment and research.