Cell cycle control

Controlled by Cyclin-Dependent Kinases (CDKs).
- CDKs: Family of proteins that require binding to cyclins for activation.
- Kinase Function: Enzymes that phosphorylate proteins, thus stimulating or inhibiting their function.
- Activated only when bound to Cyclin, leading to phosphorylation of critical molecules for cell division.

Cyclins vary during the cell cycle, regulating it through synthesis and degradation cycles.
Most body cells are in the G1 phase, requiring growth signals for division.
- Example: Skin injury leads to platelet accumulation and release of growth factors.

Biochemical signals that modify cellular responses and control growth/differentiation.
Found in blood, particularly in platelets.
Short peptide sequences that modulate cellular activity, involved in events like mitosis and chemotaxis.

Initiate repair and regeneration processes post-injury.
Act through specific membrane receptors to promote or inhibit cellular responses.
Classified as:
- Broad-specialty growth factors (e.g., PDGF, EGF) act on multiple cell types.
- Narrow-specialty growth factors only affect specific cell types (e.g., Erythropoietin - EPO).

Growth factors bind to cell surface receptors, spurring Cyclin synthesis.
This leads to CDK-Cyclin complex formation, promoting DNA synthesis.
Transition to S phase occurs for DNA replication, followed by activation of CDKs in G2 to proceed to Mitosis.
Key processes include:
- Chromosome condensation.
- Nuclear envelope breakdown.
- Spindle formation and chromosome alignment.
- Separation of sister chromatids during Anaphase.

Proper regulation is crucial; unchecked division can lead to mutations, cancerous growths, or cell death.
Key checkpoints:
- G1 to S: Checks DNA integrity for replication suitability.
- G2 to Mitosis: Verifies proper and complete DNA replication.
- Metaphase to Anaphase: Assesses spindle attachment and chromosome alignment.
Checkpoint proteins regulate cyclin production or CDK activity, controlling phase transitions.
Poor checkpoint control is a major contributor to cancer.

Minimizes errors, though some mutations inevitably occur:
- Mutations can be neutral, harmful, or beneficial (raw material for evolution).

Mutations in gametes may be inherited, becoming fixed in the species’ genetic makeup.
Alleles: Alternate gene forms producing variations (e.g., hair color, mating calls).
Sexual reproduction combines different alleles from parents, enhancing genetic diversity.