Cell Growth, Division, and Reproduction Notes

Reasons for Cell Division:
- Information Overload: As a cell increases in size, the demands on its DNA increase. The DNA may not be able to keep up with the needs of the cell, leading to inefficiency.
- Exchange of Materials: Cells consume nutrients and expel wastes through their cell membranes.
- Larger cell volumes require more materials but have relatively smaller surface areas, causing a lower surface-area-to-volume ratio.
- A diminished ratio complicates material exchange, making it inefficient for larger cells to function.
Conclusion: Cell division mitigates both the information overload and exchange of materials challenges.

Asexual Reproduction:
- Produces genetically identical offspring.
- Common in single-celled organisms and some multicellular organisms.
- Facilitates rapid reproduction in favorable conditions.
Sexual Reproduction:
- Produces offspring with genetic contributions from two parents, enhancing genetic diversity.
- Typical in most animals, plants, and various single-celled organisms.
- Supports species survival in shifting environments.

Cells grow, but there are limits to their size due to information overload and material exchange difficulties.
Cell division aids in overcoming these limits, allowing for both asexual and sexual reproduction.
Asexual reproduction results in genetically identical offspring, while sexual reproduction leads to genetic diversity.

Chromosomes: Compact structures made of DNA that maintain genetic information.
- Prokaryotic cells have a single, circular chromosome.
- Eukaryotic chromosomes are organized with DNA wrapped around histones to form chromatin.
- Ensure precise DNA separation during division.

Phases:
- G1 Phase: Cell grows.
- S Phase: DNA replication occurs.
- G2 Phase: Further growth and preparation for division.
- M Phase: Cell division takes place in two stages—mitosis and cytokinesis.

Prophase: Chromatin condenses, spindle formation begins, and the nuclear envelope disintegrates.
Metaphase: Chromosomes align at the cell's equator, spindle fibers attach to centromeres.
Anaphase: Sister chromatids separate and move toward opposite poles.
Telophase: Chromatids unwind, and nuclear envelopes re-form around each set of chromosomes.

Definition: Final step of cell division, dividing the original cell's cytoplasm into two new cells.
Differences in Cells:
- Animal Cells: Pinch off membrane.
- Plant Cells: Form a cell plate, developing a new cell wall.

Cyclins: Signal when to start cell cycle steps (growth, DNA synthesis, mitosis, cytokinesis).
Internal Regulatory Proteins: Prevent advancement in the cycle without necessary events.
External Regulatory Proteins: Influence cell cycles by accelerating during growth or slowing to prevent tissue disruption.

Definition: Disorder where cells lose growth control.
Tumors:
- Malignant Tumors: Invasive, destroying surrounding tissues.
- Benign Tumors: Non-invasive, localized.
Impact: Cancerous cells consume resources from healthy tissues, disrupting normal function and possibly leading to death.
Causes: Defective genes controlling cell growth lead to the cancerous state.
Treatment: Radiation affects DNA replication; chemotherapy targets rapidly dividing cells, including cancer and hair follicle cells.

Gametes: Contain a single set of genes; are haploid while body cells are diploid.
Diploid Count: If a haploid number is 6, the diploid count would be 12.

Meiosis I: Replicated chromosomes pair and cross over, leading to genetic diversity. Key steps:
- Prophase I: Pairing and crossing-over.
- Metaphase I: Alignment of pairs.
- Anaphase I: Homologous separation.
- Telophase I and Cytokinesis: New cells form.
Meiosis II: Similar to mitosis with no pairing of homologous chromosomes. Ends with four genetically varied haploid cells.

Mitosis:
- Forms: Asexual, 2 daughter cells, no change in chromosome number, 1 division, identical daughter cells.
Meiosis:
- Forms: Sexual, 4 genetically diverse daughter cells, halves the chromosome number, 2 divisions.