Cell Division, Proliferation, Cancer, and Reproduction Lecture Review

Multicellular Organisms: Begin as a single fertilized egg, undergoing millions or trillions of cell divisions to form a fully grown adult.
Purpose of Cell Division: Once fully grown, cellular reproduction is vital for maintaining, replacing, and repairing cells and tissues.
- Example: A sea urchin develops from a single cell through division to form a complex, mature organism.

Genome: The complete complement of DNA within an organism.
Eukaryotic Cells: Chromosomal DNA is coiled around proteins to form chromatin.
Karyotypes: Visual representations that display an individual's chromosomes organized in homologous pairs, arranged from longest to shortest.
- Homologous Chromosomes: Pairs of chromosomes, one inherited from each parent, that are similar in length, gene position, and centromere location.
- Human Chromosomes: Organized into 23 homologous pairs.

Locus (plural, Loci): The specific location of a gene on a chromosome.
Alleles: Paired forms of a gene, inherited one from each parent after sexual reproduction.
- Alleles can be identical or contain alterations, leading to different characteristics (e.g., eye color, blood type).
Human Chromosome Size: The longest human chromosome contains over $200$ million base pairs, while the shortest has fewer than $50$ million.

The number of chromosome pairs does not necessarily correlate with an organism's complexity.
- Corn: $10$ pairs
- Fruit flies: $4$ pairs
- Dogs: $39$ pairs
- Chickens: $39$ pairs
- Goldfish: $47$ pairs
- Humans: $23$ pairs
Total Chromosome Count: Individuals inherit one copy of each chromosome from each parent, effectively doubling the number of pairs in a diploid cell (e.g., a dog has $78$ chromosomes, humans have $46$ ).

Rapid Evolution: Prokaryotes evolve quickly due to their short generation times, coupled with genetic recombination and high mutation rates, enabling them to adapt to environmental changes.
Genome Structure: Possess a single circular piece of double-stranded DNA, lacking multiple chromosomes or a nucleus.
DNA Replication: Always begins at the origin of replication (near the attachment site) and is bi-directional.
Reproduction (Binary Fission): An asexual process involving:
1. Copying the genome.
2. Synthesizing additional cytoplasmic materials.
3. Formation of a cleavage furrow in the middle to divide cytoplasmic contents and the cell membrane.
4. Formation of a septum (from periphery to center) to divide the cell wall.
- This results in two genetically identical daughter cells (DNA and all cytoplasmic materials) to the parent cell.
Reproduction Speed: Varies from minutes to days depending on species and conditions.
- Example: E. coli doubles every $20$ minutes under ideal conditions; M. tuberculosis takes $20$ hours.
- Prokaryotic cells replicate faster than eukaryotic cells due to their simpler, single circular genome.
- Replication Rate Example: E. coli replicates DNA at $1,000$ nucleotides/second; human DNA replicates at $50$ nucleotides/second.

Purpose: Essential for normal tissue development, maintenance throughout life, and reproduction.
Two Processes:
- Mitosis: For growth and repair of somatic cells (e.g., muscle, skin cells), where one cell produces two identical daughter cells.
- Meiosis: For sexual reproduction of gametic cells, where one diploid cell produces four haploid daughter cells.