Purpose and content of
THE CELL CYCLE
Interphase (Preparation):
G1: Cell grows and performs normal functions
S: DNA replicates (sister chromatids are formed)
G2: Final growth and preparation for division
M Phase (Division):
Mitosis or Meiosis: Division of the nucleus
Cytokinesis: Physical division of the cytoplasm
MITOSIS: THE CLONE MAKER
Purpose: Growth, tissue repair, and asexual reproduction
Location: Somatic (body) cells
Outcome: 2 identical diploid (2n) daughter cells
Process:
Prophase: Chromosomes condense; spindle forms
Metaphase: Chromosomes line up in a single file at the center
Anaphase: Sister chromatids are pulled to opposite sides
Telophase: Two new nuclei form
MEIOSIS: THE DIVERSITY MAKER
Purpose: Sexual reproduction (producing sperm and eggs)
Location: Germ cells in gonads
Outcome: 4 genetically unique haploid (n) daughter cells
Key Differences:
Meiosis I: Homologous pairs swap DNA (Crossing Over) and then separate. This reduces the chromosome count by half
Meiosis II: Sister chromatids separate (similar to mitosis), resulting in four unique cells
QUICK RECAP
Mitosis = One division, identical cells, stays diploid
Meiosis = Two divisions, unique cells, becomes haploid
PMAT = Prophase, Metaphase, Anaphase, Telophase
HELA CELLS CHEAT SHEET
1. Origin & The Woman Behind the Cells
The Source: HeLa cells were taken from Henrietta Lacks, a 31-year-old Black American woman, during her treatment for aggressive cervical cancer in 1951.
The Name: “HeLa” is derived from the first two letters of her first and last name
The Location: The cells were isolated at Johns Hopkins Hospital by Dr. George Gey
Historical Context: At the time, Henrietta’s cells were taken without her knowledge or consent, which was common practice in the 1950s but is now a major focal point for medical ethics.
Johns Hopkins Medicine
Johns Hopkins Medicine
+6
Entific) over the commercial use of the cells
2. Why They Are “Immortal”
Most human cells die after about 40–60 divisions (the Hayflick limit). HeLa cells are unique because they divide indefinitely.
npwomenshealthcare.Com
npwomenshealthcare.Com
Active Telomerase: They possess an overactive enzyme called telomerase that constantly rebuilds their telomeres (the protective caps on DNA), preventing the aging process that normally kills cells.
HPV Interaction: Henrietta’s cancer was caused by HPV-18. The virus inserted its DNA into her genome, producing proteins that deactivated her cells’ natural “checkpoints” that would normally stop uncontrolled growth.
Speed: HeLa cells are extremely robust and double roughly every 20–24 hours
Technology Networks
Technology Networks
3. Scientific Breakthroughs
HeLa cells have been used in over 70,000 studies and are responsible for some of the biggest jumps in modern medicine:
Polio Vaccine: Used by Jonas Salk to test and perfect the first polio vaccine in the 1950s
Chromosome Counting: A lab error with HeLa cells helped scientists discover that humans have 46 chromosomes (not 48, as previously thought).
HPV Vaccine: Research on these cells directly led to the discovery that HPV causes cervical cancer, resulting in the development of the HPV vaccine.
Space Travel: They were some of the first human cells sent into outer space to study the effects of zero gravity and radiation on human tissue.
COVID-19: Most recently, they were used to characterize the SARS-CoV-2 virus and develop mRNA vaccines
Technology Networks
Technology Networks
4. Modern Ethics & Legacy
Consent & Privacy: The Lacks family did not find out about the cell line until the 1970s. This case prompted massive changes in informed consent laws regarding human tissue samples.
Ownership: While companies have made billions selling products derived from HeLa, the Lacks family lived in poverty for decades without health insurance.
Recent Settlements: In 2023, the Lacks family reached a milestone settlement with a major biotech company (Thermo Fisher Sci