Скачать или смотреть Cancer Is a Disease of the Cell Cycle —Explained. | Why Chemotherapy Has Unavoidable Side Effects

Cancer is not mysterious — it is mechanical, predictable, and deeply connected to the cell cycle.

To understand cancer, you must understand how healthy cells grow, rest, replicate DNA, check for errors, and divide.

Cancer begins the moment these safety rules break.

Here is the full 5-phase Cell Cycle, explained clearly:


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0️⃣ G₀ Phase — Resting / Quiescent State

The cell is alive and functioning but not dividing.

Classic examples of permanent G₀:

Neurons

Skeletal muscle cells

Cardiac muscle cells


These cells do not re-enter the cycle.

(Stable cells like hepatocytes are not true G₀ — they can re-enter when needed.)


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1️⃣ G₁ Phase — Growth & Preparation

The cell increases in size, produces proteins, and prepares for DNA replication.

G₁/S Checkpoint — the most important checkpoint

Checks for DNA damage

Confirms nutrients and environment are adequate

Controlled by p53 and RB protein


➡️ When these genes mutate, cancer risk skyrockets.


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2️⃣ S Phase — DNA Synthesis

The entire genome is duplicated

Chromosomes form sister chromatids

Very energy-intensive


Chemotherapy drugs that act here (S-phase specific):

Methotrexate

5-Fluorouracil (5-FU)

Hydroxyurea


These drugs attack rapidly replicating DNA — but they do not fix the root cause.


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3️⃣ G₂ Phase — Final Preparation

Cell grows further

Produces microtubules & proteins needed for mitosis

Repairs DNA replication errors


G₂/M Checkpoint

Ensures DNA is intact before division.
Failure here → damaged DNA advances → cancer formation.


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4️⃣ M Phase — Mitosis + Cytokinesis

The cell divides into two daughter cells.

Stages:
Prophase → Metaphase → Anaphase → Telophase → Cytokinesis

This is the shortest but most dramatic stage.

Chemotherapy drugs that target M-phase (Mitotic Spindle Inhibitors):

These disrupt microtubules, preventing proper chromosome separation.

Vinca Alkaloids (inhibit microtubule formation):

Vincristine

Vinblastine

Vinorelbine


Taxanes (freeze microtubules so mitosis cannot complete):

Paclitaxel

Docetaxel


➡️ These drugs halt cell division, but they do not repair the defective genes that caused cancer in the first place.


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5️⃣ Return to G₁ or Exit to G₀

Daughter cells either:

Re-enter G₁ and continue dividing, OR

Exit to G₀ if they become specialized.



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🔥 Why This Matters for Cancer

Cancer is fundamentally a cell-cycle disorder:

Cells escape G₀

They proliferate uncontrollably

Checkpoints fail (p53, RB mutations)

DNA damage is ignored

Mutated cells continue dividing


Chemotherapy targets symptoms (rapid division), NOT root cause (gene malfunction).

That is why the side effects are massive — it attacks all fast-dividing cells, not just cancer cells.

Lifestyle Medicine addresses the upstream triggers of genetic instability:

Chronic inflammation

Poor diet

Alcohol

Smoking

Stress

Poor sleep

Sedentary lifestyle


These factors accelerate DNA damage and weaken the cell’s natural checkpoints.

Treat cancer at the root — treat the biology that allowed cancer to form.


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— Dr. Chris (Mbubah Chris)

Lifestyle Medicine Consultant Family Physician
@DrChrisFitnessPro

Health is decisions, not destiny.
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