BIO 1A03 T4M1-2: Applied lecture - DNA replication and mitosis

kinetochore

proteins found on both sides of the chromosome that allow kinetochore microtubules to attach

kinetochore microtubules

microtubules that attach to the kinetochore regions

non-kinetochore microtubules

microtubules that dont attach to kineto chore, but form cage-like network that allow cell to elongate and pull chromosomes to the poles during anaphase

laser beam experiment

• chromosomes are dyed blue, kinetochore are yellow

• a section of the kinetochore microtubules are photobleached (not cut) — done to compare the lengths of the microtubules on either side fo the photobleached ref. point as anaphase occurs

• results — photobleached section remains but the distance btw chromosomes shortens

  • tft. microtubules shorten, not pulled

how do microtubules move chromosomes during mitosis 

• Microtubules are attached to the kinetochore on the chromosomes… but during anaphase, as the chromosomes are being pulled towards the poles, the microtubules are broken down into tubulin subunits – and recycled/reused 

johnson and raos cell fusion experiment

→ investigates cell cycle control enzymes and where they’re located and their function 

• Cell membranes are dynamic and fluid ⇒ can get chemicals/electrical charges in diff phases of cell cycle to fuse together 

• When M (mitotic) phase fuse with interphase cell ⇒ results in the interphase cell’s chromosome condensation and signaling start of M-phase  

markert and masui microinjection experiment

• Collected cytoplasm of a cell in one phase, injected it into the cytoplasm of another cell in a diff phase ⇒ bc cell cycle enzymes would prob be floating in the cytoplasm 

• [ref to image] M-phase cytoplasm cell is injected into interphase cell’s cytoplasm ⇒ appearance of centrioles + spindle fiber network 

• ∴ control enzymes are in the cytoplasm 

cancer cell characteristics 

• Cancer = large in size + variable nuclei shaped

• Cancer = dividing cells + disorganized in arrangement

• Cancer = has variation in size and shape 

• Cancer = lost of normal features 

characteristics

• Cancer cells divide faster than normal cells 

• Uncontrolled cell division 

• Cell cycle is not regulated

• Cell cycle checkpoints are disrupted

normal cells exhibit limited growth, compared to cancer cells that display excessive cell division 

In normal cells 

1. Anchorage dependence: when normal cells anchor to the surface of the dish and divide 

2. ⤷ density-dependent inhibition: when cells have formed a complete single layer, they stop dividing 

⤷ if some cells are scraped away, the remaining cells divide to fill the gap and then stop once they contact each other 

In cancer cells

1. Cancer cells do not display anchorage dependence or density-dependent inhibition – 

⤷ if you place a cancer cell in a growth dish, the cancer cells usually continue dividing more than a single layer ⇒ will form clumps of overlapping cells

stages of cancer

Stage 1: tumor is small and has not grown outside of organ which the cancer started in 

Stage 2: the tumor is larger than stage 1 but has not spread to nearby tissues 

Stage 3: the tumor is large and has spread to nearby tissues and lymph nodes 

Stage 4: tumor has spread through the blood or lymphatic system to a distant site in the body 

chemotherapy drugs

Vincristin: anti-cancer drug that is extracted from rosy periwinkle – native to madagascar 

Taxol: anti-cancer drug that is extracted from pacific yew tree’s bark 

⤷ concerns – when bark is removed from tree, the tree dies 

⤷ both are anti-microtubule agents (inhibit spindle fiber formation) ⇒ disrupting mitosis and prevents cell division 

steve jobs + drug that helps his disease 

• Creator of apple – died of rare form of pancreatic cancer 

• He had his whole genome sequenced and found Pim 1 biomarker for pancreatic cancer 

• Afinitor: chemotherapy drug used to treat this rare form of pancreatic cancer 

CAR-T cell therapy

• Canada received approval for CAR-T cell therapy in sept 2018 

CAR-T cell therapy: uses own immune cells to target and destroy cancer cells 

⤷ removes blood from pt to get T-cells 

⤷ make CAR-T cells in the lab 

⤷ grow millions of CAR-T cells 

⤷ infuse CAR-T cells into the patient 

⤷ CAR-T cells bind to cancer cells and kill them 

preventation fo alcohol and cancer

• Acetaldehyde is toxic and can lead to DNA damage ⇒ cancer 

• The liver converts most of the ethanol in alcohol drinks into acetaldehyde + small amounts are also broken down in the mouth and stomach 

• If too much alcohol is consumed, body has difficulty processing the acetaldehyde fast enough and it builds in the body 

Effects of too much alcohol 

• Acetaldehyde can cause irreversible DNA damage ⇒ cancer (eg. bowel cancer) 

• Can circulate oestrogen levels to increase ⇒ breast cancer (with abnormal development of breast tissues, increased cell production and rearrangement, increased DNA damage) 

• Can alter cells in the mouth/throat ⇒ act as a solvent and making other carcinogens more easily absorbed (eg. tobacco) to be absorbed into the cell ⇒ mouth, throat, esophagus cancer