Cell Division These chromosomes have been marked with RED fluorescence. DNA is found in the cell nucleus Dividing (mitotic) cell non-mitotic cell (This movie has been sped up.)
Cell Division and Cancer Our cells divide many times during development, and for some cell types, throughout our lives. Today: how do cells reproduce? Next week: what happens if cells reproduce out of control?
What needs to happen for a cell to reproduce (copy itself)? In order for a cell to produce a copy of itself, it must: Replicate its DNA (we ve talked about this!) Condense its DNA (why?) Divide the DNA into two cells (Mitosis!).
DNA needs to be condensed before it can be separated into daughter cells
DNA gets condensed just prior to cell division
In order for a cell to produce a copy of itself, it must: Replicate its DNA Condense its DNA Divide the DNA into two cells (Mitosis!)
A cell undergoing Mitosis These chromosomes have been marked with RED fluorescence. Dividing (mitotic) cell DNA is found in the cell nucleus non-mitotic cell
You already know: Natural selection favors variants that reproduce the most. The drawback: cells that are dividing all the time can t do much else. To pass on its genes an organism has to reproduce, but it may also have to perform complex functions.
How to reconcile? There can be a division of labor!
Evolution of cooperative groups of cells swimmers dividers Volvox carteri
Evolution of cooperative groups of cells Somatic cells Cells that do not give rise to gametes (gametes = oocytes,sperm) Germline cells Cells that give rise to gametes swimmers dividers Volvox carteri
Division of labor: the bee hive The queen bee is the only reproductive female in the colony.
Cells that give rise to gametes Cells that do not give rise to gametes
Division vs. Differentiation Our somatic cells divide many times during development. But most of our cells stop dividing at some point, and start doing their jobs. This is called differentiation. (They start doing different jobs)
Us! Time (thousands of generations) Evolution Evolution The tendency for our somatic cells to compete with their neighbors is a vestige of our single-celled ancestry. Single-celled ancestor!
Breaking Bad Mutiny is a perpetual problem for multicellular organisms. Every day in your tissues there is a cell that breaks rank and sets out on its own. but usually it is stopped. usually.
Breaking Bad When regulation fails Unrestricted cell division can lead to Cancer.
Multicellular Organisms require teamwork We have a system that keeps most cells from going rogue, and takes out those that do. How does this system normally work? How can it get broken?
In a nutshell The system can t get broken with a single mutation- it takes many mutations: Most mutations arise during your lifetime Some mutations can be inherited
In a nutshell The system can t get broken with a single mutation- it takes many mutations: Most mutations arise during your lifetime Some mutations can be inherited Inheritance of one of these mutations is a head start towards accumulating enough mutations to get cancer.
Cancer: some common questions Is it genetic? Is it environmental? Is it contagious? Is it on the rise? Can my immune system protect me? Is the treatment worse than the disease?
The cell cycle A cell may receive a signal to start dividing when needed Genes that promote cell-division are called proto-oncogenes
Cell Cycle Control and Mutation Mutations in DNA can: oops. Turn a gene off Turn a gene always on Alter the function of the encoded protein Have little or no effect
Cell Cycle Control and Mutation Which type of mutation would cause the most trouble: a mutation that inactivates a proto-oncogene or a mutation that activates it?
Cell Cycle Control and Mutation If a proto-oncogene happens to get mutated in a way that it gets stuck on, we call it an Oncogene
Cell Cycle Checkpoints Tumor Suppressor genes make proteins that stop cell division. What s more dangerous? A mutation that activates or inactivates a tumor suppressor?
Cell Cycle Checkpoints What if your checkpoints fail?? - cells can divide even with widespread errors in DNA replication! more mutations accumulate!
Cell Cycle Checkpoints Tumor Suppressor genes make proteins that stop cell division. eg) BRCA1 is a tumor suppressor - Monitors and repairs mistakes in DNA replication - If mistakes are widespread, it instructs cell suicide!
Cell suicide is called Apoptosis
Tumors Unregulated cell division leads to the production of a tumor- a mass of cells with no function in the body. Not all tumors are a problem. Some are benign- (non-cancerous) why? contact inhibition (cells are polite to their neighbors)
Cancer Progression Tumor Benign invasive Malignant = cancer
Metastasis when cells leave the original site In order for cells to leave their original place, they must lose their anchorage dependence
Cancer Progression Tumor Benign invasive Malignant = cancer traveling Non-metastatic Metastatic
Cancer Progression takes many steps