What are the steps of mitosis? What happens in each?
Cell Checkpoints, Cancer & Prokaryotic Cell Division Cell Cycle Checkpoints: # 1 – 11 Cancer # 12 – 15 Prokaryotic Cell Division: # 16 - 20
Division of different cells Some cells :skin= continuous muscle and nerve cells= G0 stage; Embryonic = few hours Adult = maybe 20 hours critical checkpoints: G1 stage S stage G2 stage M stage
Eukaryotic Cells Cycle • The Cell-Cycle Clock Cyclins signaling proteins: must be present for cell to continue • Kinasestakes phosphate group from ATP
Tumor-suppressor genes = prevent cancer; • e.g., p53 causes production of protein that combines with a cyclin kinase complex to stop that kinase from being active; this stops the cell cycle.
Cancer • The uncontrolled growth of cells
This femur has a large eccentric tumor mass arising in the metaphyseal region. This is an osteosarcoma(a variant known as parostealosteogenic sarcoma) of bone. These tumors most often occur in young persons
How Cancer Develops • Carcinogenesis is development of cancer. • A tumor indicates a failure in controlling cell division, often due to a faulty p53 gene. • Normal p53 gene halts the gene cycle
Carcinogens – agents that cause cancer • radiation (e.g. U-V light, X rays, radon gas, etc.), • organic chemicals (e.g. tobacco smoke, some foods, pesticides, etc.), and • certain viruses.
How Cancer Develops • Apoptosis is programmed cell death. • shattering the nucleus, • chopping up the chromosomes • WHAT? Does this? • p53 • Caspases
How Cancer Develops • Apoptosis research may lead to new therapy. • Tumor cells contain high levels of survivin protein which blocks apoptosis; if we can inactivatesurvivin, cells more vulnerable to radiation and chemicals. • Excess apoptosis kills off brain cells in Parkinson’s disease and stroke;
Characteristics of cancer Cancer cells lack differentiation. • Normal cells enter the cell cycle only about 50 times; cancer cells are immortal. • Cancer cells have abnormal nuclei. • abnormal number, and be enlarged. • chromosomes duplicated or deleted. • Extra copies of specific genes
Characteristics of Cancer • Tumors – multiple layers of disorganized cells • NEOPLASIA: invade and destroy • Benign tumor: encapsulated • Malignant tumor: metastasizes (spreads)
Characteristics of Cancer • NO contact inhibition
Characteristics of Cancer • Angiogenesis • release a growth factor that caused nearby blood vessels to grow and bring more nutrients and oxygen to the tumor.
Proto-oncogenes • Genes that code for proteins that promote cell cycle • Prevent apoptosis • Proto-oncogenes mutate and turn into oncogenes • Onco = cancer
Prokaryotic Cells: How do they divide? cyanobacteria
How Prokaryotic Cells Divide • Introduction • Prokaryotic cells (eubacteria and archaea) lack a nucleus and other membranous organelles. • Chromosome consists of nucleoid • Chromosome, when stretched out, is a circular loop; about 1,000 times the length of the cell. • Binary fission of prokaryotic cells produces two genetically identical daughter cells by division (fission).
How Prokaryotic Cells Divide • 1. Before cell division, DNA is replicated so two chromosomes are attached inside plasma membrane. • 2. Following DNA replication, the two chromosomes separate as a cell lengthens and pulls them apart. 3. When cell is approximately twice its original length, the plasma membrane grows inward, a new cell wall forms dividing the cell into two approximately equal daughter cells.
And Theeeennn? • Generation times of Escherichia coli is 20 minutes; most bacteria need up to one hour to a day.