Cell Cycle

1. Cell Cycle 6.4 – 6.9

2. The Cell Cycle • alternation of activities between cell division and other processes  • describes series of phases leading to cell division • mitosis and three phases of interphase—Gap 1, DNA synthesis, and Gap 2 • cell division phase – mitosis • phase of growth and non-reproductive activities – interphase

4. In which part of the cell cycle does the cell spend most of its time? Interphase Mitosis G2 DNA synthesis

5. DNA Review • DNA = deoxyribonucleic acid • long, spiraling “ladder” with a sugar-phosphate backbone • Four bases – thymine (T), adenine (A), cytosine (C), guanine (G) form the “rungs” of the DNA ladder. (2 bases form a rung -- one for each side of the ladder) • Sugar + base + phosphate = nucleotide

6. Chromosome Structure • Single strand of DNA forms a chromosome • DNA is wrapped around spools of a protein called histone • Therefore, DNA is much, much longer than the chromosome it makes up

8. DNA Replication • Copy double-stranded DNA • Necessary for cell division • Replication is termed semiconservative since each new cell contains one strand of original DNA and one newly synthesized strand of DNA

9. DNA Replication • Special enzymes move up along DNA ladder and “unzip” the molecule as it moves along • New nucleotides move in to each side of the unzipped ladder • Cytosine (C) pairs with guanine (G), adenine (A) pairs with thymine (T). • Arrangement of bases is what determines genetic code

10. DNA Replication • When enzyme has passed the end of the DNA, two identical molecules of DNA are left behind • Each contains one side of the original DNA and one side made of "new" nucleotides • It is possible that mistakes were made along the way -- in other words, that a base pair in one DNA molecule doesn't match the corresponding pair in the other molecule • On average, one mistake may exist in every billion base pairs

12. Mutation • Variety of errors can occur during replication • Several DNA repair processes occur after replication • If error remains sequences in a replicated DNA molecule (including the genes) can be different from those in parent DNA molecule

13. Review: If an incorrect base is placed in the DNA during replication, the mutation would be called a: deletion insertion substitution chromosomal breakage

14. Reason for Mitosis • To enable cells to generate new, genetically identical cells – why? • Growth • Replacement

17. Apoptosis • Apoptosis : Pre-planned cell “suicide” called apoptosis • parts of body where the cells are likely to accumulate significant genetic damage over time,  high risk of becoming cancer cells • cells lining the digestive tract, liver, etc • cells are almost constantly in contact with harmful substances

18. Mitosis • # of (somatic) cells that must be replaced by mitosis every day is huge • Rate @ which mitosis occurs varies dramatically • average RBC ~ 6 weeks • cells lining the intestines ~ 3 weeks • hair follicles also divide rapidly

19. What cellular process listed below might involve mitosis? 1. Wound healing 2. Making insulin 3. Glucose transport 4. Muscle contraction

20. Mitosis – Overview • Parent cell duplicates DNA  duplicate copy of each chromosome • Remaining organelles duplicate • Cell divides into two new duplicate cells (daughter cells) • Usually the shortest period in eukaryotic cell cycle

21. Mitosis – Overview

22. Interphase • In preparation for mitosis, chromosomes replicate • DNA synthesis (S) part of interphase, every chromosome creates an exact duplicate of itself by replicating • Before replication, each chromosome was a single long linear strand of genetic material • After replication, each chromosome is a pair of identical long linear strands, held together at the center, a position called the centromere

23. Interphase

24. Sister Chromatids

25. Mitosis – The Details • Prophase • chromosomes condense, coil, become visible • official beginning of mitosis

27. Mitosis – The Details • Prophase • chromosomes condense, coil, become visible • official beginning of mitosis

28. Mitosis – The Details • Metaphase • chromatids separate and move in opposite directions • Anaphase • pairs of sister chromatids are all simultaneously pulled apart by the spindle fibers • one full set of chromosomes goes to each side of the cell • chromosome sets will eventually reside in nucleus of new daughter cells

29. Mitosis – The Details • Telophase • New nuclear membranes re-form around the two complete chromosome sets. • chromosomes begin to uncoil and fade from view • nuclear membrane is reassembled • cell begins to pinch into two

32. Cytokinesis • cell’s cytoplasm is also divided into approximately equal parts • some of organelles go to each new cell • two new daughter cells (each w/identical nucleus) enter interphase

33. Cancer • unrestrained cell growth and division • can lead to tumors • second leading cause of death in the United States (heart disease is #1)

34. Cancer • Disruption of DNA in a normal cell interferes with cell’s ability to regulate cell division • caused by : • chemicals that mutate DNA • sources of high energy (X-rays, sun, nuclear radiation) • viruses

35. Cancer

36. Cancer: Benign vs. Malignant • Benign tumors (moles, warts, etc.) • masses of normal cells that do not spread • usually be removed safely without any lasting consequences

37. Cancer: Benign vs. Malignant • Malignant tumors • cancerous • grow continuously • shed cells • shedding of cancer cells from malignant tumors is how cancer spreads (metastasis

39. Cancer Treatment • Rapidly dividing cells must be removed surgically, killed, or slowed down • Chemotherapy • anti-mitoticdrugs are administered that interfere w/cell division. • Slows growth of tumors, but because the drugs interfere with cell division throughout the body they have terrible side effects.