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Cell Cycle 6.4 – 6.9 1 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 3 4 In which part of the cell cycle does the cell spend most of its time? 1. 2. 3. 4. Interphase Mitosis G2 DNA synthesis 5 DNA Review DNA = deoxyribonucleic acid long, spiraling “ladder” with a sugarphosphate 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 7 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 11 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: 1. 2. 3. 4. deletion insertion substitution chromosomal breakage 14 Reason for Mitosis To enable cells to generate new, genetically identical cells – why? 1. 2. Growth Replacement 15 16 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. 2. 3. 4. Wound healing Making insulin Glucose transport 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 26 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 30 31 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 etc.) tumors (moles, warts, 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 38 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.