1 Cells Grow and ReproduceChapter 9 Cells Grow and Reproduce

2 1 DNA replication 2 The cell cycle Cancer 3 4 DNA damage and repair

3 DNA Replication DNA polymeraseAddition of a nucleotide to the 3’ end of a growing strand Use dNTPs as substrate  Release of pyrophosphate

4 Initiation of ReplicationReplication origin The site where replication starts Binding of several proteins involved in replication Helicase Separation of the DNA strands Primase Synthesis of RNA primer

5 Proofreading of DNA PolymeraseIncorporation of wrong nucleotide e.g. alternative form of G base pairs with T Mismatch Induction of mutation Preventing mutation Proofreading by DNA polymerase Repair system for DNA damage Quality control: no cell division if damaged DNA is present

6 Division of DNA molecules during cell divisionBacteria Attachment of DNA to the membrane Eukaryotes Two copies of different chromosomes (human: 23) Connected two daughter chromosome after DNA replication Chromatids Joined at centromere kinetochore: centromere + binding proteins Mitosis : Distribution of chromosome to daughter cells

7 Mitosis DNA replication Mitosis Cytokinesis Interphase ProphaseCondensation of chromosomes and disappearance of nuclear membrane Metaphase Alignment of chromosome in the center Pulling by spindle fibers attached to the kinetochore Anaphase Splitting of chromatids and pulling to the opposite ends of the cell Telophase Decondensation of chromosome Formation of new nuclear membrane Cytokinesis Cell division after mitosis Interphase The time between cell division and the next mitosis

8 Mitosis and Cytokinesis

9 1 DNA replication 2 The cell cycle Cancer 3 4 DNA damage and repair

10 The Cell Cycle Cell Cycle Regulation of cell cycleS phase: DNA synthesis G1, G2 : gap between S and M phase M phase: mitosis Regulation of cell cycle Restriction point : late G1 With growth factor  S phase Without growth factor  G0 : metabolism without growing e.g. platelet-derived growth factor during blood clotting  Growth of skin fibroblasts Ras protein Activated by many growth factors Signal transduction to induce DNA synthesis

11 Cell Cycle CheckpointsRoles of cell cycle checkpoints Prevent entry into the next phase before the completion of the previous phase DNA damage checkpoints Cell cycle checkpoints G1 check point P53 : activated by damaged DNA  activates the G1 check point  stops DNA replication Success in damage repair  proceeds DNA replication Fail in damage repair  Apoptosis : programmed cell death G2 check point Activated by damaged DNA and unreplicated DNA M check point Activated by chromosome misalignment

12 1 DNA replication 2 The cell cycle 3 Cancer 3 4 DNA damage and repair

13 Unregulated Cell Division : CancerCancer: caused by failure in regulation of cell division Carcinoma Originated from epithelial cells (85%) Sarcomas Originated from cells of connective tissue, bone, or muscle tissue Leukemia Originated from white blood cells (leukocytes) Adenocarcinomas Originated from glandular tissue Gliomas and astrocytomas Cancers of the nonneuronal cells of the brain Tumor : A mass of cancer cells derived from a single parent cell Benign: no invasion Malignant: invasion of surrounding tissue Metastasis: migrate to new sites and establish new tumors

14 Genes Involved in CancerOncogenes Mutant genes that promote cell division Genes in signaling pathway to cell division Ras, PDGF(platelet-derived growth factor) receptor Mutant ras constitutively active  cell division 20% of human cancer Tumor suppressor genes Genes that halt cell replication Mutation cause cancer p53 : DNA damage check point protein 50% of human cancers; leukemias, brain tumors, breast, colon, and lung cancer BRAC1, and BRAC2 Breast cancer MADR2 and APC Colon cancer

15 Genes Involved in Cancer

16 Development of Cancer Accumulation of mutations during cancer development

17 Inherited Mutation in Tumor Suppressor GenesMutation and inheritance Mutations in somatic (soma, body) cells No inheritance Mutations in reproductive cells (eggs, sperm) Inheritance Inherited mutations and cancer Breast cancer genes BRCA1: involved in DNA repair 80% chance of developing breast cancer (normal; 10%) 40% chance of developing ovarian cancer Mutations of BRCA1 and BRCA2 in 5 to 10% of breast cancers  sporadic mutations are the major cause

18 Cancer Drugs Classic anticancer treatment Cancer-specific drugsTargeting rapidly dividing cells Side effects to other fast growing cells Blood cell progenitors, cells lining the digestive tract, hair follicle cells Cancer-specific drugs Tamoxifen Mimic estrogen : binding to estrogen receptor of estrogen-sensitive cancer cells Herceptin Binding to and inactivate Her2 (receptor for EGF): inhibit the growth of Her2-overproducing breast cancer cells Greevec Inhibition of Abl in chronic myelogenous leukemia

20 1 DNA replication 2 The cell cycle Cancer 3 4 4 DNA damage and repair

21 Molecular mechanisms of DNA mutagenesiscomplémentaires : Molecular mechanisms of DNA mutagenesis  Recall: Nucleotide interchanges are of two types transitions   - alternative pyrimidines [ C  T ] or purines [ A  G ]  transversions -  purine  pyrimidine [C / T  A / G] Most mutations are transitions : interchanges of bases of same shape purine pyrimidine A T G C

22 Spontaneous mutation tautomeric shift - spontaneous, transient rearrangement to alternative form                keto (standard)  enol  (rare) forms of G & T                amino (standard)  imino (rare) forms of A & C Non-standard bases have altered pairing rules :                modified purine pairs with "wrong" pyrimidine                modified pyrimidine pairs with "wrong" purine T' (enol)     pairs with G(keto)         C' (imino)  pairs with A(amino)         G' (enol)    pairs with T (keto)         A' (imino)  pairs with C (amino)         A tautomeric shift produces a transition mutation in the complementary strand

23 Example of Transition

24 Old random mutagenesisA. Chemical Mutagens - base analogs: bromouracil(BU), aminopurine - chemicals which alter structure and pairing properties of bases: nitrous acid, N-methyl-N′-nitro-N-nitrosoguanidine (NTG) - intercalating agents: acridine orange, proflavin, ethidium bromide(EtBr) B. Radiation EM(electro magnetic) radiation ionizing radiation: X- and gamma rays UV : pyrimidine dimers(thymine dimers  (T^T)) in DNA

25 Induced mutation - chemical modification of DNA change base pairingalkylation - addition of alkyl group (methyl CH3- or ethyl CH3-CH2-)           ethyl methane sulfonate (EMS) is a common laboratory mutagen        G  6-ethyl G , pairs with T      deamination - conversion of amino   keto group            nitrous acid (HNO2) is a common food additive / preservative        C   U by loss of NH2, pairs with A        A  hypoxanthine by loss of NH2, pairs with C      depurination - loss of purine (A or G) base in intact nucleotide             produces an apurinic  site             replacement of base may produce transversion                        [a common form of damage in 'ancient' DNA]             apyrimidinic sites are similar: loss of C or T      intercalation - base analogue wedged into DNA double helix             acridine dyes resemble 3-ring base pair             intercalated analogue read as 'extra' base:            DNAPol "stutters"  frameshift mutations                      (ethidium bromide is a fluorescent dye of DNA)     ionizing radiation:  radiochemical damage to DNA     Stutters: 말더듬다. 더듬거리다.

26 DNA Damage and Repair DNA damaging agents Environmental carcinogensMutagens : mutation-promoting agents Carcinogen : cancer-inducing agents Environmental carcinogens UV Thymine dimer formation  blocking transcription and DNA replication DNA-binding chemicals Benzopyrene Smoke from cigarette, burning leaves, diesel exhaust etc. Bind to DNA G residue and induce mutation

27 Repair System Mismatch repair Excision repairRepair distorted DNA (T-T, benzopyrene binding) Excision of damaged region by nuclease and helicase, and repair by DNA polymerase Xeroderma pigmentosum (XP) Mutation in excision repair system Extreme sensitive to UV  skin cancer