7/5/2010 ������������� • Cell division is necessary for reproduction, repair and growth. Cell division is necessary for reproduction, repair and growth. • The cell cycle is a continuum of processes undergone by cells The cell cycle is a continuum of processes undergone by cells during their lifetime, which involves growth and functioning, during their lifetime, which involves growth and functioning, �������������� and culminates in division. and culminates in division. • Mitosis produces two new identical cells. Mitosis produces two new identical cells. • Interactions of physical and chemical signals control the Interactions of physical and chemical signals control the events of the cell cycle. events of the cell cycle. • Cancer results from abnormal or lacking control signals of the Cancer results from abnormal or lacking control signals of the cell cycle. cell cycle. • Meiosis is a special kind of division that produces four (4) Meiosis is a special kind of division that produces four (4) haploid, non haploid, non- -identical cells. identical cells. • Errors may occur during cell division, producing cells with Errors may occur during cell division, producing cells with abnormal chromosome number. abnormal chromosome number. �������������� �������� Roles of Cell Division • anaphase • Reproduction • Renewal and • Growth and • centromere • genome development repair • non-disjunction • chromatin • haploid • prophase • homologue • chromosome • sister chromatid • interphase • crossing-over • spindle • kinetochore • cytokinesis • synthesis • meiosis • diploid • telophase • metaphase • tetrad • G1 • mitosis • G2 �������������� �������������� Stages of the cell cycle Types of cell division • Mitosis – May have evolved from binary fission in prokaryotes – Method of asexual reproduction in unicellular eukaryotes • Meiosis – Responsible for production of gametes in multicellular eukaryotes 1
7/5/2010 ��������������� ������������������������ • genome - genetic material of a cell • 1 chromosome � 2 • chromatin – unorganized mass of DNA sister chromatids, and proteins that condense during cell division connected at a • chromosomes – packaged DNA centromere, which molecules in nuclei – somatic cells have 2 sets of separate during cell chromosomes (2N, diploid) division – gametes have 1 set of chromosomes (N, haploid) • mitosis – division of • interphase – preparation for cell division the nucleus – cell grows – DNA is replicated • cytokinesis – division – centrosomes are replicated* of cytoplasm – chromosomes condense Mitosis consists of five distinct phases – Prophase – Prometaphase PROPHASE PROMETAPHASE G 2 OF INTERPHASE Centrosomes Aster Fragments Early mitotic Kinetochore (with centriole pairs) Chromatin Centromere of nuclear spindle (duplicated) envelope Nonkinetochore microtubules Kinetochore Nucleolus Nuclear Plasma Chromosome, consisting of two sister chromatids microtubule envelope membrane ����������������������� – Metaphase – Anaphase – Telophase Nucleus Chromatin Chromosome condensing Nucleolus METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Metaphase plate Cleavage Nucleolus furrow forming 1 2 3 Metaphase. The 5 4 Prometaphase. Telophase. Daughter Prophase. Anaphase. The spindle is complete, The chromatin We now see discrete chromatids of each nuclei are forming. and the chromosomes, chromosomes; each Meanwhile, cytokinesis is condensing. chromosome have attached to microtubules consists of two separated, and the has started: The cell The nucleolus is at their kinetochores, beginning to identical sister daughter chromosomes plate, which will are all at the metaphase chromatids. Later divided the cytoplasm disappear. are moving to the ends plate. Although not in prometaphase, the of cell as their in two, is growing Nuclear nuclear envelop will toward the perimeter yet visible kinetochore envelope in the micrograph, fragment. microtubles shorten. of the parent cell. Daughter Centrosome at forming Spindle chromosomes the mitotic spindle is one spindle pole staring to from. 2
7/5/2010 �������������� �������������� • Events in the cell cycle triggered and Restriction Point coordinated by a molecular control system • Checkpoints – critical control points where stop and go-ahead signals can regulate the cycle 3
7/5/2010 ��������������������� ����������������������������������� �������������� 2. Regulatory proteins 1. Telomeres Cyclins - concentration • – Repeated DNA cyclically fluctuates in the cell sequences at tips of • Cyclin-dependent kinases chromosomes (Cdks) – activate other – TTAGGG sequences lost proteins in the presence of cyclin every time a cell divides • e.g. Maturation-promoting – Restored to their original factor (MPF) length by telomerase – M-phase promoted (normally found in • Chromatin condensation gametes) • Mitotic spindle formation • Degradation of nuclear envelope – Deactivated when proteolytic enzymes digest the cyclin ����������������������������������� 3. Growth Factors • proteins that stimulate other cells to divide • promote the binding of cyclin to cdks ex. platelet-derived growth factor (PDGF) • ������� �������� �������������������������� �������������������������� ����������������������������������� • Cells do not heed Cells do not heed 4. Density-dependent 5. Anchorage dependence normal signals to normal signals to • Most animal cells must be inhibition STOP cell division STOP cell division attached to a substrate before they can grow • Can invade Can invade neighboring cells and neighboring cells and interfere with normal interfere with normal body function body function • “immortal” “immortal” – – can keep can keep dividing as long as dividing as long as nutrient supply is kept nutrient supply is kept constant constant 4
7/5/2010 ������ • Oncogenes – Gene that enables transformation when �������������� mutated or expressed in high levels • Viruses and bacteria • Numerous diverse Numerous diverse – e.g. HPV and cervical cancer; causes causes Hep B and C and liver cancer; H.pylori and stomach cancer Cancer cell � � tumor � � � � � � • Cancer cell tumor • Ionizing and UV – Benign Benign radiation – Malignant Malignant • Carcinogens • Metastasis Metastasis ������� ��������� ������������ ������������!�"���� ������������ • Surgery • Types of reproduction – Asexual • Radiation – Sexual • Chemotherapy • Genes – hereditary units of DNA • Immunotherapy • Locus – gene’s specific and Gene therapy location in the chromosome ����������� �����������������$� !�"����#���������� ������������������ �������� • Generation-to-generation sequence of stages in the reproductive history of an • Interphase organism – G 1 , S, G 2 • Homologous chromosomes • Meiosis – pair that has the same length, centromere position, – Meiosis I staining pattern – Meiosis II • Humans: 22 pairs of autosomes + 1 pair of sex chromosomes 5
7/5/2010 ��������%�������������&��������� �"�������������������'������������������������ �������������������������������������� • Homologues pair up � tetrad • Synapsis � “crossing- over” that occurs at a chiasma • Does not normally happen to sex chromosomes • Purpose: to increase genetic variation ���������������(���������������������� ����������������������������������������� )������(����������* +������������ 1) Meiosis • Random fertilization - Gametes (n) formed from – 1/64 million embryonic primordial germ cells (PGC’s) via meiosis • Independent assortment PGC’s (2n) � meiosis � - – 1/2 23 sex cells (n) • Crossing-over - Spermatogonium and oogonium – occurs an average of 2-3 times 2) Maturation per chromosome pair – distinctive characteristics of sperm and egg cells are formed 6
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