Lecture: chapter 12: cell cycle 10/25/11 The continuity of life- - is based upon the reproduction of cells, or cell division Unicellular organisms- - reproduce by cell division Multicellular organisms depend on cell division for - -development- -growth- -repair The cell division process- - is an integral part of the cell cycle Cell division results in genetically identical daughter cells Cells duplicate their genetic material- - before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA A cells endowment *- -* Cellular organization of the genetic material- the DNA molecules in a cell - are packaged into chromosomes- Eukaryotic chromosomes - consist of chromatin, a complex of DNA and protein that condenses during cell division.- In animals - Somatic cells (all body cells except the sex cells) have 2 sets of chromosomes (diploid or 2n). -Gametes have one set of chromosomes (haploid or 1n). Distribution of chromosomes during cell division- In preparation for cell division - DNA is replicated and the chromosomes condense.- Each duplicated chromosome - has 2 sister chromatids, which separate during cell division. Eukaryotic cell division consists of - - mitosis, the division of the nucleus.- -Cytokinesis, the division of the cytoplasm. In meiosis- - sex cells are produced after a reduction in chromosome number. The mitotic phase alternating with interphase in the cell cycle. The cell cycle consists of- Figure 12.5 Phases of the cell cycle- - interphase can be divided into subphases -G1 phase -S phase -G2 phase- The mitotic phase - is made up of mitosis and cyto*- Mitosis consists of 5 distinct phases - Prophase (figure 12.6) -prometaphase - Metaphase (figure 12.6) -Anaphase -Telophase The mitotic spindle: a closer look - is an apparatus of microtubules that controls chromosome movement during mitosis.- The spindle arises from the centrosomes - and include*- Some spindle microtubules - attach to the kinetochores of chromosomes and move the chromosomes to the metaphase plate.- In anaphase, sister chromatids separate -and move along the kinetochores microtubules toward opposite ends- Nonkinetechore microtubules from the opposite poles - overlap and push against each other, elongating the cell- In Telophase - genetically identical daughter nuclei form* Cytokinesis: a closer look- In animals -Cytokinesis occurs by a process known as cleavage, forming a cleavage furrow.- In plants -a cell plate forms. Mitosis in a plant (figure 12.10) Binary fission- Prokaryotes (bacteria) -reproduce by a type of cell division called binary fission.- In binary fission -the bacterial chromosomes (circular DNA) replicates. -the 2 daughter chromosomes actively move apart. Figure 12.11 The evolution of mitosis- Since prokaryotes precede eukaryotes by billions of years - it is likely that mitosis evolved from bacterial cell division- Certain protists - exhibit types of cell division that seem intermediate between binary fission and mitosis*- A hypothetical sequence for the evolution of mitosis - figure 12.12 The cell cycle is regulated by a molecular control system The frequency of cell division- - varies with the type of cell. These cell cycle differences- - result from regulation at the molecular level. Evidence for Cytoplasmic signals- Molecules present in the cytoplasm - regulate progress through the cell cycle. The cell cycle control system- The sequential events of the cell cycle - are directed by a distinct cell cycle control system, which is similar to a clock. Stop and go signs: internal and external signals at the checkpoints- The clock has specific checkpoints -where the cell cycle stops until a go-ahead signal is received.- Both internal and external signals - control the cell cycle checkpoints. The cell cycle clock: cyclins and cyclin-dependent kinases- 2 types of regulatory proteins are involved in cell cycle control.- Cyclin and cyclin-dependent kinases (Cdks).- The activity of cyclins and Cdks -fluctuates during the cell cycle.- Figure 12.16 Cell cycle control: external factors- Growth factors - stimulate other cells to divide.- In density-dependent inhibition -crowded cells stop dividing.- Most animal cells exhibit anchorage dependence -in which they must be attached to a substratum to divide. Loss of cell cycle controls in cancer cells- Cancer cells -exhibit density-dependent inhibition nor anchorage dependence. - do not respond normally to the body’s control mechanisms Don’t stop dividing when growth factors are depleted. If they stop dividing it is at random points in the cycle rather than the normal checkpoints. Some can go on dividing indefinitely if given a continual supply of nutrients. Form tumors- Malignant tumors invade surrounding tissues and can metastasize - exporting cancer cells to other parts of the body where they may form secondary tumors. You should know :- Describe the structural organization of the prokaryotic genome and the eukaryotic genome- List the phases of the cell cycle; describe the sequence of events during each phase- List the phases of mitosis and describe the events characteristic of each phase- Draw or describe the mitotic spindle, including centrosomes, kinetochore microtubules, nonkinetochore microtubules, and asters- Compare cytokinesis in animals and plants- Describe the process of binary fission in bacteria and explain how eukaryotic mitosis may have evolved from binary fission- Explain how the abnormal cell division of cancerous cells escapes normal cell cycle controls- Distinguish between benign, malignant, and metastatic tumorsLecture: Chapter 13: Meiosis 10/27/11- Living organisms are distinguished by their ability to reproduce their own kind.- Genetics is the scientific study of heredity and variation.- Heredity is the transmission of traits from one generation to the next.- Variation is demonstrated by the differences in appearance that offspring show from parents and siblings. Offspring acquire genes from parents by inheriting chromosomes- In literal sense, children don’t inherit particular physical traits from their parents- It is genes that are
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