Chapter 12: The Cell Cycle (How do cells divide?) cell division in prokaryotes chromosomes eukaryotic cell cycle mitosis cytokinesis . Prokaryotes binary fission generation time as short as 20 minutes . Chapter 12: The Cell Cycle (How do cells divide?) cell division in prokaryotes chromosomes eukaryotic cell cycle mitosis cytokinesis . • Define: – chromosome – chromatin – gene – genome – karyotype • Describe the human genome and karyotype in terms of: – number of basepairs – number of genes – number of chromosomes . Eukaryotic DNA in chromosomes chromatin: long DNA molecule with associated proteins chromosomes: densely packaged chromatin during cell division protects the DNA sets up DNA distribution . each chromosome contains hundreds to thousands of genes functional units of heredity typically instructions for a protein or RNA genome – organism’s complete DNA sequence humans apparently have ~25,000 genes in the now-sequenced human genome . chromosomes each species has a characteristic number of chromosomes number varies between species does not reflect complexity humans: 46 some ferns: 1000+ chromosomes for an individual is the karyotype . chromosomes function: chromosomes carry the genetic information of a cell from one cell generation to the next from one organism to its offspring . • Define: – chromosome – chromatin – gene – genome – karyotype • Describe the human genome and karyotype in terms of: – number of basepairs – number of genes – number of chromosomes . Chapter 12: The Cell Cycle (How do cells divide?) cell division in prokaryotes chromosomes eukaryotic cell cycle mitosis cytokinesis . • Draw a circle diagram of the eukaryotic cell cycle. Label all phases. • Discuss what goes on in each of the phases on the diagram. Note where checkpoints exist. Also, discuss G0, and discuss cell cycle regulation in general terms. Eukaryotic Cell Cycle when cells reach a certain size, growth either stops or the cell must divide cell division is generally a highly regulated process (not all will divide!) the generation time for eukaryotic cells varies widely, but is usually 8-20 hours . Eukaryotic Cell Cycle . Eukaryotic Cell Cycle cyclins and cyclin-dependent protein kinases (Cdks) cytokinins; growth factors; suppressors; cancer cells . • Draw a circle diagram of the eukaryotic cell cycle. Label all phases. • Discuss what goes on in each of the phases on the diagram. Note where checkpoints exist. Also, discuss G0, and discuss cell cycle regulation in general terms. Chapter 12: The Cell Cycle (How do cells divide?) cell division in prokaryotes chromosomes eukaryotic cell cycle mitosis cytokinesis . • Describe what “PMAT” means. • With a partner, do the “chromosome dance” for mitosis. Make sure that you distinguish between chromosomes and chromatids, and note at each stage the number of sister chromatids per chromosome. • Discuss what happens in each stage of mitosis. Mitosis 4 stages: prophase metaphase anaphase telophase * (PMAT) . Mitosis: prophase chromatin condenses to form chromosomes each chromosome (duplicated during S phase) forms a pair of sister chromatids sister chromatids are joined at a centromere by protein tethers centromeres contain a kinetochore where microtubules will bind each sister chromatid has its own kinetochore sister chromatids become attached by their kinetochores to microtubules from opposite poles . Mitosis: prophase a system of microtubules, called the mitotic spindle, organizes between the two poles (opposite ends) of the cell each pole has a microtubule organizing center (MTOC) in animals and some other eukaryotes, centrioles are found in the MTOC . Mitosis: prophase by the end of prophase: the nuclear membrane has disappeared (actually divided into many small vesicles) nucleoli have disintegrated the sister chromatids are attached by their kinetochores to microtubules from opposite poles . Mitosis: prophase some call the later part of prophase prometaphase, usually defined to include vesicularization of the nuclear membrane and attachment of kinetochores to microtubules in some eukaryotes the nuclear membrane never vesicularizes . Mitosis: metaphase chromosomes line up along the midplane of the cell (the metaphase plate) chromosomes are highly condensed the mitotic spindle, now complete, has two types of microtubules kinetochore microtubules extend from a pole to a kinetochore polar microtubules extend from a pole to the midplane area, often overlapping with polar microtubules from the other pole the mitosis checkpoint appears to be here; progress past metaphase is typically prevented until the kinetochores are all attached to microtubules . Mitosis: anaphase sister chromatids separate and are moved toward opposite poles the protein tethers at the centromere between the chromatids are broken each former sister chromatid can now be called a chromosome . Mitosis: anaphase model for the mechanism that moves chromosomes to the poles motor proteins move the chromosomes towards the poles along the kinetochores microtubules kinetochore microtubules shorten behind the moving chromosomes * polar microtubules lengthen the entire spindle motor proteins on the polar microtubules slide them past each other, pushing them apart (the microtubules may grow a bit, too) this pushes the MTOCs away from each other, and thus has the effect of pushing kinetochore microtubules from opposite poles away from each other . Mitosis: anaphase overall, this process assures that each daughter cell will receive one of the duplicate sets of genetic material carried by the chromosomes . Mitosis: telophase prophase is essentially reversed the mitotic spindle is disintegrated the chromosomes decondense nuclear membranes reform around the genetic material to * form two nuclei each has an identical copy of the genetic information nucleoli reappear, and interphase cellular functions resume . • Describe what “PMAT” means. • With a partner, do the “chromosome dance” for mitosis. Make sure that you distinguish between chromosomes and chromatids, and note at each stage the number of sister chromatids per chromosome. • Discuss what happens in each stage of mitosis. Chapter 12: The Cell Cycle (How do cells divide?) cell division in prokaryotes chromosomes eukaryotic cell cycle mitosis cytokinesis . • Describe cytokinesis in both plant cells and animal cells, noting the differences. • Describe what is meant by the term “polar division” and why this process was (and still is) important in your development. cytokinesis divides the cell into two daughter cells cytokinesis usually begins in telophase and ends shortly thereafter . cytokinesis in animals, a cleavage furrow develops usually close to where the metaphase plate was a microfilament (actin) ring contracts due to interactions with myosin molecules, forming a deepening furrow eventually, the ring closes enough for spontaneous separation of the plasma membrane, resulting in two separate cells * . cytokinesis in plants, a cell plate develops usually close to where the metaphase plate was vesicles that originate from the Golgi line up in the equatorial region the vesicles fuse and add more vesicles grow outward until reaching the plasma membrane and thus separating the cells the vesicles contain materials for making the primary cell wall and a middle lamella * . cytokinesis cytoplasm (and with it most organelles) is usually distributed randomly but roughly equally between daughter cells sometimes cell division is a highly regulated polar division that purposefully distributes some materials unequally . • Describe cytokinesis in both plant cells and animal cells, noting the differences. • Describe what is meant by the term “polar division” and why this process was (and still is) important in your development. • In the following slide, look for examples of interphase, prophase, metaphase, anaphase, and telophase/cytokinesis. * . .