UNIT II Patterns of Inheritance Mendelian genetics also cell division and cell cycle 1 Describe a duplicated or replicated chromosome A replicated chromosome 2 sister chromatid joined at a centromere Chromosomes either have one or two molecules of DNA plus associated proteins A chromosome with one molecule of DNA is called an unduplicated chromosome because it only contains one molecule of DNA On the other hand a duplicated chromosome contains two identical daughter DNA molecules that have come from an original DNA molecule In the case of a duplicated chromosome each molecule of DNA and associated proteins is called a sister chromatid 2 To what does the cell cycle refer and what events stages steps etc are involved The cell cycle cell growth cell division Parts of eukaryotic cell cycle Interphase G1 S G2 a b Mitotic M Phase Mitosis Cytokinesis G1 a new cell grows S Chromosomes DNA replicate G2 cell prepares to divide M Phase the nucleus divides mitosis and the cytoplasm divides cytokinesis 2 daughter cells each with same of chromosomes as parent cell More Specifically There are two parts of the cell cycle Interphase which consists of G1 S and G2 phase And then the Mitotic phase which contains mitosis and cytokinesis G1 the cell grows S the chromosomes are replicated and G2 the cell prepares the cell to divide by synthesizing proteins and structures In G2 the centrosomes replicate microtubule organizing center The centrioles in the centrosomes begin synthesizing microtubules that make spindle fibers Mitotic phase begins with Prophase In prophase the centrosomes move to opposite poles Mitotic spindles and asters anchorage to the cell membrane polls begin to form There are replicated chromosomes attached by cohesion proteins at a centromere in the middle These chromosomes are identical and are called sister chromatids Then pro metaphase begins which the chromosomes are clearly visible and the nuclear membrane breaks down In pro metaphase the centromere attaches to a protein called kinetochore The kinetochores attach to spindle fibers which then attach to the pole These proteins allow for the spindle fibers to pull the sister chromatin apart Aster microtubules anchor the centrosomes to the cell membrane Metaphase then occurs which the spindle fibers begin to pull the sister chromatids to the metaphase plate along the center of the center between the two poles The two sister chromatids face opposite poles so they can be pulled apart Anaphase then occurs which the spindle fibers completely pull the sister chromatids away from each other toward opposite poles and the centromeres split apart In Telophase the nuclear envelope begins to re form the spindle disassembles the cell begins to cleave When Telophase occurs mitosis is complete and the nuclear division is complete Then cytokinesis begins when the cell completely cleaves and cytoplasmic division is complete creating two identical diploid daughter cells 3 Why do cells organisms need to regulate or control the cell cycle Cells need to regulate the cell cycle because they need to know when to proceed through the cell cycle and when to stop when something goes wrong or needs to be fixed 4 How do cells organisms regulate or control the cell cycle Explain the role of checkpoints Explain the chemical control system that gets cells through the G2 checkpoint There are molecular signals in the cytoplasm that regulate the cell cycle The cycle is regulated at various checkpoints G1 G2 and M Checkpoints The presence and absence of specific chemical signals determines whether a cells stops or proceeds through a checkpoint G2 checkpoint cells assess if preparations are okay and if they are then signals direct them to enter M Phase An activated cyclin and CDK complex is need to move a cell through checkpoint MPF is a particular cyclin CDK complex needed to get through G2 Checkpoint 5 What is the general purpose of mitotic cell division Describe the step wise process of mitotic cell division Compare the number of chromosomes before the start of mitosis at each step and at the end The general purpose is to create two daughter cells that are identical to the parent The two daughter cells contain the same number of chromosomes and identical DNA as the parent 2n The function of mitotic cell division is asexual reproduction development and tissue growth and repair Step wise process question number 2 6 What do cancer and the cell cycle have to do with one another What do cancer and gene regulation have to do with one another Cancer is a genetic disease that results when there are errors in cell cycle control and cell division is unregulated It takes several gene mutations to make a cell cancerous There are different types of genes that are involved in cancer causing mutations Cancer causing mutations involve TSGs tumor suppressing genes restrict cell division POG s Proto oncogenes stimulate cell division and other genes regulating the cell cycle cdk a molecule that regulates a Cdk or a cyclin Possible errors in a cell cycle stimulate pathways A POG mutation results in uncontrolled cell growth which results in cancer A cell cycle stimulating protein gets overexpressed so the cell cycle gets over stimulated TSG mutation a cell cycle inhibiting protein is absent so the cell cycle is not inhibited Both POG and TSG mutations lead to uncontrolled cell growth Another possible error with the POG causes it to stimulate cell division when it shouldn t These mutations are called Ras which may lead to cancer Another error in a cell cycle inhibits pathways which results in uncontrolled cell growth A defective or missing transcription factor protein such as p53 cannot activate a gene that makes a protein needed to stop cell division So basically if p53 gets mutated it won t stop the cell cycle and then unrestricted growth occurs and you get cancer You get cancer because cell can replicate with damaged DNA which results in more mutations accumulating 7 Compare contrast somatic vs germ cells a k a sex cells or gametes with respect to location in an organism function how they are formed and chromosome number Somatic cells are body cells contain the full amount of dna diploid and are produced by mitosis Germ cells sex cells in the ovaries testes they contain half the amount of DNA and are produced by meiosis 8 Describe a karyotype What does a karyotype reveal Why are karyotypes useful A picture of all the chromosomes lined up in a diploid cell that are arranged in
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