BSC2011 Exam1 Unit 1 Developmental Biology 1 I Introduction What is Science The scientific process the investigation of rational concepts that can be evaluated by observation and experimentation o Science is a way of knowing It is built up with facts that work together to help us understand the world o Science involves the process of Observation Questioning your Observations Forming your Hypothesis Predicting what will occur and then Testing your Hypothesis When you test your hypothesis you go through another process of deductive and inductive reasoning o Deductive reasoning You start with a general statement hypothesis then you examine the possibilities to reach a specific conclusion based on theory o Inductive reasoning You start from the specifics and go to the general based on observations Hypothesis driven and experimental science is inductive reasoning II Chapter 12 The Cell Cycle A 12 1 Most cell division results in genetically identical daughter cells Cell division reproduction of cells Cellular Organization of the Genetic Material o Genome a cells endowment of DNA o DNA is a cell s genetic information It consists of a sugar phosphate backbone It is coded by four nucleotide bases T A G C These nucleotides form Hydrogen bonds between the airing nucleotides T A and G C DNA is universal meaning we all share the same DNA structure DNA replication begins with parental DNA that is then replicated to make two shorter daughter DNA strands o Before a cell can divide properly its DNA must be copied then the two copies must be separated so that each daughter cell ends up with a complete genome BSC2011 Exam1 2 CENTRAL DOGMA OF BIOLOGY The flow of genetic info is basic to all living things based on gene expression DNA RNA Proteins Replication Transcription Translation Happens in nucleus nucleus cytoplasm Replication is where the DNA continually copies itself Transcription going from DNA to RNA RNA synthesis Translation Ribosomes read RNA and use the sequence to create a protein from various amino acids o RNA primer recruits in DNA polymerase When the RNA primer leaves the DNA strand is left with a gap where it wasn t copied Because a small piece of DNA is lost and another DNA polymerase cannot fit in this gap the whole DNA strand will either be killed or the non copied area will be cut off For neither of these to happen telomerase must take the spot of the RNA primer and continue to copy the DNA Somatic cells have inactive telomerase Telomerase activity is essential to preserve many cancer types It is not only hyper active in tumor cells but it is also hyper active in germ line and stem cells o DNA molecules are packaged and bundled into structures called chromosomes Prokaryotic chromosomes are in loops Eukaryotic chromosomes are linear DNA molecules associated with many The proteins maintain structure of the chromosome and help control the proteins activity of the genes o The entire complex of DNA and proteins that is the building material of the chromosomes is referred to as chromatin BSC2011 Exam1 3 o The nuclei of human eukaryotic somatic cells all body cells except the reproductive cells each contain 46 chromosomes made up of two sets of 23 one set inherited from each parent o The reproductive cells gametes are sperm and egg cells They have one set of half as many chromosomes as somatic cells Human gametes have 23 chromosomes Distribution of Chromosomes During Eukaryotic cell division o When a cell is not dividing and while it s replicating its DNA each chromosome is in the form of a long thin chromatin fiber When replication is complete the chromosome condenses and becomes densely coiled and folded as a part of cell division o Each duplicated chromosome has two sister chromatids which are joined copies of the original chromosome The sister chromatids are attached by protein complexes called cohesions Each sister chromatid has a centromere which is a region of the chromosomal DNA where the chromatid is attached closely to its sister chromatid Later in cell division the two sister chromatids of each duplicated chromosome separate and move into new nuclei Once the sister chromatids separate they are no longer called sister chromatids but are considered individual chromosomes this step doubles the chromosomes in the cell The complex of DNA and protein that makes up a eukaryotic chromosome is properly called a chromatin The process of cells dividing that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus is called Mitosis BSC2011 Exam1 4 Cytokinesis immediately follows mitosis This process is where the cytoplasm divides Each human somatic cell has a total of 46 chromosomes Only half are maternal chromosomes B 12 2 The Phases of the Cell Cycle of the cell cycle The Mitotic phase M includes mitosis and cytokinesis is usually the shortest part The longest phase Interphase takes up 90 of the cell cycle and can be divided into 3 sub phases o G1 phase the first gap growth phase of the cell cycle consisting of the portion of interphase before DNA synthesis begins o S phase the synthesis phase of the cell cycle the portion of interphase during which DNA is replicated There is twice as much DNA than there was in the G1 phase BSC2011 Exam1 5 o G2 phase the second gap growth phase of the cell cycle consisting of the portion of interphase after DNA synthesis occurs During this phase the DNA is scrambled o A cell grows during all three of the interphase sub stages by producing proteins and cytoplasmic organelles MPF promotes the entrance into mitosis the M phase from the G2 phase by phosphorylating multiple proteins needed during mitosis MPF is activated at the end of G2 by a phosphotase which removes an inhibitory phosphate group added earlier Therefore MDF reaches its highest concentration during the 3rd stage G2 right before the M phase A particular human cell might undergo one division in 24 hours M phase less than an hour S phase would be 10 12 hours 4 6 G2 and 5 6 G1 Mitosis is broken down into five stages o Prophase 1st stage of mitosis in which the chromatin condenses into discrete chromosomes visible with a light microscope the mitotic spindle begins to form and the nucleus disappears but the remains intact o Pro metaphase 2nd stage of mitosis in which the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the chromosomes o Metaphase 3rd stage of mitosis in which the spindle is complete and the
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