Foundations of Bio 1 Unit 3
Foundations of Bio 1 Unit 3 BIOSC 0150
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Date Created: 01/19/15
121 How Do Cells Replicate Tuesday November 4 2014 1148 PM Basic requirements of cellular replication 1 Copy DNA 2 Separate copies 3 Divide cytoplasmCreate two new cells Purpose 1 Growth 0 Trillions of cells in your body are result of mitotic divisions 2 Wound Repair 0 Cellular replication generates cells that repair wounds 3 Reproduction o Asexual reproduction produces genetically identical offspring and parents What is a chromosome Consists ofa single long DNA double helix that is wrapped around proteins called histones in a highly organized manner Before mitosis chromosomes are replicated to form two sister chromatids still referred to as a single chromosome Then each sister is distributed to one of two daughter cells Cells Alternate between M Phase and Interphase Dividing phase is known as quotMquot phase mitotic or meiotic The rest of the time is Interphase 0 Bulk of time The Discovery of S Phase Synthesis phase 0 Replication of genetic material The Discovery of the Gap Phases Why 0 Parent cell must grow large enough to divide into two cells that will be normal in size and function 0 Allow cell to complete all requirements for cell division other than chromosome replication Module 3 Page 1 repaira Each at the 46 H w ehramaaamee i5 duplicated by theyquot tell ll n quotUH l duplicated ehramaaamea far V errer making any needed quot Cellular ear39iteata excluding the ehr amzaaamea are duplicated 39 Cell cycle arrest 122 What Happens during the M Phase Tuegdayp Nevember 4p Z 14 1148 PM Module 3 Page 2 123 Tuesday November 4 2014 1148 PM Module 3 Page 3 124 Tuesday November 4 2014 1148 PM Module 3 Page 4 131 How Does Meiosis Occur Friday October 24 2 14 142 AM Chromosomes come in distinct sizes and shapes Chromosomes that are the same size and shape are called homologous or homologs o The pair is called an homologous pair Homologous chromosomes carry the same genes 0 Gene is a section of DNA that influences some hereditary trait in an individual Allele is a different version of the same gene Homologous chromosomes carry the same genes but each homolog may contain different alleles The Concept of Ploidy Organisms that contain two types of each chromosome are considered diploid 0 Contain two alleles of each gene Organisms that contain only one type of each chromosome are considered haploid Haploid number n indicates the number of distinct types of chromosome present In contrast a cell39s ploidy n 2n 3n 4n indicates the number of each chromosome present An Overview of Meiosis Unreplicated eukaryotic chromosomes consist of a single long DNA double helix organized around histones When chromosomal replication is complete each chromosome consists of two identical sister chromatids Unreplicated chromosomes and replicated chromosomes are both considered single chromosomes even though the replicated chromosome contains two sisters Unreplicated chromosomes never called chromatid Chromatid is only the structure in a replicated chromosome Meiosis Comprises Two Cell Divisions ME 0339 Cyfoklnuil Intcrphm Prophase 1 Manphau x Anaphase 1 Telophase 1 i a s 39 quot of a 1 39 l I v39 I f 139 tw 0 k1 quotI I39 7 7 quot II k max k H i 39 39 l I I gt i i 39 39 V quot f 39 v I Lquot quot 39 A c p 39 I g k f x I l g zt 12 nlf f l Vquot l lquot 39 c 13973 v 1 A A 1 lt9 L gal gj gquot kg J V Cytoxinuis Telephone 11 Anaphase II During meiosis I the homologs in each chromosome pair separate from each other 0 One homolog goes to one daughter cell the other homolog goes to the other daughter cell At the end of meiosis I there are two daughter cells each containing a single replicated chromosome During meiosis sister chromatids from each chromosome separate The cells produced by meiosis II also have one 0 each type of chromosome but they are no longer replicated Chromosome movement is controlled by the microtubules of the spindle apparatus that attach onto kinetochores located at the centromere Meiosis is a Reduction Division The outcome of meiosis is a reduction in chromosome number For this reason meiosis is known as a reduction division Crossing Over in Depth Step 1 Chromosomes begin to condense Module 3 Page 5 Phase Interphase Ea y prophase 1 Late prophase 1 Metaphase 1 Anaphase 1 Telophase 1 and cytokinesis Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 and cytokinesis Function Uncondensed chromosomes replicated in cell Chromosomes condense Spindle begins to form Pairing of homologous chromosomes Nuclear envelope beings to break down Nuclear envelope broken down Crossover occurs Homologous replicated chromosomes line up at equator bivalents Homologs separate and begin to move to opposite poles of spindle Movement complete Partial decondense of replicated Chromosomes Spindle broken own Daughter cells formed Spindle reforms Replicated Chromosomes re condense Replicated chromosomes line up at the equator Sisters begin to move towards poles of spindle Movement complete Spindle dissembles Daughter cells created Step 2 Replicated chromosomes pair into bivalents Break occurs in the DNA of one of the chromatids Step 3 Network of proteins forming the synaptonemal complex hold the homologues together Step 4 Synaptonemal complex dissembles in late prophase and the homologues are held together at the chiasma At a chiasma the nonsister chromatids have both been physically broken at the same point and attached to each other Module 3 Page 6 132 Meiosis Promotes Genetic Variation Friday ctober Z42 2M4 142 AM Asexual reproduction Any mechanism of producing offspring that does not involve the production and fusion of gametes Asexual reproduction in eukaryotes is based on mitosis The chromosomes in cells produced by mitosis are identical to the chromosomes in the parental cell Sexual reproduction The production of offspring through the production and fusion of gametes Sexual reproduction results in offspring that have chromosome complements unlike those of their siblings or their parents Chromosomes and Heredity The changes in chromosomes produced by meiosis and fertilization are significant because chromosomes contain the cells hereditary material The Role of Independent Assortment When pairs of homologous chromosomes line up during meiosis and the homologs separate a variety of combinations of maternal and paternal chromosomes can result Each daughter cell gets a random assortment of maternal and paternal chromosomes The Role of Crossing Over Crossing over produces new combinations of alleles within a chromosome combinations that did not exist in either parentgt This phenomenon is known as recombination Crossing over is an important part of genetic recombination How Does Fertilization Affect Genetic Variation Crossing over and the independent assortment of maternal and paternal chromosomes ensure that each gamete is genetically unique Module 3 Page 7 141 Mendel39s Experimental System Tuesday ctober Z1 2 14 8132 PM What Questions Was Mendel Trying to Answer What are the basic patterns in the transmission of traits from parents to offspring Dominant theories at the time 1 Blending inheritance a Claimed that the traits observed in a mother and father blend together to form the traits observed in their offspring As a result an offspring39s traits are intermediate between the mother39s and father39s traits 2 Inheritance of acquired characters a Traits present in parents are modified through use and passed on to their offspring in the modified form The Garden Pea Served as the First Model Organism in Genetics Why did Mendel choose Peas Inexpensive Easy to grow from seed Short generation Large numbers of seeds How did Mendel control Matings Removed the male reproductive organs from a peas and put sperm from one plant onto the female reproductive organs of that plant What traits did Mendel study Seed 0 Shape color Pod 0 Shape color Flower color Flower and pod position Stem length Module 3 Page 8 142 IVIendel39s Experiments with a Single Trait Tuesday ct loer 21 2 14 918 PM The Monohybrid Cross P Only differed in a single trait RR mm l quot wrinkled Took pollen from round seed plants and placed it on the female reproductive organs of wrinkled seed plants 1 The traits did not blend to form an intermediate phenotype F1 2 The genetic determinant for wrinkled seeds seemed to have disappeared where did it go Rr round Dominant and Recessive Traits l In the F2 generation wrinkled trait had reappeared why FZ Mendel coined the terms dominant and recessive to describe the events that had occurred 34 Rounld m wrinkled In modern genetics dominantrecessive refers only to the phenotype observed in individuals carrying two different genetic determinants for a given trait I quotDominantquot not necessarily better or more common Particulate Inheritance Hereditary determinants maintain their integrity from generation to generation Instead of blending together they act as discrete entities or particles Genes Alleles and Genotypes Each of the hereditary traits Mendel was describing was actually a gene The versions of any gene are referred as alleles Alleles found in and particular individual is the genotype which is expressed as the phenotype The Principle of Segregation The two alleles in each gene pair separate into different gametes during formation of eggs and sperm Module 3 Page 9 143 ende39s Experiments with Two Traits Tuesday ctober 212 2 14 956 PM Working with one trait allowed Mendel to establish that blending inheritance does not occur also allowed him to infer that each pea plant had two copies of each gene as well as recognizing the principle of segregation The Dihybrid Cross Mendel got two purebred lines RRYY x rryy First possibility would be that seed shape and seed color genes would separate from eachother and be present independently because the two gametes would be sorted into alleles independently of each other Second possibility would be that seed shape and seed color would be transmitted in gametes together The hypothesis can be called dependent assortment because transmission of one allele would be dependent on the transmission of the other Principle of independent assortment states that alleles of different genes are transmitted independently of one another Module 3 Page 10 144 The Chromosome Theory of Inheritance Tuesday ctober Z12 2 14 956 PM Meiosis Explains Mendel39s Principles The physical separation of alleles during anaphase of meiosis 1 is responsible for Mende39s theory of segregation If the alleles are located on separate Chromosomes they assort independently of one another at meiosis 1 This is the basis of Mendel39s principle of independent assortment Chromosome theory states that Mendel39s rules can be explained by the independent alignment and separation of homologous chromosomes at meiosis 1 Testing the Chromosome Theory Morgan bred flies until he obtained the whiteeyes mutant male Cross bred whiteeye with redeyed female 0 One generation had only white eyed males Sex linkage Males only contain one X and one Y Females contain 2 Xs Gene on the X is Xlinked Gene on the Y is Ylinked Genes on nonsex show autosomal inheritance Module 3 Page 11 161 What Do Genes Do Tuesday ctober 212 2 14 956 PM The knockout function creates mutated alleles and allows researchers to infer the genes function by observing the phenotype of the mutant The OneGene OneEnzyme Hypothesis Beadle and Tatum pioneers of the knockout method exposed a large number of cells to radiation and examined the following mutant cells Found certain cells had inability to synthesize pyridoxine Was due to a defect in a single gene Claimed that each gene contains the information to make an enzyme An Experimental Test of the Hypothesis Mutated cells along a certain metabolic pathway containing 3 enzymes Some cells could not create certain enzymes along the pathway Led biologists to learn that genes contain instructions for making proteins More accurate gene model One Gene One Polypeptide Module 3 Page 12 162 The Central Dogma of Molecular Biology Tuesday ctober 21 ZDM 957 PM We know that DNA is made of4 nitrogenous bases and two helical antiparallel strands This shape is too regular to bring a variety of substrates that would be required to catalyze reaction that would produce proteins How was info in the DNA translated into action The Genetic Code Hypothesis Crick proposed the only function of DNA was as an informationstorage molecule Argued that DNA was similar to Morse code Different combination of bases could specify the 20 amino acids However information encoded in the DNA was not translated into the amino acid sequences of proteins directly RNA as the Intermediary between Genes and Proteins Because DNA was contained in the nucleus and ribosomes needed to assemble proteins were located outside the nucleus there had to be an intermediary molecule mRNA is one of many forms of RNA RNA polymerase allowed for the polymerization of ribonucleotides into RNA strands Dissecting the Central Dogma DNA gt RNA gt Proteins The sequence of bases in the DNA specifies the sequence of bases in the RNA which specifies the sequence of amino acids in a protein The Roles of Transcription and Translation 1 DNA is transcribed to RNA by RNA polymerase Transcription is te process of copying hereditary information in DNA to RNA 2 Messenger RNA is translated to proteins in ribosomes Translation is the process of using the information in nucleic acids to synthesize proteins Linking Genotypes and Phenotypes An organisms genotype is determined by the sequence of bases in its DNA while its phenotype is a product of the proteins it produces Alleles of a gene differ in their DNA sequence As a result the proteins produced by different alleles of the gene ay differ in their amino acid sequence Exceptions of the Central Dogma Many genes code for RNA molecules that do not function as mRNAs they are not translated into proteins In some cases information flows from RNA back to DNA virus39 Module 3 Page 13 163 The Genetic Code Tuesday October 212 ZDM 957 PM How Long is a Word In the Genetic Code 3 letters constitute a codon which codes for one amino acid Code is read in a reading frame quotThe fat cat ate the ratquot A single deletion would result in quotThe atc ata tet her at Occasionally functional proteins can be created if three letters are delted quotTha tca ate the ratquot One start codon that codes for methionine 3 stop codons that do not code for an amino acid Analyzing the Code The Code is redundant 0 All amino acids except methionine and tryptophan are coded by more than one codon The code is unambiguous O A single codon never codes for more than one amino acid The code is nonoverlapping 0 Once the ribosome locks onto the first codon it then reads each separate codon one after another The code is nearly universal 0 With a few minor exceptions all codons specify the same amino acids in all organisms The code is conservative 0 When several codons specify the same amino acid the first two bases in those codons are almost always identical Using the Code 1 Predict the codons and amino acid sequence encoded by a particular DNA sequence 2 Determine the set of mRNA and DNA sequences that would code for a particular sequence of amino acids Module 3 Page 14 164 How Can Mutation Modify Genes and Chromosomes Tuesday ctober 21 2 14 957 PM A mutation is any permanent change in an organism39s DNA It is a modification in a cell39s information archive a change in its genotype Mutation create new alleles Point Mutation Single base change Silent mutation 0 Causes no change in the amino acid sequence I CGC and CGU bot code for arginine Frame shift mutation O Throws codon sequence out of order and alters all subsequent codons I The fat cat ate the rat gt The atc ata tet her at Nonsense mutation 0 Amino acid mutated into stop codon results in early termination of peptide china Mutation are divided into three categories 1 Beneficial a Some mutation increase the fitness of the organism The GgtA mutation is beneficial in beach habitats because it camouflages mice 2 Neutral a If a mutation has no effect on fitness it is termed neutral Silent mutation are usually neutral 3 Deleterious a Mutation that lower overall fitness and are termed harmful or deleterious Chromosome Mutations Aneuploidy fewer than normal amount of chromosome Polyploidy too many of chromosome Inversion When broken segments of chromosome are placed upside down Translocation Broken segments of chromosome are repaired onto the wrong chromosome Deletion Segment of a chromosome is lost Replication Additional copies of a segment are present Module 3 Page 15
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