chapter 10 notes
chapter 10 notes BS 161
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This 9 page Class Notes was uploaded by Elisa Chaparro on Monday October 26, 2015. The Class Notes belongs to BS 161 at Michigan State University taught by j. urbance in Summer 2015. Since its upload, it has received 78 views. For similar materials see Cell and molecular biology in Biology at Michigan State University.
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Date Created: 10/26/15
Chapter 10 101Bacterial cell division s Clonal Binary ssion divides Bacterial Cells in Two Binary ssion Asexual reproduction by division of one cell or body into two equal or nearly equal parts Most bacteria have a genome game up of a single circular DNA molecule It is packaged very tightly to t into the cell inside the Nucleoid it is not surrounded by a membrane The compaction and organization of the nuceoid is achieved by a class of proteins called structural maintenance of chromosome SMC proteins These are ancient proteins that have diversi es over evolutionary time to ful ll a variety of roles related to DNA organization in different lineages eukaryotic cohesion and condensing proteins Bidirectional DNA replication 1 Prior to cell division the bacterial DNA molecule replicates The replication of the doublestranded circular DNA molecule that constitutes the genome of a bacterium begins at a speci c site called the origin of replication green area 2 The replication enzymes move out in both directions from that site and make copies of each strand in the DNA duplex The enzymes continue until they meet at another speci c site the terminus of replication red area 3 As the DNA is replicated the cell elongates and the DNA is partitioned in the cell such that the origins are at the 14 and 34 positions in the cell and the termini are oriented toward the middle of the cell 4 Separation then begins in which new membrane and cell wall material begin to grow and form a septum at approximately the midpoint of the cell A protein molecule caed FtsZ orange dots facilitates this process 5 When the septum is complete the cell pinches in two and two daughter cells are formed each containing a bacterial DNA molecule Proteins control chromosome partitioning and septum formation During replication rst the origin and the rest of the newly replicated chromosomes are moved to opposite ends of the cell as two new nuceoids are assembled The nal event of replication is decatenation untangling of the nal replication products The force behind chromosome segregation has been attributed to DNA replication itself to transcription and to the polumerization of actinlike molecules Septum a wall between two cavities Septation n prokaryotic cell division the formation of a septum where new cell membrane and cell wall is formed to separate the two daughter cells This usually occurs at the midpoint of the cell It begins with the formation of a ring composed fo many copies of the protein FtsZ A number of other proteins then accumulate including one embedded in the membrane This structure contracts inward radially until the cell divides into two new cells The FtsZ protein is found in prokaryotes including archaea and shows similarities to eukaryotic tubulin However the roles are different STUDY FIGURE 103 Most bacteria divide by binary ssion with DNA replication and segregation occurring simultaneously This process involves active partitioning of the single bacterial chromosome and positioning of the site of septation Would binary ssion work as well if bacgteria had many chromosomes 0 The process of binary ssion would likely not work as well if they had many chromosomes 102 Eukaryotes have linear chromosomes Chromosome number varies among species Most eukaryotes have 10 to 50 chromosomes in their body cells horses have 64 dogs have 78 and mice 40 Human cells each have 46 chromosomes consisting of 23 nearly identical paIrs Monosomy when human embryos missing one chromosome do not long survive Trisomy is Having an extra copy of any one chromosome a condition that is usually fatal except where the smallest chromosomes are involved Haploid n geneticists count the number of chromosomes necessary to de ne an organism Diploid 2n humans its 46 twice the haploid number they re ect the equal genetic contribution that each parent makes to offspring The maternal and paternal chromosomes are referred to as being homologous and each one of the pair is called a homologue Homologous refers to similar structures that have the same evolutionary orIgIn Refers to a par of the same kind of chromosome in a diploid cell Homologueone of a pair of chromosomes of the same kind located in a diploid cell once copy of each pair of homologues comes from each gamete that formed the zygote Eukaryotic chromosomes have complex structure Compositions of chromatin Chromosomes are composed of chromatin a complex of DNA and protein 40 DNA and 60 protein A signi cant amount of RNA is also associated with chromosomes because chromosomes are the sites of RNA synthesis Each chromosome contains a single DNA molecules that runs uninterrupted through the chromosomes entire length A typical human chromosome contains about 140 million nucleotides in its DNA Heterochromatin a domain of chromatin not expressed Euchromatin domain of chromatin that is expressed Chromosome coiling 1DNA strand from a single chromosome is about 5 cm 2 inches long 2Every 200 nucleotides the DNA duplex double strand is coiled around a core of 8 histone proteins any of 8 proteins with an overall positive charge that associate in a complex It is held by its negatively charged phosphate groups forming a nucleosome 3the nucleosomes are further coiled into a solenoid 4the solenoid is then organized into chromatin loops in domain up scaffold proteins 5 The nal organization of the chromosome is unknown but it involves further looping into rosetes around a preexisting scaffolding of protein This process if aided by a complex of proteins called condensin which are evolutionarily related to the bacterial SMC that compacts the nucleoid 6 Further condensation occurs when the cell divides Histones are positively charged because of an abundance of the casic amino acids arginine and lysine Histone cores act as 39magnetic formsquot that promote and guide the coiling of DNA Chromosome vary in size staining properties the location of the centromere and the positions of constricted regions along the arms Karyotype the particular array of chromosomes an individual organism possessesex Female or male normal and abnormal Chromosome replication Each chromosome is composed of a single DNA molecule that is arranged into the 30nm ber Cohesin a protein complex that hold sister chromatids together during cell division The loss of cohesion at the centromere allows the anaphase movement of chromosomes One chromosome is composed of two sister chromatids The difference between homologous chromosomes and sister chromatids homologous chromosomes are the maternal and paternal copies of the same chromosome Sister chromatids are the two replicas of a single chromosome held together at the centromeres by cohesion proteins after DNA replication The cell keeps the products of replication together until the moment of chromosome segregation ensuring that one copy of each chromosome goes to each daughter cell The separation of sister chromatids is the key event in the mitotic process ls chromosome number related to organismal complexity o No silkworms have 56 and human have 46 103 The eukaryotic cell cycle is complex and highly organized The cell cycle is divided into ve phases Cell cycle the repeating sequence of growth and division through which cells pass each generation o It is depicted as a circle The rst gap phase 61 involves growth and preparation for DNA synthesis 0 During S phase a copy of the genome is synthesized o The second gap phase 62 prepares the cell for mitosis 61 S and 62 are called interphase During this phase microtubules begin to reorganize to form a spindle o M phase mitosis where replicated chromosomes are partitioned in prophase prometaphase metaphase anaphase and telophase Cytokinesis divides the cell into two cells with identical genomes The phases are based on key events of genome duplication chromosome segregation and distribution of cytoplasm Mitosis is the phase of the cell in which the spindle apparatus assembles prophase binds to the chromosomesprometaphasemetaphase and moves the sister chromatids apart anaphase Mitosis is the essential step in the separation of the two daughter genomes Cytokinesis is the phase of the cell cycle when the cytoplasm divides creating two daughter cells In animal cells the microtubule spindle helps position a contracting ring of actin that constricts to pinch the cell in two In cells with a cell wall like plants and fungi a plate forms between the dividing cells The duration of the cell cycle varies depending on cell type Animal embryos under 20 min Mammalian cell 24 hours beause mature cells require time to grow their cycles are much longer than those of embryonic tissue Human liver has cell cycles lasting more than a year lnterphase requires most of the time M phase is only about an hour Most of the variation in the length of the cell cycle between organism or cell types occurs in the 61 phase Cells often pause in 61 before DNA replication and enter a resting state called GO the stage of the cell cycle occupied by cells that are not actively dividing Cells can remain in this phase for days to years before resuming cell division When during the cycle is a cell irreversibly commited to dividing o The rst irreversible step is the commitment to DNA replication During interphase cells grow and prepare for Mitosis lnterphase includes the synthesis and gap phases of the cell cycle 61 major portion of growth 5 each chromosome replicated to produce two sister chromatids which remain attached to each other at the centromere Chapter 10 learn smart Part 1 Sister chromatids are two identical copies of chromosome connected by a centromere whereas homologous chromosomes are the paternal and maternal copies of a particular chromosome The cells of most eukaryotes have between 10 and 50 chromosomes Chromatin the structural component of eukaryotic chromosomes is composed of a complex of DNA and protein Heterochromatin not genetically expressed Euchromatin genetically expressed Cell cycle the sequence of growth replication and division that produces new cells When the cells of an organism carry two sets of chromosomes that organism is said to be diploid MPF is sensitive to chemicals that affect o Damage DNA 0 Delay replication DNA bers found within each chromosome are doublestranded If an organism is diploid the two members of a pair of chromosomes are called homologues The haploid number of chromosomes for humans is 23 The diploid number is 46 In eukaryotic chromosomes DNA is wound around proteins called histones and together this complex is called a nucleosome Nucleosomes are further coiled into the solenoid which is then organized into looped domains Active MPF further activates itos own activating phosphatase This is an example of a positive feedback mechanism Monosomy missing a copy of a chromosome Trisomy having an extra copy of a chromosome Chromosome features 0 Staining properties 0 Location of the centromere 0 Length of two arms 0 Size Haploid means that cells contain one set of chromosomes The Cdkcyclin complex is also called mitosispromoting factor Two forms of cyclin have been found in organisms Identify the peak times of these proteins 0 625 boundary o 62 m boundary Which of the following phases occurs after the replication of DNA and before the start of mitosis o Gap 2 phase A nucleosome is a complex of DNA and histone proteins Proteins describe cyclins that are produced at different times in the cell cycle of sea urchin embryos Condensation of chromosomes is initiated in 62 phase and continues until the end of the prophase stage of mitosis The cell determines whether or not to divide at the 61 S checkpoint During interphase of the cell cycle the cell grows and copies chromosomes APC marks the protein securing for destruction thus triggering the separation of the sister chromatids Cytokinesis is the division of the cytoplasm to produce two distinct cells called daughter cells GO is the resting phase An unreplicated chromosome consists of 1 double stranded DNA molecule Checkpoints that occur in the cell cycle of eukaryotic cells are critical regulatory points in cell division The primary molecular mechanism of cell cycle control is which of the following 0 Phosphorylation of proteins Typically a dividing mammalian cell completes its cell cycle in about 24 hours Cdks are enzymes which regulate proteins within the cell cycle via phosphorylation Consider the overall cell cycle of a human cell during the different phases of mitosis chromatids are separated and sorted so that each daughter cell receives 46 chromosomes Maximum compaction of the chromosomes occurs when chromatin bers are coiled around a scaffold of proteins like the bers on a wire brush Centrioles are replicated in 62 Centromeres occur at a speci c location along a chromosome Replication of genetic material and separation of sister chromatids are irreversible points in the cell cycle Soleinoid ber diameter is 30nm The cell cycle of multicellular eukaryotes is regulated by Cdks and external signals The coiling of DNA around histone cores is the result of Electrostatic attraction between the negatively charges DNA molecule and the positively charged histone core ln actively dividing cells the g1g2 and 5 phases are collectively known as interphase Spindle checkpoint ensures that all chromosomes are attached to the spindle Both the g1 and g2 checkpoints check for damage in DNA A karyotype is an individual39s chromosomes which have been arranged by length shape and the location of the centromere Replicated chromosomes consist of two identical DNA molecules held together by cohesins The Cdk enzymes controls progression through the checkpoints in the cell cycle Replication of each chromosome and its centromere takes place during which phase of the cell cycle S After a chromosome is replicated how do we refer to it and its chromatids one chromosome made of two sister chromatids Cdc2 is the gene necessary for cells to commit to DNA synthesis and to mitosis Variation in the length of the cell cycle varies among tissue types due to the time spent in GO Which of the following is a condition that will typically lead to a cell entering the G phase when cells are deprived of the appropriate growth factors The number of chromosomes in eukaryotic cells varies considerably between different species The centromere contains repeated DNA sequences that can bind speci c protein These proteins form the kinetochore which is shaped like a disk Mitosis promoting factor is cyclin plus cdc2 protein Chapter 10 Learn Smart Part 2 Bacterial cell division produces two genetically identical daughter cells Bacterial cells divide to produce new cells for population growth and reproduction Cell division in bacterial and eukaryotic cells produces genetically identical cells Events in the order they occur during the segregation of bacterial chromosomes during binary division 0 Replication begins at the origin of replication 0 Origins move to the opposite ends of the cell 0 The entire replicated chromosomes move to the opposite ends of the cell 0 Chromosomes are untangled Cytokinesis incvolves the formation of cleavage furrow in animal cells and a cell plate in plant cells Which is the rst stage of mitosis prophase Binary ssion is the means by which bacterial cells perform cell division The ftsZ protein is necessary for bacterial cells to perform which of the following activities separation and cell division Binary ssion steps 0 The bacterial DNA molecule replicates o The cell elongates and the DNA is partitioned such that the origins are at the 14 and 34 positions in the cell 0 Separation begins 0 The cell pinches in two forming two daughter cells During cytokinesis in plants the newly formed cell plate is coated with cellulose Mechanisms that have been proposed to explain the force that moves chromosomes to the equator of the cell 0 Motor proteins located at the kinetochore and poles of the cell pulling on microtubules 0 Assembly and disassembly of microtubules During anaphase two forms of movement takes place simultaneously and as a result sister chromatids are pulled towards opposite poles of the cell Two forms of movement are commonly referred to as Anaphase A and B The spindle apparatus is formed during prophase During metaphase kinetochore microtubules move chromosomes to the middle of the cell where they are lined up on the metaphase plate During telophase the changes made to the cell during prophase are reversed The metaphase plate is a plane halfway between the poles along which chromosomes align during mitosis Cytokinesis in plant cells involves the formation of an internal membrane called a cell plate which starts in the interior of the cell and extends out to the plasma membrane The spindle apparatus is broken down during which of the following phases of mitosis Even thought centrioles are absent in plants the cells can still form a microtubule spindle apparatus between opposite cellular poles During Anaphase B microtubules slide past each other pulling the poles anchored to them away from the center of the cell At the same time chromosomes are also pulled apart because a different set of microtubules attaches the chromosomes to the poles ln prophase the centrioles start to move apart forming an axis of spindle bers between them The group of proteins involved in the compaction and organization of bacterial DNA in the nucleoid is called structural maintenance of chromosome or SMC proteins The separation of sister chromatids during anaphase which results in the partitioning of genetic material is the shortest event in all the stages of mitosis Nuclear division occurs after mitosis in most fungi and some protists During anaphase a sister chromatids are pulled towards opposite poles as their kinetochore microtubules which are attached to the poles are shortened Telophase is the nal phase of mitosis Anaphase is the shortest phase in mitosis The bacterial genome consists of a single loop of DNA located in the Nucleoid Binary ssion involves replication and partitioning of chromosomes for cell division During the segregation of the duplicated bacterial chromosome the origins of replication move towards the opposite ends of the cell rst Metaphase is considered a checkpoint phase for the preparation of sister chromatids for cell division Cytokinesis is the phase of the cell cycle when the cell divides into two equal halves In animal cells the cleavage furrow pinches the cell until it is divided in two Chromosomes continue to condense throughout the prophase stage of mitosis During cell division the two complete daughter cells are produced after the cell undergoes cytokinesis The key event in anaphase is the removal of cohesion proteins from the centromeres of sister chromatids During telophase in mitosis the nuclear envelope reforms to produce two separate nuclei During prophase a bridge of microtubules forms between centrioles that have reached opposite poles of the cell Kinetochore microtubules attach to and separate the chromosomes during cell division The aster is thought to brace the centrioles against the membrane The pairs of sister chromatids align themselves in a single row along a plane halfway between the poles during metaphase In the cell cycle the rst part of the M phase is known as mitosis During telophase chromosomes uncoil to allow for gene expression to resume Mitosis occurs as a continuous process During anaphase of the cell cycle the centromeres of sister chromatids split apart allowing sister chromatids to move away from each other Asters are not present in plant cells Mitosis occurs in the order of Prophase Prometaphase metaphase anaphase and telophase The nuclear envelope breaks down during the formation of the spindle apparatus During cell division in both bacterial cells and eukaryotic cells genetic information is replicated and segregated and the contents of the cell are divided between the daughter cells During prometaphase which protein complex on each sister chromatid attaches to the spindle Cell division takes place after mitosis In most fungi and some protists the nuclear membrane does not break down before mitosis therefore mitosis takes place within the nucleus After the centrioles have reaches opposite poles of the cells a bridge of microtubules forms between them During Anaphase B microtubules slide past each other pulling the poles anchored to them away from the center of the cell At the same time chromosomes are also pulled apart because a different set of microtubules attaches the chromosomes to the poles Plant cells form a spindle apparatus during division but do not utilize centrioles in the formation of said spindle apparatus