Biol 1107 chap 12 notes 03 19 2013 Chapter 12 Genome Character Prokaryotes Eukaryotes Single circular or linear Multiple linear chromosomes Nucleus None Yes Cell division Binary fission Mitosis Cell cycle None Interphase G1 S G2 mitosis Cell cycle the life of a cell from the time it first forms from a dividing parent cell from the time it first forms from a dividing parent call until its own Most cell division except meiosis involves distribution of identical DNA to 2 division into 2 daughter cells daughter cells Genome a cell s endowment of DNA DNA is packaged into chromosomes Chromosomes one very long linear DNA molecule associated with many proteins DNA carries genes the units of info that specify an organism s inherited traits Chromatin entire complex of DNA and proteins that serve as building material for chromosomes When not dividing chromosomes are in form of thin long chromatin fiber After replication chromosomes condense chromatin fibers become densely coiled and folded making chromosomes shorter and thick Somatic cells nonreproductive cells body cells have two sets of chromosomes diploid 2n 46 chromosome 2 sets of 23 in humans Gametes reproductive cells sperm and eggs have half as many chromosomes as somatic cells haploid 1n 1 set of 23 in humans Sister chromatids joined copies of original chromosome Each contain identical DNA molecules Attached to each other by cohesins Attachment known as sister chromatid cohesion Centromere region containing specific DNA sequences where the chromatid is attached most closely to its sister chromatid Part of chromatid on either side of centromere is known as an arm Sister chromatids 12 2 Mitosis division of genetic material in nucleus Cytokinesis division of cytoplasm Zygote fertilized egg Cell cycle can be divided into Mitotic M phase mitosis and cytokinesis shortest part of cell cycle Interphase 90 a cell that is about to divide grows and copies its chromosomes in preparation for cell division G1 phase first gap most variable in time cell doing job in organism S phase only times chromosomes are duplicated G2 phase second gap During these subphases a cell that will eventually divide grows by producing proteins and cytoplasmic organelles The Mitotic Spindle First begins to form during prophase Made up of microtubules and proteins Microtubules of cytoskeleton disassemble to supply material to construct Polymerizes through subunits of protein Tubulin Depolymerizes by losing mitotic spindle subunits Assembly of spindle microtubules start at centrosome Centrosome a subcellular region containing material that functions through cell cycle to organize the cell s microtubules Pair of centrioles are located at center of centrosomes These centrioles are nonessential to cell division together near nucleus During interphase centrosome duplicates to form 2 centrosomes that remain The centrosomes move apart during prophase and prometaphase as spindle microtubules grow out of them on opposite ends of the cell At end of prometaphase there is a centrosome at each pole of the spindle Aster a radical array of short microtubules extending from each centrosome Kinetochores a structure of proteins associated with specific sections of chromosomal DNA at each centromere Each sister chromatid of duplicated chromosomes have a kinetochore Face in opposite directions Some spindle microtubules attach to kinetochores during prometaphase Attachment to a kinetochore makes chromosome move toward whichever pole the kinetochore is on Since there are kinetochores on both sides there is no net movement Metaphase plate term used to describe the plate boundary between the spindle s two poles that centromeres of duplicated chromosomes are found on during metaphase Polar microtubules microtubules not attached to kinetochores Start elongating and by metaphase are overlapping and interacting with other nonkinetechore microtubules from opposite poles of spindle By metaphase microtubules of asters have grown and are in contact with plasma membrane completing the spindle During anaphase separase cleaves the cohesins holding together the sister chromatids of each chromosome Once chromatids separate into chromosomes they move toward opposite ends of cell In a dividing animal cell nonkinetochore microtubules are responsible for elongating the whole cell during anaphase Nonkinetochore microtubules overlap during metaphase Region of overlap reduced as motor proteins walk microtubules away from Cell elongates as microtubules push apart since spindle poles are pushed Microtubules lengthen through addition of tubulin to overlapping ends and one another apart continue to overlap At end of anaphase duplicate groups of chromosomes arrive at opposite ends of an elongated parent cell Nuclei reform during telophase Cytokinesis in animal cells Usually begins during anaphase or telophase Occurs through cleavage in animal cells Cleavage furrow a shallow groove in cell surface near old metaphase plate Contractilve ring of actin microfilaments located on cytoplasmic side of furrow Actin molecules interact with myosin and cause ring to contract Causes cleavage furrow to deepen until parent cell is pinched into 2 separated cells Cytokinesis in plant cells During telophase vesicles from Golgi move along microtubules to middle of cell and coalesce to form a cell plate Cell wall materials carried in vesicles collect in cell plate to make it grow Cell plate enlarges until its surrounding membrane fuses with plasma membrane eukaryotes Results in 2 daughter cells with their own plasma membrane Content of cell plate form a cell wall between the 2 daughter cells Binary fission in bacteria prokaryotes Binary fission a type of reproduction in which cell grows to double its size and then divides to form 2 cells asexual production of single celled Involves mitosis in eukaryotes does not in prokaryotes Bacteria genes are carried on a bacterial chromosome that consists of circular DNA and associated proteins Origin of replication location at which DNA of bacterial chromosome begins to replicate in order to form 2 origins As chromosome replicates one origin moves toward opposite ends of cell Cell elongates as chromosome is replicating After replication a bacterium reaches about 2x its initial size Plasma membrane pinches inward and divides parent cell into 2 daughter cells A protein resembling actin functions in bacterial chromosomal movement A protein related to tubulin helps pinch plasma membrane inward