The Somatic Cell Cycle Maternal chromosome Diploid Zygote Diploid Zygote Paternal chromosome MITOSIS MITOSIS Maternal chromosome Diploid organism Diploid organism Paternal chromosome
Int terpha ase The Somatic Cell Cycle Stages of the cell cycle: M Mitosis= period of cell division G 1 Gap 1 =period during cellular interphase from the end of one telophase to the beginning of DNA replication S Synthesis=period of pre-mitotic interphase when DNA is replicated G 2 Gap 2 =period during interphase after completion of DNA replication and before beginning of prophase G 1 and G 2 are called gaps in the cell cycle when no DNA synthesis occurs Cytological observations of the cell cycle are divided into two parts, interphase and mitosis
The Somatic Cell Cycle Mitosis G 2 Phase Cell division G 0 Phase Interphase G 1 Phase SPhase
The Mitotic cell cycle is essential to cell division and growth of an organism Gene Expression and Cell Division conflict: Gene expression requires that chromosomal DNA be uncoiled to allow access to enzymes such as RNA polymerase Cell division requires that chromosomes be tightly coiled to allow orderly migration of chromosomes to daughter cells Gene Expression and Cell Division are separated into Gene Expression and Cell Division are separated into different stages
Life cycle of a sexually reproducing organism correlated with the amount of DNA per cell Amo Fertilization 4 Mitotic divisions Meiotic divisions S A S A S A1 unt of DN NA/cell C values 3 2 1 0 G Z C C A2 Sequence of stages G= Gamete, Z=Zygote, S=Period of DNA synthesis, A=Mitotic Anaphase, C=Somatic Cells, A1=First meiotic anaphase, A2= Second meiotic anaphase G
Mitosis A mechanism by which replicated chromosomes are evenly distributed to two daughter cells. Each of the daughter cells will have the same number and kind of chromosomes as the parent. Stages of mitosis: Interphase Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis
Stages of Mitosis Interphase: Chromosomes are fine diffuse strands and are difficult to see with light microscopy Chromosomes are duplicated The nuclear envelope is intact Prophase Chromosomes condense into distinct structures Chromosomes become visible with light microscopy Prometaphase Further chromosome condensation Nuclear envelope disintegrates Chromosomes become associated with spindle apparatus Sister chromatids remain attached at the centromere, but begin to separate at other regions
Stages of Mitosis Metaphase Sister t chromatid pairs are aligned near the spindle with centromeres still associated The centromeres orient toward opposite pools and are lined up on the metaphase plate Anaphase Sister chromatid pairs separate with one member of each pair moving toward the poles Telophase Chromatids reach opposite poles and poleward movement ceases New nuclear envelope is formed around each diploid chromosome set Chromosomes begin to decondense
Stages of Mitosis Cytokinesis During i mitosis i doubling of all the cytoplasmic organelles also occurs, they are distributed to daughter cells during this stage Central ring of myosin and actin fibers contract to separate the daughter cells In plants the cell plate is laid down in preparation for the rigid cell wall Cytokinesis
Interphase Prophase Prometaphase Prometaphase Metaphase
Anaphase Anaphase Telophase Cytokinesis Cytokinesis
Inactive P Phosphates block active site Dephosphorylation Phospho orylat ion S G 2 M active site P G 1 Cyclin B Breakdown of Cyclin B Buildup of Cyclin B Inactive P34 cdc2 (Protein kinase) = MPF or maturation-promoting factor or mitosis promoting factor
DNA Endoreduplication During Maize Endosperm Development
Attributes of endoreduplicating nuclei Cell cycle consists of alternating G and S phases Chromosome condensation does not occur Eti Entire genome replicates Results in exact doubling of DNA content from one round to another Leads to polytenization of the chromosomes No strand separation No karyokinesis No cytokinesis
S phase S phase G1 G2 G phase Mitosis Endoreduplicating cell cycle Mitotic Cell Cycle polytene Normal
Endoreduplication in Maize Endosperm All l53 lines evaluated had increase DNA content per nucleus Some individual nuclei reached levels of 384C (7 rounds of endoreduplication) Mean DNA content per nucleus in the central region of the endosperm is 90C in some inbred lines 15dap Mean DNA content per nucleus across the entire endosperm is 12.8C at 15dap
Allele-specific DNA degradation during maize endosperm development
Allele l Specific Loss and Methylation ti Test for methylation status indicated that regions undergoing allele loss were hypermethylated Hypthesis Regions of chromatin no longer needed for transcription are targeted/marked for degradation, and the resulting nucleotides form a reserve for use by the developing and germinating embryo and perhaps the emerging seedling