Cell cycle and cell division Charpter 9 Cell cycle and cell division 2nd Edition

Cell cycle and cell division Overview of the cell cycle Regulation of the cell cycle Cell division

duplicated chromosomes I. Overview of the cell cycle cell growth DNA replication distribution of the duplicated chromosomes cell division

Overview of the cell cycle The cell cycle can be divided into two major phases based on cellular activities, interphase and M phase.

Overview of the cell cycle

M phase includes mitosis and cytokinesis. Overview of the cell cycle M phase includes mitosis and cytokinesis. Interphase is the interval between divisions divided into G1, S and G2 phases.

so the cell cycle includes four phases: G1, S, G2 and M phases. Overview of the cell cycle so the cell cycle includes four phases: G1, S, G2 and M phases.

Overview of the cell cycle Analysis of a large variety of cells has revealed great variability in the lengths of their cell cycle. The four stages of cell cycle, G1 is the most variable. While the total time of S, G2 and M phases is relatively fixed.

Regulation of The cell cycle

Regulation of The cell cycle It is the cell-cycle control system that ensures correct progression through the cell cycle by regulating the cell-cycle machinery. The progression of cells through the division cycle is regulated by extracellular signals from the environment and internal signals.

II. Regulation of The cell cycle Cell cycle control Cell Cycle Checkpoints Cyclins Progression regulatory of cell cycle

Cell cycle control A major cell cycle regulatory point in many types of cells occurs late in G1 and controls progression from G1 to S. In addition to serving as a decision point for monitoring extracellular signals, START is the point at which cell growth is coordinated with DNA replication and cell division.

Cell cycle control

Cell cycle control The proliferation of most animal cells is similarly regulated in the G1 phase of the cell cycle. In particular, a decision point in late G1, called the restriction point in animal cells.

Cell cycle control The proliferation of these cells is triggered by platelet-derived growth factor, which is released from blood platelets during clotting and signals the proliferation of fibroblasts in the vicinity of the injured tissue.

Cell Cycle Checkpoints In most cells, the coordination between different phases of the cell cycle is dependent on a system of checkpoints and feedback controls that prevent entry into the next phase of the cell cycle until the events of the preceding phase have been completed.

Cell Cycle Checkpoints At least, there are three major checkpoints exist within the cell cycle, G1/S checkpoint , G2/M checkpoint and M checkpoint .

Cell Cycle Checkpoints The G1/S checkpoint monitors the cell size achieved following the previous mitosis, and whether the DNA has been damaged.

Role of p53 in G1 arrest induced by DNA damage Cell Cycle Checkpoints Role of p53 in G1 arrest induced by DNA damage

The second checkpoint: G2/M checkpoint Cell Cycle Checkpoints The second checkpoint: G2/M checkpoint Check for: Whether DNA replication is completed? Whether centrosome has finished duplication?

Cell Cycle Checkpoints The final checkpoint, M checkpoint, occurs during mitosis. It monitors the alignment of chromosomes on the mitotic spindle, thus ensuring that a complete set of chromosomes is distributed accurately to the daughter cells.

Cyclins A series of experiments on the oocytes and early embryos of frogs revealed the existence of factors trigger DNA replication and promote a cell into mitosis or meiosis, and showed that entry of a cell into M phase is initiated by a protein kinase called MPF (maturation promoting factor or M phase-promoting factor ).

Cyclins MPF is a dimeric kinase, containing a catalytic subunit and a regulatory subunit. Regulatory subunit triggers the onset of mitosis, while the catalytic subunit transfers phosphate groups from ATP to specific serine(Ser) and threonine (Thr)residues of specific protein substrates.

The structural basis of the cyclin-dependent protein kinases Cyclins The structural basis of the cyclin-dependent protein kinases

Cyclins The regulatory subunit’s concentration rises and falls in a predictable pattern as the cell cycle progresses, so called “cyclin”.

Cyclins The cyclin that helps drive cells into M phase is called M-cyclin, cyclin A, cyclin B etc. Whereas, the cyclin that becomes active toward the end of G1 phase and is responsible for driving the cell into S phase is called G1-cyclin, for example, cyclin C and cyclin D.

Cyclin-Dependent Kinase and its Inhibitors Cyclins Cyclin-Dependent Kinase and its Inhibitors

Cyclins

Progression regulatory of cell cycle Cyclins Progression regulatory of cell cycle A model for cell cycle regulation in fission yeast

Cdk phosphorylation state Cyclins Cdk phosphorylation state Progression through the fission yeast cell cycle requires the phosphorylation and dephosphorylation of critical cdc2 residues

Control of proteolysis by SCF and APC Cyclins Control of proteolysis by SCF and APC

III. Cell division Mitosis Meiosis

Mitosis Mitosis is a process of nuclear division in which replicated DNA molecules of each chromosome are faithfully partitioned into two nuclei. Mitosis is conventionally divided into six stages, prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis.

Mitosis prophase prometaphase metaphase anaphase telophase

Prophase 1.The chromosomal material condenses to form chromosomes. Mitosis Prophase 1.The chromosomal material condenses to form chromosomes. 2.Cytoskeleton is disassembled and mitotic spindle is assembled. 3.Golgi complex and ER fragment. 4.Nuclear envelope disperses.

chromosome condensation Mitosis chromosome condensation

Centromeres and kinetochores Mitosis Centromeres and kinetochores

Mitosis

Formation of the Mitotic Spindle Mitosis Formation of the Mitotic Spindle

The Dissolution of Nuclear Envelope and Mitosis The Dissolution of Nuclear Envelope and the Partitioning of Cytoplasmic Organelles The nuclear membranes are progressively fragmented, initially into flattened, saclike vesicles that surround the condensing chromatin, and eventually into a population of small spherical vesicles that disperse throughout the mitotic cell.

Mitosis Prometaphase The disassembly of the nuclear envelope, which breaks up into small membrane vesicles and dispersed into cytoplasm, marks the start of the second phase of mitosis, prometaphase.

1, mitotic spindle assembly is completed Mitosis 1, mitotic spindle assembly is completed 2, the chromosomes are moved into the center of the cell

Mitosis Microtubule behavior during formation of the metaphase plate

Mitosis Metaphase Once all of the chromosomes has become aligned at the spindle equator, halfway between the two spindle poles, thereby forming the metaphase plate (equatorial plate) .

Mitosis equatorial plate

three types microtubules of the metaphase spindle Mitosis three types microtubules of the metaphase spindle

Mitosis

Anaphase Centromeres split, and sister chromatids separate to form Mitosis Anaphase Centromeres split, and sister chromatids separate to form two daughter chromosomes. 2. The separated chromosomes move to opposite spindle poles.

Mitosis Anaphase can be divided into two stages, anaphase A and anaphase B, and they occur more or less simultaneously. In anaphase A, the kinetochore microtubules are shortened by depolymerization, and the attached chromosomes move poleward. In anaphase B, the polar microtubules are gradually elongated, and the two spindle poles move farther apart.

Mitosis Anaphase A Anaphase B

Microtubules and motors in the spindle Mitosis Microtubules and motors in the spindle In anaphase A, the (1) motors (dyneins) move to the minus ends of kinetochore microtubules and help the sister chromatids separate apart. In anaphase B, (2) motors (kinesins) walk to the plus ends of interpolar microtubules and push the ploes to be far away each other. The (3) motors (dyneins) which is on the astral MT will fix two centrosomes at the poles of the cells.

Mitosis Telophase 1.The two sets of daughter chromosomes cluster at opposite spindle poles and decondense. 2.Nuclear envelope reassembles around each sets of chromosomes cluster. 3.Golgi complex and ER reforms.

Mitosis Cytokinesis The cytoplasm is divided at equator plate to create two daughters, each with one nucleus.

Cytokinesis in animal cells Mitosis Cytokinesis in animal cells the cleavage furrow

Mitosis the contractile ring

Cytokinesis in plant cell Mitosis Cytokinesis in plant cell Cytokinesis in a plant cell is guided by phragmoplast

Meiosis Meiosis Meiosis is a special kind of cell division, which only occurs at some stage of the sexual cell reproduction. Meiosis involves a single round of DNA replication that duplicates the chromosomes, followed by two successive cell divisions, called meiosisⅠand meiosisⅡ.

Meiosis MeiosisⅠ It can be factitiously divided into five stages, prophaseⅠ, prometaphaseⅠ, metaphaseⅠ, anaphaseⅠand telophaseⅠ. ProphaseⅠincludes leptotene, zygotene, pachytene, diplotene and diakinesis five stages.

Meiosis ProphaseⅠ

leptotene The chromosomes condense and become Meiosis leptotene The chromosomes condense and become gradually visible in the light microscope, and revealed to be composed of paired chromatids. Near the end of leptotene, there is a dramatic reorganization so that the telomeres become localized at the inner surface of the nuclear envelope at one side of the nucleus.

Meiosis zygotene

Meiosis synaptonemal complex Electron micrographs indicate that chromosome synapsis is accompanied by the formation of a complex structure called the synaptonemal complex (SC). The SC is a ladderlike structure composed of three parallel bars with many transverse filaments connecting the central element with the two lateral elements.

Meiosis

Meiosis pachytene The end of synapsis marks the end of zygotene and the beginning of pachytene. During this period, the homologues are held closely together along their length by the SC . Recombination nodules form in this period.

Meiosis

Meiosis diplotene Diplotene is recognized by the dissolution of the SC and the tendency of the homologous chromosomes of the bivalents to pull away somewhat from each other.

Meiosis diakinesis During diakinesis the meiotic spindle is assembled, and the chromosomes are prepared for separation. Diakinesis ends with the disappearance of the nucleolus, the breakdown of the nuclear envelope, the terminalization of the crossover, and the movement of the tetrads to the metaphase plate.

Meiosis Separation of homologous chromosomes during meiosis I and separation of chromotids during meiosis II.

Meiosis ---sexual cell reproduction

Summary Overview of the cell cycle Regulation of the cell cycle Cell division