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applied biology: cell cycle

For a cell to divide requires 4 events:
- signal reproductive →
internal or external - DNA replication
- segregation → duplicated DNA is divided into daughter cells
- cytokinesis → daughter cells are separated

I prokaryotes divide to division, environmental conditions determine the rate of reproduction and the playing time. In DNA replication, usually contained in a single chromosome in circular form, are important regions gold (the origin of replication) and b (end of replication). The DNA is replicated at the center of the cell and then the gold regions at the poles move with increasing the plasma membrane. The cytokinesis begins with a constriction of the plasma membrane with a ring, is synthesized new cell wall material. The

eukaryotes divide to mitosis or meiosis (only gametes). Eukaryotic cells do not divide continuously or for environmental condition and contain more chromosomes and organelles in the cytoplasm.
The set of events that make up life is said eukaryotic cell cycle. Macrophases are 2: interphase and mitosis (M). The interphase consists of three phases: stability phone (G1), DNA synthesis (S) and period between synthesis and division (G2).
The enzyme that causes the shift in M \u200b\u200bis said cyclin-dependent kinase or Cdk activated by a cyclin. The cell proceeds with duplication once passed the restriction point in G1 R . retinoblastoma protein (RB) inhibits the cycle, but if there shall be phosphorylated S. During the duplication

chromatin condenses to form chromosomes once duplicates are two sister chromatids together in a centromere protein that coesina and coated condense.
Chromatin is the DNA sequence folded into nucleosomes, ie 4 pairs of DNA wrapped around histones and locked from the outside ' histone H1.
During DNA replication the centrosomes (centrioles pairs, starting points of the microtubules) reach the opposite poles of the nucleus.
The 6 phases of mitosis are: prophase in chromatids are still united and formed the kinetochores, the sites where the chromatids are attached to the spindle (web of microtubules). In prometaphase lìinvolucro nuclear dissolves and is attached to the spindle. In the metaphase chromatids are divided into chromosomes and are arranged in equatorial plate the nucleus. In ' anaphase the daughter chromosomes move to opposite poles, and then in the telophase chromatin despiralizza, nuclei are formed and begin cytokinesis.
In cytokinesis the actin and myosin form a contractile ring that separates the cytoplasm, the organelles are separated inside. The

mitosis can be repeated indefinite times, while meiosis results in only 4 daughter cells.
Meiosis is used to produce a gamete that contains a karyotype half (haploid ) compared to the cell zygote . The zygote is the union of two gametes with two different chromosome pairs (diploid ).

During meiosis the nucelo divides twice, but the DNA is duplicated only once. The first meiotic division (meiosis I ) halves the number of chromosomes and the chromosomes migrate to the poles of the cell. In prophase I , the chromosomes (that year, the same genes) are displayed along the major axis. The adjacent chromatids form a chiasm that allows you to exchange genetic material from one chromatid to another ( crossing over). This further increases the genetic variability and allows an individual to be able to transmit genes that may be two different chromosomes.
At the end of meiosis II means 4 daughter cells stateless.