CELL CYCLE, CELL DIVISION Human histology CELL CYCLE • The cell cycle is the period of a cell's existence from the moment of its formation by division of the mother cell to its own division or death. • The eukaryotic cell cycle consists of two periods: • The period of cell growth, called "interphase", during which the synthesis of DNA and protein takes place and preparation for cell division is carried out. • The period of cell division, called "phase M" (mitosis). INTERPHASE • Interphase consists of several periods: • G1-phase (from English gap - gap), or the phase of initial growth, during which there is a synthesis of mRNA, proteins, other cellular components; • S-phase (from the English synthesis - synthesis), during which replication of the DNA of the cell nucleus takes place, the doubling of centrioles also occurs (if they are, of course). • G2 phase, during which there is preparation for mitosis. INTERPHASE • G1 follows the telophase of mitosis. During this phase, the cell synthesizes RNA and proteins. The duration of the phase is from several hours to several days. • G2 cells can exit the cycle and are in the G0 phase. In the G0 phase, cells begin to differentiate. • S. In the S phase, protein synthesis continues in the cell, DNA replication occurs, centrioles are separated. In most cells, the S phase lasts 8-12 hours. • G2. In the G2 phase, the synthesis of RNA and protein continues (for example, the synthesis of tubulin for the microtubules of the mitotic spindle). Daughter centrioles reach the size of definitive organelles.This phase lasts 2-4 hours. CELL DIVISION • Differentiated cells that no longer divide may lack the G1 phase in the cell cycle. Such cells are in the G0 resting phase. • The period of cell division (phase M) includes two stages: • karyokinesis (division of the cell nucleus); • cytokinesis (division of the cytoplasm). MITOSIS • During mitosis, the nucleus (karyokinesis) and the cytoplasm (cytokinesis) divide. Phases of mitosis: prophase, prometaphase, metaphase, anaphase, telophase. • Prophase. Each chromosome consists of two sister chromatids connected by a centromere, the nucleolus disappears. The centrioles organize the mitotic spindle. A pair of centrioles is part of the mitotic center, from which microtubules extend radially. First, mitotic centers are located near the nuclear membrane, and then diverge, and a bipolar mitotic spindle is formed. • This process involves pole microtubules interacting with each other as they elongate. MITOSIS • Prometaphase. The nuclear envelope disintegrates into small fragments. In the area of centromeres, kinetochores appear, functioning as centers of organization of kinetochore microtubules. The departure of kinetochores from each chromosome in both directions and their interaction with the pole microtubules of the mitotic spindle is the reason for the movement of chromosomes. • Metaphase. Chromosomes are located at the spindle equator. A metaphase plate is formed, in which each chromosome is held by a pair of kinetochores and associated kinetochore microtubules directed to the opposite poles of the mitotic spindle. MITOSIS • Anaphase is the divergence of daughter chromosomes to the poles of the mitotic spindle at a rate of 1 μm / min. • Telophase. Chromatids approach the poles, kinetochore microtubules disappear, and the polar ones continue to elongate. A nuclear envelope is formed, a nucleolus appears. MITOSIS MEIOSIS • During meiosis, haploid gametes are formed. • The first division of meiosis (prophase I, metaphase I, anaphase I and telophase I) is reduction. • The second division of meiosis - equational proceeds in the same way as mitosis (prophase II, metaphase II, anaphase II and telophase), but much faster. • Daughter cells receive a haploid set of chromosomes (22 autosomes and one sex chromosome). TASK • Make a short summary of the lesson in your notebooks, answering the questions, and send their photos to my private messages. • Cell theory: basic theses. • The main organelles of the cell: function and structure. • Cell membrane: structure, transport across the membrane. • The cell cycle. NEXT TIME • Seminar about first two topics. • Questions are uploaded to TEAMS. • Format of seminar: orally test and written test.