biology_cell-cycle (1).pdf

GENERAL BIOLOGY 1  Cell cycle enables an organism to continue its existence by multiplying itself in controlled and systematic process. All types of cells have the ability to reproduce Cell Division - part of the step of cell cycle CELL CYCLE MITOSIS Active eukaryotic cells...

GENERAL BIOLOGY 1  Cell cycle enables an organism to continue its existence by multiplying itself in controlled and systematic process. All types of cells have the ability to reproduce Cell Division - part of the step of cell cycle CELL CYCLE MITOSIS Active eukaryotic cells undergo a series of phases to make new cells and sustain the demand of a living organism.  M PHASE or MITOSIS PHASE Observable phase under microscope where you see the chromosomes and nuclei  M PHASE or MITOSIS PHASE - very short in comparison to the larger time that the cell is undergoing the interphase INTERPHASE -DNA exist as chromatin rather than chromosomes -divided into 3 phases INTERPHASE -DNA exist as chromatin rather than chromosomes -divided into 3 phases 3 phases of INTERPHASE G1 PHASE S PHASE G2 PHASE G1 PHASE (GAP 1) G1 PHASE -this is the “decision-making step” when the cell decides if it will start the cycle or rest or permanently exit the cell cycle to become a differentiated cell (G0 phase) G0 PHASE G0 PHASE - also known as the resting phase, is the time when the cell is neither dividing nor preparing to divide. During this time, the cell is performing maintenance and its other functions  S PHASE (Synthesis) S PHASE -DNA replication occurs where the nucleus becomes larger with twice the amount of the DNA. G2 PHASE (GAP 2) G2 PHASE -is where final growth and final preparation for mitosis happen M PHASE M PHASE -at the end of M phase, the cell undergoes a physical division via cytokinesis Cytokinesis -is the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells.  It is important to understand that at the start of the cell cycle, a eukaryotic cell is usually diploid (2n). Despite the fact that the DNA content doubles during S phase, the replicated strand is only a duplicate copy of the other, thus termed as chromatids  These are not considered as separate chromosomes. This will be then be divided into each of the daughter cells at the end of M phase or Mitosis MITOSIS Prophase -where chromatin in the nucleus supercoils or condenses to form chromosomes -these chromosomes are then recognizable under the light microscope Chromosomes -condensed chromosome is made up of two identical sister chromatids that are densely packed in a region termed centromere Prophase -this is also the phase when mitotic spindle starts to form on the outside of the nucleus -mitotic spindle involved in this process originates from centrosome Centrosome -compose of paired centrioles that have been duplicated interphase Chromosomes -condensed chromosome is made up of two identical sister chromatids that are densely packed in a region termed centromere Prometaphase -transition stage from prophase to metaphase -nuclear envelope starts to break down allowing the spindle to interact with the chromosomes Metaphase -the equilibrium “central” positioning of the chromosomes means that one of the sister chromatids has an attached spindle fiber on one centrosome and the other sister chromatid is attached too the other centrosome Anaphase -sister chromatid separates and moves apart toward the opposite poles of the cell Anaphase -as the poles move further apart, the cell elongates the spindle Telophase -begins when the chromosomes at the end of each pole decondense -a new nuclear envelope forms and chromosomes further decondense into a chromatin Telophase -also marks the end of cytokinesis -the cell breaks apart at the cleavage furrow -the cell divides into two identical daughter cells, each with its own nucleus and cytoplasm. Importance of Cell Cycle The importance of cell cycle is very evident that the growth and sustainability of multicellular organisms depend on this process MEIOSIS MEIOSIS -special type of cell division which is exclusively for gametes - consists of two set of cell division (meiosis 1 and meiosis 2) DIFFERENCE OF MITOSIS & MEIOSIS 1. Allows the exchange of genetic material between homologous chromosomes when they line up side by side during prophase 1 (synapsis) DIFFERENCE OF MITOSIS & MEIOSIS 2. Independent assortment of chromosomes increases the genetic variability among the daughter cells produce during meiosis DIFFERENCE OF MITOSIS & MEIOSIS This independent assortment, in which the chromosome inherited from either the father or mother can sort into any gamete, produces the potential for tremendous genetic variation. DIFFERENCE OF MITOSIS & MEIOSIS 3. Alleles of the same gene separate during meiosis MEIOSIS Prophase I -create tetrads (XX) by paring homologous chromosomes -this is where crossing over occurs Metaphase I -tetrads line up along the metaphase plate -this phase is when independent assortment takes place Anaphase I -homologous chromosomes move to opposite ends of the cell Telophase I -each number of chromosomes is observed in each of nuclei Cytokinesis -divide the cell membrane so that you have two daughter cells. -these daughter cells are now haploid (n), wherein the number of chromosomes has been halved Prophase II -each of two cells should contain the chromosomes made up of sister chromatids Metaphase II -align the chromosomes along the middle of each of your cells Anaphase II -separate sister chromatids then move one sister chromatid from each chromosome to opposite sides of your cell Telophase II -at this stage, you should now have for nuclei, with two single chromatids in each of the cells Cytokinesis -divide the cell membrane so that you have four daughter cells