Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The Cell Cycle Cellular and nuclear division Boehm 2014 The Cell Cycle Boehm 2013 Why do cells divide? • To reproduce- unicellular organisms. • To repair dead or damaged cells • To grow and get bigger- multicellular organisms • Cells need to remain small! – Think agar block lab Fig. 12.1 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Boehm 2013 DNA and Cell Division • A dividing cell replicates its DNA, separates the two copies to opposite ends of the cell, and then splits into two daughter cells. Boehm 2013 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • DNA molecules are packaged into chromosomes for cell division. • Human somatic cells (body cells) have 46 chromosomes. • Human gametes (sperm or eggs) have 23 chromosomes, half the number in a somatic cell. • When the cell is not Fig. 12.2 undergoing division, the DNA is in the form of chromatin (unwound DNA). Boehm 2013 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Each duplicated chromosome consists of two sister chromatids which contain identical copies of the chromosome’s DNA . • The region where the strands connect is the centromere. Fig. 12.3 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Boehm 2013 Division of the cell • Mitosis, is followed by division of the cytoplasm, cytokinesis. – These processes take one cell and produce two cells that are the genetic equivalent of the parent. • Each of us inherited 23 chromosomes from each parent: one set in an egg and one set in sperm. • The fertilized egg or zygote underwent trillions of cycles of mitosis and cytokinesis to produce a fully developed multicellular human. Boehm 2013 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Review and reflect • What are 2 reasons why cells must divide? • Do you think all cells continually divide? • Where is DNA located in eukaryotic cells? • How does the original cell compare to the 2 daughter cells? • Any other questions/points unclear? Cell Cycle • The mitotic (M) phase of the cell cycle alternates with the much longer interphase. – The M phase includes mitosis and cytokinesis. – Interphase accounts for 90% of the cell cycle. Fig. 12.4 Boehm 2013 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Interphase • Interphase has three subphases: – the G1 phase • The cell grows and produces organelles – the S phase • the chromosomes are copied – G2 phase • The cell finishes growing and makes sure all organelles are copied. • DNA is in the form of chromatin during interphase- why? Boehm 2013 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Mitosis – For description, mitosis is usually broken into 4 subphases: • • • • Prophase, metaphase, anaphase, and Telophase. Boehm 2013 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Prophase • Chromatin condenses into chromosomes. • The nuclear envelope disappears. • Spindle fibers begin to form from the centrioles. • Spindle fibers attach to the centromere of each Fig. 12.5b chromosome. Boehm 2013 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Metaphase • The spindle fibers push the sister chromatids until they are all arranged at the metaphase plate – An imaginary line between the poles • The centrioles are now at the poles. Fig. 12.5d Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Boehm 2013 Anaphase • The centromeres divide, separating the sister chromatids. • Each is now pulled toward the pole to which it is attached by spindle fibers. Fig. 12.5e Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Boehm 2013 Telophase • Two nuclei begin to form • DNA (chromatin) becomes less tightly coiled. • Cytokinesis, division of the cytoplasm, begins. Fig. 12.5f Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Boehm 2013 Fig. 12.5 left Boehm 2013 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.5 right Boehm 2013 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 12.9 Boehm 2013 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Cytokinesis • Cytokinesis, division of the cytoplasm, typically follows mitosis. • In animals, the first sign of cytokinesis (cleavage) is the appearance of a cleavage furrow in the cell surface near the old metaphase plate. Fig. 12.8a Boehm 2013 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Review and reflect • In what stage of mitosis do chromosomes line up in the middle of the cell? • What do you think happens when cells divide too quickly and out of control? • Any other questions/points unclear?