BIOL 125 Introduction to Biology, Lecture 13 Preview

Lecture 13 Preview Big Ideas: • • • Cells have a hard time taking in nutrients and getting rid of wastes sufficiently if they get too large; so they divide. In the process of division, new cell parts are made, DNA is replicated, the nucleus goes through mitosis (splitting into two bodies carrying identical genetic information), and then the rest of the cell splits by cytokinesis. In eukaryotic cells replicated DNA is carried in sister chromatids, which separate during anaphase of mitosis. So daughter nuclei and cells get identical genetic information. For a moving animation of mitosis, go to: http://www.cellsalive.com/mitosis.htm Overview of Mitotic Cell Division for Growth and Asexual Reproduction During interphase DNA is stretched out and protected by proteins when it is being used as a template for transcription and replication; it is not yet folded into chromosomes. Modern biologists subdivide interphase into G1, S and G2. • • • G1: Gap 1 when chromosomes not visible and DNA not yet replicating; transcription and translation occur; proteins and lipids made and assembled S: SYNTHESIS of DNA by semi-conservative replication G2: Gap 2 when chromosomes not visible and DNA replication is over; organelles assembled Semi-conservative Replication is copying exactly the genetic information carried in a double-stranded DNA molecule, by breaking the weak, H-bonds between complementary bases so that the two strands can separate, and using each strand as a template to build a new complementary strand with nucleotides made in the cell. The result is two identical double-stranded DNA’s--each with one old strand and one new strand, which can each be passed on to a daughter cell when the cell divides. For more background, see pages 230-235. For an animation of replication, see http://www.lewport.wnyric.org/jwanamaker/animations/DNA%20Replication.html Replicated DNA is carefully folded around proteins and condensed into chromosomes for tidy distribution to daughter cells. DNA replication produces chromosomes with 2 side-by-side structures, known as sister chromatids. Sister chromatids carry identical copies of DNA. Every organism has a characteristic set of chromosomes carrying all of its genetic information for making all of its proteins, tRNA's, and rRNA's. The human set (karyotype) consists of 23 pairs of homologous chromosomes (1 from Ma, 1 from Pa). Homologs = look alike chromosomes from 2 parents, carrying information for the same traits Sister chromatids = linear structures joined at a centromere, formed by DNA replication and carrying identical information for traits During mitosis (prophase, metaphase, anaphase, telophase) the replicated chromosomes line up in single file and the sister chromatids are pulled to opposite sides of the cell by cytoskeletal proteins called spindle fibers. Division of the nucleus is followed by division of the rest of the cell, called cytokinesis. Cell division is basically the same for all cells; there are just minor variations. Plant cells form a cell plate instead of a plane of constriction (aka cleavage furrow) during cytokinesis, and prokaryotic cells double their cell parts and then divide them. Mitosis in eukaryotic cells is like fission in prokaryotic cells. In fission prokaryotic cells replicate their circular DNA, grow, and divide into two identical daughter cells. Understanding how life is based on cells and molecules gives us ways to detect and treat diseases. Cancer detection and treatment is developing based on molecular knowledge. Treatment of diseases like AIDS is developing based on molecular knowledge. The use of antibiotics and its problems is based on molecular knowledge.