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
Cell Replication Cell Replication Overview Need for Cell Replication Cell Cycle Controls & Regulators of Cell Replication G0 phase Animal vs Plant Cell Division Cell Death Cell Replication Why Should Cells Replicate? ● Growth ● Repair ● Reproduction Cell Replication Cell Cycle ● ● ● ● Cells grow but eventually their larger size makes it difficult for a cell to maintain itself metabolically When a cell divides the “parent” cell produces two genetically identical “daughter” cells, each of which are more capable of maintaining themselves metabolically The cell cycle also allows for growth and reproduction of the individual Controlled by chemical signals Cell Replication ● Cell Cycle – Interphase ● Day-to-day cell processes take place – G1 ● ● – S ● – Early preparation for cell division Centrioles replicate Chromosomes replicate G2 ● Remaining cell organelles replicate Cell Replication ● Cell Cycle – S ● DNA Synthesis – Deoxyribonucleic Acid ● Nucleotides ● Deoxyribose sugar ● phosphate group and a base ● Bases ● Pyrimidines ● Cytosine ● Thymine ● Purines ● Guanine ● Adenine Cell Replication ● Cell Cycle – S ● DNA Synthesis – – – Double stranded molecule (double helix) Sugar and phosphate backbone Bases of the two strands form hydrogen bonds according to the law of complementary base paring Cell Replication ● Cell Cycle – S ● DNA Synthesis – – – DNA wraps around proteins (histones) to form nucleosomes Long fibers of DNA wrapped around the histones represent the chromatin Chromatin condenses, forming chromosomes, to carefully organize the nucleosomes Cell Replication ● Cell Cycle – S ● DNA Synthesis – – – – DNA is the primary component of a cell's chromosomes Genes-small sections of the chromosome that contain the instructions for synthesizing a specific kind of protein Genome-all the genes in a cell Prior to a cell dividing, each chromosome of the cell replicates to produce two identical chromosomes (sister chromatids) Cell Replication ● Cell Cycle – S ● DNA Synthesis – – Helicase (enzyme) breaks hydrogen bonds between bases of the two strands of a DNA molecule DNA polymerase (enzyme) binds to each of the free strands of the original DNA molecule & makes a new complimentary strand using base pairing rules Cell Replication ● Cell Cycle – S ● DNA Synthesis – – One of the original free strands of the DNA molecule is replicated in a continuous fashion The other free strand is replicated in small segments call Okazaki fragments which are later spliced together Cell Replication ● Cell Cycle – S ● DNA Synthesis – – – Each of the two new doublestranded DNA molecules produced is composed of 1 newly synthesized strand & 1 old strand from the original DNA molecule. Thus, DNA replication is considered semiconservative replication Original DNA sequence is preserved Cell Replication ● Cell Cycle – Interphase ● ● ● – Karyokinesis ● ● – G1 S G2 Division of the nucleus Occurs by mitosis Cytokinesis ● Division of the cytoplasm Cell Replication ● Cell Cycle – Karyokinesis ● ● ● Division of the nucleus Occurs by mitosis Stages of mitosis – – – – Prophase Metaphase Anaphase Telophase Cell Replication Cell Cycle ● Karyokinesis – Prophase ● ● ● Nuclear envelope breaks down Spindle fibers form between centrioles Chromosomes (duplicated) condense and attach to the spindle fibers via centromeres Cell Replication Cell Cycle ● Karyokinesis – Metaphase ● ● Chromosomes are carried by the spindle fibers toward the center of the cell Chromosomes align at the equator of the cell Cell Replication Cell Cycle ● Karyokinesis – Anaphase ● ● ● Centromeres divide Spindle fibers begin to shorten Chromosomes are pulled toward the opposite sides of the cell Cell Replication Cell Cycle ● Karyokinesis – Telophase ● ● ● ● Chromosomes reach opposite poles of the cell Spindle fibers begin to dissolve Nuclear envelope begins to reform around each new set of chromosomes Cytokinesis begins Cell Replication Cell Cycle ● Cytokinesis – Cytoplasm divides – Proceeds by shortening of protein microtubules on the plasma membrane – Cleavage furrow – Begins concurrently during the end of mitosis Cell Replication ● Cell Cycle (Summary) – Interphase ● ● ● – S G2 Karyokinesis ● ● – G1 Division of the nucleus Occurs by mitosis Cytokinesis ● Division of the cytoplasm Cell Replication ● Cell Cycle Controls – 3 Cell Cycle Checkpoints ● ● ● – G1 Checkpoint – Aka, “restriction checkpoint” – No DNA damage – Adequate cell resources – Appropriate cell size G2 Checkpoint – Correct cell size & protein reserves – Chromosomes replicated without damage M Checkpoint – Aka, “spindle checkpoint” – Sister chromotids attached to spindle fibers Prevent genetically mutated cells from replicating Cell Replication ● Cancer & Cell Cycle Regulators – Normal cell cycles are regulated by proteins produced from normal positive cell cycle regulatory genes call protooncogenes – Oncogenes = mutated protooncogenes – When oncogenes occur cancerous cells result – Cancer: uncontrolled cell divisions Cell Replication ● Cancer & Cell Cycle Regulators – Negative cell cycle regulatory genes like the tumor suppressor gene can produce proteins that prevent cancerous cells from replicating – A cell that carries a mutated form of a negative regulator gene might not be able to halt the cell cycle and thus allow uncontrolled cell divisions Cell Replication ● G0 Phase – An “inactive” phase which some cells enter after mitosis rather than going into interphase – External chemical signals trigger some cells to leave G0 for G1 – Others, like nerve & heart cells, never exit G0 Cell Replication Animal vs Plant Cell Division Animal Cell Division is characterized by a cleavage furrow created when actin proteins at the cell’s equator shorten resulting in a pinching of the cell membrane in two Plant Cell Division is characterized by Golgi bodies merging together at the former metaphase plate forming the cell plate. The cell plate grows from the center outwards eventually dividing the cell. New cells walls are made from the merged Golgi body contents Cell Death ● ● ● Cells replication is finite Each cell cycle caused the some of the tips of DNA molecules (telomeres) to be lost to replication When the last of the telomere is lost lysosomes auto-digest the cell and it dies – ● Called apoptosis (normal cell death) Cells which die before their time result in cell death called necrosis