Biology Test 3 Notes Chapter 11 Cell Communication Cellular Messaging o Cell cell communication is essential for both multicellular and unicellular organisms o Cells communicate with each other via chemical signals Example fight or flight response is triggered by epinephrine Cell communication involves three stages o Reception Communication starts with receptors Divided into three receptors GPCR example of a receptor o Have attachment sites for signal molecule o Ligand gated ion channel o Transduction Cascade of reactions o Response Activate enzyme cytoskeleton to change shape Short and Long distance communication Chapter 12 The cell cycle In unicellular organisms divisions of one cell reproduces the entire organism Multicellular organisms depend on cell division for o Development from a fertilized cell o Growth o Repair Most cell division results in genetically identical daughter cells o Most cell division results in daughter cells with identical genetic information DNA o The exception is meiosis This is a special type of cell division that can produce sperm and egg cells Cellular organization of the genetic material o All the DNA in a cell constitutes the cell s genome A genome consists of a single DNA molecule common in prokaryotic cells or a number of DNA molecules common in eukaryotic cells o DNA molecules are packaged into chromosomes Eukaryotic chromosomes consist of a chromatin a complex DNA and protein that condenses during cell division Somatic cells nonreproductive cells have two sets of chromosomes Gametes reproductive cells sperm and eggs have half as many chromosomes Distribution of chromosomes during eukaryotic cell division as somatic cells o In preparation for cell division DNA is replicated and the chromosomes condense o Each duplicated chromosome has two sister chromatids joined copies of the original chromosome which separate during cell division o The centromere is the narrow waist of the duplicated chromosome where the two chromatids are mostly attached o During cell division the two sister chromatids of each duplicated chromosome separate and move into two nuclei o Once separate the chromatids are called chromosomes Eukaryotic cell division consists of o Mitosis the division of the genetic material in the nucleus o Cytokinesis the division of the cytoplasm Gametes are produced by a variation of cell division called meiosis Meiosis yields nonidentical daughter cells that have only one set of chromosomes half as many as the parent cell The mitotic phase alternates with interphase in the cell cycle o Interphase is about 90 of the cell cycle and can be divided into subphaeses G1 phase first gap S phase synthesis G2 phase second gap The cell grows during all three phase but chromosomes are duplicated only by the S phase Phases of the cell cycle o Mitotic phase mitosis and cytokinesis o Interphase cell growth and copying of chromosomes in preparation for cell division Mitosis is conventionally divide into five phases o Prophase o Prometaphase o Metaphase o Anaphase o Telophase Cytokinesis overlaps the latter stages of mitosis The Mitotic Spindle A closer look o The mitotic spindle is a structure made of microtubules that controls chromosome o In animal cells assembly of spindle microtubules begins in the centrosome the movement during mitosis microtubule organizing center o The centrosomes replicate during interphase forming the two centrosomes that migrate to the opposite ends of the cell during prophase and prometaphase o An aster a radial of short microtubules extends from each centrosome o The spindle includes the centrosomes the spindle microtubules and the asters o During prometaphase some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes o Kinetochores are protein complexes associated with centromeres o At metaphase the chromosomes are all lined up at the metaphase plate an imaginary structure at the midway point between the spindle s two poles o In anaphase sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell o The microtubules shorten by depolymerizing at their kinetochore ends o Nonkinetochore microtubules from opposite poles overlap and push against each other elongating the cell o In telophase genetically identical daughter nuclei form at opposite ends of the cell o Cytokinesis begins during anaphase or telophase and the spindle eventually disassembles Cytokinesis A closer look furrow o In animal cells cytokinesis occurs by a process known as cleavage forming a cleavage o In plant cells a cell plate forms during cytokinesis Binary Fission in Bacteria o Prokaryotes reproduce by a type of cell division called binary fission o In binary fission the chromosome replicates beginning at the origin of replication and the two daughter chromosomes actively move apart o The plasma membrane pinches inward dividing the cell into two The evolution of mitosis o Since prokaryotes evolved before eukaryotes mitosis probably evolved from binary o Certain protists exhibit types of cell division that seem intermediate between binary o Certain protists exhibit types of cell division that seem intermediate between binary fission fission fission and mitosis The eukaryotic cell cycle is regulated by a molecular control system o The frequency of cell division varies with the type of cell o These differences result from regulation at the molecular level o Cancer cells manage to escape the usual controls on the cell cycle The cell cycle control system o The sequential events of the cell cycle are directed by a distinct cell cycle control system which is similar to a clock o The cell cycle control system is regulated by both internal and external controls o The clock has specific checkpoints where the cell cycle stops until a go ahead signal is received o For many cells the G1 checkpoint seems to be the most important o If a cell receives a go ahead signal at the G1 checkpoint it will usually complete the S G2 and M phases and divide o If the cell does not receive the go ahead signal it will exit the cycle switching into a nondividing state called the G0 phase The cell cycle clock cyclins and cyclin dependent kinases o Both molecules are proteins o Two types of regulatory proteins are involved in cell cycle control cyclins and cyclin dependent kinases Cdks o Cdks activity fluctuates during the cell cycle because it is controlled by cyclins so named because their concentrations vary