LESSON 4 THE ORGANELLES OF THE CELL Cell Nucleus o Usually the largest membranous organelle o The cells control center contain all the info to create more than 100 000 proteins found in human body o Most cells have 1 nucleus skeletal muscle cells have multiple mature red blood cells have none o Surrounded by Nuclear envelope double membrane around nucleus Nuclear pores cover 10 of membrane are passages that allow ions RNA very small molecule to enter leave Contents of the cell nucleus o DNA deoxyribonucleic acid All information to build and run organisms Composed of deoxyribonucleic acid subunits nucleotides o Nucleoplasm Fluid contains ions enzymes nucleotides and some o Nuclear matrix RNA Support filaments may be involved in the regulation of genetic activity o Necloli most cells contain several of these dark staining areas Are composed of RNA enzymes and histones Are related to protein production Produces rRNA and ribosomal subunits Prominent in cells that produce lots of proteins liver nerve o Nucleosomes DNA coiled around histones helps organize and pack and muscle cells DNA DNA coiling the degree of coiling can determine the level of compactness o Chromatin loosely coiled DNA cells not dividing Fine filaments makes the nucleus appear grainy o Chromosomes tightly coiled DNA cells dividing Visible under the light microscope DNA contains instructions for every protein in the body Genetic code The chemical language of DNA instructions o Sequence of nitrogenous bases Adenine Thymine Cytosine Guanine o Triplet code sequence of 3 bases that code for an amino acid Gene functional unit of heredity o The DNA containing instructions for one protein o Sequence of triplet codes that dictate the sequence of amino acids in a protein o The nucleus contains chromosomes o Chromsomes contain DNA o DNA stores genetic instructions for proteins o Proteins determine cell structure and function o To produce the proteins the portion of DNA containing the gene for that protein must unwind exposing the nucleotide sequence for RNA production Gene activation requires uncoiling of DNA o The copying of DNA into RNA controlled by Promoter region of DNA that regulates gene transcription Terminator stop signal o Transcription copies instructions in DNA to mRNA Occurs in nucleus RNA polymerase enzyme produces messenger RNA mRNA uses DNA as a template o Translation ribosome reads the genetic code form mRNA Occurs in the cytoplasm Assembles amino acids into polypeptide chain o Protein Processing occurs in the rough ER and Golgi Apparatus to produce proteins Differentiation Note Since all somatic cells have the same DNA o All cells carry complete DNA instructions for all body functions o Cells specialize or differentiate To form tissues liver cells fat cells and neurons o Differentiation depends on which genes are active and which are inactive o All somatic cells contain the same 46 chromosomes The transcription of mRNA o A gene is transcribed to mRNA in three steps Gene activation DNA uncoils and the histone s are removed Start promoter and stop codes on DNA mark location of gene codes for a polypeptide or RNA strand DNA to mRNA the enzyme RNA polymerase transcribes DNA sequence RNA polymerase binds to the promoter start Reads DNA code for gene The enzyme attaches nucleotides that complement the DNA strand to form a strand of messenger RNA mRNA RNA uses the same nitrogenous bases as DNA except thymine is replaced with uracil RNA processing At stop signal mRNA detaches from DNA molecule o Code is edited RNA processing Unnecessary codes introns removed RNA sequence that codes for the protein exons spliced together o Triplet of three nucleotides codon on the mRNA strand represents one amino acid Translation o mRNA moves From the nucleus through a nuclear pore to a ribosome in cytoplasm mRNA binds to ribosomal subunit tRNA delivers amino acids to mRNA o tRNA anticodon binds to mRNA codon 1 mRNA codn translate to 1 amino acid o Enzymes join amno acids with peptide bonds Polypeptide chain has specific sequence of amino acids o At the stop codon components ribosome subunits and mRNA separate and translation ends Two levels of control o Direct through synthesis of Structural proteins cytoskeletal components membrane proteins including receptors Secretions in response to the environment o Indirect control over metabolism Regulation of enzyme synthesis Ex Increase rate of glycolysis by increasing number of enzymes used in glycolysis in cytoplasm Most of a cells life is spent in a nondividing state interphase Body somatic cells divided in three stages o DNA replication duplicates genetic material exactly protein and organelles synthesis also occurs interphase o Mitosis nuclear division divides genetic material equally o Cytokinesis divides cytoplasm and organelles into two daughter cells o NOTE mitosis occurs in somatic cells meiosis occurs to produce sex cells with half the genetic information Interphase the nondividing period o G zero G0 phase specialized cell fucntions only Ex Skeletal muscle cells neurons usually stay in this stage do not divide o G1 phase cell growth organelle duplication protein synthesis o S phase DNA replication and histone synthesis o G2 phase finishes protein synthesis and centriole replication Mitosis divides duplicated DNA into two sets of chromosomes exact copies o DNA coils tightly into chromatids o Chromatids connect at a centromere Stages of mitosis include Prophase Metaphase Anaphase and Telophase NOTE compared to the rest of the phases of the cell cycle mitosis is relatively short Prophase o Nucleoli disappear o Centriole pairs move to cell poles o Microtubules spindle fibers extend between centriole pairs o Nuclear envelope disappears o Spindle fibers attach kinetochore located on chromatids o Chromosomes align in a central plane metaphase plate o Microtubules pull chromosome apart o Daughter chromosomes group near centrioles Metaphase Anaphase Telophase o Nuclear membranes re form o Chromosomes uncoil o Nucleoli reappear o Cell has two nuclei Cytokinesis division of the cytoplasm o Starts in late anaphase and continues throughout Telophase o Cleavage furrow forms around metaphase plate Involves microfilaments and the motor protein myosin o Membrane closes producing daughter cells The mitoic Rate and energy use o Mitoic Rate rate of cell division Cell division requires large amounts of energy ATP Slower mitoic rate means longer cell life expectancy o Exposed cells skin and digestive
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