Cells and Organelles

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  • Created by: jessica
  • Created on: 22-04-13 13:44
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  • Cells and Organelles
    • Prokaryotes
      • 2 types of prokaryotes bacteria and archaeons
        • have nucleoid where supercoiled double stranded DNA is located
          • DNA in operons, one regulatory section for multiple genes to be switched on at the same time
        • bacteria have ribosomes free in the cytoplasm with sedimentation constant of 70S
        • bacteria have storage granules which are store of carbon with either glycogen or polybeta hydroxybutyrate
        • mesosomes are aggregates of tubular membrane structures in bacteria
        • bacterial cell wall resists internal osmotic pressure and prevents bursting in hypotonic environments, determines cell structure
          • peptidoglycan is the main component, made of repeating units of n-acetyl glucosamine and n-acetyl muramic acid in a beta 1-4 linkage
        • bacteria have 1000-6000 genes
      • have periplasmic space and cell wall, plasma membrane and nucleoid
      • capsule is a layer of polysaccharides and glycoproteins creating a slime surrounding the bacteria
      • various cell structures, coccus, bacillus, vibrio, filamentous, endospores
    • Diversity of microorganisms
      • gram staining reaction separates bacteria into Gram +ve and -ve types, depends on ability of organism to retain crystal violet after alcohol exposure
        • alcohol decolourises Gram-ve bacteria and appears pink, gram +ve bacteria looks purple
        • gram +ve cell wall is 40-90% peptidoglycan by weight creates laminate type structure. also contains lipoteichoic acid and teichoic acid, anchors peptidoglycan layer to the phospholipid bilayer
        • teichoic acids have a varying r group with negative charge, have a role in regulating immune response and adhesion
      • Acidophiles, alkophiles, aerobes, anaerobes, psychrophiles, psychotrophs, mesophiles, thermophiles, hyperthermophiles, halophiles are all types of microorgansim classification
    • Eukaryotes
      • can be uni and multicellular, with linear DNA molecules packaged as chromosomes in a nucleus
        • unicellular are the most complex eukaryotic cells as they carry out all metabolic functions
      • membranes are composed of phospholipids and proteins, asymmetric with two faces
      • membrane functions to regulate transport of nutrients into the cell and to take waste out of the cell
        • also maintains proper chemical concentrations inside the cell and provides a site for chemical reactions to take place
      • cytosol contains cytoskeleton, polyribosomes, metabolic enzymes
      • cytoskeleton is made of filaments and fine tubules
        • fine tubules are microtubules, microfilaments and intermediate filaments
          • microfilaments are made of actin and have some elasticity
            • F actin double helices are made from G actin subunits, fibres can contract and expand by further polymerization and depolymerization by ATP
            • have roles in microvilli, cell cortex, adherens belt, filopodia, lamellipodium, cell cortex, stress fibres, and contractile ring
          • microtubules are made of alphabeta tubulin dimers
            • form track ways in cells along which motor proteins drag vesicles and other organelles, have a role in positioning of chromatids in cell division
          • intermediate filaments are 10nm thick and have a role in maintaining cell shape and tissue integrity
        • involved in cell movement, cell division, cell shape and intracellular trafficking of organelles and the coordinated movement of tissue
      • two major types of motor protein, dyenin and kinesin
        • dyenin carries secretory vesicles, golgi ER, mitochondria towards the positive end
        • kinesin carries endosomes, lysosomes and pigment granules to the negative end
    • Diversity of cell types
      • stem cells are directed to differentiate by growth factors
        • major growth transcription factors Oct4, Sox2, Nanog
      • differentiation produces different cell types
        • fully differentiated cells have limited/no capacity to divide
      • totipotent stem cells, pluripotent stem cells
      • apoptosis is programmed cell death, has roles in embryogenesis, tissue homeostasis, damage limitation, control and functioning of the immune system
        • 2 main gene families controlling it BCL2 Caspase
        • very quick process, cell swallowed up by macrophages
        • too little apoptosis = cancer, autoimmune disease, prolonged viral infection
        • too much apoptosis = neurodegenerative disorders, autoimmune disease, additional tissue damage and progression of AIDS
      • cell surface recptors belong to four major classes either g protein coupled receptors, tyrosine-kinase linked receptors, ion channel receptors and receptors with intrinsic enzymatic activity
      • epithelia form sheet like layers covering extenal and internal surfaces of organs
    • Cells in tissues
      • basal lamina is a specialized region of extracellular matrix that provides a solid substratum for epithelial cells to connect to
      • different types of cellular junctions
        • tight junction, adherens junctions, gap junction, desmosome
          • gap junctions are homophilic interactions that form a connexon hemichannel.
            • connexon hemichannels provide chemical and electrical coupling between adjacent cells, permitting movement of ions and small molecules
              • important for intercellular signalling
          • adherens junctions connect contractile bundles of actin and myosin filaments that run parallel to the plasma membrane
            • allows contraction of epithelial layers
          • desmosome are button like contact points that rivet cells together
            • connect intermeiate filament networks of adjacent cells, anchor cytoskeleton to plasma membrane, connecting cytoskeleton of surrounding cells giving strength
      • extracellular matrix is a fibrous network of proteins and polysaccharides that fills the spaces between cells
        • holds cells and tissues together, plays a role in embryogenesis, wound healing and cell migration
      • cells aggregate to form tissues, use cell adhesion molecules
        • four main classes of adhesion molecules
          • homophilic interactions which use cadherins and immunoglobulin superfamilies
          • heterophilic interactions which use integrins and selectins
    • Secretory Pathway
      • most cytosolic transmembrane proteins have an N terminal signal sequence and an internal topogenic sequence
      • regulated secretory proteins are produced at certain times/triggered to produce
      • constitutive secretory proteins are those that are always produced
      • multipass transmembrane proteins have multiple topogenic sequences
      • 2 secretory pathways for proteins
      • some proteins when inserted into the ER membrane are transferred to a GPI anchor
      • protein glycosylation occurs in the ER and Golgi and most secretory proteins go through this process
        • 2 types of glycosylation, N linked and O linked
          • N linked is more comlex
            • Addition of preformed branched precursor in the ER, which has been synthesized on the dolichol carrier
            • occurs in the rough ER at specific residues
              • Target sequences are Asn-X-Ser, Asn-X-Thr
          • O linked is just the addition of simple linear molecules
      • different vesicles to transport molecules to different locations
        • use snare proteins to help polymerization of vesicle membrane
    • Targeting proteins to organelles
      • cytosolic chaperones deliver proteins to channel linked receptors in the mitochondrial membrane
      • Matrix targeting sequences are found at the amino terminus
      • chaperones can either prevent the protein from folding or can help the protein fold
      • proteins targeted to organelles have uptake target sequences
        • cleaved upon entry to organelle, different sequences for different organelles
      • entry into mitochondria requires uptake target sequence and ATP hydrolysis at several stages
      • Three different pathways for proteins to take into the membrane
        • Path A for proteins with matrix targeting sequence and internal stop transfer sequence
        • Path B for proteinswith a matrix targeting sequence and an Oxa1 targeting sequence
        • Path C for proteins with no matrix targeting sequence but have several internal targeting sequences
      • important of proteins into peroxisomes doesnt use chaperones
    • G protein linked receptors and secondary messengers
      • G protein linked receptors bind to a ligand activating the G protein
      • cAMP, cGMP, GTP, GDP, ATP, PIP2, IP3, DAG, 7TM receptors
      • G proteins are located on the intracellular side of the plasma membrane,
      • Second messengers which are intracellular messengers triggered by the activation of the G protein
        • cyclic AMP is the most common secondary messenger
      • 2 types of G proteins
        • heterotrimeric g proteins have three basic types, those that affect ion channels, those that are stimulatory and those that are inhibitory
          • stimulatory G proteins activate the amplifier enzyme
          • inhibitory G proteins inhibit the amplifier enzyme
        • heterotrimeric G proteins which are composed of three subunits of different sizes
          • are regulatory proteins that mediate interaction between activated receptor and other target proteins in the plasma membrane called effectors
    • Membrane transport
      • glucose transporters are selective for glucose
      • Untitled
      • valinomycin increases the permeability of K+ ions across the membrane
        • is a cyclic peptide with folded conformation and rich in hydrophobic CH3 groups with an interior ring of N and O
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      • Gramicidin A is a pore which is cation specifiic
      • ionophores can dissolve in membranes and catalyze transport of cations
      • various types of transport acrross the membrane, facilitated passive transport, active transport, diffusion, osmosis
    • Intercellular communication
      • direct communication through gap junction or recognition of surface markers
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      • messengers that dissolve in plasma have a short half life, those that are bound to the plasma protein have a longer half life
      • types of indirect solubility are endocrince, paracrine, autocrine and synaptic
        • endocrine and synaptic are used for long range communication
        • paracrine is used for short distance, autocrine is within the same cell
      • chemical messengers can be classified by solubility, chemical prperties,
      • indirect communication through chemical signals
    • The role of receptors
      • receptor antagonist binds to the receptor, not producing a response
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      • down regulation when the receptor number decreases on target
        • caused by excess of messenger
      • different types of receptor
        • intracellular receptor, cell surface receptor, ion channel coupled receptors, G protein coupled receptors, enzyme coupled receptors
      • receptor agonist binds to the receptor and mimics the normal response
      • strength of response depends on concentration of messenger/ligand, number of receptors per target cell and receptor affinity for messenger
      • cell surface receptors are integral membrane proteins
        • have three basic domains, extracellular, transmembrane and intracellular
    • protein kinases
      • carry out phosphorylation, specific to one substrate, depending on the amino acid sequence
      • protein kinase A is activated by cAMP, has effects in gene transcription
      • protein kinase C is one of the largest kinase families, three subgroups
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Comments

adam scolen

is this title suposed to rime

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