Cells and Organelles
- 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 nucleoid where supercoiled double stranded DNA is located
- 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
- 2 types of prokaryotes bacteria and archaeons
- 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
- gram staining reaction separates bacteria into Gram +ve and -ve types, depends on ability of organism to retain crystal violet after alcohol exposure
- 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
- microfilaments are made of actin and have some elasticity
- involved in cell movement, cell division, cell shape and intracellular trafficking of organelles and the coordinated movement of tissue
- fine tubules are microtubules, microfilaments and intermediate filaments
- 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
- can be uni and multicellular, with linear DNA molecules packaged as chromosomes in a nucleus
- 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
- stem cells are directed to differentiate by growth factors
- 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
- connexon hemichannels provide chemical and electrical coupling between adjacent cells, permitting movement of ions and small molecules
- 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
- gap junctions are homophilic interactions that form a connexon hemichannel.
- tight junction, adherens junctions, gap junction, desmosome
- 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
- four main classes of adhesion molecules
- 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
- N linked is more comlex
- 2 types of glycosylation, N linked and O linked
- 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
- heterotrimeric g proteins have three basic types, those that affect ion channels, those that are stimulatory and those that are inhibitory
- Membrane transport
- glucose transporters are selective for glucose
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- 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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- Prokaryotes
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