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12/28/11 Overview of lecture: • An introduc7on to Eukaryo7c microorganisms • General characteris7cs of Eukaryo7c cell structure and func7on Introduction to Microbiology
• Highlight how eukaryo7c cells differ from prokaryo7c cells Eukaryotic microorganisms:
Cell structure and function
• Eukaryo7c cells are more complex than prokaryo7c cells Dr A. Fleming Eukaryotic cell morphology is diverse
You are here Algae;
Volvox
Protozoa;
Paramecium
Fungi;
Yeast
Fungi;
Aspergillus
•  3 domains • Arose from a common ancestor • Archaea and Eucaryota evolved independently from bacteria 1 12/28/11 Eukaryotic microorganisms exhibit
extreme diversity
Eukaryotic microorganisms can exist
as multicellular macroscopic structures
• Have a silicon-­‐based cell wall Diatoms Mushroom Amoeba • Have no cell wall Eukaryo7c cells are complex Cell organelles • Defini7on: intracellular structures that perform specific func7ons • Analagous to the func7on of organs in the body • Have membrane bound nuclei • Have numerous organelles • Have more complex reproduc7on processes -­‐ mitosis and meiosis • Organelles do not have to be membrane bound 2 12/28/11 The cytoplasmic matrix is an organelle • Supports all other organelles and biochemical processes A major component of the cytoplasmic matrix is the cytoskeleton • Highly dynamic • Changes in the cytoplasmic matrix are essen7al for cell func7on • A network of 3 types of filaments • plays roles in cell shape and movement Cytoskeleton filaments: 1. Microfilaments 2. Microtubules • Ac7n protein • 4 – 7 nm in diameter • Can be scaQered or organised into networks • a helix of α-­‐tubulin and β-­‐tubulin subunits • Thin cylinders ~ 25 nm in diameter • Role: • Role : • Involved in cell mo7on and cell shape change 1.  Maintain cell shape 2.  Cooperate with microfilaments for cell movement 3.  Par7cipate in intracellular transport 3 12/28/11 Pathogens can hijack the eukaryo7c cytoskeleton 3. Intermediate filaments • Assembled from a mixed groups of proteins • 10 nm in diameter Role: • Not well characterised • Can have a role in cell-­‐cell adhesion The nucleus • Listeria monocytogenes releases a virulence factor • Ac7n polymerisa7on propels Listeria monocytogenes through a host cell Eukaryo7c Genomes are large Organism Nucleus Prokaryote Eukaryote • Contains DNA Genome size / bp No. of genes Phi-­‐X 174 5,386 10 Epstein-­‐Barr Virus 172,282 80 Bacillus sub*lis 4,214,814 4,779 E. coli K12 4,639,221 4,377 Saccharomyces cerevisiae 12,495,682 6000 Drosophila melanogaster 122,653,977 13,379 Anopheles gambiae 278,244,063 13,683 Human 3.3 x 109 ~20,500 Human mitochondria 16,569 37 • Bound by the double membrane nuclear envelope 4 12/28/11 DNA is packaged as chroma7n Gene transcrip7on in eukaryotes DNA double helix nucleosome Eukaryo7c RNA Polymerases folded nucleosomes Histones: H2A, H2B H3, H4 Pol II Pol I Pol III Transcrip7on chroma7n loop: ~100,000 bp DNA rRNA Transla7on 50 – 70 % of total transcrip7on mito7c chromosome 5SrRNA and transfer RNA Messenger RNA Proteins • Bacteria have one RNA polymerase Gene expression in prokaryotes RNA Polymerase σ -­‐35 -­‐10 Gene expression in eukaryotes RNA Polymerase gene1 gene2 gene3 DNA TF Operon TBP Gene X TATA box Polycistronic mRNA Nucleus Monocistronic mRNA Cytoplasm Protein • Transcrip7on and transla7on can occur simultaneously Export Cytoplasm Protein • Genes are transcribed in the nucleus •  mRNAs are exported to the cytoplasm 5 12/28/11 Eukaryo7c ribosomes The nucleolus Prokaryo7c Eukaryo7c Nucleus Nucleolus Prokaryote Eukaryote • Very dense structure • not membrane bound • Role: Site of ribosomal RNA synthesis and ribosome assembly Organelles of the secretory pathway • Movement of materials within and out of the cell • Eukaryo7c ribosomes are bigger protein factories The endoplasmic re7culum (ER) • Membranous tubes and flaQened sacks (cisternae) • Con7nuous with nuclear envelope Smooth ER Rough ER • Role: synthesis, modifica7on & export of proteins / lipids • Site of cell membrane synthesis 6 12/28/11 The Golgi apparatus • Composed of flaQened membranous sacks (cisternae) Maturing face Dis7nct polarity A stack = dictyosome The biosynthe7c-­‐secretory pathway E.g. Protein Secre7on • Movement of materials within or outside of cell 1.Protein synthesis 2.Glycosyla7on in ER 1. 3. Fusion with Cis face of Golgi Forming face 4.Packaging in Golgi Role: • Processing, packaging and secre7on of macromolecules Proteins are subject to quality control 5.Transport Vesicle release 4. 5. 2. 3. The proteosome • A huge cylindrical protein complex Proteosome • Misfolded proteins are ubiquitylated then degraded by the proteosome 7 12/28/11 The Endocy7c pathway •  cellular uptake occurs via three pathways 1.Phagocytosis (protrusions) Lysosomes • Single membrane bound spherical structures • Range from 50nm to several um in size • Contain hydroly7c enzymes 2.Endocytosis (invagina7ons) 3.Autophagy (recycling of cytosolic components) • Diges7on occurs in the lysosome • diges7on products exit the lysosome for use as nutrients Mitochondria Role: • Intracellular diges7on Eukaryo7c reproduc7on is complex 1. Asexual reproduc7on: Mitosis • The site of ATP synthesis Size = 0.5 – 10um 1 -­‐ 1000 / cell • They are double membrane structures: an inner membrane and outer membrane • The inner matrix is where ATP is formed • Mitosis involves several stages • Each new cell acquires a duplicate set of chromosomes 8 12/28/11 Sexual reproduc7on: Meiosis • Chromosome number is reduced from diploid (2N) to haploid (1N) • Haploid cells may act as gametes to reform diploid organisms Diversity of eukaryo7c external cell structures Yeast Diatom (algae) Rigid cell wall Glucose-­‐based Other eukaryotes have no cell wall Silica-­‐based cell wall (frustule) Pro7sts have a pellicle underneath the membrane Amoeba proteus Euglena spirogyra • the pellicle is striated 9 12/28/11 Cilia and Flagella Eukaryotic cilia and flagellar structure
Cilia Flagella Euglena Paramecium • Aid in mo7lity / adhesion • Membrane bound organelle, ~0.2m thick
• Extensions of microtubules
• Originate from a basal body (centriole)
PaQerns of Flagellar and Ciliary movement Comparison of Prokaryo7c and Eukaryo7c cells Prokaryote Eukaryote • Eukaryotes are more structurally and func7onally complex • Eukaryotes have a membrane – bound nucleus wave beat • Eukaryotes have a diverse collec7on of organelles • Replica7on is more complex –mitosis and meoisis • Eukaryotes carry out complex processes such as enodcytosis, amoeboid movement etc. 10 12/28/11 Archaea: General cell morphology The Archaea: a third form of life • Look similar to bacteria • Cell membrane is bound by a cell wall • Range in size from 0.1 – 200 μm • Commonly unicellular Methanococcus Janaschii -­‐cocci with flagella Methanothermus fervidus -­‐Short bacillus • The Archaea: • Originally described as bacteria (archaebacteria) • prokaryotes – have no nucleus • Now proposed to form a dis7nct domain – a ‘third form’ of life Methanosarcina Barkeri -­‐lobed cocci Methanobacterium Thermoautotrophicum -­‐filamentous Archaea have unique proper7es Archaea and eukaryotes share a common ancestry • Archaea and Eukaryotes evolved separately from the bacteria Haloquadratum Walsbyi -­‐square ? * * • Archaea and eukaryotes diverged and became separate domains • This common evolu7on is reflected in the way they process gene7c informa7on 11 12/28/11 Archaea
Thermophiles and hyperthermophiles •  Originally iden7fied in extreme environments •  extremophiles –  Hyperthermophiles –  Methanogens –  Extreme halophiles Pyrolobus
fumarii
• Pyrolobus was found at a Hydrothermal vent (Black Smoker) The thermophile record holder (so far....) • Archaea Strain 121 • 105 ºC is its op7mal growth temperature. •  It cannot live below 90 ºC Psychrophiles: found in cold regions Strain 121 • Found at a hydrothermal vents 12 12/28/11 Halophile habitat and structure • Resistant to high salt concentra7ons Were the Archaea resistant to the violence of early earth? Barophiles: •  Found at the boQom of ocean trenches & gorges, such as the Mariana Trench • Resistant to extreme pressures Did life on earth arrive from outer space ? Comets & Meteorites 13 12/28/11 Has life on earth spread to outer space ? Could life originate/exist on other planets ? • Via comets & Meteorites • Europa is a large moon of Jupiter • It is completely encased in water ice • Volcanoes could be ac7ve Alien life ? Alien life ? ?
14 12/28/11 Could Archaea be the future of life on earth ? Summary •  Eukaryotes have a more complex cell structure than prokaryotes –  They have a nucleus and numerous organelles •  The Archaea form a third way of life •  They have features of both prokaryotes and eukaryotes Extra Reading PrescoQ, LM et. Al., Microbiology 7th edi7on McGraw-­‐Hill, Boston, 2008 Pages 70 -­‐99 15