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12/28/11 Introduction to Microbiology
Eukaryotic microorganisms:
Cell structure and function
Dr A. Fleming Overview of lecture: • An introduc7on to Eukaryo7c microorganisms • General characteris7cs of Eukaryo7c cell structure and func7on • Highlight how eukaryo7c cells differ from prokaryo7c cells • Eukaryo7c cells are more complex than prokaryo7c cells 1 12/28/11 You are here •  3 domains • Arose from a common ancestor • Archaea and Eucaryota evolved independently from bacteria Eukaryotic cell morphology is diverse
Algae;
Volvox
Protozoa;
Paramecium
Fungi;
Yeast
Fungi;
Aspergillus
2 12/28/11 Eukaryotic microorganisms exhibit
extreme diversity
Diatoms • Have a silicon-­‐based cell wall Amoeba • Have no cell wall Eukaryotic microorganisms can exist
as multicellular macroscopic structures
Mushroom 3 12/28/11 Eukaryo7c cells are complex • Have membrane bound nuclei • Have numerous organelles • Have more complex reproduc7on processes -­‐ mitosis and meiosis Cell organelles • Defini7on: intracellular structures that perform specific func7ons • Analagous to the func7on of organs in the body • Organelles do not have to be membrane bound 4 12/28/11 The cytoplasmic matrix is an organelle • Supports all other organelles and biochemical processes • Highly dynamic • Changes in the cytoplasmic matrix are essen7al for cell func7on A major component of the cytoplasmic matrix is the cytoskeleton • A network of 3 types of filaments • plays roles in cell shape and movement 5 12/28/11 Cytoskeleton filaments: 1. Microfilaments • Ac7n protein • 4 – 7 nm in diameter • Can be scaQered or organised into networks • Role : • Involved in cell mo7on and cell shape change 2. Microtubules • a helix of α-­‐tubulin and β-­‐tubulin subunits • Thin cylinders ~ 25 nm in diameter • Role: 1.  Maintain cell shape 2.  Cooperate with microfilaments for cell movement 3.  Par7cipate in intracellular transport 6 12/28/11 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 Pathogens can hijack the eukaryo7c cytoskeleton • Listeria monocytogenes releases a virulence factor • Ac7n polymerisa7on propels Listeria monocytogenes through a host cell 7 12/28/11 The nucleus Nucleus Prokaryote Eukaryote • Contains DNA • Bound by the double membrane nuclear envelope Eukaryo7c Genomes are large Organism 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 8 12/28/11 DNA is packaged as chroma7n DNA double helix nucleosome folded nucleosomes Histones: H2A, H2B H3, H4 chroma7n loop: ~100,000 bp DNA mito7c chromosome Gene transcrip7on in eukaryotes Eukaryo7c RNA Polymerases Pol I Pol II Pol III Transcrip7on rRNA 50 – 70 % of total transcrip7on Messenger RNA 5SrRNA and transfer RNA Transla7on Proteins • Bacteria have one RNA polymerase 9 12/28/11 Gene expression in prokaryotes RNA Polymerase σ -­‐35 -­‐10 gene1 gene2 gene3 DNA Operon Polycistronic mRNA Cytoplasm Protein • Transcrip7on and transla7on can occur simultaneously Gene expression in eukaryotes RNA Polymerase TF TBP Gene X TATA box Nucleus Monocistronic mRNA Export Cytoplasm Protein • Genes are transcribed in the nucleus •  mRNAs are exported to the cytoplasm 10 12/28/11 The nucleolus Nucleus Nucleolus Prokaryote Eukaryote • Very dense structure • not membrane bound • Role: Site of ribosomal RNA synthesis and ribosome assembly Eukaryo7c ribosomes Prokaryo7c Eukaryo7c • Eukaryo7c ribosomes are bigger protein factories 11 12/28/11 Organelles of the secretory pathway • Movement of materials within and out of the cell 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 12 12/28/11 The Golgi apparatus • Composed of flaQened membranous sacks (cisternae) Maturing face Dis7nct polarity A stack = dictyosome Forming face Role: • Processing, packaging and secre7on of macromolecules 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 4.Packaging in Golgi 5.Transport Vesicle release 4. 5. 2. 3. 13 12/28/11 Proteins are subject to quality control Proteosome • Misfolded proteins are ubiquitylated then degraded by the proteosome The proteosome • A huge cylindrical protein complex 14 12/28/11 The Endocy7c pathway •  cellular uptake occurs via three pathways 1.Phagocytosis (protrusions) 2.Endocytosis (invagina7ons) 3.Autophagy (recycling of cytosolic components) • Diges7on occurs in the lysosome • diges7on products exit the lysosome for use as nutrients Lysosomes • Single membrane bound spherical structures • Range from 50nm to several um in size • Contain hydroly7c enzymes Role: • Intracellular diges7on 15 12/28/11 Mitochondria • 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 Eukaryo7c reproduc7on is complex 1. Asexual reproduc7on: Mitosis • Mitosis involves several stages • Each new cell acquires a duplicate set of chromosomes 16 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 Silica-­‐based cell wall (frustule) 17 12/28/11 Other eukaryotes have no cell wall Amoeba proteus Pro7sts have a pellicle underneath the membrane Euglena spirogyra • the pellicle is striated 18 12/28/11 Cilia and Flagella Cilia Flagella Euglena Paramecium • Aid in mo7lity / adhesion Eukaryotic cilia and flagellar structure
• Membrane bound organelle, ~0.2m thick
• Extensions of microtubules
• Originate from a basal body (centriole)
19 12/28/11 PaQerns of Flagellar and Ciliary movement wave beat Comparison of Prokaryo7c and Eukaryo7c cells Prokaryote Eukaryote • Eukaryotes are more structurally and func7onally complex • Eukaryotes have a membrane – bound nucleus • 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. 20 12/28/11 The Archaea: a third form of life • The Archaea: • Originally described as bacteria (archaebacteria) • prokaryotes – have no nucleus • Now proposed to form a dis7nct domain – a ‘third form’ of life Archaea: General cell morphology • 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 Haloquadratum Walsbyi -­‐square ? Methanosarcina Barkeri -­‐lobed cocci Methanobacterium Thermoautotrophicum -­‐filamentous 21 12/28/11 Archaea and eukaryotes share a common ancestry • Archaea and Eukaryotes evolved separately from the bacteria • Archaea and eukaryotes diverged and became separate domains • This common evolu7on is reflected in the way they process gene7c informa7on Archaea have unique proper7es * * 22 12/28/11 Archaea
•  Originally iden7fied in extreme environments •  extremophiles –  Hyperthermophiles –  Methanogens –  Extreme halophiles Thermophiles and hyperthermophiles Pyrolobus
fumarii
• Pyrolobus was found at a Hydrothermal vent (Black Smoker) 23 12/28/11 The thermophile record holder (so far....) • Archaea Strain 121 • 105 ºC is its op7mal growth temperature. •  It cannot live below 90 ºC Strain 121 • Found at a hydrothermal vents Psychrophiles: found in cold regions 24 12/28/11 Halophile habitat and structure • Resistant to high salt concentra7ons Barophiles: •  Found at the boQom of ocean trenches & gorges, such as the Mariana Trench • Resistant to extreme pressures 25 12/28/11 Were the Archaea resistant to the violence of early earth? Did life on earth arrive from outer space ? Comets & Meteorites 26 12/28/11 Has life on earth spread to outer space ? • Via comets & Meteorites Could life originate/exist on other planets ? • Europa is a large moon of Jupiter • It is completely encased in water ice • Volcanoes could be ac7ve 27 12/28/11 Alien life ? Alien life ? ?
28 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 29 12/28/11 Extra Reading PrescoQ, LM et. Al., Microbiology 7th edi7on McGraw-­‐Hill, Boston, 2008 Pages 70 -­‐99 30