Lecture 1 Nature of the Microbial World Flashcards
Living cells can be divided into 2 sharply differentiated groups
Eukaryotes
Prokaryotes
Cells possessing true nuclei containing chromosomes, replicating by mitosis
Contains organelles (mitochondria, golgi apparatus, lysosomes, ribosomes)
Eukaryotes
Lack true membrane-bound nuclei, circular chromosome, plasmids
Prokaryotes
Phylogeny of the 3 domains of life
Eubacteria
Eukaryotes
Archaebacteria
Common features of eukaryotes and prokaryotes
DNA - genetic material
Plasma membrane - phospholipid bilayer
Cytoplasm - fluid portion called cytosol
Ribosomes - protein synthesis
Size or prokaryotic and eukaryotic cell
Prokaryotic cell - 0.1-10 micrometers
Eukaryotic cell - 10-100 micrometers
Central dogma of prokaryotes vs eukaryotes
Prokaryotes - DNA replication, transcription, and protein translation occurs in undivided compartment
Eukaryotes - transcription and translation occur separately
Prokaryotic cell
(Size) Generally small (1-10 micrometers)
(Genome) Genome in nucleoid, not surrounded by membrane
(Cell division) Fission or budding, no mitosis
(Membrane-bound organelles) None
(Nutrition) Absorption, some photosynthesis
(Energy metabolism) No mitochondria, oxidative enzymes bound to plasma membrane
(Cytoskeleton) None
(Intracellular movement) None
Eukaryotic cell
(Size) Generally large (5-100 micrometers)
(Genome) Chromosomes in nucleus with membranous envelope
(Cell division) Mitosis, centrioles
(Membrane-bound organelles) Mitochondria, chloroplasts, ER etc
(Nutrition) Absorption, ingestion, photosynthesis
(Energy metabolism) Oxidative enzymes packaged in mitochondria
(Cytoskeleton) Complex, with microtubules and filaments
(Intracellular movement) Endocytosis, phagocytosis, mitosis
Bacteria vs virus sizes
RBC > bacteria > virus
10,000 nm > 3,000×1,000 nm > 10-970 nm
Comparison of morphology and size of bacterial cells relative to mammalian RBC
RBC - 7 mu m - readily seen using conventional light microscopy
Bacillus - 5 mu m - using bright-field microscopy, magnification of 1000x required
Coccus - 1 mu m
Spirochaete - 10 mu m - dark-field microscopy or special staining methods
Comparison of bacterial cell and large and small virus
Bacterial cell
- Coccus - 1 mu m - readily seen at 1000x magnification
Viruses
- Poxvirus - 300 nm - can’t be seen using bright-field microscopy
- Parvovirus - 20 nm - electron microscopy up to 100,000x magnification
Acellular
Obligate intracellular parasites - multiply inside of living cells using host cell machinery
No ribosomes or means of ATP synthesis
No ATP generation
Viruses
A typical virus
Viral size 20-14,000 nm
Composed of
- nucleic acid - single/double stranded, DNA, RNA
- capsid - protein coat, sometimes surrounded by envelope
A typical virus
Nucleic acid
General morphology
NA - circular, linear, or separate molecules
GM - helical, polyhedral (icosahedron, 20 triangular faces), enveloped, or complex (bacteriophages) viruses
Specific types of cells a virus can infect in its host represent the ____ _____
Usually species specific
Determined by attachment sites (receptors)
Host range
Classification of viruses is based on
Type of nucleic acid
Strategy for replication
Morphology
Virus family names end in
Genus names end in
Family -viridae
Genus -virus
Group of viruses sharing same genetic information and ecological niche
Viral species
Infectious pieces of naked RNA
Causes plant diseases
300-400 nucleotides long
Closed, folded 3d shape
Does not act as mRNA
Structure - circular, single-stranded RNA with some pairing between complementary bases and loops where no such pairing occurs
Viroids
Proteinaceous infectious particle
Infectious proteins, rogue proteins
Normal cellular proteins that have undergone conformational change as a result of post-transactional processing of a normal cellular protein
Pathogenic
Undergoes biogenesis and accumulation in cells
- conversion of normal to abnormal protein molecules
Normal protein PrPc is found in neurons and lymphoreticular cells
Abnormal protein PrPsc (scrapie isoform)
- seed crystal acting as template
Prions
Classification of host range of virus
Animal/human virus
Plant virus
Bacterial virus (bacteriophage)
