Advanced microbiology

75 flashcards · Biology · by Baher Nazar Gul

microbes
prokaryotes most of eukaryotes
prokaryotic cell structure
Prokaryotes (bacteria and archaea)
•Unicellular for the most part. •Lack membrane-bound nucleus, membrane- bound organelles, and internal membranous structures.
Prokaryotic cells
lack true, membrane delineated nucleus lack true, membrane delineated organelles {mitochondria,golgi apparatus} usually have a single, linear or circular chromosome Plasmids are very common in prokaryotes, rare in eukaryote Ribosomes are smaller in prokaryotes. Flagella are much smaller, simpler, but much more common in prokaryotes. cells have gas vesicles,
Prokaryotic Cell Membranes
Membranes are an absolute requirement for all living organism •plasma membrane encompasses the cytoplasm.
functions of cell membrane
•separation of cell from its environment. •selectively permeable barrier: (nutrient uptake) some molecules are allowed to pass into or out of the cell transport systems aid in movement of molecules} location of crucial metabolic processes {respiration} detection of and response to chemicals in surroundings with the aid of special receptor molecules in the membrane
naturally occurring, mostly hydrophobic, storage and structural molecules in prokaryotic and eukaryotic cells (fats, oil, waxes, cholesterols)
tail
polar ends head
–interact with water (usually phosphorylated ethanol amine) –hydrophilic
nonpolar ends tail
insoluble in water –hydrophobic (Glycerol esters of long chain fatty acids)
Other membrane lipids (nonpolar): hopanoids stero structures
membrane proteins
peripheral and integral proteins
•peripheral proteins
loosely associated with the membrane and easily removed {detoxifies}
integral proteins
–embedded within the membrane and not easily removed
A highly organized structure that is also asymmetric, flexible, and dynamic
Plasma membrane infoldings
observed in many photosynthetic bacteria and in procaryotes with high respiratory activity
Amphipathic lipids arranged in a bilayer (Similar to Bacteria) 1. Polar head of archaeal lipids have variable structures (Phosphate, sulfur, and sugar containing groups) as opposed to ethanolamine in bacteria 2. Non polar tail of Archaeal lipids are ether linked glycerolipid hydrocarbons (e.g. phytanol), as opposed to ester-linked glycerolipid lipid acids (e.g. stearic acids) in Bacteria
Amphipathic lipids in Archaea sometime dimerize, form a lipid monolayer plasma membrane
two heads many but not all live in extreme environments
1.Polar head: Phosphorylated ethanolamine in Bacteria, variable in Archaea 2.Nonpolar tail: Glycerol ester of various fatty acids in Bacteria. Glycerol ether of C20 hydrocarbons in Archaea (e.g. Phytanol). 3. Additional nonpolar lipids are present in Archaea (Squalene, tetrahydrosqualene), Bacteria (Hopanoids). 4. Non polar tail can dimerize to form a membrane monolayer in some Archaea.
cytoskeleton functions
–Role in cell division, protein localization, and determination of cell shape
Actin: forms microfilaments Tubulin: Forms Microtubules Lamin, Keratin and other Proteins: Intermediate filaments.
sequences of genes
Homologs of all 3 eukaryotic cytoskeletal elements have been identified in bacteria and 2 in archaea.
FtsZ – many bacteria and archaea –forms ring during septum formation in cell division (Tubulin analogue) •MreB – many rod shaped bacteria, some archaea –maintains shape by positioning peptidoglycan synthesis machinery (Actin homologue) •CreS – rare, maintains curve shape (lamin and keratin homologue).
i. Storage inclusions: granules of organic or inorganic material that are stockpiled by the cell for future use. ii. Non Storage inclusions: Granules of enzymes, structures, or specific chemicals that are required for proper cell function.
storage inclusions
storage of nutrients, metabolic end products, energy, building blocks 1. Glycogen storage 2. poly-β-hydroxybutyrate (PHB) 3. Cyanophycin granules 4. Phosphate - Polyphosphate (Volutin) 5. Sulfur granules
Glycogen
Glucose polymer. Formed when bacteria is an a carbon rich environment that is lacking in another essential nutrient.
Poly b-hydroxybutyrate PHB
Polymers of a hydroxy fatty acid Interest in utilization for plastics.
cyanophycin:
large polypeptides containing about equal quantities of arginine and aspartic acid –Found in Cyanobacteria, used as a nitrogen storage mechanism
4. Phosphate
- Stored as polyphosphate granules (also called volutin or metachromatic granules). - Used in biosynthesis, could act as an energy reserve
5. Sulfur:
- Accumulates as an end product from bacteria that use hydrogen sulfide as an electron donor (e.g. green sulfur photosynthetic bacteria)
1.Carboxysomes 2.Gas vacuoles 3.Magnetosomes
Carboxysomes
In Autotrophic (CO2) fixing bacteria –contain the enzyme ribulose-1,5,-bisphosphate carboxylase (Rubisco), enzyme used for CO2 fixation
Gas vacuoles
–found in aquatic, photosynthetic bacteria and archaea –Vacuole is an aggregate of thousands of cylindrical single protein structure called gas vesicle –provide buoyancy, adaptation to optimum environmental conditions
3. Magnetosomes
–found in aquatic bacteria, formed of magnetite (Fe3O4) –Particles arranged in chains (magnetosome chain) –cytoskeletal protein MamK is thought to be responsible for establishing a framework upon which the chain may form –magnetite particles for orientation in Earth’s magnetic field (why?)
Ribosomes
•complex structures consisting of protein and RNA (What are the different types of RNA, which one is present in the ribosome?) •site of protein synthesis •70S ribosome is composed of 2 units 50S and 30s –50S (LSU): 23S rRNA + 5S rRNA + ribosomal proteins •Some archaea have an additional 5.8S rRNA unit in the LSU, similar to eukaryotes –30S (SSU) : 16S rRNA + ribosomal protein •smaller than eukaryotic ribosomes –prokaryotic ribosomes Þ 70S –eukaryotic ribosomes Þ 80S •S = Svedburg unit
Nucleoid
•irregularly shaped region •location of chromosome –usually 1/cell •not membrane-bound
chromsomes
•a closed circular, double-stranded DNA molecule •looped and coiled extensively •nucleoid proteins probably aid in folding
3. Magnetosomes
–found in aquatic bacteria, formed of magnetite (Fe3O4) –Particles arranged in chains (magnetosome chain) –cytoskeletal protein MamK is thought to be responsible for establishing a framework upon which the chain may form –magnetite particles for orientation in Earth’s magnetic field (why?)
Ribosomes
complex structures consisting of protein and RNA (What are the different types of RNA, which one is present in the ribosome?) •site of protein synthesis •70S ribosome is composed of 2 units 50S and 30s –50S (LSU): 23S rRNA + 5S rRNA + ribosomal proteins •Some archaea have an additional 5.8S rRNA unit in the LSU, similar to eukaryotes –30S (SSU) : 16S rRNA + ribosomal protein •smaller than eukaryotic ribosomes –prokaryotic ribosomes Þ 70S –eukaryotic ribosomes Þ 80S •S = Svedburg unit
Nucleoid
•irregularly shaped region •location of chromosome –usually 1/cell •not membrane-bound
•a closed circular, double-stranded DNA molecule •looped and coiled extensively •nucleoid proteins probably aid in folding
the bacteria cell wall
rigid structure that lies just outside of the plasma membrane
cell functions
Maintains shape of bacterium almost all bacteria have one helps protect cell from osmotic lysis helps protect from toxic materials may contribute to pathogenicity
cell walls of bacteria
gram + purple gram - pink
outline
meshlike polymer composed of identical subunits. •Each unit contains N-acetyl glucosamine and N-acetylmuramic acid and several different amino acids. •Links together to make chains. •chains of linked peptidoglycan subunits could be cross linked by peptides.
GRAM +
•composed primarily of peptidoglycan. •may also contain large amounts of teichoic acids.
polymer of glycerol or ribitol joined by phosphate groups. Amino acids, sugars are attached to the glycerol or ribitol group. Connected to the peptidoglycan or the plasma membrane (Lipoteichoic acid). Function not clearly known, thought to help confer a negative charge on cell surface.
Periplasmic Space of Gram positive bacteria
•lies between plasma membrane and cell wall and is smaller than that of Gram negative bacteria. •periplasm has relatively few proteins. •Peptidoglycan is permeable, enzymes that stay in the periplasms of gram positive cells are attached to the plasma membrane (integral proteins). •enzymes secreted by Gram + bacteria are called exoenzymes (pass through the periplasm but are not retained). Examples? amylases, proteases, pectinases, lipases, xylanases, cellulases
•more complex than gram + walls •consist of a thin layer of peptidoglycan surrounded by an outer membrane •peptidoglycan is ~2-5% of wall weight. •periplasmic space differs from that in gram + cells. –may constitute 20-40% of cell volume –many enzymes present in periplasm Braun’s lipoproteins connect outer membrane to peptidoglycan. •outer membrane composed of a lipid bilayer, lipoproteins, porins, and lipopolysaccharide (LPS). •no teichoic acids. How are outer membrane connected to the cell? B…
Lipopolysaccharides (LPSs)
–lipid A –core polysaccharide –O side chain (O antigen)
structure of lps
Lipid A:
Glucosamine phosphate units with long fatty acid chains. –Anchors LPS to the outer membrane –Acts as an endotoxin in pathogenic gram negative bacteria
Core polysaccharide:
Substituted collection of sugars, including heptose and octose sugars
•O side chain
– Composition varies, but is made of polysaccharides –Antigenic
•helps stabilize outer membrane structure (lipid A). •can act as a toxin (lipid A). •contributes to negative charge on cell surface (core polysaccharide). •protection from host defenses (O antigen).
Other Characteristics of the Outer Membrane
Other Characteristics of the Outer Membrane •more permeable than plasma membrane due to presence of porin proteins and transporter proteins. •porin proteins form channels through which small molecules (600-700 daltons) can pass.
The Mechanism of Gram Staining
Shrinkage of the pores of the peptidoglycan layer of gram-positive cells. •Constriction prevents loss of crystal violet during decolorization step. •Thinner peptidoglycan layer and larger pores of gram-negative bacteria does not prevent loss of crystal violet.
The Mechanism of Gram Staining
•What is being stained? Cytoplasm, and cytoplasmic structures. •Alcohol dissolves lipids, hardens polysaccharides.
Archaeal cell walls
Lack peptidoglycan. •Cell wall varies from species to species but usually consists of complex heteropolysaccharides, glycoproteins. A. Some bacteria have a layer of protein (S layer) as the only structure outside the plasma membrane (e.g. Halobacterium spp). B-D. Others would have additional layers in addition to the S. layer e.g. Proteins sheath (e.g. Methanospirillium spp.), methanochondroitin (e.g. Methanosarcina spp) or pseudomurein (e.g. Methanothermus spp.) E. Few have no S layer, only th…
gram -
protein to sugar ratio more protien gram-
gram +
the Cell Wall and Osmotic Protection
•osmotic lysis –can occur when cells are in hypotonic solutions. –movement of water into cell causes swelling and lysis due to osmotic pressure. •cell wall protects against osmotic lysis.
Evidence of protective nature of the cell wall
•lysozyme breaks the bond between N-acetyl glucosamine and N-acetylmuramic acid. •penicillin inhibits peptidoglycan synthesis. •If cells are treated with either of the above they will lyse if they are in a hypotonic solution.
•protoplast – cell completely lacking cell wall (e.g. G+ve cells treated with penicillin). • •Spheroplasts-cell partially lacking cell wall (e.g. G-ve cells treated with penicillin).
Components external to the Cell Wall
Glycocalyx: Layers of material lying outside the cell wall –capsules •usually composed of polysaccharides. •well organized and not easily removed from cell. –slime layers •similar to capsules except diffuse, unorganized and easily removed.
•S-layers
–regularly structured layers of protein or glycoprotein. –In bacteria the S layer is external to the cell wall. –common among Archaea, where they may be the only structure outside the plasma membrane.
Functions of capsules, slime layers, and S-layers •
Protection from host defenses (e.g., phagocytosis). •Protection from harsh environmental conditions (e.g., desiccation). •Attachment to surfaces. •Protection from viral infection or predation by bacteria. •Protection from chemicals in environment (e.g., detergents). •Facilitate motility of gliding bacteria. •Protection against osmotic stress.