Prokaryotic structure and function 1

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1 - 1 - Prokaryotic structure and function 1 Morphology, size and other features to distinguish Size Bacteria 1-6!m length, !m wide/thick = prokaryote no nuclear membrane, mitochondria, golgi bodies, ER. Eukaryotes approx 20!m Shape Spherical (coccus), rod (bacillus, cylindrical), curved (spiral = spirillum, helical = spirochete), square (halophile) Spatial single cells, chains, clusters Bacteria Pleomorphism existence of an organism in different morphological forms environmental factors influence size and shape. Fungi! Yeasts (unicellular) + Molds (filamentous form). Have no basic shape. Eukaryotes well defined nucleus, mitochondria, ER and golgi bodies. Protozoa variation due to flexibility of plasma membrane Algae various: plankton photosynthesiser. Composition of bacterial cells Water 70% Dry weight 30%! DNA (3%), RNA (12%), Protein (70% = ribosomes, enzymes and surface structures - = polysaccharides, lipid, phospholipids).! All bacterial cells (except mycoplasma suffix of plasma = no cell wall) have Cell wall Extracellular polymeric substance (EPS), pilus, mesosome. Is outside cytoplasmic membrane. Almost all bacteria have a rigid layer of material that surrounds the plasma membrane = CW. All bacteria (except mycoplasma no cell wall, and Archaea unusual polysaccharide proteinaceous walls) havee a wall made up of 2 alternating sugars! N-Acetylglucosamine and N-Acetylmuramic acid joined together by Glycosidic bonds an attack site for many antibacteria s! Forms polysaccharides, disaccharides joined together by short peptides (tetrapeptide attach to each N-acetylmuramic acid) into 3D framework called Peptidoglycan. Peptide cross bridges consisting of as many as 5 AA s (pentapeptide), crosslink tetrapeptides and hold the polysaccharides together. Functions of cell wall bacteria often grow in aqueous environments where concentration of salts and sugars is much lower than inside cell therefore water tends to diffuse into the cell. CW prevents this by resisting excessive influx of water, water flows into cell until osmotic pressure balanced by resistance of CW. CW pretective and structural function, allows passage of nutrients. Cytoplasmic (plasma) membrane Thin pliable lipid and protein envelope that defines the cell controls movement of small molecules in + out of cell 7nm thick. Consists of 2 layers of phospholipids (lipid bilayer) in which proteins and glycoproteins embedded. Proteins are free to move in the phospholipid. PL s form the matrix of cytoplasmic membrane, but proteins that carry out the functions. Some bacteria respiratory enzymes associated with the membrane. Has role in distribution of genetic information to daughter cells. Genome binds to membrane after genome replicates both copies attached to

2 - 2 - membrane membrane grows, a copy of genome foes to each end of cell. Daughter cells have complete copy of genetic material after cell division. Functions barrier, nutrient transport, energy metabolism. - Releases toxins, bacteriocins (affects other bacterium), enzymes produced in cytoplasm. - Bacterial PM is bound to interior of cell wall but sometimes membrane appears to be invaginated into cytoplasm forming a mesosome (used for DNA attachment during replication or cell wall synthesis). Mesosome A coiled cytoplasmic membrane acts as an anchor to bind and pull apart daughter chromosomes during cell division. DNA genome hereditary material Ribosomes protein synthesis Other structures for selective advantage etc only associated with particular bacteria Endospores - Capsules around for protection Thylakoids membrane-enclosed compartment Gas vesicles Reserve materials Purple bacteria and cyanobacteria Photosynthetic membrane thylakoids continuous with plasma membrane Green bacteria photosynthetic bacteria chlorosomes Bacterial flagella anchored in plasma membrane and powered by energy from energygenerating systems found in membrane allow movement. Most bacteria divided into 2 groups based on chemical components outside peptidoglycan (PG) layer a rigid mesh made up of repetitive linear polysaccharide chains cross-linked by peptides. PG can be degraded with lyzozyme. Effect of decolourising solution of alcohol on crystal violet-iodine complex based on the ability of cell wall to absorb crystal violet-iodine complex. Gram positive e.g. Staphylococcus. Multilayered PG 30-60nm thick surrounding cytoplasmic membrane. Almost exclusively PG and attached teichoic acid polymers (for cell viability) + lipoteichoic acids (surface antigens). No outer membrane. Stain purple. Gram negative e.g. E. Coli. Thin PG (2-3nm thick), no teichoic acid. Additional outer membrane 7nm thick surrounding PG later it is part of cell wall similar to plasma membrane (e.g. lipid bilayer). Many have polysaccharide attached (e.g. lipopolysaccharide LPS). The outer membrane is a selectively permeable barrier but small molecules pass through. When LPS fratction of outer membrane is toxic to animas = endotoxin (powerful stimulator of innate + immune responses). - Stain pink/red. The 2 membranes are separated by periplasmic space containing a variety of hydrolytic enzymes. - Outer membrane functions molecular sieve (barrier to certain molecules that pass through Gram +ve bacteria eg crystal violet, antibiotics, bile salts), endotoxin (lipid A portion of LPS acts as antigen), antigen (varying sugars), attachment for bacterial viruses.! relative impermeability to hydrophobic compounds (bile salts) may be reason why many Gram ve bacteria in gut, where bile salts are present, e.g. selective advantage.

3 - 3 - Structures outside the cell wall Extracellular polymeric substances (EPS). Adjacent to CW these polymers provide certain advantages to cells that posses them S-layers Sub-unit surface layers represent outermost structure of the cell. Protein or glycoprotein linked to each other and CW probably protective. E.g. Archaea and Bacillus (shield against degradation). Capsules and slime layers Polymers surrounding CW (many bacteria). Capsules Loose polysaccharide or protein layers. Firmly adherent to CW with structural integrity slimy or sticky layers of polysaccharide or polypeptide. Influenced by cultural conditions (e.g. require sucrose). Protective promote attachment some require to cause disease. If no capsule, are ingested by macrohages, when encapsulated resist digestion. The presence of capsule does not mean pathogenic. - India ink shows boundary/boarder of capsule Slime layer amorphous mass released by cell Glycocalyx polysaccharide fibres that extend from bacterial surface, allows bacteria to attach to objects, other bacteria, plant or animal cells. Thick glycocalyx = capsule. Many disease by bacteria are due to ability to synthesise glycocalyx. Sheaths- stiff polysaccharide coverings that some bacteria secrete around a chain or group of bacteria Flagella built from microtubules and dynein in many protozoa. Movement not essential but advantageous. Bacterial flagella are thin hairlike appendages 10-20!m in diameter. Originate in plasma membrane. - A rope-like propeller composed of helically coiled protein subunits (Flagellin) anchored in the bacterial membranes through hook and basal body structures driven by membrane potential. Rotates, pushes against water propels bacterium. Flagellated bacterium moves in one direction then tumbles, before moving off in another direction. Moving towards nutrients long runs, tumbles less Moving away more tumbling. - Not seen under light microscope require flagella stains to coat and thicken flagella. Flagella suitable for movement in non-viscous liquids. Suffix Trichous has flagella. Axial filaments Spirochetes have modified flagella fibrils which form axial filaments which coil around body of cell b/w PG layer and outer membrane, rotating filaments like a corkscrew not hampered by viscosity. Gliding micro-organisms no flagella, no axial filaments. Produce slime layer at forward end of cell contracts b/w cell and surface to propel forward. OR flagella stubs that act as paddle wheels (no organelles, no wriggling or contraction). Pili or fimbriae Long hollow tubes protruding peritrichously (from everywhere/all over) from some bacteria. Made of Pilin, 0.02!m diameter, 0.2!m length. 6 different groups of pili classified on adhesive, morphological properties. Mostly found on Gram-ve bacteria. - Pili are antigenic immune system can make antibodies. Sex pili Bind to other bacteria and are a tube for transfer of large segments of bacterial chromosomes b/w bacteria. Involved in transfer of DNA from donor ( male ) bacteria to recipient ( female ) bacteria may also draw cells together. Contribute to adhesiveness of bacteria. Adhesiveness determines Virulence (disease-causing ability) of some bacteria. Some bacteria need to be palliated to cause disease

4 Pili and glycocalyx allow bacteria on surface of liquid medium to form thin films = Pellicles allows bacteria to float on surface where O2 is greatest. Prosthecae bacterial extensions that increase surface area to absorb nutrients for attachment. A few bacteria form stalks from polysaccharide they secrete become encrusted with inorganic materials (e.g. Fe(OH)3) for attachment. Infection diseases epidemiology Epidemiology The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems embracing all diseases whether infectious or not Sporadic Occurs infrequently at irregular intervals. Isolated eg typhoid fever Endemic Regular, low-level frequency, infection maintained within a population eg common cold. The habitual presence of a disease within a given geographic area. Hyperendemic Frequency increased above endemic level but not epidemic eg winter colds Epidemic A sudden increase above the expected level. The occurrence in a community or region of a group of illnesses of similar nature, clearly in excess of normal expectancy Pandemic transcontinental spread (worldwide epidemic) Index case the 1 st case Outbreak sudden increase in disease usually in a limited segment of population eg Legionnaires disease in Philadelphia Zoonoses animal disease which can be transmitted to humans - All findings must related to a defined population Target pop! Study pop! study sample (may possibly not reflect accurately represent target population)! oriented to groups rather than individuals, conclusions are based on comparisons, epidemiologists measure rates and compare them Case definition should be precise and unambiguous Sensitive Lots of false +ve s with the true +ve results will get lots of results. Sensitivity The proportion of people who truly have the designated disorder who are so identified by the test. The ability of the test to identify correctly those who have disease Specific Will get minimised false +ve s but many true +ve s with false ve s Specificity The proportion of people who truly are free of a designated disorder, who are so identified by the test. Measure of the probability of correctly identifying a nondiseased person w a screening test. Ability of the test to correctly identify those who do not have the disease. Measuring disease frequency Fractions/proportions Numerator number of individuals experiencing event Denominator population at risk! Expressed as a % but usually per population Prevalence The proportion of a population that are cases at a point in time Incidence number of new cases of disease for a particular time period (true rate) Specific rates eg gender specific rate specifying a selected denominator.

5 - 5 - Classification of disease ICD 10 = International classification of disease Attributable risk Disease rate in exposed disease rate in unexposed! e.g. rate of lung cancer in smokers rate of lung cancer in non-smokers - Shows proportion of the disease in exposed subjects due to exposure Relative risk ratio of disease rates in exposed Vs unexposed. (Risk in exposed/risk in unexposed). Confounding An extraneous variable that correlates to both the in/dependent variables Measurement error and bias selection bias (for control or case), information bias, measurement error (regression towards mean), analysing validity, sensitivity Vs specificity. Validity ability to distinguish b/w who has disease or not 2 components specificity and sensitivity.! Causative agent, transmission, receiver, the source/reservoir, host/environmental factors, and control Surveillance The systematic, active, ongoing observation of the occurrence and distribution of disease within a population and of events or conditions that inc/dec the risk of such disease occurrence. Define event to be surveyed! collecting the data in systematic way! tabulating data! analysing/interpretation! using information to bring about changes. Study design Case control-study to examine possible relation to an exposure for a certain disease. Ecological studies eg relationship b/w eating meat in certain countries + bowel cancer Longitudinal or cohort studies over selected time Case-control or cross-sectional studies observation at a single point in time/interval Experimental studies eg randomised clinical trial. Prokaryotic structure and function 2 Cytoplasm: Fluid portion of cytoplasm consists of soluble enzymes and various in/organic compounds. Cytoplasm is very granular (ribosomes). Cytoplasmic membrane has a lipid bilayer but has no steroids. Nucleoids: Bacterial chromosome is a single, double-stranded circle (genome contains all information for controlling development and metabolic cell activities), not contained in a nucleus but a discrete area (nucleoid). Nuclear material occupies nucleoid region. Multiple copes of mitochondrial + chloroplast DNA are contained within the matrix or stroma + organelles are usually distributed in several clusters (= nucleoids) attached to inner mitochondrial membrane. Genome is supercoiled and folded into a tight mass, complexed w protein + RNA core keeps it folded. Plasmids: smaller, circular extra-chromosomal (additional) DNA s, most commonly in gram ve. In cell, but not part of genome. Not often for cell survival but often provide a selective advantage (e.g. offer resistance to antibiotics, heavy metals or able to synthesise or break down unusual compounds). Are multiple copies of small self-duplicating pieces