Bacterial Structure and Function Flashcards
Algae: characteristics
no human pathogens; all photosynthetic
Fungi: characteristics
some human pathogens; non-photosynthetic; rigid cell wall
Protozoa: characteristics
some human pathogens; no rigid cell wall; unicellular; non-photosynthetic
Bacteria: characteristics
many human pathogens; most require compounds as energy source but some of the non-pathogens are photosynthetic; all (except 1) have a rigid cell wall
Microorganisms are unicellular or multicellular?
unicellular BUT they can act like multicellular organisms, and differentiate into functionally distinct regions.
examples of microorganisms acting as functionally distinct regions?
stalk and spore formation in soil microbe Myxococcus xanthus; formation of surface microbial communities on implants by pathogenic microbes.
microorganisms are divided into 2 subgroups on the basis of what?
structure of the individual cell. this has clinical importance because different classes of abx are used to treat pathogens in each group. The groups are Bacteria v. Fungi/Protozoa/Algae
higher microorganisms include what?
fungi, protozoa, algae. (eucaryotic cells: true nucleus). Eucarya domain.
lower microorganisms include what?
bacteria. (procaryotic cells). bacterial domain.
eucaryotic: chromosomes and replication
each cell contains a number of different linear chromosomes contained within the nuclear membrane. mitosis occurs.
procaryotic: chromosomes and replication
each cell generally contains one circular chromosome. not bound by a circular membrane. the mechanism of chromosome segregation during division does not involve mitosis.
eucaryotic: mitochondria, and other membrane-bound structures.
mitochondrion contains oxidative enzymes and carries out oxidative phosphorylation. euk cells also contain other membrane-bound structures, such as vacuoles, perixosomes, etc
prokaryotic: mitochondria and other membrane-bound structures
contain no mitochondria. (mitochondria likely evolved from prok’s). oxidative enzymes and oxidative phosphorylation are associated with cytoplasmic membrane of cell.
general characteristic of prok cell, re: membrane bound structures
no membrane-bound structures that are smaller than the cell itself. prok cells do have internal organization at the level of protein localization (some to pole, some to center of cell)
euk: mechanism of cellular movement
cytoplasmic streaming (amoeboid movement) or contraction of flagella/cilia
prok: mechanism of cellular movement
no cytoplasmic streaming or amoeboid movement. some bacterial cells have flagella (but structure of bacterial flagellum is different: long helical filament composed of repeating protein subunits with a hollow tube). no microtubules in flagellum, typically has no membrane coat.
euk: cell wall?
in higher plants and green algae the cell wall is composed of polysaccharide celluose (polymer of glucose). in fungi, the cell wall is chitin (polymer of acetyl glucosamine) and beta 1,3 glucan (polymer of glucose)
prokaryotic: cell wall
cell wall composed of peptidoglycan polymer containing muramic acid (derivative of acetyl glucosamine), D-amino acids and other unusual AAs. peptidoglycan polymer = reason why antibiotics work without harming human cells.
eucaryotic: RNA
RNA transcribed in nucleus, spliced and transported to the endo reticulum where it is translated to protein.
prok: RNA processing?
no nucleus, so RNA is translated as it is transcribed. No splicing.
Nuclear division of proks and euks?
Prok: nonmitotic. Euk: mitotic
Nuclear membrane and chromosome # of proks and euks?
Prok: no nuclear membrane, single circular plasmid chromosome.
Euk: nuclear membrane, more than one chromosome.
Prok and euk: sexual reproduction
Prok: partial, unidirectional transfer of DNA
Euk: Meiosis
Prok and euk: cytoplasmic structure: mitochondria, ER, lysosomes and other organelles
Prok: all absent.
Euk: all present.
Prok and Euk: Ribosome weight?
Prok: ribosomes 70S.
Euk: ribosomes 80S (except in mitochondria: 70S)
Prok and Euk: mRNA splicing?
Prok: absent.
Euk: Present.
Prok and Euk: sterols?
Prok: absent with exception of Mycoplasma (may contain sterols in membrane)
Euk: present (impt for drug treatments, since certain antifungal antibiotics also react with sterols in the host membranes).
Prok and Euk: muramic acid?
Prok: present in most
Euk: absent
Prok and Euk: cell wall?
Prok: peptodiglycan with muramic acid
Euk: not present, or of another polymer (not peptidoglycan)
Prok and Euk: Bacterial flagella?
Prok: present in some
Euk: absent
Prok and Euk: multistranded flagella or cilia?
Prok: absent
Euk: present in some
in clinical microscope specimens, what is the size cutoff for a cell that is too large to be a bacterium?
cells larger than 10 micrometers are not bacterial.
spherical bacterium or coccus: general diameter?
0.8 -1.0 micrometers.
pneumococcus and gonococcus: what shape?
elongated cocci
staphylococcus: what shape?
perfect sphere
what are spirochetes?
bacteria with a spiral shape. however, do not have a rigid wall and therefore are classified differently.
what will happen with mammalian cells in distilled water that will not happen with bacterial cells?
in distilled water, mammalian cells will burst; bacterial cells will not. in general, mammalian cells will change shape depending on the ionic strength of the medium, while bacterial cells will remain stable.
what determines the pattern of clustering/stranding of bacteria?
the pattern of division. streptococci (grape-like clusters) result from irregular division patterns. chain of cocci like streptococci results from division along the same axis.
what will happen to a bacterial cell if the cell wall is digested? what is the result called?
bacterium will assume a spherical shape, regardless of original shape (which was maintained by cell wall). result is called protoplast. cell may now burst if placed in hypotonic media.
do bacteria have ribosomes?
YES, smaller than mammalian ribosomes: 70s vs 80s)
another item found in cytoplasm of bacteria?
granules. storage vesicles, can contain glycogen, lipid. nutrients
structure of cell wall subunit?
peptidoglycan.
N-acetyl glucosamine + muramic acid (muramic acid is N-acetyl glucosamine + lactic acid). NAG-NAG-LA.
4 amino acids are linked to LA.
describe cross-linking in the cell wall subunits
bonding between amino acid side chains. gives cell wall strength and flexibility.
what does penicillin do?
blocks the formation of a cell wall by blocking cross-linking between peptidoglycan units.
what is the action of lysozyme?
cleaves the bond between NAG and MA. therefore digests the cell wall of some bacteria –> acts as antibacterial. present in tears.
gram positive bacteria stain what color?
blue
gram negative bacteria stain what color?
red
are gram + or gram - bacteria more susceptible to abx and disinfectants?
gram positive are more susceptible
what is the difference between the outer membranes of gram + and gram - bacteria?
Gram +: have a cytoplasmic membrane (like mammalian cells). have a THICK peptidoglycan layer. then have teichoic and lipoteichoic acids sticking out, along with other proteins.
gram neg: cytoplasmic membrane, THIN peptidyglycan layer, then outer membrane containing lipopolysaccharides.
what are the antigenic components of gram pos bacteria?
teichoic/lipoteichoic acids
what is the antigenic component of gram neg bacteria?
the lipopolysaccharides in the outer membrane.
which bacteria have a periplasmic space? what is contained in this space?
gram neg bacteria have a periplasmic space. it contains some binding proteins and some digestive/hydrolytic enzymes.
describe the structure of an LPS unit
outer component = sugar tail, “O-specific side chain”. central portion = Lipid A. internal to that are lipids reaching into the bilayer of the outer membrane.
which type of protein has porins in the outermost portion of membrane?
gram neg has porins embedded within the outer membrane. they allow entry of nutrients via passive diffusion.
what is it about gram neg bacterial that makes them less susceptible to abx and disinfectants?
the substances can’t get through the outer membrane: abx are too big to fit through the porins. however, smaller abx could get to the periplasmic space via porins. but may be degraded by enzymes in the periplasmic space.
lipopolysaccharide is also called…
endotoxin
what is the toxic part of LPS/endotoxin?
Lipid A.
do gram pos bacteria secrete degradative enzymes (parallel to the ones found in periplasmic space of gram neg?)
YES, they just secrete them into extracellular region or tether them to their cell wall.
what is endotoxin responsible for? it is found only in what type of bacteria?
resp for shock and fever during sepsis. found only in gram neg bacteria
what is it about the gram pos bacterial that causes them to hold on to the crystal violet stain?
the higher carbohydrate content that retains the dye-iodine complex.
what is a capsule?
non-essential secretion on the cell surface. usually polysaccharide, hence different from the cell wall. doesn’t stain at all. may be a loose slime layer
what helpful function does the capsule play for bacteria?
plays a key role in resisting phagocytosis.
what are flagella composed of?
proteins (flagellins). long helical filament composed of repeating units with a hollow tube down the middle
what are the different variations of flagella on bacteria?
some are single flagellum, some bacteria have flagella covering entire cell
function of pili? (2)
- adherence to other cells.
2. found only on male bacteria, needed for transfer of DNA from one bact to another. ‘sex pilus’
molecular structure of pili?
hollow tubes, filamentous, shorter than flagella
why would adhesion to host cells be impt?
affects bacterial survival: UTI bacterial can survive flow of urine and remain in urinary tract.
where are spores found? (which bacteria?)
only found in a few species of bacteria – the large gram positive rods in genera Bacillus and Clostridia.
what prompts formation of a spore?
nutrient deprivation.
at what point will a spore be formed? how many per bacterium?
will be formed after the logarithmic phase. one per bacterium.
describe the qualities of a spore
dormant, very resistant to drying, heat, and chemicals. can survive boiling and must be subjected to at least 121’C to be killed
what will cause a spore to become a bacterium again? what is this process called?
called germination. occurs in response to a specific trigger, such as presence of a specific nutrient and/or environment (ie lung tissue -> anthrax). spore coat ruptures, bacterium emerges.
describe chemotaxis
motile bacteria may move in response to chemical gradients. rotation of flagellum causes motion: counter-clockwise will cause travel in a line, but otherwise bacterium will tumble randomly until re-directed.
