intro to microbiology

Question 1

macroparasites vs microparasites

Answer 1

macroparasites are helminths, visible with naked eye, eggs leave host, long genereation time, poor immunity
microparasites are viruses/bact/protozoa/fungi, not visible with naked eye, replication product remains in host, short generation time, immunity present

Question 2

how are bacteria classified

Answer 2

morphology: cell wall nature/staining/shape/spore-forming ability
biochemical properties: enzyme/toxin production/effect of oxygen on bacterial growth
DNA sequencing of genome

Question 3

how are viruses classified

Answer 3

DNA/RNA
nucleic acid ss/ds + physical construction
polarity of viral genome (+ve or -ve RNA)
symmetry of nucleocapsid
lipid envelope (present or absent)

Question 4

nucleocapsid shapes

Answer 4

icosahedral/helical

Question 5

helminths characteristics, transmission, examples

Answer 5

multicellular worms that infest body organs
direct transmission: ingestion or penetration of skin
indirect transmission: vector
eg tapeworms

Question 6

protozoa characteristics/transmission/examples

Answer 6

single-cellular
life cycle has metabolically active growth stage (trophozoite) and dormant stage
free-living or require host
transmitted by vehicles or insect vector
eg malaria

Question 7

fungi types/characteristics/cell wall

Answer 7

single cell (yeast)/branched filaments (hyphae, which forms a mycelium) /both (dimorphic)
fungi have thick cell wall made of chitin

Question 8

what is peptidoglycan made of?

Answer 8

polymer of hexose sugars N-acetylglucosamine + N-acetylmuramic acid + tetrapeptide chain

Question 9

gram-ve vs gram+ve bacteria

Answer 9

gram-ve: thin (5-10nm) peptidoglycan layer; has outer membrane; has LPS; high lipid+lipoprotein content; no techoic/lipotechoic acid; has porins
gram +ve: thick (20-80nkm) peptidoglycan layer; has outer membrane; no LPS; low lipid+lipoprotein content; has techoic/lipotechoic acid; no porins

Question 10

what is acid fast bacteria

Answer 10

cant be seen with gram stain; outer thick layer of complex waxy lipids-> resist decolourisation with acid-alcohol

Question 11

structure of bacterial capsules and their characteristics

Answer 11

gelatinous layer made of polysaccharides
allows bacterial adherence
protects bacteria from phagocytosis
has antigens-> determines virulence/used for lab diagnosis

Question 12

functions and appearance of pili

Answer 12

mainly in gram -ve bacteria
aka fimbriae, they are hair-like filaments
attachment
conjugation

Question 13

how are plasmids transmitted

Answer 13

conjugation 
transformation (DNA from external environment incorporated into genome)
transduction (genetic material exchanged using bacteriophage)

Question 14

characteristics of bacterial spores

Answer 14

only produced by some gram positive bacteria
has bacterial DNA surrounded by thick keratin coat
forms when nutrients are depleted from environment
resistant to heat (must kill by autoclaving)
resistant to chemicals (must use sporicidal solutions)
can survive for long time (wounds contaminated with soil might have spores)

Question 15

viral capsid structure and types

Answer 15

constructed from virally-encoded protein subunits called capsomeres
icosahedral (20 solid equilateral triangles)
helical (only in RNA viruses)
complex (poxviruses only; surrounded by lipid layer and pallisade layer

Question 16

viral envelope characteristics

Answer 16

not in all viruses
has spikes (viral glycoproteins)-> heavily glycosylated-> carbs not immunogenic-> protection from antibodies
viral matrix protein mediates interaction between capsid and envelope
enveloped viruses only survive transiently outside host, unlike naked viruses

Question 17

importance of viral surface proteins, where to find

Answer 17

attach to host cell receptors-> determines tropism 
antibody target 
determines antibody specificity 
can be capsid proteins (naked virus) 
or spikes

Question 18

how is viral mrna transcribed

Answer 18

RNA dependent RNA polymerase: transcribes from RNA template

DNA dependent DNA polymerase: transcribed from DNA template

Question 19

sources of gene expression and replication

Answer 19

DNA genomes: large viruses use host’s genome which encodes enzymes viruses need/small viruses use host enzymes
RNA genome: encode their own RNA dependent RNA polymerase
retroviruses: use reverse transcriptase to copy ssRNA-> SSDNA-> template for protein synthesis