Intro to microbiology

Question 1

Compare viruses, bacteria, fungi, protozoa&helminths in terms of: cells, nucleic acid, types of nucleus, ribosomes, membrane bound organelles, nature of outer surface, method of replication

Answer 1

ref. notes

Question 2

Compare macroparasites and microparasites in terms of: organism, size, replication product, immunity

Answer 2

ref. notes

Question 3

What kind of characteristics for bacteria are used for its classification

Answer 3

Morphological characteristics (nature of the cell wall, staining, shape, spore forming abilities), Biochemical properties (metabolism, production of specific enzymes), DNA sequencing their genome

Question 4

What kind of characteristics for viruses are used for its classification

Answer 4

Types of nucleic acid, number of strands of nucleic acid, and their physical condition, polarity of viral genome, symmetry of nucleocapsid, lipid envelope

Question 5

What are helminths and how can it be transmitted

Answer 5

Multicellular worms that infest organs e.g. GI tract

transmission: indirect=via intermediate non human hosts direct=swallowing infective stages or by larvae penetrating skin

Question 6

What are protozoa and how can it be transmitted

Answer 6

single cell organisms, free living/host requiring,

Transmission: ingestion of contaminated water/food

Question 7

What types of fungal diseases are there and where do they arise

Answer 7

Superficial=hair shaft, dead layer of skin
Cutaneous=epidermis, hair, nails
Opportunistic=Internal organs

Question 8

What are essential and non essentail components of a bacterial cell

Answer 8

Essential: cell wall, plasma membrane, ribosome, nucleoid

Non essential: capsule, flagella, pili, plasmid, spore

Question 9

What is peptidoglycan comprised of

Answer 9

Is a polymer composed of hexose sugars (N-acetylglucosamine and N-acetylmuramic acid) and amino acids

Question 10

Gram staining procedure

Answer 10

primary stain: crystal violet (blue)->mordant fixes the dye: iodine->decolourising agent alcohol/acetone->counter stain: safranin (red)

Question 11

Why does gram positive and negative stain differently

Answer 11

Negative doesn’t retain primary staining due to thin peptidoglycan

Question 12

Compare gram positive and negative in terms of: peptidoglycan layer, outer membrane, LPS, lipoprotein content, teichoic acid, porin

Answer 12

ref. notes

Question 13

Why can’t some bacteria be gram stained

Answer 13

thick outer layer of complex waxy lipids mean that gram stain don’t penetrate the walls. These are acid-fast because they resist decolourisation with acid-alcohol after being stained. Ziehl-Neelsen stain used to stain acid-fast bacteria

Question 14

Describe properties of the bacterial capsule

Answer 14

gleatinaous layer outside cell wall mainly comprised of polysaccharides. Determinants of virulence, helps bacterial adherence, antigenic (can be vaccine component)

Question 15

Describe properties of the flagella

Answer 15

organ of motility, role in pathogenesis, identification+lab diagnosis

Question 16

What are fibriae and what do they do

Answer 16

hair-like filaments that extend from cell surface. Thinner and shorter thean flagella
Function: attachment, conjugation

Question 17

What are properties of plasmids and what are they transmissable by

Answer 17

mostly circular dsDNA, capable of self replication, can contain antibiotic resistance genes,
Transmission: conjugation, transduction, transformation

Question 18

What are the properties of spores

Answer 18

only produced by some gram positive bacteria, highly resistant structures formed in response to adverse conditions, contain bacterial DNA surrounded by thick keratin-like coat that confers resistance to: heat (resistance to boiling, killed by autoclaving)
chemical (only sporicidal kills it)
drying, can survive long time (wound contaminated with soil can be infected by spores)

Question 19

What is required for viral propagation

Answer 19

Machinery for translation of viral mRNA
Enzymes for replication of genome and assembly of new virions.
Transport parthways to reach site of replication, viral assembly
energy source

Question 20

Virus essential and nonessential components

Answer 20

Essential-DNA or RNA genome, capside core, polymerase protein
Nonessential-envelope

Question 21

What are capsids and what are its properties

Answer 21

Constructed from small number of virally encoded protein subunits=capsomeres. Viral genome enclosed by capsid protein coat is called nucleocapsid
symmetry shown by virus particles: icosahedral (20 triangles arranged around sphere), helical, complex (neither helical nor icosahedral.

Question 22

What are the properties of viral envelopes and its functions

Answer 22

lipid bilayer containing viral glycoproteins that project from membrane
Function: determines the stability of virions outside the host and correlates with mode of transmission.(nonenveloped=stable in environment, transmitted by food/water, enveloped=only survive transiently outside host and infectious viruses do not persist in environment)

Question 23

Importance of viral surface protein

Answer 23

attach to receptors - determinant of tropism
target for antibodies-neutralisation
determinant of antibody specificity (serotype)

Question 24

What are the steps for viral replication

Answer 24

Surface proteins of virus interact with receptor on target cell. Whilst enveloped viruses bind to their receptor via spikes in their envelope, naked viruses recognise receptors directly by coat->Many barriers to entry into host overcome by fusion of envelope onto host membrane or translocation of virion across the host cell membrane or receptor mediated endocytosis->uncoating so nucleic acid available for transcription->production of viral proteins and replication of viral genome->bringing together newly formed viral nucleic acid and the structural proteins to form the nucleocapsid of virus->release+dissemination/transmission

Question 25

What does transcprition and translation of viral DNA result in and why does it take these steps

Answer 25

DNA->(transcription)mRNA->(translation)protein
Viral protein synthesis dependent on cellular translation machinery (ribosomes) so all viral genomes must produce mRNA to express viral proteins

Question 26

Difference between RNA dependent RNA polymerase and DNA dependent RNA polymerase

Answer 26

RNA dependent=enzyme catalysing the transcription of RNA from RNA template
DNA dependent=catalyses the transcription of RNA from DNA template

Question 27

How do the purposes of the following differ: DNA genomes, RNA genomes, retroviruses

Answer 27

DNA genomes: large viruses encode many of the enzymes they need (DNA dependent RNA polymerase). Small viruses use host cell enzymes
RNA genomes: most encode own RNA dependent RNA polymerase which uses a complementary RNA as template
Retroviruses: use reverse transcriptase to copy a +ve ssRNA genome into dsDNA which is template for protein and new genome synthesis