introduction to microbio and bacterial cells

Question 1

how many Cellular organisms are there

Answer 1

2 cell types
Prokaryotes
Eukaryotes

Question 2

Prokaryotes

Answer 2

Bacteria
Archaea
1-5µm
Haploid
Asexual reproduction
Unicellular
No true nucleus
Cell wall*

Question 3

Eukaryotes

Answer 3

Fungi (yeasts)
Protozoa, Helminths
Slime moulds, Algae

10µm
Diploid *
Sexual reproduction*
Unicellular /multicellular
True nucleus

Question 4

viruses

Answer 4

No cellular
Structure.
(Genetic material surrounded by protein)

Question 5

Prions

Answer 5

No nucleic acid
(Pieces of infectious protein)
e.g. Bovine Spongiform Encephalopathy

Question 6

Bacteria

Answer 6

Unicellular
Huge diversity:
size,
shape,
habitat & metabolism
Majority are harmless or even beneficial

Question 7

Morphology

Answer 7

cell shape
size
motility
spore forming

Question 8

Metabolism

Answer 8

use of energy sources/nutrients

Question 9

Molecular characteristics

Answer 9

protein, lipid structure
sequence of gene encoding 16S RNA

Question 10

Plasma (cytoplasmic) membrane in bacterial cells

Answer 10

Selectively semi-permeable barrier
Mediates nutrient transport
Site of secretion & respiration
Site of environmental response regulators

Question 11

Cytoplasm in bacteria

Answer 11

Between plasma membrane & nucleoid
* Ribosomes – protein translation (70S: 50S & 30S subunits)
Inclusion bodies: Storage bodies Contain important nutrients (C,P,N,S)
No mitochondria! – (Energy production occurs on the cytoplasmic membrane)
No True Nucleus

Question 12

Double-stranded DNA in bacteria

Answer 12

Not enclosed by a nuclear membrane
- Usually a single closed circular chromosome
- DNA is supercoiled
- 1 copy of each gene

Question 13

Plasmids- bacteria

Answer 13

extrachromosomal ;small, circular dsDNA
- replicate independently of chromosome (multiple copies)
- Encode auxiliary functions

Question 14

Prokaryotic cell wall- bacteria

Answer 14

An extremely important structure
-Protects from the environment
Provides rigidity, strength
Unique to bacteria ( makes an excellent drug target)
Composed of peptidoglycan cross-linked to form a mesh

Question 15

Peptidoglycan structure

Answer 15

A glycan backbone made of a chain of sugar residues-
Each sugar is joined by a strong glycosidic bond.
Every other sugar is linked to a short peptide (chain of amino acids)
These peptide sidechains crosslink to a peptide on an adjacent glycan backbone.
A strong mesh like structure is formed- It is NOT a solid barrier
Mesh like structure allows molecules to pass in and out.
2 types of bonds make it strong and rigid
Glycosidic bonds and peptide bonds
Contains other components that contribute to pathogenicity
(lipopolysaccharide, lipoteichoic acids)

Question 16

peptidoglycan (PG) structure
divide MOST pathogenic bacteria into 2 Groups

Answer 16

Gram positive: stain PURPLE
Gram negative: stain PINK

Question 17

Gram positive: stain PURPLE

Answer 17

THICK (20-80nm) PG layer which constitutes 60-80% cell wall
-X-linked to form thick mesh
Eg- Staphylococcus aureus

Question 18

Gram negative: stain PINK

Answer 18

THIN (1-3nm) PG layer which
constitutes 10-20% cell wall
- Surrounded by an outer membrane
Eg. E.coli

Question 19

Lipoteichoic acids- Gram-positive cell walls

Answer 19

Teichoic acids bonded
to membrane lipids
Released by killed
bacteria during infection.
Trigger inflammatory
response

Question 20

Teichoic acids-Gram-positive cell walls

Answer 20

Acidic polysaccharides
bonded to peptidoglycan
Transport metal cations

Question 20

Periplasm-Gram-negative cell walls

Answer 20

Gel-like consistency
Contains proteins

Question 20

Lipopolysaccharide-Gram-negative cell walls

Answer 20

Stabilises membrane structure
Strongly immunogenic
Extremely toxic to animal cells
Heat resistant

Question 20

Outer membrane-Gram-negative cell walls

Answer 20

Impermeable to large molecules

Question 21

Porins-Gram-negative cell walls

Answer 21

Water filled channels

Question 22

Lipopolysaccharide (endotoxin)-Lipid A

Answer 22

Embedded in
outer membrane.
Toxic: ENDOTOXIN

Question 23

Lipopolysaccharide (endotoxin)-Core polysaccharide

Answer 23

10 sugars linked to lipid A

Question 24

Lipopolysaccharide (endotoxin)-O-specific polysaccharide

Answer 24

On surface of outer membrane.
Immunogenic

Important that lipopolysaccharides are not present in injectable medicines

Question 25

Bacterial endospores

Answer 25

Tough outer coat-Multiple layers of proteins and peptidoglycans
Dehydrated Core-Cytoplasm and DNA

Tough:
Resistant to: UV radiation, Desiccation, Freezing, High temperature and
MOST disinfectants (highly impermeable)

Question 26

Capsules & slime layers

Answer 26

Capsule: Firm, rigid hard to remove.
Slime layer: loose layer which is easier to remove

A Network of polysaccharides secreted outside of the peptidoglycan cell wall
Function:
Give protection
Aid attachment
Contribute to virulence
- Evade body defences

Question 27

Fimbriae (P-pili)

Answer 27

Aid attachment to surfaces
e.g. some pathogenic E. coli

Hair-like structures composed of protein subunits

Question 28

F-pili

Answer 28

Used in bacterial conjugation
Hair-like structures composed of protein subunits