Bacteria: Structure and Function

Cell Envelope

thick wall that covers the bacteria

fimbriae

can be found in both gram-positive and gram-negative bacteria

plasmid

can only be found in gram-negative bacteria

Lipoteichoic Acid (LTA)

stimulates white blood cell (macrophages) to produce a septic like reaction

Periplasm

only present in gram-negative bacteria

penicillin-binding protein

has a domain called transpeptidase domain which forms bonds that are formed between the glycan bones

gram-negative

shouldn't stay purple

Appendages

- Flagella
- Fimbrae
- Pilus
- Endospore

Bacterial Chromosome (nucleoid)

- entangled DNA
- the DNA that sits in the cytoplasm called as nucleoid

Plasmid

- another piece of DNA, not part of the bacterial chromosome
- circular small piece of DNA

Flagella

- primary function for motility

Flagella

- allows bacteria to move around different areas which creates a crux-type of action

Flagella

- powered by ATP in order to beat

Components of the flagella

- basal body
- hook
- filament

Monotrichous

located in one pole of the bacteria (Vibrio)

Lophotrichous

multiple flagella coming from one polar end of the bacteria (pseudomonas)

amphitrichous

flagella on both ends of the bacteria

peritrichous

flagella on the entire surface area of the bacteria (E. coli)

fimbriae

is shorter and thinner in comparison to pilus

fimbriae

has a larger number spread around the surface area of bacteria

fimbriae

formed from bacterial chromosome

fimbriae

function is to attach or adhere to cell surfaces

pilus

is longer and thicker in comparison to fimbriae

pilus

has a lower number spread around the surface area of the bacteria compared to fimbriae

pilus

attachment that is formed from plasmid

plasmid

structure that has DNA, and genes transcribed which makes protein to form pilus

pilus

plays a role in bacterial conjugation

bacterial conjugation

The transfer of plasmids between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells.

B - lactamase

Breaks down the beta-lactam ring of the penincilin

plasmid

has b-lactamase gene

penicillin

prevents bacterial growth

endospore

specialized structure that can only be found in several bacteria

Clostridium
Bacillus anthrasis

endospore can be found in:

endospore

allow bacteria to be very resistant to very harsh environment:
- high temperature
- high uv radiation
- less nutrients
- lots of chemicals
- dry environments

keratin

coating that makes the endospore more resistant to the harsh environment

- capsule/slime layer
- outer membrane
- cell wall
- periplasm
- inner membrane

layers from the most outer to inner component

capsule

an organized polysaccharide network

capsule

has a clinical significance of virulence factor and causes nasty infection in certain population

slime

a loose polysaccharide network

slime

- allow adherence to cell surface and foreign substances/molecules

outer membrane

only present in gram-negative bacteria

outer membrane

made of phospholipid bilayer

porin

part of the outer membrane which allows the transport of molecules, drugs in and out from the bacterial cell

lipopolysaccharide (LPS)

endotoxin which stimulates the release of IL-1, IL-6, TNF-A (sepsis)

O antigen
Core polysaccharide
Lipid A

parts of the lipopolysaccharide structure

core polysaccharide

polymer of sugar molecule

o-antigen

our immune system gets activated, recognizes the bacteria, produces antibody

o-antigen

where antibodies attack/attach

cell wall

gives shape and integrity of bacteria which gives resistance against osmosis changes

cell wall

present in both gram-positive and gram-negative bacteria

gram-positive peptidoglycan

thicker

gram-negative peptidoglycan

thinner

cell wall

made of peptidoglycan

peptido-

peptides

glycan

sugar

NAM

n-acetylmuramic acid

NAG

n-acetylglucosamine acid

glycan or sugar backbone

NAM and NAG get polymerized together to form

transpeptidase

domain of enzyme called penicillin binding protein

transpeptidase

forms a peptide chain which links together the glycan backbones

Lipoteichoic Acid (LTA)

present only in gram-positive bacteria

Lipoteichoic Acid (LTA)

analogous to LPS in gram-negative bacteria

Lipoteichoic Acid (LTA)

extends from inner membrane to the cell wall

Teichoic Acid

extends to the cell wall, doesn't touch inner membrane

Periplasm

space between outer and inner membrane

b-lactamase

found in the periplasmic space which inhibits penicilline

Periplasm

space between the outer membrane and inner membrane which is only found in gram-negative bacteria

b-lactamase

present in the periplasmic space which inhibits penicillin

Inner Membrane

found on both gram-positive and gram-negative bacteria

inner membrane

- phospholipid bilayer
- penicillin-binding protein

penicillin

inhibits the transpeptidase domain on penicillin-binding protein

Effects of penicillin on the transpeptidase domain on penicillin-binding protein

- no longer able to cross-link to stabilize the cell wall
- losing structure integrity
- losing the ability to resist osmotic fluctuation

structures that are only present in gram-positive bacteria

- capsule/slime layer
- thicker cell wall
- lipoteichoic acid and teichoic acid
- inner membrane with penicillin-binding protein
- flagella

structures that are only present in gram-negative bacteria

- capsule/slime layer
- outer membrane (porin, LPS (endotoxin)
- thinner cell wall
- periplasmic space
- b-lactamase enzyme
- penicillin-binding protein
- flagella
- pilus

gram-positive

bacteria with very thick peptidoglycan layer

gram-negative

bacteria that has a outer membrane which makes it selectively permeable which results in less crystal violet

iodine (mordant)

fixates the crystal violet inside the peptidoglycan layer which keeps the cell violet

iodine (mordant)

locks the crystal violet in the peptidoglycan layer

ethanol wash (acetone)

- compresses the peptidoglycan layer
- to wash some of the crystal violet out of the peptidoglycan layer

ethanol

suck out tons off crystal violet in the gram-negative bacteria

gram-positive

retain the crystal violet

safranin

- gives colour to the gram-negative bacteria
- goes into the peptidoglycan layer without crystal violet

safranin

causes gram-negative bacteria to be stained pink

crystal violet

causes gram-positive bacteria to stain violet

atypical bacteria

doesn't follow the classic gram-positive/gram-negative staining

atypical bacteria

gram-negative bacteria:
These → Treponema o Atypical → Anaplasmosis Microbes →Mycoplasma
Usually → Ureaplasma Lack → Leptospiral / Legionella
Color → Chlamydia Because → Bartonella Microbes → Mycobacteria
Barely → Borrelia burgdorferi (Lyme's disease)
Eat → Ehrlichia (Ehrlichiosis)
Ramen → Rickettsia (Bacteria from ticks)