Bacterial Structures

Question 1

Bacterial cells divide by

Answer 1

BINARY FISSION: DIVISION IN HALF
LESS COMPLEX THAN MITOSIS (although more complex than you would think)
CELLS DIVIDE INTO TWO NEARLY IDENTICAL DAUGHTER CELLS FOLLOWING REPLICATION OF GENETIC MATERIAL

Question 2

Eucharyotic cell walls in Animals, Fungi and Plants

Answer 2

ANIMALS: no cell wall
FUNGI: chitin cell wall, a linear polymer of N-acetyl glucosamine
PLANTS: cellulose cell wall, a linear polymer of glucose units with few cross links

Question 3

Bacterial Cell Walls

Answer 3

BACTERIA: Peptidoglycan is not a linear but heavily cross-linked polymer
The crosslinks make this a rigid cell wall
It contains both, sugar and peptide components

Question 4

Cocci

• shape
• gram+/-?
• clinically relevant examples

Answer 4

• Shape: Spherical
• Gram + or -

Clinically relevant examples for Gram-negative cocci
Neisseria species
Moraxella species

Clinically relevant examples of Gram-positive cocci
Staphylococcus species
Streptococcus species
Enterococcus species

Question 5

Rods (Bacilli)

• shape
• gram+/-?
• clinically relevant examples

Answer 5

• shape: cylendrical
• can be individual cells or filamentous
• gram +/-

Clinically relevant examples for Gram-negative rods
Escherichia coli
Salmonella species
Shigella species
Pseudomonas species

Clinically relevant examples of Gram-positive rods
Clostridium species
Bacillus species
Mycobacterium species

Question 6

Spirochetes

• shape
• grame +/-?
• clinically relevant examples

Answer 6

• spiral shaped
• Gram-Negative

Clinically relevant examples for Gram-Negative Spirochetes
Leptospira species (leptospirosis)
Treponema pallidum (syphilis)
Borrelia burgdorferi (lime disease)

Question 7

Cell Envelope

• what does it tell you?
• what is the one universal characteristics?
• what are the non-universal characteristics?

Answer 7

• difference between gram +/-

Universal:	 Cytoplasmic membrane
Not universal:
Cell wall
Periplasmic membrane
Teichoic acid
Lipopolysaccharide
Capsule

Question 8

Cytoplasmic membrane in bacteria

Answer 8

• all bacteria have it

The cytoplasmic membrane is a lipid bilayer
It incorporates many proteins involved in various cellular processes
Molecules that can not diffuse through the membrane are subject to active transport
Membrane is polarized to allow for energy generation (analgous to Mitochondria in Eukaryotes)
The antibiotic Daptomycin depolarizes the membrane

Question 9

Peptidoglycan cell wall in bacteria

Answer 9

Almost all bacteria have it

Peptidoglycan is a large macromolecule encompassing the entire bacterial cell
Gives cells their shape
Stabilizes cells in hypotonic or hypertonic environments

Question 10

Murein

Answer 10

The BUILDING BLOCK OF THE CELL WALL IS CALLED Murein, A NAG-NAM-Tetrapeptide

The sugar chain is invariant in bacterial peptidoglycan
The tetrapeptide shows species specific variation and unusual aminoacids not found in proteins e.g. D-alanine and di-amino-pimelic acid
Some bacteria (Staphylococcus aureus) utilize a glycine bridge to cross link two pentapetides

Question 11

Peptidoglycan

Answer 11

Peptidoglycan consists of polysaccharide chains
The chains are crosslinked via peptide side chains
So called penicillin binding proteins (PBP) are building the cell wall from precursors.
These proteins have two activities, transglycosylation (chain elongation) and transpepdidation (cross linking of chains)

Question 12

CELL WALL Biosynthesis

Answer 12

Target of many antimicrobials

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Question 13

What are the bacteria that don’t have a cell wall

Answer 13

Mycoplasma
Mycoplasma are streamlined simple bacteria without a cell wall.
Some are clinically relevant and naturally resistant to cell wall targeting antibiotics.
Mycoplasma are the only bacteria whose membrane contains sterols, which they accumulate from the host.

L-forms
L-forms are cell wall less mutants of bacteria that typically have a cell wall.
There is conflicting evidence whether L-forms are of clinical relevance.

Question 14

Periplasmic membranes

Answer 14

• gram negatives

The outer membrane contains pores (porins) that allow smaller molecules to readily pass

Larger molecules are excluded from the periplasmic space between the membranes protecting the cell from damaging effects.

Question 15

Lipopolysaccharide (LPS)

Answer 15

• HALLMARK OF GRAM -

Where: Found in the outer membrane of gram-negative bacteria
Why: Essential to the integrity of the outer membrane and giving rigidity to the cell
LPS elicits a strong immune response in animals and thus is also called endotoxin. This response to LPS is one of the main causes of septic shock, a potentially lethal condition.
The toxic part is Lipid A

Question 16

Teichoic acid

Answer 16

• HALLMARK OF GRAM +
  There are two different types, wall teichoic linked to the cell wall and lipoteichoic acid linked to the membrane
  Wall teichoic acid is an essential structure for Gram-positives (i.e. a potential drug target)
  Teichoic acid provides rigidity to the cell wall
  Teichoic acid is a copolymer of glycerol phosphate and various carbohydrates.
  Teichoic acid is immunogenic and also functions in adhesion

Question 17

capsule or slime layer

Answer 17

• various pathogens can gave a capsule or slime layer

Both, Gram negatives and Gram positives can feature capsules
Capsules are typically polysaccharide layers but can also be composed of other materials, e.g. poly-D-glutamic acid of Bacillus anthracis.
Capsules are a virulence factor enhancing the ability to cause disease by protecting from phagocytosis

Question 18

MOST IMPORTANT FACTS ABOUT BACTERIA CELL ENVELOPE

Answer 18

Gram-negatives and Gram-positives cell envelopes are distinct
All bacteria have a cytoplasmic membrane
Almost all bacteria have a peptidoglycan cell wall
Gram-negatives have as important additional feature a periplasmic membrane and LPS
Gram-positives feature wall- and lipoteichoic acid and a thick cell wall
Some pathogenic bacteria have additional protection via a capsule