SESIÓN 02 ESTRUCTURA Y REPLICACIÓN (MULTIPLICACIÓN) DE LAS BACTERIAS.

Question 1

List the processes of gram staining.

Answer 1

• 1) Bacteria are heat fixed or dried on to a slide
• 2) Stained w/ crystal violet
• 3) Stained w/ a precipitated w/ iodine
• 4) Excess stain is removed by washing w/ the acetone-based decolorizer and water.

Question 2

What color do gram positive bacteria turn?

Answer 2

• Purple (P-PURPLE-POSITIVE)

Question 3

What color do gram negative bacteria turn?

Answer 3

• Cannot retain the crystal violet stain, so they are counterstained w/ safranin and turned red.

Question 4

What conditions of bacteria are not dependable for gram staining?

Answer 4

• Bacteria that are starved, or treated with antibiotics.

Question 5

What are bacteria that cannot be classified with Gram stain and why? (2)

Answer 5

• Mycobacteria (waxy outer shell and are distinguished w/ acid-fast stain)
• Mycoplasmas which have no peptidoglycan

Question 6

What is serotyping?

Answer 6

• Classification of a bacteria using antibodies to detect characteristic antigens on the bacteria

Question 7

What are plasmids and why are they so important?

Answer 7

• They are smaller, circular, extrachromosomal DNAs which are commonly found in G(-)

Question 8

Which type of Gram bacteria has a thick, multilayered cell wall consisting mainly of peptidoglycan?

Answer 8

• Gram (+) bacteria

Question 9

Is peptidoglycan essential for the bacteria and for which aspects?

Answer 9

• Yes for structure, replication and survival in the normally hostile conditions in which bacteria grow.

Question 10

What does lysozyme do to the cell wall?

Answer 10

• Degrades the glycan backbone of the peptidoglycan.

Question 11

What is the name of the Gram (+) bacteria w/o cell wall?

Answer 11

• Protoplast

Question 12

What 3 components are parts of the cell wall?

Answer 12

• Teichoic, lipoteichoic acids and complex polysaccharides (usually called C polysaccharides)

Question 13

What is teichoic acid and what is its role?

Answer 13

• Water-soluble, anionic polymers of polyol phosplates which are covalently linked to the peptidoglycan & essential to cell viability.

Question 14

What are lipoteichoic acids and what are its roles?

Answer 14

• Fatty acids that are common surface antigens that distinguish bacterial serotypes & promote attachments to other bacterial to specific receptors on mammalian cell surfaces.

Question 15

How many layers do Gram (-) have external to their cytoplasmic membrane?

Answer 15

• 2 : Thin peptidoglycan layer and outer membrane (which is unique to Gram (-) )

Question 16

What is the periplasmic space?

Answer 16

• Between the external surface of the cytoplasmic membrane and the internal surface of the outer membrane.

Question 17

What things can we find inside the periplasmic space (3)?

Answer 17

• Components of transport systems, variety of hydrolytic enzymes, and many of the lytic virulence factors.

Question 18

Describe the inner and outer leaflet of the outer membrane.

Answer 18

• Inner leaflet = phospholipids

- Outer leaflet = lipopolysaccharide (LPS)

Question 19

What is another name for LPS and what is it’s role?

Answer 19

• Endotoxin, a powerful stimulator of innate and immune response.

Question 20

What does LPS do in terms of immune response?

Answer 20

• Activates B cells and induces macrophages, dendritic, and other cells to release interleukin-1, interleukin-6, tumor necrosis facor, and other factors. It induces fever and can cause shock.

Question 21

What is the Shwartzman reaction?

Answer 21

• Disseminated intravascular coagulation

Question 22

What is a porin?

Answer 22

• A group of transmembrane proteins that allow the diffusion of hyfrophilic molecules less than 700 Da in mass thru the membrane.

Question 23

How is the outer membrane held together?

Answer 23

• By divalent cation (Mg2+ and Ca2+) linkage between phosphate on LPS molecules and hydrophobic interactions between the LPS and proteins.

Question 24

What are Gram (-) bacteria with a disrupted outer membrane called?

Answer 24

• Spheroplasts

Question 25

What is glycocalyx?

Answer 25

• The capsules and slime layers.

Question 26

Which bacteria doesn’t have a glycocalyx?

Answer 26

• Bacillus anthracis

Question 27

Describe the mesh that makes up the peptidoglycan?

Answer 27

• Repeating disaccharides of N-acetylglucosamine and N-acetylmuramic acids (which a tetrapeptide of both L and D amino acids)

Question 28

Compare the peptidoglycan layer of Gram (+) to Gram (-).

Answer 28

• Gram (+): multiple layers, often cross-linked and very strong.
• Gram (-): one layer thick

Question 29

What are the 5 steps of peptidoglycan synthesis?

Answer 29

1. Cell glucosamine is enzymatically converted into MurNAc and then energetically activated by a reaction w/ UTP to produce UDP-MurNAc
2. UDP-MurNAc-pentapeptide precursor is assemble in a series of steps.
3. UDP-MurNAc pentapeptide is attached to the bactoprenol (conveyor belt) w/ the release of UMP GlcNAc
4. The bactoprenol molecule translocates the disaccharide: peptide precursor to the outside of the cell, attached to a peptidoglycan chain by the enzyme transglycosylases.
5. Peptide chains from adjacent glycan chains are cross-linked to each other by a peptide bond exchange (trans peptidation) between the free amineof the amino acid in the third position.

Question 30

Where are techoic acids attached?

Answer 30

• Attached to the N-terminus of the peptide of peptidoglycan

Question 31

Describe the structure of Lipopolysaccharide

Answer 31

• 3 Structures sections: Lipid A, core polysaccharide (rough core), and O antigen.

Question 32

What is Lipid A responsible?

Answer 32

• For the endotoxin activity of LPS

Question 33

Describe the core polysaccharide.

Answer 33

• Branched polysaccharide of 9-12 sugars. Contains an unusual sugar: 2-keto-3-deoxy-octanoate (KDO). It is phosphorylated.

Question 34

What is the O antigen used for?

Answer 34

• It distinguishes serotypes (strains) of a bacterial species.