Bacterial Structure and Physiology Flashcards Preview

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Flashcards in Bacterial Structure and Physiology Deck (153)
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1

How big are bacteria?

Generally: 1-2 um

The smallest bacteria overlap with viruses

2

What is included in a cell envelope?

Minimum: Cell membrane and cell wall 

Gram (+): Cell membrane and cell wall

Gram (-): Outer and inner membrane, thin cell wall, periplasm

3

What is the difference between the outer and inner membranes in Gram (-) bacteria?

Outer membrane: Contains lipopolysaccharides (LPS) instead of phospholipids

- Lipid A

- Core polysaccharide

- O-antigen

Inner membrane: a phospholopid bilayer similar to the cytoplasmic membrane of gram (+) bacteria

4

What are the functions of bacterial cell membranes?

  • Permeability barrier with transport mechanisms
  • Electron transport
  • Export of membrane and secreted proteins
  • Biosynthesis of cell wall components
  • Partition of newly replicated chromosome into daughter cells during cell division

5

What compound do most bacterial membranes NOT contain?

Sterols

Exception: wall-less organisms (mycoplasmas)

6

What kinds of bacterial cell membranes contain sterols?

Mycoplasma

(These bacteria do not have cell walls)

7

Which bacteria have an external cytoplasmic membrane but no cell wall?

Mycoplasma 

8

What are cocci?

Spherical

9

What are bacilli?

Rods

10

What are coccibacilli?

Short rods that appear to be spherical

11

What are the three components of LPS?

  • Lipid A
  • Core polysaccharide
  • O antigen (or O-specific side chain)

12

What is Lipid A?

Where is it found?

What does it do?

Lipid A: a phosphorylated diglucosamine molecule with substituted fattey acids

Found in: Outer membrane of gram negative bacterial cell envelope; part of LPS

Function: contributes to the toxic effects of LPS

13

What is core polysaccharide?

A region attached to lipid A consisting of 7-9 sugar residues

(Ketodeoxyoctonate and heptose are two unusual sugar residues found there)

14

What is O-Antigen?

Where is it found?

What does it do?

O-Antigen: Repeating units of 3-5 sugar residues

Found in: Outer membrane of gram (-) cell envelope. Part of LPS. (However, not present in all gram (-) bacteria)

Function: Protective against complement-mediated lysis; it confers serum resistance

BUT: antibodies can recognize O-antigens, leading to clearance of the bacteria 

15

What component of LPS is toxic to humans? 

Lipid A

16

What is the unique component of bacterial cell walls?

Peptidoglycan

 

Also known as murein

17

What are the functions of peptidoglycan?

  • Gives bacterial cells their shape
  • Protects cell against osmotic lysis

18

What is the basic structure of peptidoglycan?

Long polymers of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) w/ alternating L-and D- amino acids

The polymers are crosslinked to each other to form 3D sheets

19

What kinds of bacteria contain teichoic acid in their cell walls?

Gram positive

20

What is teichoic acid?

Where is it found?

What does it do?

Teichoic Acid: Long polymers of glycerol phosphate or ribitol phosphate. Contains sugars and amino acids

Where found: Embedded in cytoplasmic membranes of gram (+) bacteria. Extends through cell wall

Function: makes the bacteria sticky! Teichoic acids function as adhesins on the bacterial surface

21

Which enzymes are responsible for proper crosslinking of NAG/NAM chains?

Penicillin-binding proteins (PBPs)

22

What class of proteins are penicillin-binding proteins?

Enzymes

23

At low concentrations, how does LPS (aka endotoxin) affect the human host?

Effects that are protective of the host

  • Fever
  • Activates Complement
  • Stimulates B cells and macrophages
  • Activates acute phase response

24

Describe the crosslinking process

PBPs link the third amino acids of some tetrapeptides to the terminal amino acids of other tetrapeptides

25

What are penicillin binding proteins responsible for?

Crosslinking NAG/NAM chains to form 3D sheets

26

Describe the gram staining process

  1. Apply crystal violet 
  2. Apply iodine 
  3. Alcohol Wash
    (Crystal violet and iodine remain in gram (+) bacteria and wash out of gram (-) bacteria)
  4. Sarafin (couterstain; stains gram (+) bacteria red)

27

Which type of bacteria have a thick cell wall?

Gram-positive

28

Which type of bacteria have a thin cell wall?

Gram-negative

29

Which types bacteria are poorly visualized by Gram staining?

Mycobacteria, some spirochetes, and mycoplasma

Mycobacteria: cause TB, leprosy, other diseases

Spirochetes: Treponema pallidum causes syphilis

30

Why are myobacteria poorly visualized using Gram staining?

Special lipids in their cell envelops prevent them from taking up crystal violet/iodine dye

 

Use acid-fast, Ziehl-Neelsen, or Kinyoun staining instead