Lecture 7: Bacterial Cell Shape

Question 1

What is the average size of bacteria?

Answer 1

0.2-1um x 2-8um

Question 2

What are the 3 basic bacterial shapes?

Answer 2

1. Spherical
2. Rod
3. Spiral

Question 3

What are some unusual bacterial cell shapes?

Answer 3

1. Star-shaped ‘stella’

2. Square ‘haloarcula’

Question 4

What does monomorphic mean?

Answer 4

having or existing in only one form (most bacteria)

Question 5

What does pleomorphic mean?

Answer 5

Occurring in various distinct forms (least common)

Question 6

What is the term used for pairs of bacteria?

Answer 6

Diplococci (spherical), diplobacilli (rod)

Question 7

What is the term used for clusters of bacteria?

Answer 7

staphylococci (spherical)

Question 8

What is the term used for chains of bacteria?

Answer 8

streptococci (spherical), streptobacilli (rod)

Question 9

What determines bacterial cell shape

Answer 9

1. cell wall (exoskeleton)
   a. strip cell wall -> spheroplast/protoplast
   b. genes involved in cell wall synthesis
2. cytoskeleton (different to eukaryotic)

Question 10

What does the bacterial cell wall do?

Answer 10

1. size
2. shape
3. prevent osmotic lysis

Question 11

what does peptidoglycan do?

Answer 11

rigidity for bacterial cell walls

Question 12

What is peptidoglycan?

Answer 12

1. Backbone of alternating sugars (dimer)
   a. N-acetylglucosamine (NAG)
   b. N=acetylmuramic acid (NAM) - unique
   c. cross links occur between back bones
   i. direct bonds
   ii. pentapeptide side chains
2. Amino acid side chains on NAM
   a. D amino acids
   b. Diaminopimelic acid (DAP)

Question 13

Explain the Gram-positive cell wall

Answer 13

1. thick peptidoglycan (60-90%)
2. Interwoven teichoic acids (acidic polysaccharides)
3. Surface studed with proteins
4. no lipids
5. molecules freely pass through peptidoglycan so they do not get trapped unless tethered to csm or wall

Question 14

Explain the Gram-negative cell wall

Answer 14

1. Two layers: thin peptidoglycan (10-20%), Outer membrane (permeability barrier)
2. Periplasm - gelatinous material between; outer membrane, peptidoglycan and cytoplasmic membrane (contains proteins needed for transport of materials to and from cells)

Question 15

Explain the outer membrane of bacteria

Answer 15

1. phospholipid bilayer
2. Lipopolysaccharide (LPS): LipidA portion embedded in outer membrane, polysaccharide extends outward from surface
3. Surface of membrane is studded with proteins
4. semipermeable with porins
5. ONLY IN GRAM NEGATIVE

Question 16

What bacteria have Atypical cell walls?

Answer 16

1. Mycobacterium

2. Nocardia

Question 17

What is the structure of Atypical cell walls?

Answer 17

1. Gram-positive cell wall structure with lipid mycolic acid
   a. pathogenicity + high resistance to certain chemicals and dyes
   b. basis for acid-fast stain used for diagnosis of infections cause by these microorganisms
2. Some have no cell wall - Mycoplasma
   a. cell wall stabilized by sterols
   b. pleomorphic
   c. ie., no peptidoglycan

Question 18

How do archaeal cell walls differ from bacterial cell walls?

Answer 18

1. no peptidoglycan
2. pesudo-peptidoglycan instead:
3. instead of NAM archaea have:
   a. N-acetyl talosaminuronic acid (NAT)
   b. No D-amino acids

Question 19

How do cell walls grow?

Answer 19

1. NAM and NAG synthesis in cytoplasm
   a. attached to membrane carrier
   molecule ‘bactoprenol’
   b. transported across cell membrane
2. links in peptidoglycan have to be broken
   a. AUTOLYSINS: break glyosidic bonds
   and peptide cross-bridges
3. New peptidoglycan monomers (NAM-
   NAG dimer) inserted
   a. TRANSGLYCOSIDASE enzymes
4. Peptide crosslinks resealed
   a. TRANSPEPTIDASE enzymes: penicillin
   binding proteins - PBPs