Bacteria Structure & Mophology

Question 1

How do prokaryotic cells differ from eukaryotic cells?

Answer 1

• Have a cell wall
• Do not have a nucleus
  
  • Do not have subcellular organelles (mitochondria, lysosomes, ER, Golgo)

Question 2

Where do electron transport and energy production take place in the prokaryotic cell?

Answer 2

Across the cytoplasmic membrane

Question 3

How is the prokaryotic phospholipid bilayer unique to that of a eukaryotic cell?

Answer 3

With the exception of Mycobacterium and Ureoplasma spp., prokaryotic phospholipids lack sterols

Question 4

What name describes a round bacteria?

Answer 4

Coccus (pl. cocci)

Question 5

What term describes a rod-shaped bacteria?

Answer 5

Bacillus (pl. bacilli)

Question 6

What term describes a curved rod-shaped bacteria?

Answer 6

Vibrio (pl. vibrios)

Question 7

What is the name of spiraled-shaped bacteria?

Answer 7

Spirillum (pl. spirilla)

Question 8

How would you describe the shape of a coccobacillus bacteria?

Answer 8

Short rod

Question 9

How would you describe the shape of a spirochete?

Answer 9

Long, loose, helical spiral

Question 10

Why do gram-negative bacteria appear pink in color?

Answer 10

The thin cell wall, stained purple by crystal violet, is washed away with alcohol. Safranin is used as a counter-stain and gives gram-negative cells a pink appearance.

Question 11

What color do gram-positive cells appear?

Answer 11

Purple

Question 12

Why do gram-negative and gram-positive bacteria appear different in color when stained?

Answer 12

Gram-positive cells have a thick peptidoglycan cell wall, whereas gram-negative cells have a thinner layer of peptidoglycan that is surrounded by an outer membrane.

Question 13

What gives peptidoglycan its strength?

Answer 13

Pentaglycine cross-links between alanine and lysine.

Question 14

Why is peptidoglycan significant clinically?

Answer 14

• It is unique to bacteria and as such can be a target of antibiotics and other treatments, without harming mammalian cells. For example, B-lactam antibiotics inhibit the formation of peptide cross links, making the cell wall vulnerable
• Is a pathogen-associated molecular pattern (PAMP) - recognizable by the immune system

Question 15

What is the mechanism of B-lactams?

Answer 15

They inhibit transpeptidases (also called penicillin binding proteins), which catalyze the formation of peptide bonds in the peptidoglycan. Without these bonds, the cell wall becomes vulnerable.

Question 16

What is a pathogen-associated molecular pattern (PAMP)?

Answer 16

A bacterial component recognized by pattern recognition receptors on immune cells that actives an innate immune response.

Question 17

What is the purpose of teichoic acids?

Answer 17

In gram-positive cells, teichoic acids attach to peptidoglycan or embed in the membrane to provide rigidity and maintain morphology.

Question 18

What is the clinical significance of teichoic & lipotechoic acids?

Answer 18

• Serve as surface antigens for gram-positive bacteria to attach to other bacteria or hosts.
• Their negative charge sequesters positively charged antibiotics, decreasing effectiveness.
  
  • Lipoteichoic acids are PAMPs.

Question 19

What is an acid-fast bacterium?

Answer 19

A gram-positive organism with an external waxy coat composed of mycolic acids above the peptidoglycan layer. (ex: Mycobacterium)

Question 20

What makes up the outer membrane of gram-negative cells?

Answer 20

Lipopolysaccharide (LPS)

Question 21

Describe the structure of LPS.

Answer 21

• Lipid A - exists in all gram-negative bacteria composed of a disaccharide with fatty acids, endotoxin activity, PAMP
• Core Polysaccharide - sugars, same for a given species
• Somatic or “O” Antigen - repeating sugar units, highly antigenic and variable, defines serotypes

Question 22

What is a serotype?

Answer 22

Groups within a single species that share distinctive morphological characteristics.

Question 23

What is the function of B-lactamases?

Answer 23

Found in the periplasmic spaces of some gram-negative cells, they break down B-lactam in antibiotics.

Question 24

What is glycocalyx?

Answer 24

A capsule or slime layer surrounding the cell wall that is composed of carbohydrates

Question 25

How do capsules affect pathogenicity?

Answer 25

Capsules protect bacteria from phagocytosis and increase pathogenicity

Question 26

What structures assist with attachment to other cells?

Answer 26

Fimbriae and pili

Question 27

How do fimbriae differ from pili?

Answer 27

Fimbriae are shorter and more numerous than pili. Pili are longer and may mediate the exchange of DNA between cells.

Question 28

What is the clinical significance of biofilms?

Answer 28

They are difficult to clear by phagocytosis. They also prevent antibiotics from reaching bacteria and may make antibiotic treatment difficult by limiting O2 and other nutrients, slowing bacterial replication. They are also difficult to remove and may be present on surfaces, equipment, etc.

Question 29

What is the function of flagella?

Answer 29

Bacterial movement

Question 30

How are the flagella powered?

Answer 30

By a proton gradient in the plasma membrane

Question 31

What dictates the direction of flagella movement?

Answer 31

Movement occurs in response to chemical gradients. This is called chemotaxis.

Question 32

What are the forms of movement in bacteria?

Answer 32

• Runs (counterclockwise spinning)
• Tumbles (clockwise spinning) - allows for directional changes

Question 33

What are some examples of PAMPS in bacteria?

Answer 33

Peptidoglycan, lipoteichoic acids, flagellar proteins, lipopolysaccharide (LPS)

Question 34

What bacterial components/structures enable attachment to host cells, other bacteria, and surfaces?

Answer 34

• Pili
• Fimbriae
• Teicholic and lipoteichoic acids
• Glycocalyx (capsules and slime layers)
• Biofilms