L1: Structure of Bacterial Cell And Targets of Antibiotics

Question 1

What is microbiology?

Answer 1

Microbiology is the study of living organisms (‘microorganisms’ or ‘microbes’); simple in structure and usually small in size (cannot be seen with the naked eye).

Question 2

What does the study of microbiology include?

Answer 2

They include bacteria, fungi, protozoa, and viruses.

Question 3

What is the importance of microbiology?

Answer 3

Microorganisms cause many diseases and some microorganisms have been used in the manufacture of antibiotics and foodstuffs.

Question 4

What are creatures classified into?

Answer 4

1. Animalia (Eukaryotic): helminths
2. Plantae (Eukaryotic)
3. Protista (Eukaryotic): Protozoa
4. Fungi (Eukaryotic)
5. Monera (Prokaryotic): cellulars like bacteria and acellular like a virus

Question 5

What is another term for prokaryotic?

Answer 5

Pre-mature

Question 6

What is the difference between cellular prokaryotic and eukaryotic?

Answer 6

Nuclear membrane: absent - present
Chromosomal number: haploid - diploid
Histones: absent - present
Ribosome: 70s - 80s
Peptidoglycan: present - absent
Mitochondria: absent - present
Mitosis: absent - present
Cell wall sterols: absent - present 
Membrane-bounded organelles: absent - present

Question 7

What is the size of bacterial cells?

Answer 7

Measured by micron (micron= 1/ 1000 mm).

Question 8

What is the shape of bacterial cells?

Answer 8

1. Cocci or spherical: e.g. Staphylococci.
2. Bacilli or cylindrical: e.g. Diphtheria bacilli.
3. Spiral:
    One curve: e.g. Vibrio.
    More than one: e.g. Spirochetes, Spirillum.

Question 9

What is the habitat of bacterial cells?

Answer 9

a. Parasitic (need host): bacterial flora (commensally) and pathogenic bacteria.
b. Saprophytic: free-living in soil, air, and water.

Question 10

What is the structure of bacterial cells?

Answer 10

1. Surface Structures (bacterial envelope):
   ● Cell wall.
   ● Cytoplasmic membrane.
   ● Capsule or slime layer.
2. Internal structures:
   - Nuclear body
   - Flagellae
   - Inclusion bodies
   - Ribosomes
   - Fimbria
   - Mesosomes

Question 11

What are the characters of the cell wall?

Answer 11

It is the rigid layer outside the cytoplasmic membrane.

Question 12

What is the chemical structure of the cell wall?

Answer 12

Composed of peptidoglycan.

Question 13

What are the Differences between Gram-positive and Gram-negative cell walls?

Answer 13

Peptydoglycan:

 Thick (~ 40 sheets)
 Comprising up to 50% of the cell wall.

 Thin (One or two sheets)
 Comprising only 5–10% of the cell wall.

Special Components:

 Teichoicacid:ribitol or glycerol.
 Polysaccharides.

• Outer membrane (thick).
   Lipoprotein.

 Lipopolysaccharide:
o Lipid A (the endotoxin).
o Polysaccharide (somatic antigen).

2- Periplasmic space
 Between cytoplasmic membrane and outer
membrane and contains hydrolytic enzymes and penicillinase.

Question 14

What is the function of the cell wall?

Answer 14

SPA GTG

1. Preservation of the shape of the cell.
2. Protectiveagainst high internal osmotic pressure.
3. Antigenic character:
    In Gram-positive: Teichoic acid.
    In Gram-negative: somatic “O” antigen(Polysaccharide).
4. Toxicity: The lipid A endotoxin of Gram-negative cell wall.
5. Cell wall is responsible for Gram staining reaction (Gram-positive bacteria stain violet while Gram-negative bacteria stain pink)
6. Cell wall is the target for the action of some antibiotics: penicillin and cephalosporins and vancomycin.

Question 15

What are the enzymes that attack the cell wall?

Answer 15

The peptidoglycan is hydrolyzed by lysozyme found in tears, saliva, and nasal secretions.

Question 16

What are the characters of the cell membrane?

Answer 16

It is a very thin elastic membrane that lies immediately under the cell wall.

Question 17

What is the chemical structure of the cell membrane?

Answer 17

• composed of biphospholipids and proteins.

- prokaryotes have no sterols in the cytoplasmic membrane except for Mycoplasma.

Question 18

What is the function of the cell membrane?

Answer 18

1. Permeability and transport: transport nutrients into and waste products out of the cell.
2. Electron transport and oxidative phosphorylation: for energy production (ATP).
3. Excretion of hydrolytic enzymes.
4. Biosynthetic function: carries enzymes and molecules for the biosynthesis of the cell wall, DNA, and membrane lipids.
5. Chemotactic function: contain receptors of binding and repellents.

Question 19

What are the characters of the capsule?

Answer 19

-Some bacteria can produce a gelatinous layer surrounding the cell outside the cell wall.

Capsule: condensed well-fined layer closely surrounds the cell.

Glycocalyx: polysaccharide-containing material lying outside the cell.

Slim layer: if glycocalyx is loosely surrounding the cell.

Question 20

What is the chemical structure of the capsule?

Answer 20

Consists of polysaccharides, except in bacillus anthracis(protein polymers).

Question 21

What is the function of the capsule?

Answer 21

1. Virulence factor as it protects the bacterial cell from phagocytosis.
2. Protects the cell wall against attack by bacteriophages, complement, and lysozymes.
3. Antigenic (K-antigen): used in serodiagnosis or vaccine preparation.

Question 22

What is the definition of flagella?

Answer 22

Long thread-like, helical filaments.

Question 23

What are the types of flagellate?

Answer 23

1. Monotrichous (single polar flagellum).
2. Lophotrichous (multiple polar flagellae).
3. Amphitrichous (One flagellum in each pole of the
   cell) .
4. Peritrichous (flagella distributed over the entire
   cell) e.g. E.coli.

Question 24

What is the structure of flagella?

Answer 24

made up of a contractile protein called flagellin.

Question 25

What are the functions of flagella?

Answer 25

1. It is the organ of Motility:

> Movement toward the optimal nutrients.
Movement toward optimal oxygen concentration in aerobic bacteria.
Choosing the locality suitable for colonization.
Assist pathogenic bacteria in penetration through a viscid mucous secretion.

2. Highly Antigenic (H-antigens).

Question 26

What is the color of gram stain in gram-positive and in gram-negative?

Answer 26

Positive: violet
Negative: red

Question 27

What are the smallest bacteria?

Answer 27

Serratla marcescens

Question 28

What are nuclear bodies?

Answer 28

• No true nuclei but nucleoid
• No nuclear membrane “prokaryotes”
• They are made of DNA.

” There is a single chromosome that can be seen by E/M very long thin thread folded on itself

Question 29

What are pili (fimbrae)?

Answer 29

It is a short and rigid appendage formed in gram-negative bacteria

Question 30

What are pili classified into?

Answer 30

Ordinary and sex pili

Question 31

What kind of microscope is used to see pili?

Answer 31

EM

Question 32

How do pili differ from flagella?

Answer 32

-Differs from flagella in the following points:

Occur in motile as well as non-motile strains
> More numerous “100-500” per cell.
> Much shorter and thinner.
more or less straight, flagella are spiral.
> Not originated from the cytoplasm.

Question 33

What is the function of pili?

Answer 33

1. Ordinary pili: adhesion to host cells, and to each other
   2 Sex pili: attachment of donor and recipient cells in bacterial conjugation
2. Antigenic.
3. Like capsule, inhibit phagocytosis.
4. Ordinary pili are responsible for virulence (colonization Ag, surface virulent-factor