Bacterial Structure, Function, Growth and Taxonomy

Question 1

What are Bacteria?

Answer 1

Unicellular, ubiquitous host dependent organisms.

Question 2

What are the 6 main parts of a typical bacterial cell?

Answer 2

1.Outer membrane (not present in all bacteria)
2. Cell wall: Made of peptidoglycan with varying thickness between gram positive and gram negative bacteria
3.Cytoplasmic Membrane composed of a protein matrix similar to a phospholipid bilayer
4. Pili: external structures essential for the adhesion step in the invasion process.
5. Flagellum: appendages important for motility. There may be multiple flagella present on a bacterial cell on the poles ore laterally around the cell. Anchored in the cytoplasmic membrane to access ATP
6. Genome: bundles of genetic information in a circular conformation known as cccDNA containing histone like proteins

Question 3

What is the mesosome?

Answer 3

This is an invagination in the cytoplasmic membrane though to be important in the division and thus replication of bacterial cells but it is also thought to be an artifact of electron microscopy.

Question 4

What is the importance of gram staining?

Answer 4

This is a key diagnosis method which differentiates between gram negative and gram positive bacteria based on the thickness of their cell wall. Gram negative bacteria with a thin cell wall and gram positive with a thicker cell wall

Question 5

What is the overall process used when conducting a gram stain?

Answer 5

1. Heat fix over a flame
2. Stain bacteria by flooding the slide with a dye like crystal violet
3. Fix stain on cell wall using a mordent like Gram’s Iodine
4. Decolorise with alcohol/acetone
5. Counter stain with a dye like Safranin Red

The result would be pink (Gram neg) or purple (Gram pos) colonies observed using light microscopy

Question 6

Give 4 examples of a Gram negative bacillus

Answer 6

1. Escherichia coli
2. Klebsiella pneumoniae
3. Pseudomonas aeruginosa
4. Haemophilus Influenzae

Question 7

Give two examples of a gram positive coccus

Answer 7

1. Staphylococcus aureus
2. Streptococcus pyogenes

Question 8

Give two examples of a gram negative diplococcus

Answer 8

1. Neisseria meningitidis
   2.Neisseria gonorrhea

Question 9

What are the three components of the cell envelope of a bacterial cell?

Answer 9

1. The outer membrane if present
2. Cell wall
3. Inner/Cytoplasmic membrane

Question 10

What are the 4 major functions of the cell wall?

Answer 10

1. Maintain rigidity and cell structure/shape
2. Maintain osmolarity: prevents osmotic lysis
3. Survival: The cell wall interacts with host membranes
4. Cell Division: Forms cross-wall separating two daughter cells in replication

Question 11

Explain how bacterial synthesis comes about.

Answer 11

-The peptidoglycan precursor is synthesized within the bacterial cell
-It is then exported across the cell membrane, this step may be interrupted by antibiotic bacitracin
-If uninterrupted a site is created in the existing cell wall by enzymatic action of PBPs
-The new nucleotide minus terminal D-ala is incorporated into the precursor and the cell proliferates

Question 12

What are PBPs

Answer 12

penicillin-binding proteins the are responsible for the modification and polymerization of peptidoglycan

Question 13

Which two species of bacteria have shown different cell wall morphologies?

Answer 13

1. Mycobacterium
   2.Mycoplasma

Question 14

What makes mycoplasma’s cell wall morphology different?

Answer 14

-No cell wall is present
- the cell membrane contains steroids

Question 15

What makes mycobacterium’s cell wall morphology different?

Answer 15

-They have a modified peptidoglycan layer
-Poor gram stain
-Acid fast needed (carbolfuchsin) as
-They are covalently attached to arabinogalactan polymer
-resulting in a mycolic waxy coat

Question 16

What are the components of the Cell membrane

Answer 16

-Lipid bilayer
-Mesosome

Question 17

What is the importance of the cell membrane?

Answer 17

-The lipid bilayer is hydrophobic, repelling water and preventing osmotic lysis
-Ion transport and energy production happens here which is why the flagella is embedded here
-The mesosome is present here and is thought to be responsible for the division of the cell.

Question 18

For growth what are the physical characteristics needed for bacteria?

Answer 18

-O2/CO2
-Temperature
-Water (4/5 of the bacterial cell is made of water and therefor the environment must have suitable enough amount of water present to prevent the cell from lysing)
-pH (mostly neutral except for Lactobacillus species which prefer acidic conditions)
-Light
-Osmolarity (5-12%salt)

Question 19

What are the nutritional requirements for bacteria?

Answer 19

-Carbon source
-Nitrogen source
-Inorganic salts (Fe/Na/K/P/Ca/Mg)
- Organic compounds (ammino acids)

Question 20

Explain why humans are good hosts for bacteria?

Answer 20

They meet alot of the nutritional and physical characteristics needed for bacteria to proliferate at rapid rates

temp- 37
GI tract- nutrients

Question 21

What four components of the bacterial cell have become relevant in the medical field?

Answer 21

-The cell wall and its synthesis (Antibiotic e.g penicillin, vancomycin)
-Cell membrane(Antibiotics-polymyxin
Vaccines)
-Capsule(Vaccines e.g-Strep. pneumoniae)
-Ribosomes (contain genetic material the aid in antibiotic production e.g-gentamicin/tetracyclines (Tetracycline HCL used to treat gastric ulcers caused by H.pylori)