Bacterial Structure

Question 1

What are prokaryotic(bacterial) ribosomes?

Answer 1

Machinery for translation of proteins

Structure:

-Subunit structure (30s + 50s = 70s)

Different from eukrayotes, good antimicrobial drug target e.g. amino glycosides

Prokrayotic is 70s

Eukrayotic is 80s

Question 2

Describe the Prokaryotic Cell Wall

Answer 2

• Determines bacterial shape
• Allows survival in diff env
• Protect bacteria from exploding in hypotonic solutions (water)
• Bacteria can be killed by hyperosmotic shock i.e. desiccation, very salty/sweet env (jam, salted meat)
• Main structural compound is peptidoglycan (unique to bacteria)
• Important site for action by antibiotics
• causes symptoms of disease in animals
• Provides immunological distinction and variation among bacterial stains (outer proteins)

Question 3

What are the differences between Gram- and Gram+ in terms of their cell wall structure?

Answer 3

Gram+ Cell Wall Structure

• Thick layer of peptidoglycan
• Teichoic and Lipoteichoic acids
• Hydrophilic: helps resists bile acids in gut

Teichoic acids = Gram positives only (Polysaccharides- polymers of glycerol and attached covalently to nam)

Lipoteichoic acids = Anchor cell wall to memrane

Surface proteins = Covalently attached to cell wall, imp in bacterial disease

Gram - Cell Wall Structure

• Thin layer of peptidoglycan
• Outer membrane
• Lipopolysaccharide (LPS)
• Fewer antimicrobial agents are effective against gram -

Outer membrane = Hydrophilic and hydrophobic components, additional permability barrier-protection

Peptidoglycan layer = Lipoproteins attach the outermembrane to the peptidoglycan, drugs like penicillin which interfere with peptidoglycan synthesis cannot easily get through the outer membrane

Lipopolysaccharide (LPS) = is in outer layer of membrane, has antigen carbohydrate chain (‘O’ antigens) and recognised by immune system + bacterial virus (bacteriophage)

Question 4

What is Glycolayx and Biofilm?

Answer 4

It is a virulence factor, material form an extra layer outside the cell which is produced by some bacteria. May be in the form of a capsule or slime layer

• It can be used as a vaccine target

A biolfim is a bacterial community living within an glycolayx adhering to a surface. Resistant to host defences since it blockets access by immune cells and antibodies

Example:

Strept. mutans is a Gram +ve bacteria which has a slime layer which helps it to adhere to tooth enamel

Question 5

What is a bacteria surface appendage and give an example

Answer 5

• Organ of motility
• Propulsion: environmental stimuli –> receptors –> flagella –> chemotaxis

Flagella is an example

> Almost all spirilla, half of all rod-shaped bacteria, and only a few of the cocci are motile by flagella

• Immunity to some pathogens is through antibodies against flagella (highly immunogenic)
• Virulence factor e.g. E.Coli cause frequent UTI –> flagella propel bacteria up urethra

Question 6

What is the three most common bacteria cell shapes? Also, how are baecteria arranged?

Answer 6

1. Coccus (cocci) = spherical
2. Bacillus (bacilli) = rod shaped
3. Spiral shaped = spirillum, spirochaetes