structure of bacteria II Flashcards
What are the differences between Prokaryotic and Eukaryotic cells?
What is the great divide between bacteria?
The great divide is between
Gram-positive and Gram-negative bacteria
Gram-positive bacteria are monoderm, contain one thick layer of peptidoglycan and contains teichoicand lipoteichoic acid.
Gram-negative bacteria are diderm, contains an outer membrane with lipopolysaccharides.
What are the subunits of the 3D peptidoglycan polymer?
Disaccharide N-
acetylglucosamine
N-acetylmuramic acid
How are the subunits of peptidoglycan bound?
Via cross-links between the sub-units to form long polymers that are further cross-linked by peptide cross-links
How is DNA contained in bacteria?
In nucleoids
Contains highly supercoiled DNA wrapped around proteins
What is the shape of nucleoids?
Nucleoids can change shape dramatically
Barely visible during restHighly visible when active
Can change its shape, form and function within the bacterial cytoplasm.
What are gas vacuoles?
Bacteria need to be able to contain gas intracellularly
Largest bacteria can fix nitrogen and sulphur via sulphur inclusions1mm in diameter
What are microcompartments?
Microcompartments are large, crystalline, structurally sophisticated
100-150 nm in X section
Consist of 10 000 -20 000 polypeptides of 10 to 20 types
What is a microcompartment shell?
Encasesmetabolic enzymes that catalyze reaction with toxic intermediate
Unifying structure of the microcompartments
Made of proteins having bacterial compartment domains
Examples of microcompartments
Carboxysome - metabolism
PDU compartment- metabolism of alcoholin Salmonella enterica
Why is the cytoskeleton important?
Cytoskeleton changes the shape of cells and aids the cell in cellfission
MreB (actin precursor) - elongates the cell to form rod-shaped bacteria
FtsZ - used in peptidoglycan formation
Crescentin- bends the wall to one side
Why can’t gram positivebacteria form vesicles?
Their peptidoglycan cell walls are too thick
How do vesicles form in gram-negative bacteria?
- Asymmetric expansion of the outer membrane relative to the inner membrane
- Ratio of inner to outer membrane buckles
- Curvature increases and the final outer membrane vesicles form
- Vesicles trap components in the periplasm
What is the periplasm?
Space between the outer and inner layer of the bacteria
What is in the most likely molecule to be found in the bacterial vesicles?
DNA
Components of the outer layer of bacteria
Short filaments S-layer proteins Lipoproteins Capsules Flagella
What are bacterial capsules ?
Extended polysaccharide structures that protect the bacteria from immune attack
What are filaments?
Adhesins
How does the flagellum work?
The rotor turns via an ATP-dependent mechanism that causes the flagella to whip
Why are flagella needed?
In order to swim in aqueous environment
hunt down nutrients
Can human and bacterial flagella be distinguished?
Yes, via their form and function
What are the three types of flagella?
Monotrichous
Peritrichous
Amphitrichous
What are monotrichous flagells?
Single
What are peritrichous flagella?
Multiple
What are amphitrichous flagella?
One on either side of the bacteria
What are S-layer proteins?
Proteins that form paracrystalline arrays on the bacterial surface
What are the functions of S-layer proteins
Structural - prevent viral infection, help biofilms, protection and inhibit complement Receptor interaction Peptidoglycan remodelling Cell wall integrity Selectivity filter Inhibition of phagocytosis and serum killing Resistance to presentation Cell division and cell length Iron uptake Swimming Aggregation and bodies formation
What are the targets of toxins in drugs attacking bacteria?
Alteration of cytoskeleton
Inhibition of membrane fusion
Alter membrane permeability
Interfere with cell signalling
