Structural Macromolecules (Dr Alderwick): Part 1 Flashcards
What is the most well studied prokaryote?
E. coli
What is the primary role of the cytoplasmic membrane (CM)?
- separates the cytoplasm from the cells enviornment
- permeability barrier
Describe the composition of the CM
- phosphatidylethanoloamine ( fatty acids)
- arranged into phospholipid bilayer
- 6-8 nanometers wide
Describe the fluid mosaic model of the bacterial cytoplasm membrane
- contains a range of diverse membrane proteins
- enzymes ( PBPs- peptidoglycan biosynthesis )
- transporters (move molecules OUT–> IN or IN—>OUT)
- site of generation and us of the proton motive force
- 2-6 atm of osmotic trudger pressure = extremely fragile
Explain briefly the architecture of the Archeal CM
- lipid tails are attached to glycerol via an either linkage
- lipids are braced with methyl (CH3) groups- isoprenes
- Phytanyl (C20) or Biphytanyl (C40) <- glycerol on both ends
- crenarchaeol - hydrocarbon moiety contaiing 5 and 6 carbon rings
Archeal CM:
- glycerol dieters made from C20 phytanyl lipids forms a ?
lipid bilayer
Archeal CM:
- diglycerol tetra ethers made from C40 Biphytanyl lipids forms a?
- lipid monolayer
Archeal CM:
- both types of membranes are extremely resistant to ? Wide spread among?
- heat denaturation
- thermophiles
Despite chemical variation in CM lipids between Archaea and Bacteria, the CM functions to ?
- form a membrane with inner and outer hydrophilic surfaces
- allows for PERMEABILITY which has its inherent problems
- anchor for membrane proteins and membrane associated proteins
- site of generating of proton motive force
What are the three major classes of transport systems for CM?
- Simple transport
- Group Translocation
- ABC transporter
Explain simple transport
- driven by the energy in the proton motive force
Explain group translocation
- chemical modification of the transported substance driven by phosphoenolpyruvate
Explain ABC transporter
- periplasmic (outside) binding proteins are involved and energy comes from ATP
ABC = ATP Binding Cassette
With the bacterial cell wall: Peptidoglycan (aka murein) there are two major classes - what are they?
- Gram-positive (ex: S. aureus)
2. Gram - negative (ex: E. coli)
Explain the study by hans christian gram for positive and negative !
- Gram + and Gram - were tested via fixation –> crystal violet–> iodine treatment–> decolorization –> counter stain safranin
- gram+ retained the initial violet colour throughout
- *gram - the colour changed as the process went on…it changed colour after the decolourization process whereas the gram + retained it
The molecular structure of bacterial peptidoglycan:
- types of linkages?
- two components?
- beta (1,4) linkages between Glycan (made from carbohydrate)
- peptide component made from aas
Describe the Gram positive cell wall!
- no outer membrane - Gram -ve
- > 90% cell wall is peptidoglycan
- forms glycol strands
- additional cell wall components
- Teichoic acids
- Wall associated protein ( ie. M-Antigen of Grp A Streptococci
Gram positive cell wall:
- Teichoic Acids?
L> examples?
- ve charged polyalcohols
- Ribitol phosphate
- glycerol phosphate
- other sugars
- D-alanine
- Wall teichoic acids WTS
- lipoteicoic acids LTA
- bind Ca 2+ and Mg 2+
The gram negative cell wall
- describe it
- outer membrane
- periplasm
- cytoplasmic membrane
- porin: water filled channel= entrance and exit of solutes specific and on specific
- contains lipopolysaccharide (LPS)
Gram negative: Explain the structure of LPS’s Lipid A
- is it a glycerol lipid?
- fatty acids are linked via to a ?
- anchors the LPS to?
- not a glycerol lipid
- fatty acids are linked via an ester amide bond to a N-acetylglucosamine phosphate disaccharide
- Caproic (C6), lauric (C12), myrristic (C14), palmitic (C16) and stearic (C18) fatty acids
- anchors the LPS molecule into the outer leaflet of the outer membrane
Gram negative: Explain the structure of LPS’s core polysaccharide
-core polysaccharide
- contains ketodeoxyoctanate (KDO)
- C7 sugars (heptoses) - phosphorylated
- Glactose, glucose, rhamnose and mannose
- other more obscure sugars
L> tyvelose, paratose, colitose and abequose
Gram negative: Explain the structure of LPS’s O-specific polysaccharide
- is it variable or not
- what is it referred to as
- full length is called?
- short length?
- location?
- sometimes referred to as the O-antigen
- extremely variable - species specific
L> >160 different O-antigens produced by different E. coli strains - full length O antigens are deemed to be smooth LPS molecules -> outer membrane is less penetrable to hydrophobic antibodies
- short O-antigens derive rough LPS molecules –> outer membrane is more penetrable to hydrophobic antibodies
- since the O antigen is exposed to the surface it is recognized by antibodies
What are the three parts to the LPS structure?
- Lipid A
- Core polysaccharide
- O-specific polysaccharide
Cell wall components of Archeae?
L> Pseudomurein
- similar to peptidoglycan
- N-acetylglucosamine
- N-acetylalosaminuronic acid
- beta (1, 3) glucosidic linkage
- all amino acids are of the L-stereoisomer
- lysozyme insensitive
Bacterial cell wall - how does the immune system keep the onslaught of a bacterial infection in check?
- first line of defence is lysozyme!
What did Sir Alexander Flemming discover?
- lysozyme is present in a number of secretions such as saliva, milk, mucus and tears
- part of the innate immune system
- natural protection from gram-positive pathogens.
- he treated bacterial cultures with nasal mucus from a pt suffering form a head cold
- whereas the skin is a protective barrier due to its dryness and acidity the conjunctiva (membrane covering the eye) is instead, protected by secret enzymes..mainly lysozymes…failure or disruption = conjunctivitis
Explain what N-acetylmuramide glycanhydrolase is
- muramidase
- a prominent cleft between the two domains forms a binding site
- recognizes and binds with a high affinity a hexasacharide of the glycol chain
- cleaves NAG-beta (1-4-NAM glycosidic bond
Flemming is also known for the discovery of penicillin.
- beta lactins
- four membered ring
- attacks an important enzyme involved in the synthesis of the bacterial cell wall
How does penicillin work?
- in bacterial cell wall an enzyme links NAG and NAM
- penicillin stops this joining
- cell has high internal osmotic pressure and it lyses under that force causing it to spill into the enviornment
**must be used on a penicillin strain strain
Mycobacterium tuberculosis??
- causative agent of TB
- aerosol route of transmission
- 1/3 worlds population will be infected with Mtb
- an individual is newly infected with TB every second
- 5-10% individulas infected go on to show clinical symptoms of TB]- ineffective vaccine
- rising incidence of multi drug (MDR-TB) and extensively drug resistant (XDR-TB) strains
- BTZ has been found to stop growing and cause them to expand via weakening the cell wall. It inhibits the cell wall synthesis of it in Mtb causing it to burst (in clinical trials )
