Lecture 18- Bacterial Structure & Function Flashcards
Describe structure of Bacterial ribosomes
- Supramolecular structures for protein synthesis
- contain rRNA and r-proteins\
- 70s, which split to 50s & 30s subunits
- The 50s (large)subunit contains ≈34 proteins and is comprised of 2 rRNAS (23S &5S)
- the 30s (small subunit contains 21 proteins and is comprised of 1 rRNA (16S)
Describe structure of Eukaryotic Ribosomes
- Larger than prokaryotic ribosomes 80S (sedimentation rate)
- 80S split to 60s & 40s
- 60S contains ≈50 proteins & is comprised of 3 rRNAS (28S, 5.8S, 5S)
- 40S contains 33 proteins and is compromised of 1 rRNA (18S)
Describe structure of Archaeal ribosomes
- Ribosome is 70S & splits to 50s & 30S
- ribosomes contain 3 rRNAS in total (16S,23s,and 5S) & 50-70 proteins
- Primary structures of actual rRNA & proteins are closer to Eukaryotes than prokaryotes
How many Archaeal r-proteins are represented in Eukaryotes, and are there any exclusive r-protiens shared between Archaea and Bacteria but not Eukaryotes?
All Archaeal r-proteins are represented in Eukaryotes and there are no exclusive r-proteins between bacteria and Archaea
How many total Archaeal r-protiens are present in ribosomes?
50-70 depending on species
Which RNA’s must interact with each other in the ribosome for protein synthesis?
All RNA’s (m,r,t)
Briefly describe the four stage process of protein synthesis
- Initiation- Initiation factors(proteins) are used to start protein synthesis - either IFs or EIFs(for Eukaryotes)
- Elongation of polypeptide chain using Elongation factors EFs or EEfs
- Termination, involving release factors (RFs or ERFs)
- Recycling subunits- using Recycling factors
explain decoding process for protein synthesis
Involves both Small & Large subunits
in SSU (decoding process) the major functioning sites are:
- m-RNA tunnel to conduct mRNA
- *Decoding center**- begins with the selection of the aminoacytl (A site) tRNA that corresponds to complement of mRNA (anticodon)
- tRNA binding sites (AminoactyltRNA Peptidebond Exit)
*peptide bond between 2 neighboring tRNA Happens at P site
In LSU- Peptide bond formation- major functional sites are-
- tRNA binding sites A,P, & E
- peptidyl transferase center (speeds up peptide bond formation )
- peptide exit tunnel
*start codon is AUG, stop is UAG, UGA, and UAA
What is the function of peptidoglycan that is contained in most bacterial cells?
- provides strength
- porous for small molecules
Disruption or cell wall structure or inhibition of synthesis causes cell lysis
Describe the Gram positive cell wall
- one phospholipid bilayer
- lower lipid content compared to gram + because of no lipopolysaccharide
- thick peptidoglycan layer
peptidoglycan polymer made out of monomers (PG monomers)
repeated units are cross-linked during cell wall synthesis to provide strength
Describe cell wall synthesis of gram + bacteria
PG monomers contain
- N-acetyl glucosamine (NAG
- N-acetyl muramic acid(NAM)- pentapeptide attached to it
- Autolysins break glycosidic bonds between PG monomers & the crosslinking at point of growth
- PG monomers are synthesized in cytosol & bind to bactoprenol (BP)
- BP transports PG monomers across membrane & inserts them into existing PG
- glycosidic bonds link PG monomers to existing PG chain
- Transpeptidases form peptide cross links between rows & layers of PG by…
- First removing terminal D-alanine from pentapeptides to form tetrapeptides
- this provides energy to link pentaglycine bridge (glycine is the link)
- transpeptidases cross link pentaglycine to D-alinine (4) to L-lysine(3) of other monomers to provide strength to cell wall
- *L-lysine is not necessarily aa#3 and cross linking is different in gram -
Which amino acid is the most abundant in peptidoglycan cell wall of gram +?
Glycine- because of the pentaglycine bridge
How is the acid fast bacterial wall different from Gram+?
- stains poorly with regular die, However with Carbon fuchsin (stronger die) it stains well (retains red color)
- has a thin peptidoglycan layer linked to a layer of arabinoglactan , linked to an atypical membrane contaning mycolic acids , overlaid with polypeptide & glycolipids with acyl lipids–> additional strength to cell wall
- contains porins, which transport small hydrophilic molecules through the outer membrane like gram - however they contain less and longer pores –> less permeable
Mycolic acids & other glycolipids also slow down entry of nutrients causing slow growth–> more resistant to antibacterial agents and lysosomal components
How is gram -be cell wall different than gram +?
- 2 cytoplasmic membranes
- Higher lipid content (lipopolysaccharide)
- Thinner peptiidoglycan cell wall
- D-glutamic acid instead of D-glutamine
- meso-Diaminopimleic acid in place of L-lysine
- D-alanine of one monomer(tetrapeptide) connects directly to meso-Diaminopimleic acid Of another monomer
Describe the process of gram staining
- Fix bacteria on solid support by gentle heating(kills)
- add primary stain (crystal violet- or gram stain)
- add Mordant Gram’s iodine stain (increases affinity for primary stain)
- decolorizer, alcohol, and or acetone (gram - becomes colorless)
- counterstain safarin
if gram + remain purple , if gram - pink
