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Loose Ends on Loose Ends on Chapters Chapters
3,5,63,5,6
Loose Ends on Loose Ends on Chapters Chapters
3,5,63,5,6Summer Summer
MicrobiologyMicrobiology
Spore survival• Dipicolinic acid and Ca++ account for 15% of
the total spore mass• Dipicolinic acid theoretically may contribute to
the stability of the nucleic acids which is a contributory to the spore’s survival- The Ca and the dipicolinic acid may enhance the activity of DNA binding proteins that are vital to the spore’s ability to resist radiation
• Calcium contributes to the ability of the spore to resist destruction by oxidizing agents and dry heat – also steam
Spore Structure
Seven Steps and More in Spore Formation
Revisited• Stress or unfavorable environmental
conditions • Replication of DNA• Membrane begins to form to separate
cells – Forespore septum begins to show the formation of the forespore
• Membrane continues to grow and engulfs the DNA into the forespore
Spore formation Continued
• The cortex is laid down and Calcium and dipicolinic acid are accumulated here
• Protein coats then form around the cortex• The exosporium and then the spore coat
are made to surround the spore• At this point the spore structure is
completed
Spore Release• Lytic enzymes destroy the
sporangium releasing the spore• This process takes about 23 hours
in B. subtilis
Flagellar Structure• The M Ring is anchored in the cel
membrane of the bacterium.• A shaft that is attached to the hook and
flagellum extends form the shaft.• In Gram Positive cells the S ring is
attached to the cell wall and does not rotate
• In Gram Negative cells, the P and L rings act as a bearing for the rotating flagellum
Flagellar Motor Proteins• Mot A and Mot B• These form a proton channel for the
establishment of a proton gradient • The Motor proteins also assist in the
anchoring of the complex to cell wall peptidoglycans
• Fli G is the motor protein that generates flagellar rotation
Rotational symmetry of the C ring and a mechanism for the
flagellar rotary motor
• Dennis R. Thomas, David Gene Morgan, and David J. DeRosier
• Proc Natl Acad Sci U S A. 1999 August 31; 96(18): 10134–10139. PMCID: 17855
Reference• The cytoplasmic component of the
bacterial flagellar motor.• I H Khan, T S Reese, and S Khan• Proc Natl Acad Sci U S A. 1992 July
1; 89(13): 5956–5960
Chemoreceptors• MCP – Methyl accepting
chemotaxis proteins• Localized in patches at the ends of
the bacilli in E. coli• React to stimuli through a series of
steps utlizing proteins
Concepts• Conformation change in protein
structure• Methylation of proteins• Phosphorylation of proteins
Increase in nutrient binding
• Environmental stimulus – nutrient molecule
• Nutrient molecule in the gradient binds to the MCP protein( change in conformation)
• Che A is dephosphorylated – loses a phosphate
• Counterclockwise rotation occurs in the bacteria
No nutrient detected in the environment
• No nutrient binding• Che A is phosphorylated( gains a
phosphate group)• Phosphate is then donated to Che Y• Interacts with Fli switch to causes
clockwise rotation or tumbling – random and undirected
Two Component Phosphorelay System
• Two Component Phosphorelay System is similar in response to oxygen, light, hear and osmotic gradients.
Active Transport• Movement against the
concentration gradient from low concentration outside of the cell to higher inside the cyotplasm
• Requires the input of energy to drive the reaction forward
Active Transport and ATP- Binding Cassette
TransportersABC Transporters• Large group of transporters• Two hydrophobic domains in the membrane
and two nucleotide binding domains at the cytoplasmic surfaces
• The membrane spanning portions form a pore • The nucleotide binding domains bind ATP for
the hydrolysis of ATP to produce energy to drive molecules through the membrane
Salmonella ABC transporter
E. Coli and active transport
• The sugars arabinose, maltose galactose, and ribose are transported by this mechanism in bacteria
• Also amino acids may pass through the cell membrane in this manner
Porins• Porins are channels located in the
outer membrane of the Gram Negative bacteria
Omp F
Siderophore
Active transport• Uniport – One ion or molecule moves
against the concentration gradient• Symport – A concentration gradient
established by an ion, drives solute transport of another molecule against the concentration gradient
• Antiport – Sodium is pumped outward in response to an inward movement of protons
Importance of this mechanism
• The sodium pumped to the outside of the cell is also used in transport
• It binds to the outside of a different transport protein.
• When it binds it changes the shape of the protein
• The protein is then able to bind to molecules to move them into the cell
E. coli • Has multiple transport systems for
many nutrients• The diversity of these transport
system provides the ability to survive in diverse environments
Group Translocation• A molecule is transported ito the
cell while being chemically altered• This is energy dependent
PTS• Best characterized system is the
PTS• Phosphoenolpyruvate: sugar
phosphotransferase system• Transports sugars while
phosphorylating them
Components• Two enzymes( EI and EII)• Low Molecular weight – heat stable
protein( HPr)
Steps• High energy Phosphate is transferred
from phosphoenolpyruvate to EII with the help of EI and HPr
• The sugar molecule to be transported is phosphorylated as it goes across the membrane by EII
• EII is specific for the sugar that it transports
PTS