Transcript Loose Ends on Chapters 3,5,6

Loose Ends on Chapters
3,5,6
Summer
Microbiology
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 ATPBinding Cassette Transporters
ABC 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