Lecture 13 -- Homeostasis Flashcards
Process used to maintain fairly stable conditions necessary for survival in living things
homeostasis definition
factor –> pertubation –> sensor –> effector –> negative feedback to factor
main steps in homeostasis
- about neutral pH but inside higher than outside (+)
- low outside pH, neutral inside (+)
- high outside pH, neutral/high inside (-)
neutrophiles; acidophiles; alkiphiles
- pump protons out
- pump K+ in to maintain electroneutrality
response to cytoplasm that is too acidic
- protons brought in via exchange with Na+ or K+
- antiport
- requires Na+ circuit symport of Na+ with another solute
response to cytoplasm that is too basic
- use K+ influx, which allows increased proton pumping
- lowering pH not well understood
how to neutrophiles dissipate membrane potential
- use Na+/H+ antiporters to bring H+ into the cell
- regenerate Na+ with symport of another solute
how do alkaliphiles keep pH lower than the environment?
- keep inward flux of K+ greater than outward flux of H+
- pumps protons against gradient
- small positive potential inside the cell used to do work
how to acidophiles keep pH higher than environment
- high solute concentration causes an influx of water
- higher in gram positives than gram negatives (because of peptidoglycan)
turgor pressure
turgor pressure goes away and the membrane collapses
becomes metabolically inert
In a high osmolarity environment, what happens?
- increase concentrations of osmoprotectants (low toxicity solutes and K+)
- increase concentrations of osmolytes (low toxicity compounds synthesized by cell, low compatibility solutes, glutamate glutamine proline sugars)
lots of K+ –> balance with negatively charged glutamate –> trehalose = electroneutral
What are some adaptations to high-osmolarity environments?
- decrease cytoplasmic osmolytes (specific excretion/catabolism –> small molecules can leave easily)
- mechanosensitive channels
How do bacteria adapt to low-osmolarity environments?
high turgor pressure –> increased tension in cell membrane –> conformational change in channel –> transiently open –> solutes exit (no specificity)
mechanosensitive channels function
- de novo synthesis produces acyl chains to optimize membrane function
- when bacteria are subjected to environmental changes, the structure of fatty acids are altered in response
how does membrane lipid homeostasis work?
- adds a cis double bond
- modification happens after product is fully formed
- controlled by regulator sensing temperature
Desaturases (DesA)
