Water Flashcards
What 6 characteristics make water important to life?
-Polar (range of temps at which it is a liquid)
-Acts as solvent for protein
-Disassociates in UV radiation (which creates ozone)
-Insulator
-Ability to be or not to be solvent based on other molecule’s properties
-Water Activity (concentration of pure water)
What makes water’s polarity important? (2 things)
-H-bonding allows water to act like a polymer, which increases the boiling point and reduces the freezing point, giving a large temperature/conditions range in which chemical reactions can take place
-polar and ionic organics can dissolve, while other molecules will not, which is basis for many cellular functions
What cell functions are possible because of water’s polarity?
-macromolecules and boundaries/surfaces/interfaces created by non-soluble molecules like lipids are able to maintain stereochemistry (not everything can pass through stable membranes)
-provides a means for concentrating organics - where they can then bind
What do we look for when searching for life on other planets or extreme environments?
- Where liquid water is/has been
- viable level of water activity for life
What does activity of water mean? How is it symbolized?
The concentration of dissolved water molecules in a solution that is available to participate in reactions (aka hydrate other molecules). A(subscript w)
Why is high water activity important?
The sum of the multitude of H-bonds in water molecules has a large impact on aqueous solutions. It outweighs the H-bond energy of other atoms with greater electronegativity than the water (until the other atoms’ concentration level grows closer to the water activity.
What is the range for activity of water?
pure = 1
no free water molecules available to hydrate anything= 0
What is the difference between the total concentration of on ion in solution to it’s effective concentration?
Ions do not behave ideally in solution. The total concentration of an ion is the ratio of ion’s in the solution. Some of them may be interacting with another molecule/ion already, so the the effective concentration (aka, activity) is the ratio of ions still available to participate in a reaction.
When do you not assume a water activity of 1?
When there are a lot of dissolved ions:
- Brines (very salty systems)
- cold systems (water freezes out available molecules)
- industrial wastes
How does water interact with proteins?
-H-bonds in water acts as a stabilizer between proteins and other molecules that are binding to it.
-Provides hydration shell around proteins, stopping them from interacting when they shouldn’t
What characteristics of water help proteins bind with other molecules?
small size (ensures good fit)
polarity (provides just enough temporary bond strength)
conformational flexibility (provides directionality and reversibility)
What is a hydration shell?
A layer of water molecules that surround a biomolecule, creating a repulsive force to keep undesirable molecules away from it or keep it from falling apart
What direction does water flow?
High activity to low activity
What happens when a cell is placed in a salty solution?
the A(w) outside the cell is low, so the water flows out of the cell and causes the cell to dehydrate
What happens when a cell is place in distilled water?
the A(w) outside the cell is high, so the water will flow into the cell, causing it to bloat and potentially burst
