Chapter 2- WATER Flashcards
Brownian Motion
- 1827 by Robert Brown
- pollen granules suspended in water
- random fluctuation of the energy content of the environment “thermal noise”
- jostling motion allowing molecules to react
- responsible for initiating many biochemical interactions (vital source for the life of the organism)
- water is the most common medium
Hydrogen bond
- due to the polarity of water
- partially positively charged hydrogen atoms of one molecule interact with
- partially negatively charged oxygen atoms of another molecule
- not unique to water molecules
- common weak bonds in bio molecules
Electrostatic Interactions
- also called ionic bonds, salt bridges
- interactions between distinct electrical charges on atoms
- usually take place between atoms bearing a complete negative charge & complete positive charge
- Coulomb’s law
- strongest in a vacuum
- weakened by water
- maximized in an uncharged environment
van der Waals interaction
- neither polar nor charged
- these molecules interact with each other electrostatically
- distribution of of electronic charge change over time so never perfectly symmetric
- transient asymmetry
- contact distance 3-4 A
- very small energy, 2 to 4 kJ mol per atom pair
- Stability in numbers especially applies
- example= geckos
Entropy
- measure of randomness
- total entropy of a system always increases in a spontaneous process
- the hydrophobic effect is entropy driven
- second law of thermodynamics: entropy increase
Hydrophobic interactions
- the aggregation of nonpolar groups in water leading to an increase in the entropy of water owing to the release of water molecules into bulk water
- form spontaneously, no input of energy required
- this is because when they form, the entropy of water increases
pH
- a measure of the hydrogen ion concentration
- values ranging from 0 to 14
- smaller numbers acidic
- larger numbers basic
- alterations in ph can drastically affect the internal electrostatic environment of an organism
Buffer
- acid-base conjugate pairs
- resists changes in pH
- crucial in biological systems because changes in pH can have drastic effects on the structure of bio molecules and even result in death
All weak interactions can be said to be fundamentally electrostatic interactions. Explain.
Ionic bonds, hydrogen bonds, and van der Waals interactions all depend on the UNEQUAL DISTRIBUTION OF ELECTRONS, resulting in an unequal distribution of charge.
Explain how the following statement applies to biochemistry: order can be generated by an increase in randomness
This describes the hydrophobic effect. Specific complicated biochemical structures can form, powered by the increase in entropy that results when hydrophobic groups are removed from aqueous solution.
What is the equation for the ion product of water
Kw= [H+] [OH-] = 1.0 x 10 ^-14
Acid
- proton donor
- ionize to produce a proton and a base
- the species formed by the ionization of an acid is its conjugate base which is distinguished from the ionized acid by having the suffix “ate”
- acids have differing tendencies to ionize: equilibrium constant Ka
- the larger the value of Ka, the stronger the acid
Why are weak bonds important in biochemistry
- They determine how chemicals interact with each other when they’re not undergoing a chemical change
- They are responsible for cohesion of membranes, folding of proteins, specific binding of signal molecules to receptors, and even the double helix of DNA
- also called intermolecular bonds
- include hydrogen bonds, van der Waals interactions, and ionic bonds
- significance in numbers, easily broken, temporary orientations
Water is said to be polar but uncharged. How is this?
Due to the hydrogen bonding which results from unequal distribution of electrons, there is no separation of free charge in the water molecules (uncharged).
Common weak bonds & how water affects them
Ionic: when ionic salt is added in water, it dissolves because the bond between sodium and chloride are weak, but the bond which forms between sodium ion–water and chloride ion–water is strong.
Hydrogen: when water is added to molecules having hydrogen bonds (other than water) these molecules also breakdown.
Van der Waals: Molecules dissolve. These instantaneous electrostatic interactions are weaker than actual electrostatic interactions.
