Water living environment Flashcards
What does water do for you?
- 70% or more of the weight of most organisms (most abundant substance in living system)
- needed by the brain to manufacture hormones and neurotransmitters
- regulates body temperature (sweating and respiration (Atmung))
- acts as a shock absorber for brain and spinal cord (Rückenmark)
- converts food to component needed for survival- digestion (Verdauung)
- helps deliver oxygen all over the body
- lubricates joints (Gelenke)
- flushes (spühlen) body waste, mainly in urine
- allows body’s cells to grow, reproduce and survive
- keeps mucous membranes (Schleimhäute) moist (feucht)
Where do chemical reactions of living systems occur? What do the water molecules influence?
-occur in aqueous milieu.
-The attractive forces between water molecules and the slight tendency of water to ionize ( to H+ and OH-) profoundly influence:
-structure,
-self-assembly
-properties
(of all biological molecules (s.a:
-Carbohydrate (starch), lipid (triacylgqcerol), protein (enzyme), nucleic acid (DNA)))
Is water polar and nonpolar and why? How does the water molecule look like?
-The oxygen nucleus draws electrons away from the hydrogen nuclei, which leaves the region around the hydrogen nuclei with a net positive charge
-The water molecule is bent, not linear, and so the distribution of charge is asymmetric
(Each water molecule has two positive spots, oriented at an angle of 104° to each other=)
What is the electric dipole moment?
- The electric dipole moment is a vector due to uneven distribution of unlike charges
- In diatomic systems, the magnitude of the electric dipole moment can be estimated as the difference between the Pauling electronegativities of the two atoms
- For centers of positive and negative charges separated by a distance l, the electric dipole moment, m is m = q l
Which properties result due to the highly cohesive (binding) nature of water?
-e.g high surface tension, specific heat and heat of vaporization (Verdampfungswärme) (+Higher melting point, boiling point) -better solvent (Lösungsmittel) -higher viscosity ->through hydrogen bonds
How much of the hydrogen bond is covalent and how much is electrostatic? The bond dissociation of water is equal to?
- The hydrogen bond is 10% covalent and 90% electrostatic
- In liquid water, the bond dissociation energy is about 23 kJ/mol, compared with 470 kJ/mol for the covalent O-H bond
How long does a H-bond last in water?
- The lifetime of H-bonds in liquid water is 1-20 ps, with water forming and breaking bonds
- The average lifetime of an H-bonded connection between two H2O molecules in water is 9.5 psec (picoseconds, where 1 psec = 10-12sec)
Which effect does the directionality have on the energy of the hydrogen bond?
-The attraction between the partial electric charges is greatest when the three atoms involved lie in a straight line.
-can be caused by:
when the hydrogen-bonded moieties are structurally constrained (beschränkt)
Why is water an excellent solvent for polar molecules?
-Water weakens electrostatic forces and hydrogen bonding between polar molecules by competing for their attractions
What can you tell about the compounds that dissolve in water?
- Compounds that dissolve easily in water are hydrophilic (“water loving”)
- They are composed of ions or polar molecules that attract water molecules through electrical charge effect
- > Solute-solute H-bonds replaced with solute-water H-bonds
What increases if crystalline substances dissolve?
- entropy (randomness) of the system increases
- The crystal acquires a greater freedom of motion
- As salts such as NaCl dissolve or ice melts , their crystalline lattice is disrupted
- > This is thermodynamically favorable
What does the dielectric constant show? Does water have a high or low dielectric constant?
- a physical property that reflects the number of dipoles in a solvent
- very high: 80
The force of attraction F depends on?
- magnitude of the charges (Q), the distance between the charged groups (r), and the dielectric constant (ε) of the solvent
- > F= Q1Q2/ εr°^2
Why is the dielectric constant of water high?
- because it is polar and it can form oriented solvent shells around ions
- These shells produce electric fields of their own, which opposes the fields produced by the ions
Name important physical properties of water
- large Heat of Vaporization
- High Specific Heat
- High Thermal Conductivity
- High Surface Tension
- Density of Water
What does specific heat mean?
- amount of energy needed to change the temperature of a substance
- > Cp = Q / m. Δ T
- Q= amount of heat
- T= temperature of the heat
What does high surface mean?
- Surface tension is a force which acts within the liquid’s surface causing it to contract and behave like a tightly stretched “skin”
- Surface tension is typically measured in dynes/cm, the force in dynes required to break a film of length 1 cm
How does the volume change if water freezes?
- When water freezes, it expands by adding about 9% by volume.
- Fresh water has a maximum density around 4°C.
In what way do non polar compounds change the structure of water? How is it possible?
- Nonpolar (hydrophobic) compounds are unable to undergo energetically favorable interactions with water molecules
- They interfere (stören) with the H-bonding among water molecules.
- the structure of water changes such as to accommodate the nonpolar substance
- This causes an increase in the order of water molecules and a decrease in entropy
How can water else prevented forming the normal number of hydrogen bonds?
-Uncharged, nonpolar molecules, such as
alkyl chains, prevent contacted waters
from forming the normal number of hydrogen bonds
-This forces more order on the system, Decreasing Entropy
Name some amphipathic molecules (biomolecules)
-proteins, pigments, certain vitamins, and the sterols and phospholipids of membranes (all have polar and non polar surface regions)
Which kind of effects do the hydrophobic interactions between nonpolar amino acids have on protein?
-stabilize the three-dimensional structures of proteins
What are the most important determinants of structure in biological membranes?
-Hydrophobic interactions among lipids, and between lipids and proteins
Which three different types of lipids in water do exist? Name the entropy that results
- dispersion (Verteilung) of lipid in H2O -> highly ordered
- cluster (Haufen) of lipid in molecules -> fewer H2O molecules are ordered
- Micelles (ally hydrophobic groups are requested (abkapselt) from water) -> entropy is further increased
Relationship between enzyme-substrate complex and ordered water
- Release of ordered water favors formation of an enzyme-substrate complex.
- disordered water will be displaced by enzyme-substrate interaction
Which properties of water are changed by the solutes?
-Vapor pressure
-Boiling point
-Melting point (freezing point)
-Osmotic pressure
^are called colligative (tied together) properties
Why do the properties of water change?
-the concentration of water is lower in solutions than pure water
On what. is the colligative effect dependent?
-Colligateive effect depends on the number of solute particles in a given amount of water
What is osmosis?
-Diffusion of water molecules from a region of higher water concentration to the region of lower water concentration (the thing they have to pass is called membrane)
What is osmotic pressure?
- Force, necessary to resist water movement
- П= iCRT (van’t Hoff equation)
- i= van’t Hoff factor; measure of the extent to which the solute dissociates into two or more ionic species
- R= gas constant 8.315 J/mol
- T= absolute temperature (Kelvin)
- C= molar concentration of solute
Is sure water ionize?
- Pure water is slightly ionized to produce a hydronium ion (H3O+) and a hydroxide ion (OH−). This is described by an equilibrium constant :
- 2 H2O (l) <> H3O+ (aq) + OH− (aq)
- Keq = [H+] [OH-]/ [55.5 M]
- (55.5 M) (Keq)= [H+] [OH-]= Kw
- > Kw: ion product of water
How is pH calculated?
- pH= log(1/[H+])= -log [H+]
- pH and pOH must always add to 14
What is counted as acid, neutral, basic in pH scale?
- increasing acid (higher concentration of H+)
- neutral = OH-= H+
- increasingly basic (lower concentration of H+)
What is proton jumping?
-The H-bonded network provides a natural route for rapid H+ transport. This phenomenon of proton jumping thus occurs with little actual movement of the water molecules themselves.
-needed:
High degree of hydrogen bonding in water.
Name some biological relevance where hydrogen bonds occur
- between alcohol and water
- between ketone and water
- between peptide groups in polypeptides
- between complementary bases of DNA
