Water living environment

Question 1

What does water do for you?

Answer 1

• 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)

Question 2

Where do chemical reactions of living systems occur? What do the water molecules influence?

Answer 2

-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)))

Question 3

Is water polar and nonpolar and why? How does the water molecule look like?

Answer 3

-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=)

Question 4

What is the electric dipole moment?

Answer 4

• 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

Question 5

Which properties result due to the highly cohesive (binding) nature of water?

Answer 5

-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

Question 6

How much of the hydrogen bond is covalent and how much is electrostatic? The bond dissociation of water is equal to?

Answer 6

• 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

Question 7

How long does a H-bond last in water?

Answer 7

• 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)

Question 8

Which effect does the directionality have on the energy of the hydrogen bond?

Answer 8

-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)

Question 9

Why is water an excellent solvent for polar molecules?

Answer 9

-Water weakens electrostatic forces and hydrogen bonding between polar molecules by competing for their attractions

Question 10

What can you tell about the compounds that dissolve in water?

Answer 10

• 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

Question 11

What increases if crystalline substances dissolve?

Answer 11

• 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

Question 12

What does the dielectric constant show? Does water have a high or low dielectric constant?

Answer 12

• a physical property that reflects the number of dipoles in a solvent
• very high: 80

Question 13

The force of attraction F depends on?

Answer 13

• magnitude of the charges (Q), the distance between the charged groups (r), and the dielectric constant (ε) of the solvent
• > F= Q1Q2/ εr°^2

Question 14

Why is the dielectric constant of water high?

Answer 14

• 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

Question 15

Name important physical properties of water

Answer 15

• large Heat of Vaporization
• High Specific Heat
• High Thermal Conductivity
• High Surface Tension
• Density of Water

Question 16

What does specific heat mean?

Answer 16

• 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

Question 17

What does high surface mean?

Answer 17

• 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

Question 18

How does the volume change if water freezes?

Answer 18

• When water freezes, it expands by adding about 9% by volume.
• Fresh water has a maximum density around 4°C.

Question 19

In what way do non polar compounds change the structure of water? How is it possible?

Answer 19

• 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

Question 20

How can water else prevented forming the normal number of hydrogen bonds?

Answer 20

-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

Question 21

Name some amphipathic molecules (biomolecules)

Answer 21

-proteins, pigments, certain vitamins, and the sterols and phospholipids of membranes (all have polar and non polar surface regions)

Question 22

Which kind of effects do the hydrophobic interactions between nonpolar amino acids have on protein?

Answer 22

-stabilize the three-dimensional structures of proteins

Question 23

What are the most important determinants of structure in biological membranes?

Answer 23

-Hydrophobic interactions among lipids, and between lipids and proteins

Question 24

Which three different types of lipids in water do exist? Name the entropy that results

Answer 24

• 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

Question 25

Relationship between enzyme-substrate complex and ordered water

Answer 25

• Release of ordered water favors formation of an enzyme-substrate complex.
• disordered water will be displaced by enzyme-substrate interaction

Question 26

Which properties of water are changed by the solutes?

Answer 26

-Vapor pressure
-Boiling point
-Melting point (freezing point)
-Osmotic pressure
^are called colligative (tied together) properties

Question 27

Why do the properties of water change?

Answer 27

-the concentration of water is lower in solutions than pure water

Question 28

On what. is the colligative effect dependent?

Answer 28

-Colligateive effect depends on the number of solute particles in a given amount of water

Question 29

What is osmosis?

Answer 29

-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)

Question 30

What is osmotic pressure?

Answer 30

• 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

Question 31

Is sure water ionize?

Answer 31

• 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

Question 32

How is pH calculated?

Answer 32

• pH= log(1/[H+])= -log [H+]

- pH and pOH must always add to 14

Question 33

What is counted as acid, neutral, basic in pH scale?

Answer 33

• increasing acid (higher concentration of H+)
• neutral = OH-= H+
• increasingly basic (lower concentration of H+)

Question 34

What is proton jumping?

Answer 34

-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.

Question 35

Name some biological relevance where hydrogen bonds occur

Answer 35

• between alcohol and water
• between ketone and water
• between peptide groups in polypeptides
• between complementary bases of DNA