Module 2: Water

Question 1

what is the most abundant molecule in living organisms

Answer 1

water

Question 2

passive roles of water

Answer 2

the structure of biomolecules forms in response to the interaction with water

Question 3

active roles of water

Answer 3

water is a participant in many biochemical reactions

Question 4

what other liquids have scientist contemplated that are suitable for life

Answer 4

ammonia or formamide

Question 5

explain the electronegativity and charges of water

Answer 5

oxygen is more electronegative than hydrogen; giving a permanent dipole
oxygen has a partial negative charge and each hydrogen has a partial positive

Question 6

the dipole of water influence its ability to:

Answer 6

form electrostatic interactions with charged molecules
form hydrogen bonds

Question 7

hydrogen bonds

Answer 7

electrostatic interactions between electronegative atom with a hydrogen covalently linked(donor) to another electronegative atom with a free electron pair (acceptor)

Question 8

what are the common hydrogen bonders within biomolecules

Answer 8

oxygen and nitrogen
they can each serve as a acceptor or donor

Question 9

strength of hydrogen bonds

Answer 9

relatively weak
longer than covalent bonds
strength depends on its geometry

Question 10

how many hydrogen bonds can each water molecule form

Answer 10

4
2 as acceptor and 2 as donor

Question 11

what is the average amount of hydrogen bonds each water molecule participates in

Answer 11

3.4 in flickering clusters

Question 12

water melting point

Answer 12

higher melting point compared to other solvents due to large amounts of hydrogen bonds

Question 13

how does water help us maintain body temperature

Answer 13

the high composition of water within our bodies, coupled with its high specific heat capacity and heat of vaporization, helps us maintain body temp

Question 14

why does ice have a lower density than liquid water

Answer 14

each water molecule participates in 4 hydrogen bonds with 4 other water molecules

Question 15

what does the small size and dipole of water offer

Answer 15

great versatility in interacting with both positively and negatively charged ions

Question 16

why is water an ideal hydrogen bond partner

Answer 16

biomolecules often have functional groups that can form hydrogen bonds
and water can act as a donor or acceptor

Question 17

what does the solubility of molecules in water depend on

Answer 17

their ability to interact with water
molecules that carry charge and/or participate in hydrogen bonds have the greatest solubility in water

Question 18

hydrophobic

Answer 18

non polar

Question 19

hydrophilic

Answer 19

polar

Question 20

amphipathic molecules

Answer 20

non-polar and polar portions

Question 21

what causes problems in the body due to solubility of water

Answer 21

many biological gases such as CO2 and oxygen are non polar and have limited solubility in water
-need specialized proteins for transport

Question 22

hydrophobic interactions

Answer 22

the forces that hold non polar regions of the amphipathic molecules together

Question 23

what happens when amphipathic molecules are mixed with water

Answer 23

the hydrophilic regions interact with water and the hydrophobic regions cluster to present smallest surface to water

Question 24

what is primary force in stabilization and formation of biomolecular structures

Answer 24

hydrophobic interactions

Question 25

the three dimensional structures formed by polymers of biomolecules are largely determined through:

Answer 25

non covalent interactions

Question 26

non covalent interactions offer:

Answer 26

transient, dynamic interactions -flexibility of structure and function

Question 27

non covalent forces influence:

Answer 27

-formation and stabilization of structure of biomolecules -recognition/interactions between biomolecules -binding of reactants to enzymes

Question 28

non covalent interactions within biomolecules include:

Answer 28

hydrogen bonds ionic interactions hydrophobic interactions van der Waals interactions

Question 29

what are hydrogen bonds critical for

Answer 29

the specificity of biomolecular interactions but not for the formation of biomolecular structures

Question 30

how is the magnitude of contribution of ionic interactions to biomolecular structures reduced

Answer 30

by shielding of these groups by water -water tends to sheild the charged groups, greatly diminishing the strength of interactions

Question 31

what determines the strength of electrostatic interactions

Answer 31

the distance separating the charged groups and the nature of the intervening medium

Question 32

van der Waals forces

Answer 32

interaction between permanent and induced dipoles; short range, low magnitude intercation

Question 33

when is the attraction maximal in VDW forces

Answer 33

when two atoms are separated by the sum of the VDW radii

Question 34

where are VDW abundant

Answer 34

in the core of folded proteins

Question 35

hydrophobic effect

Answer 35

drive to have polar groups interacting with water and non-polar regions shielded away from water

Question 36

thermodynamics of the hydrophobic effect

Answer 36

the folding of polypeptide decrease the entropy of the polypeptide but increases the entropy of the associated water

Question 37

Kw=

Answer 37

[H] [OH] = 1.0 x 10^-14 M^2

Question 38

strong acids and bases _____ _____ in water

Answer 38

dissociate completely

Question 39

weak acid and bases _____ ______ in water

Answer 39

do not completely dissociate

Question 40

where does the buffering region extend in titration curves

Answer 40

one pH unit on either side of the pKa point

Question 41

at what pH is the solution best able to resist changes in pH

Answer 41

when pH =pKa

Question 42

the lower the pKa the stronger the _____

Answer 42

acid

Question 43

why are buffers important to biological systems

Answer 43

organisms need to be able to maintain a constant pH -changes in pH could alter the protonation state of biomolecules, potentially changing their structure and function

Question 44

the Henderson-Hasselbalch equation describes the relationship between:

Answer 44

the pH of the solution the pKa of the weak acid the relative concentration of the weak acid and conjugate base

Question 45

the strength of electrostatic interactions within biomolecules is often reduced by

Answer 45

shielding of charged groups by water molecules

Question 46

a monoprotic weak acid has the greatest buffering capacity:

Answer 46

-at the pKa point -at the midpoint of the buffering region -when there is an equal concentration of the HA and A forms -when the desired pH matches the pKa of the weak acid