Chapter 2: Water and Intermolecular Forces

Question 1

What is Brownian motion

Answer 1

• motion is the movement of molecules powered by random fluctuations of environmental energy.
• initiates many biochemical interactions by supplying energy

Question 2

What hybrid is oxygen in water?

Answer 2

Oxygen in water is sp3 hybridized

Question 3

Is water bent?

Answer 3

Yes, H-O-H is close to a 109.5 angle

Question 4

Is water polar or nonpolar

Answer 4

The H-O bond is polar because O is electronegative
- the molecule of water is a dipole
- the oxygen atom bearing a partial negative charge
- the hydrogen atoms a partial positive charge.

Question 5

List some consequences of water polarity

Answer 5

• allows it to dissolve (it is a universal solvent)
• allows the formation of hydrogen bonds between water and biopolymers
• inability to dissolve creates hydrophobic effects

Question 6

Explain the disruption of hydrogen bonds by water

Answer 6

Water disrupts hydrogen bonds between two molecules by competing for the hydrogen-bonding capability

Question 7

What are some characteristics of Van der Waals?

Answer 7

• Asymmetry in electrical charge
• the more polar the group, the stronger the van der Waals
• the energy of van der Waals attractions depends on distance

Question 8

What contributes to the stability of the DNA double helix

Answer 8

Hydrogen bonds
 However, these bonds are weak enough to be broken by the enzymes of DNA metabolism, thereby allowing access to the genetic information

Question 9

What is the hydrophobic effect?

Answer 9

Hydrophobic molecules (non-polar) cluster in aqueous solutions, covered by water molecules
- entropy driven

Question 10

Examples of the hydrophobic effect

Answer 10

1) protein folding
2) DNA double helix formation
3) membrane assembly

Question 11

What are amphipathic/amphiphilic molecules

Answer 11

• molecules contain both polar and nonpolar groups
• tend to form micelles, colloidal aggregates with the charged “head” facing outward to the water and the nonpolar “tail” part inside.

Question 12

Describe the bilayer lipid membrane

Answer 12

hydrophobic tail and a hydrophilic head

Question 13

How is protein folding powered by the hydrophobic effect?

Answer 13

Hydrophobic collapse: Non-polar amino acids have a strong tendency to associate with one another in the interior of the folded protein
o The increased entropy of water compensates for the entropy losses inherent in the folding process.