Biochemistry PS

1-8. When 1 g of urea (MW = 60) is diluted to 100 ml of water, what is the osmotic pressure of the solution (assume T = 209 K, R = .0821 L . atm K-‐1 . mol-‐1). What is the osmotic pressure of the same concentration of NaCl, assuming complete dissociation of the salt.

"π = iMRT

1-6. For this question, you may ignore units. Consider two positively charged particles, each with a charge (q = +1), at a distance of 1 in water (dielectric = 80). At what distance would they have to be spaced apart to maintain the same net repulsive force if they were transferred to oil (dielectric = 4). Show all you work.

"F = q1 x q2/(dielectric constant)(r2)

3-24. What amino acids are more likely to be found in the interior of a protein? Why? What amino acids are likely to be on the exterior of a protein? Why?

"Interior - Hydrophobic - Because they clump together due to the hydrophobic effect

1-4. Suppose the major solutes in intact lysosomes (a cellular organelle) are KCl (0.1 M) and NaCl (0.03 M). We wish to isolate lysosomes from intact cells in our lab, such that the membrane of the lysosomes does not rupture. Assuming the experiment is performed at room temperature (25 oC), what concentration of sucrose should we use in the extracting solution to make sure the lysosomes do not rupture, with the knowledge that the sugar sucrose does not dissociate?

"KCl = .1M x 2 = .2M

3-23. What are prions? Name two prion diseases.

"Prions are misfiled proteins that cause other protein they come in contact with to also misfold.

1-11. A common practice of competitive short distance runners is breath rapidly and deeply (hyperventilate) for about half a minute to remove CO2 from the lungs just before a race. As a result, the pH may rise to 7.6. Explain the rise of pH.

Blowing off CO2 leaves less of it in the body in solution and therefore less carbonic acid forms and the body is more basic and the pH rises.

3-3. Which amino acid is most likely to be found in a cis-peptide conformation?

Cysteine

1-10. Normally, gaseous CO2 is efficiently expired in the lungs. Under certain conditions, such as obstructive lung disease or emphysema, expiration is impaired. The resulting excess of CO2 in the body may lead to respiratory acidosis, a condition in which excess acid accumulates in bodily fluids. How does excess CO2 lead to respiratory acidosis?

Excess CO2 reacts with water to produce carbonic acid.

1-5. In EXACTLY two words (no more, no less) explain the following three observations: (1) solid water (ice) is less dense than liquid water; (2) water has a high heat capacity; (3) water has a high heat of vaporization.

Hydrogen Bonds

1-7. Explain the similarity between a hydrogen bond and a covalent bond. Explain a similarity between a hydrogen bond and an electrostatic interaction. Explain a difference between an electrostatic interaction and a hydrogen bond.

Orientation matters for strength of the bond.

H3N+-CH(CH2OH)-COO- Clockwise: COO- at top, lone H oriented toward viewer, R-group at bottom"

Serine, L Form

2-13. Does the peptide bond normally form a structure that is trans or cis? Why? What is the most common exception to the rule? Why?

Trans, except for cysteine

1-1. Explain the significance of Wohler's synthesis of urea from ammonium cyanate. Include in your explanation the distinction between vitalism and biochemistry.

Wohler's synthesis of urea from ammonium cyanate was significant as the first major step to disproving the theory of vitalism. Vitalism held that the processes and chemistry of living organisms were distinctly different in terms of the rules they followed. Urea was a well know biological compound and it synthesis led to the field of biochemistry, which is the now universally accepted theory that the same chemical processes and rules that exist outside a living organism also occur within living organisms.

1-2. Draw a generic structure of an α-‐amino acid. What chemical feature distinguishes one amino acid from another?

π = iMRT