Lecture 4

Question 1

1 in 10

Answer 1

• 1 of 10 parts

- 1 in 2 = 50%

Question 2

1 to 10 dilution

Answer 2

• 1 to 2 = 33%

Question 3

pH less than pKa

Answer 3

• more acid
• acid % will be more than base %
• acid moles will be more than base moles

Question 4

Amino Acids and pH

Answer 4

• both amino and carboxyl ends act as acid/c.base pair
• at low pH = both ends are protonated and charge = +1
• at high pH = both ends are deprotonated and charge = -1
• moderate pH = 0

Question 5

Isoelectric Point

Answer 5

• neutral point

- pI = (pK1 + pK2) / 2

Question 6

Triprotic Amino Acids

Answer 6

• have an R group that can act as acid/c.base pair
• aspartic acid (pKa = ~4)
• glutamic acid (pKa = ~ 4)
• histidine (pKa = ~6)
• cysteine (pKa = ~8)
• tyrosine (pKa = ~10)
• lysine (pKa = ~10)
• arginine (pKa = ~12.5)
• can only buffer at one additional pH, only one pI

Question 7

Storage of Solutions

Answer 7

• many chemical solutions have indefinite shelf-lives
• some solutions are unstable
• -> “make fresh”, “store aliquots”, “prevent exposure to light”
• other solutions are food for microorganisms and must be kept sterile

Question 8

Sterilization for Storage of Nutrient Solution

Answer 8

• high temps. will denature proteins making them non-functional
• the effectiveness of heat killing is altered by: temp, time, conductance
• if any one of these is increase, another can be decreased to get the same killing effect