Tyrosine has a polar side chain because: a.) It is asymmetrical b.) It has two t
ID: 13321 • Letter: T
Question
Tyrosine has a polar side chain because:a.) It is asymmetrical
b.) It has two types of atoms that have large differences in electronegativity
c.) It is symmetrical
d.) both a and b
e.) both b and c
2. Consider the amino acid T at pH 9.23. Its alpha carboxyl group has a pKa of 2.63. What is the ratio of
base to acid for this group at this pH?
a.) 1:1
b.) 45637:1
c.) 2,634,678:1
d.) 3,981,072:1
e.) 9,364,345:1
3. Which statement about pKa is not true?
a.) It represents a pH at which 50% of the titratable group is in the acid form and 50% is in the
base form.
b.) If the pH is less than the pKa, more than 50% of the titratable groups are unprotonated.
c.) If the pH is greater than the pKa, more than 50% of the titratable groups are in the base
form.
d.) If the pH is less than the pKa, more than 50% of the titratable groups are in the acid form.
e.) All of the above are true.
4. At what approximate pH will D most likely exist as a zwitterion?
a.) 3.0
b.) 4.0
c.) 5.0
d.) 6.0
e.) 7.0
5. Cysteine is the only amino acid that can form covalent bonds with other amino acids (i.e. cysteine)
through its side chain.
a.) true
b.) false
6. At pH 2, will the R group of H likely be charged OR uncharged?
Explanation / Answer
1)Tyrosine has a polar side chain because:
d.) both a and b [ there is a net dipole because of the high electronegativity of oxygen and nitrogen]
2. Consider the amino acid T at pH 9.23. Its alpha carboxyl group has a pKa of 2.63. What is the ratio of base to acid for this group at this pH?
d.) 3,981,072:1
pH=pka + log [base/acid]
9.23=2.63+log [base/acid]
[base/acid]= antilog of [6.6]= 3,981,072:1
3. Which statement about pKa is not true?
e.) All of the above are true.
It can be determine from the HH equation pH=pka+log[base/acid]
4. At what approximate pH will D most likely exist as a zwitterion?
e.) 7.0 [they contain bout positive and negative charge, hence neutral]
5. Cysteine is the only amino acid that can form covalent bonds with other amino acids (i.e. cysteine) through its side chain.
b.) false [because there are some other amino acid which can form di-sulfur bond like cysteine]
6. At pH 2, will the R group of H likely be charged OR uncharged?
it will be charged
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