Download Chapter 25 Amino Acids, Peptides, and Proteins

Chapter 25
Amino Acids, Peptides, and Proteins
Review of Concepts
Fill in the blanks below. To verify that your answers are correct, look in your textbook at
the end of Chapter 25. Each of the sentences below appears verbatim in the section
entitled Review of Concepts and Vocabulary.
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Amino acids in which the two functional groups are separated by exactly one
carbon atom are called _______ amino acids.
Amino acids are coupled together by amide linkages called ____________ bonds.
Relatively short chains of amino acids are called ___________.
Only twenty amino acids are abundantly found in proteins, all of which are ___
amino acids, except for ____________ which lacks a chirality center.
Amino acids exist primarily as _______________ at physiological pH
The ___________________ of an amino acid is the pH at which the concentration
of the zwitterionic form reaches its maximum value.
Peptides are comprised of amino acid _________ joined by peptide bonds.
Peptide bonds experience restricted rotation, giving rise to two possible
conformations, called _______ and _______. The _______ conformation is more
stable.
Cysteine residues are uniquely capable of being joined to one another via
______________ bridges.
______ is commonly used to form peptide bonds.
In the Merrifield synthesis, a peptide chain is assembled while tethered to
__________________________.
The primary structure of a protein is the sequence of _____________________.
The secondary structure of a protein refers to the ________________________
_____________________ of localized regions of the protein. Two particularly
stable arrangements are the ___ helix and ____ pleated sheet.
The tertiary structure of a protein refers to its _________________________.
Under conditions of mild heating, a protein can unfold, a process called
_________________.
Quaternary structure arises when a protein consists of two or more folded
polypeptide chains, called _____________, that aggregate to form one protein
complex.
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CHAPTER 25
Review of Skills
Fill in the blanks and empty boxes below. To verify that your answers are correct, look
in your textbook at the end of Chapter 25. The answers appear in the section entitled
SkillBuilder Review.
25.1 Determining the Predominant Form of an Amino Acid at a Specific pH
CONSIDER THE FOLLOWING AMINO ACID,
AND DRAW THE FORM THAT PREDOMINATES
AT PHYSIOLOGICAL pH.
O
H2N
OH
NH2
25.2 Using the Amidomalonate Synthesis
IDENTIFY REAGENTS THAT WILL ACHIEVE THE FOLLOWING TRANSFORMATION:
1)
O
2)
O
O
OEt
EtO
H
OH
N
3)
O
4)
N
H
NH2
25.3 Drawing a Peptide
DRAW A
BOND-LINE
STRUCTURE FOR
THE TRIPEPTIDE
Phe-Val-Trp.
25.4 Sequencing a Peptide via Enzymatic Cleavage
IDENTIFY THE FRAGMENTS OBTAINED FROM ENZYMATIC CLEAVAGE OF THE FOLLOWING PEPTIDE:
Ala-Phe-Lys-Pro-Met-Tyr-Gly-Arg-Ser-Trp-Leu-Hist
trypsin
chymotrypsin
CHAPTER 25
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25.5 Planning the Synthesis of a Dipeptide
IDENTIFY ALL REAGENTS NECESSARY TO PREPARE THE DIPEPTIDE Ala-Gly:
Ala
Boc
Gly
+
Ala
Gly
Boc
OCH3
Ala
Gly
OCH3
Ala
Gly
25.6 Preparing a Peptide using the Merrifield Synthesis
IDENTIFY ALL REAGENTS NECESSARY TO PREPARE THE PENTAPEPTIDE Ile-Gly-Leu-Ala-Phe:
POLYMER
Boc
Phe
Boc
POLYMER
Phe
Ile
Gly
Leu
Ala
Phe
Ile
Gly
Leu
Ala
Phe
Boc
POLYMER
Ala
Phe
POLYMER
POLYMER
Review of Reactions
Identify the reagents necessary to achieve each of the following transformations. To
verify that your answers are correct, look in your textbook at the end of Chapter 25. The
answers appear in the section entitled Review of Reactions.
Analysis of Amino Acids
O
O
R
O
H2O
COOH
OH
+
N
+
OH
NH2
O
O
O
CO2
RCHO
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CHAPTER 25
Synthesis of Amino Acids
O
R
O
O
R
R
OH
OH
Br
O
O
O
OH
NH2
O
O
R
EtO
OEt
EtO
H
N
N
NH2
H
O
O
O
N
O
R
OH
OEt
R
H2 N
H
R
NaCN
H2 N
C
H
R
O
C
OH
H
O
OH
NHAc
O
OH
NHAc
OH
NH2
Analysis of Amino Acids
Ph
O
PEPTIDE
H
PEPTIDE
NH2
N
N
H
+
NH
O
H
R
S
N
R
Synthesis of Peptides
O
O
+
OH
H2 N
N
H
O
O
H2N
O
H
N
OH
OH
O
R
[H+]
ROH
O
H2N
O
H2N
OH
R
OR
R
NaOH
H2O
R