a serine b aspartate Sample Problem 191 Structural Formulas of Amino Acids Solution a b Study Check 191 Draw the zwitterion for leucine Answer Continued Sample Problem 191 ID: 585894
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Slide1
Draw the zwitterion for each of the following amino acids:a. serine b. aspartate
Sample Problem
19.1 Structural Formulas of Amino Acids
Solution
a. b
.
Study Check 19.1Draw the zwitterion for leucine.Slide2
Answer
Continued
Sample Problem 19.1
Structural Formulas of Amino AcidsSlide3
Using Table 19.2, indicate each of the following for the amino acid shown:
a. name, three-letter, and one-letter abbreviations b.
polar or nonpolarc. has a neutral, acidic, or basic R group d. interaction with water as hydrophobic or hydrophilic
Sample Problem
19.2 Classification of Amino Acids
Solution
a. phenylalanine, Phe, F b. nonpolarc. neutral
d. hydrophobicSlide4
Continued
Sample Problem 19.2
Classification of Amino AcidsSlide5
Study Check 19.2Using Table 19.2, indicate each of the following for the amino acid shown:
a
. name, three-letter, and one-letter abbreviations b. polar or nonpolarc. has a neutral, acidic, or basic R group d. interaction with water as hydrophobic or hydrophilic
Answera. serine, Ser, S b. polarc. neutral d. hydrophilic
Continued
Sample Problem 19.2
Classification of Amino AcidsSlide6
Solution
a. At a pH of 6.0, glycine has an ammonium group and a carboxylate group, which give it an overall change of zero
(0). b. At a pH of 8.0 (basic solution), the —NH3+ group loses H+ to become —NH2
, which has no charge. Because the carboxylate group (—COO–) remains ionized, the overall charge of glycine at pH 8.0 is negative (1–).
Study Check 19.3
Draw the structural formula for glycine at pH 3.0 and give the overall charge.
The pI of glycine is 6.0. Draw the structural formula and state the overall charge for glycine at a. pH 6.0 and at b. pH 8.0.Sample Problem 19.3 Amino Acids in Acidic or Basic SolutionSlide7
Answer
Continued
Sample Problem 19.3
Amino Acids in Acidic or Basic SolutionSlide8
Draw the structure and give the name for the tripeptide Gly–Ser–Met.
Sample Problem
19.4 Drawing a Peptide
Solution
Step 1
Draw the structures for each amino acid in the peptide, starting
with the N-terminus.Slide9
Step 2 Remove the O atom from the carboxylate group of the N-terminus and two H atoms from the ammonium group in the adjacent
amino acid. Repeat this process until the C-terminus is reached.
Continued
Sample Problem 19.4
Drawing a PeptideSlide10
Step 3 Use peptide bonds to connect the amino acid residues.
The
tripeptide is named by replacing the last syllable of each amino acid name with yl, starting with theN-terminus. The C-terminus retains its complete amino acid name. N
-terminus glycine is named glycyl serine is named seryl C-terminus methionine
keeps its full nameThe tripeptide is named glycylserylmethionine.
Continued
Sample Problem 19.4 Drawing a PeptideSlide11
Study Check 19.4Draw the structure and give the name for Phe–Thr, a section in glucagon, which is a peptide hormone that increases blood glucose levels.
Answer
Continued
Sample Problem 19.4
Drawing a PeptideSlide12
SolutionThe tetrapeptide starts with the N-terminus, histidine, followed by two valine
residues, and ends with the C-terminus, proline. Three
-letter abbreviations: His–Val–Val–Pro One-letter abbreviations: HVVP Study Check 19.5What are the three-letter and one-letter abbreviations of a tripeptide containing two glycines and one tyrosine, if theN-terminus is tyrosine?
AnswerTyr–Gly–Gly (YGG)
What are the three-letter and one-letter abbreviations of the
tetrapeptide
that contains two valines, one proline, and one histidine if the N-terminus is histidine and the C-terminus is proline?Sample Problem 19.5 Primary StructureSlide13
Solutiona. β-pleated sheet
b. triple helixc. α helix
Study Check 19.6Which attractive force holds secondary structures together in proteins?Answerhydrogen bonding
Identify the secondary structure
(
α helix, β-pleated sheet, or triple helix) described in each of the following statements:a. a
structure that has hydrogen bonds between adjacent polypeptide chainsb. three helical polypeptides woven togetherc. a peptide chain with a coiled or corkscrew shape that is held in place by hydrogen bondsSample Problem 19.6 Identifying Protein StructuresSlide14
Solution
a.
Two cysteines, each containing —SH, will form a disulfide bond.b. The interaction of the —COO– in the residue of glutamate and the —NH3+ in the residue of lysine will form an ionic bond called a salt bridge.c. The residue in tyrosine has an —OH
group that is attracted to water by hydrophilic interactions.Study Check 19.7Would you expect to find valine and leucine on the outside or the inside of the tertiary structure? Why?
AnswerBoth valine and leucine have nonpolar residues and would be found on the nonpolar inside of the tertiary structure.
What type of interaction would you expect between the residues of each of the
following amino acids in a tertiary structure of a protein?a. cysteine and cysteine b. glutamate and lysinec. tyrosine and waterSample Problem 19.7 Interaction Between Residues in Tertiary StructuresSlide15
Solution
a. Disulfide bonds are a type of interaction between amino acid residues found in the
tertiary and quaternary levels of protein structure.b. The peptide bonds in the sequence of amino acids form the primary level of protein structure.c. The hydrogen bonds between the peptide bonds along the polypeptide chain form the secondary structures of α helix or β-pleated sheetStudy Check 19.8What structural level is represented by the hydrophobic side chains of the
amino acid residues at the center of a globular protein?Answertertiary structure
Indicate whether the following interactions are responsible for primary, secondary, tertiary
, or
quaternary protein structures:a. disulfide bonds that form between portions of a protein chainb. peptide bonds that form a chain of amino acidsc. hydrogen bonds between the H of a peptide bond and the O of a peptide bond four amino acids awaySample Problem 19.8 Identifying Protein StructureSlide16
Solutiona. The acids in lemon or lime juice break down the hydrogen bonds between polar residues
and disrupt salt bridges, which denature the proteins of the fish.b. The heat during baking breaks apart hydrogen bonds and hydrophobic interactions between nonpolar residues in the milk proteins. When the milk denatures, the
proteins become insoluble and form solids called curds.Study Check 19.9Why is a dilute solution of AgNO3 used to disinfect the eyes of newborn infants?AnswerThe heavy metal Ag+ denatures the proteins in bacteria that cause gonorrhea.
Describe the denaturation process in each of the following:
a
. An appetizer known as ceviche is prepared without heat by placing slices of raw fish in a
solution of lemon or lime juice. After 3 or 4 h, the fish appears to be “cooked.”b. When baking scalloped potatoes, the added milk curdles (forms solids).Sample Problem 19.9 Denaturation of Proteins