Draw the zwitterion for each of the following amino acids - PowerPoint Presentation

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