Passage
Antimicrobial peptides are an important component of innate immunity. Since their discovery in 1939, over 5,000 peptides with antimicrobial properties have been isolated from organisms in every domain of life. They have demonstrated activity against enveloped viruses, bacteria, fungi, and even tumor cells and have recently gained interest for their potential in fighting antibiotic-resistant bacteria. Most known antimicrobial peptides are positively charged, but some with negative charges have also been discovered.Frogs are known to secrete a variety of antimicrobial peptides as a major source of immunity. Secretions from a new species of frog were collected and the peptides were separated by cation exchange chromatography. Four of the isolated peptides demonstrated strong antibacterial activity and were characterized by isoelectric focusing and sequencing:
Figure 1 Results of isoelectric focusing of four antimicrobial peptidesTable 1 Amino Acid Compositions of Four Antimicrobial Peptides
Adapted from Wang Z, Wang G. APD: the Antimicrobial Peptide Database. Nucleic Acids Res. 2004;32(Database issue) :D590-2.
-Suppose the peptides had been purified by size exclusion chromatography instead of cation exchange. Which peptide would elute last?

Question

Passage
Antimicrobial peptides are an important component of innate immunity. Since their discovery in 1939, over 5,000 peptides with antimicrobial properties have been isolated from organisms in every domain of life. They have demonstrated activity against enveloped viruses, bacteria, fungi, and even tumor cells and have recently gained interest for their potential in fighting antibiotic-resistant bacteria. Most known antimicrobial peptides are positively charged, but some with negative charges have also been discovered.Frogs are known to secrete a variety of antimicrobial peptides as a major source of immunity. Secretions from a new species of frog were collected and the peptides were separated by cation exchange chromatography. Four of the isolated peptides demonstrated strong antibacterial activity and were characterized by isoelectric focusing and sequencing:

Figure 1 Results of isoelectric focusing of four antimicrobial peptidesTable 1 Amino Acid Compositions of Four Antimicrobial Peptides

Adapted from Wang Z, Wang G. APD: the Antimicrobial Peptide Database. Nucleic Acids Res. 2004;32(Database issue) :D590-2.
-Suppose the peptides had been purified by size exclusion chromatography instead of cation exchange. Which peptide would elute last?

Quizplus · Accepted Answer

11ecba2d_0df3_aac9_a3bf_5fac30fb3309_MD0008_00 Like gel electrophoresis, size exclusion chromatography separates molecules by size. Unlike gel electrophoresis, small molecules move more slowly through size exclusion columns than do large molecules. The column is filled with tiny beads that have pores of varying sizes. Molecules that are too large to fit into any of the pores are "excluded" from some of the column volume and travel only through the space surrounding the beads, called the "void volume." Molecules that can fit into the large pores travel through the additional volume that they provide, and those that are small enough to fit inside all the pores travel through the entire available volume. Because they have a longer effective distance to travel before reaching the end of the column, small molecules take longer to elute. Peptide 3 is composed of only 9 amino acids and is substantially smaller than the other peptides, so it will elute last. (Choices A, B, and D) These molecules are all much larger than Peptide 3 and will travel through less total volume. They will therefore elute sooner than Peptide 3. Educational objective: Size exclusion chromatography separates small molecules from large molecules. Smaller molecules take longer to elute because they effectively cross a greater distance than large molecules, which are excluded from the pores and travel only through the void volume.

Passage Antimicrobial Peptides Are an Important Component of Innate Immunity. Since