Extracts from the bacterium Bacillus brevis contain a peptide with antibiotic properties. This peptide forms complexes with metal ions and seems to disrupt ion transport across the cell membranes of other bacterial species, leading to bacterial death. The structure of the peptide has been determined from a series of observations. (a) Complete acid hydrolysis of the peptide, followed by amino acid analysis, yielded equimolar amounts of Leu, Orn, Phe, Pro, and Val. Orn is ornithine, an amino acid not present in proteins but present in some peptides. Orn has the structure H 'H,N-CH, - CH2 CH2 CH2 - C - COO- NH, (b) The molecular weight of the peptide is approximately 1,200 Da. (c) The peptide failed to undergo hydrolysis when treated with the enzyme carboxypeptidase. This enzyme catalyzes the hydrolysis of the carboxyl-terminal residue of a polypeptide unless the residue is Pro or the peptide does not contain a free carboxyl group. (d) Treatment of the intact peptide with 1-fluoro-2,4-dinitrobenzene (FDNB), followed by complete hydrolysis and chromatography, yielded only free amino acids and the derivative shown here. O,N NO₂ H NH— CH, - CH₂- CH₂ - - C - COO- +NH3 (Hint: The 2,4-dinitrophenyl derivative involves the amino group of a side chain rather than the a-amino group.) (e) Partial hydrolysis of the peptide followed by chromatographic separation and sequence analysis yielded these di- and tripeptides (the amino-terminal amino acid is always the first amino acid): Leu-Phe Phe-Pro Orn-Leu Val-Orn Val-Orn-Leu Phe-Pro-Val Pro-Val-Orn Given this experimental information, deduce the amino acid sequence and the structure of the peptide antibiotic. Orn Leu Val Pro Phe linear peptide of Leu-Phe-Pro-Val-Orn Leu Orn Phe Val Pro + Pro Val Phe Orn Leu linear peptide of Pro-Val-Orn-Leu-Phe-Pro-Val-Orn-Leu-Phe-Pro linear peptide of Leu-Phe-Pro-Val-Orn-Leu-Phe-Pro-Val-Orn

The pH of lemon juice is 2, and the pH of orange juice is 4. Which of these is more acidic, and by how much? What does this mean?

Which of the following levels of protein structure may be affected by hydrogen bonding? (a) primary and secondary (b) primary and tertiary (c) secondary, tertiary, and quaternary (d) primary, secondary, and tertiary (e) primary, secondary, tertiary, and quaternary

The pH of black coffee is 5, and that of milk of magnesia is 10. Is the coffee twice as acidic as milk of magnesia?

If the disaccharide maltose is formed from two glucose monosaccharides, which are hexose sugars, how many atoms of carbon, hydrogen, and oxygen does maltose contain and why?

a. Can a mutation change a proteins tertiary structure without changing its primary structure? b. Can a mutation change a proteins primary structure without affecting its secondary structure?

The synthetic process by which monomers are covalently linked is (a) hydrolysis (b) isomerization (c) condensation (d) glycosidic linkage (e) ester linkage

Plasma contains more sodium than chloride. How can this be if individual ions of sodium and chloride exactly balance each other out, and plasma is electrically neutral?

Below is the structure of glycine. Draw a tripeptide composed exclusively of glycine. Label the N-terminus and C-terminus. Draw a box around the peptide bonds.

In the following list, identify the carbohydrate, the fatty acid, the amino acid, and the polypeptide: a. NH2CHRCOOH b. C6H12O6 c. (methionine)20 d. CH3(CH2)16COOH