Concept explainers
Interpretation:
The mechanistic arrows for resonance structures on adenine residue for proton transfer during peptide bond formation are to be drawn.
Concept introduction:
舧 Amino acids are organic compounds containing
舧 A nucleoside consists of a nucleobase (also termed as nitrogenous base) and a five-carbon sugar (either ribose or deoxyribose).
舧 A
舧 In a nucleoside, the anomeric carbon is linked through a glycosidic bond to the N9 of a purine or N1 of a pyrimidine.
舧 Examples of nucleosides include cytidine, uridine, adenosine, guanosine and thymidine.
舧 Sugar (ribose/deoxyribose) and nitrogenous bases are linked through N-glycosidic bonds.
舧 These glycosidic bonds are formed by condensation reaction of first carbon of sugar molecule with the nitrogen atom
舧 This particular glycosidic bond is stable in basic solutions, but readily hydrolyzes in the presence of acids.
舧 DNA is the genetic material in human beings and most of the biological systems. The proportion of DNA is constant in all diploid human cells. However, gamete cells are haploid and are composed of half of the amount of DNA present in diploid cells.
舧 DNA exists in the form of a double-stranded helix in which complementary bases are present opposite to each other and form base pairs.
舧 In most common form of DNA, that is, B-DNA,
舧 Cytosine and uracil are pyrimidines present in
舧 During translation, a peptide bond is formed between amino group of one amino acid and carboxyl group of and other amino acid. Ribosomes are composed of rRNA (ribosomal ribonucleic acid), which consists of ribonucleotides linked together by phosphodiester bonds. Nitrogen 3 of adenine of rRNA is involved in proton transfer, which is resonance stabilized by the adjacent ribosomal residues.
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Chapter 25 Solutions
Organic Chemistry
- Give the sequence of the following tetrapeptide:arrow_forwardAlthough the bond energy for the hydrogen bond in a vacuum is estimated to be about 20 kJ/mol, we find that each hydrogen bond in a folded protein contributes much less--probably less that 5 kJ/mol--to the enthalpy of protein stabilization. Suggest an explanation for this difference. Explain briefly.arrow_forwardAll amino acids have two ionizable functional groups: an a-amino group (average pK, of 9.4) and an a-carboxylic acid group (average pK, of 2.2). Tyrosine also has an ionizable side chain (R group) with a pK, of about 10.1. One of the possible ionization states of tyrosine is shown.arrow_forward
- Outline the four general stages in an enzyme-catalyzedreaction.arrow_forwardThe activity of an enzyme requires a glutamic acid to display its -COOH functional group in the protonated state. Suppose the pK, of the -COOH group is 4.07. (a) Will the enzyme be more active at pH 3.5 or 4.5? Explain. (b) What fraction of the enzymes will be active at pH = 4.07? Explain. (c) At what pH will the enzyme show 78% of maximal activity?arrow_forwardA peptide has the sequence Glu–His–Trp–Ser–Gly–Leu–Arg–Pro–Gly The p?a values for the peptide’s side chains, terminal amino groups, and carboxyl groups are provided in the table. Amino acid Amino pKa Carboxyl pKa Side‑chain pKa glutamate 9.609.60 2.342.34 4.254.25 histidine 9.179.17 1.821.82 6.006.00 tryptophan 9.399.39 2.382.38 serine 9.159.15 2.212.21 glycine 9.609.60 2.342.34 leucine 9.609.60 2.362.36 arginine 9.049.04 2.172.17 12.4812.48 proline 10.9610.96 1.991.99 Calculate the net charge of the molecule at pH 11 and estimate the isoelectric point (pI)(pI) for this peptide.arrow_forward
- In the double-helical structure of DNA, the base guanineis always bonded to cytosine, and adenine is alwaysbonded to thymine. What do you expect to be the relativeproportional amounts of A, T, C, and G in a givenlength of DNA?arrow_forwardEach ionizable group of an amino acid can exist in one of two states, charged or neutral. The electric charge on the functional group is determined by the relationship between its pKą and the pH of the solution. This relationship is described by the Henderson-Hasselbalch equation. Histidine has three ionizable functional groups. Complete the equilibrium equations by assigning the proper pKą for each ionization and the net charge on the histidine molecule in each ionization state. H || H,N*-C-C-OH H|| H,N*-C-C-o- H|| H,N*-C-C-o- H|| H,N-C-C-o- CH, CH, CH, CH, HN HN N -NH -NH -NH -NH Answer Bank pK, = 6.0 -1 pк, - 9.17 +2 -2 +1 pK, = 7.59 pK, = 1.8 %3D 1 1arrow_forwardIn relation to the spatial structure of the proteins select the INCORRECT alternative: (a) The quaternary structure of proteins consists of the association of two or more protein chains to form the complete protein. (b) The tertiary structure of proteins is mainly due to long-range interactions between amino acids that are far apart in the protein sequence but spatially close due to protein coiling. (c) Disulfide bridges are produced or broken as a result of oxidation-reduction processes. (d) The interactions between peptide chains in the secondary structure of proteins are basically due to Van der Waals forces. (e) The primary structure of proteins is basically due to the existence of covalent bonds between the different amino acids that constitute them.arrow_forward
- At very low pH, alanine is a diprotic acid that can be represented as H3N1-CH(CH3)-COOH. The pKa of the carboxyl group is 2.3, and the pKa of the UNH1 3 group is 9.7.(a) At pH 7, what fraction of the amino acid molecules dissolved in an aqueous solution will have the form H3N1-CH(CH3)-COO2?(b) What fraction of the molecules at this pH will havethe form H2N-CH(CH3)-COOH?arrow_forwardA tetradecapeptide (14 amino acid residues) gives the following peptide fragments on partial hydrolysis. (i) From this information, deduce the primary structure of this polypeptide. Fragments are are grouped according to size. Pentapeptide Fragments TetrapeptideFfragments Phe-Val-Asn-Gln-His His-Leu-Cys-Gly-Ser Gly-Ser-His-Leu-Val Gln-His-Leu-Cys His-Leu-Val-Glu Leu-Val-Glu-Ala Predict the products formed if the tetradecapeptide is acted upon by trypsin and elastse.arrow_forwardConsider the following peptide : Phe – Glu – Ser – Met and Val – Trp – Cys – Leu. Do these peptides have different net charges at (a) pH 1? (b) pH 7? Indicate the charges at both pH valuesarrow_forward
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