Chapter 25, Problem 16P

Interpretation Introduction

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 amine ($-{\text{NH}}_2$) and carboxyl ($-\text{COOH}$) functional group along with a side chain (R group) specific to each amino acid.

舧 A nucleoside consists of a nucleobase (also termed as nitrogenous base) and a five-carbon sugar (either ribose or deoxyribose).

舧 A nucleotide consists of a nucleobase (also termed as nitrogenous base), a five-carbon sugar (either ribose or deoxyribose) and one or more phosphate groups.

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 $(\text{N1 of pyrimidines and N9 of purines)}$ of the nitrogenous base.

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, $10\text{ base pairs occupy a distance of 34 }\AA$ >.

舧 Cytosine and uracil are pyrimidines present in nucleic acids. Cytosine is present in DNA (deoxyribonucleic acid), whereas uracil is not present in DNA and is a specific component of the RNA (ribonucleic acid). Cytosine can undergo deamination to form uracil, which creates mismatch in DNA strands.

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.