The “central dogma of Molecular Biology“ describes the transfer of genetic information from DNA via — Analytical Chemistry Chemistry Question
DNA, RNA, Proteins
The “central dogma of Molecular Biology“ describes the transfer of genetic information from DNA via RNA to protein:
DNA → RNA → PROTEIN
(a) (b) (c)
(a): replication (b): transcription (c): translation
The chemical structures of the biopolymers DNA, RNA and proteins enable them to play such important roles for all forms of life. Fifty years ago, in 1953, James Watson and Francis Crick published a structure of DNA in the journal “Nature” which involves specific interactions between nucleobases in complementary strands.
Draw the line–bond structure of the nucleotide 2’–deoxyadenosine 5’–mono– phosphate (dAMP, disodium salt) and of the bases cytosine, guanine, and thymine. Indicate the correct hydrogen bonds between the nucleobases as they occur in the Watson–Crick double strand.
Model Answer
The worked solution provides drawn structures for the nucleotide 2’-deoxyadenosine 5’-monophosphate (dAMP, disodium salt), as well as base pairings showing Watson-Crick hydrogen bonds between Cytosine and Guanine, and between Thymine and Adenine.
[VISUAL]
How does the composition of RNA differ from that of DNA, and how does that affect the chemical stability of the molecule?
Model Answer
RNA contains ribose instead of 2’–deoxyribose as the sugar moiety. Uracil (in RNA) takes the place of the nucleobase thymine (in DNA).
The 2’–OH group in ribose affects the stability of RNA against base–catalysed hydrolysis, which is initiated by deprotonation of the 2’–OH group and results in backbone cleavage. This 2’–OH group is missing in DNA which is therefore more stable than RNA.
Write down three general functions of proteins.
Model Answer
Proteins
– build structures (cytoskeleton, keratin, connective tissue,...)
– generate motive forces (myosin,...)
– transport ions/small molecules (ion carriers, protein complexes,...)
– catalyse reactions (enzymes)
– fight against infections (immune response)
Other answers are also possible.
Draw a reaction scheme with line–bond structures that shows how two amino acids combine to form a dipeptide. What conformation does the peptide bond usually adopt?
Which high–molecular weight particle catalyses the formation of peptide bonds in human cells during translation?
Model Answer
Reaction scheme of peptide formation: [VISUAL]
The peptide bond is almost planar (due to the partial double–bond as indicated in the figure). The two Cα carbon atoms are arranged in trans–configuration.
The human ribosome is a particle made up by 4 ribosomal RNA molecules and several dozen protein subunits with a total molecular weight of 4,200,000 u. It binds to the messenger RNA and, depending on the base sequence, catalyses the formation of peptide bonds between the COO– group of the nascent polypeptide chain and the NH3+ group of the correct activated amino acid.
Draw the stereochemical formula of the tripeptide L–Ser–L–Val–L–Gly indicating the charges at the isoelectric point.
Model Answer
Tripeptide SVG (note the zwitterionic state):
[VISUAL]