Bases in DNA

Messenger RNA (mRNA) (Section 28 11) A polynucleotide of nbosethat reads the sequence of bases in DNA and inter acts with tRNAs in the nbosomes to promote protein biosynthesis... 

These relationships are general. Hydroxyl-substituted purines and pyrimidines exist in their keto forms fflnino-substituted ones retain structures with an anino group on the ring. The pyrimidine and purine bases in DNA and RNA listed in Table 28.1 follow this general rule. Beginning in Section 28.7 we ll see how critical it is that we know the correct tautomeric forms of the nucleic acid bases. 

Proteins are a diverse and abundant class of biomolecules, constituting more than 50% of the dry weight of cells. This diversity and abundance reflect the central role of proteins in virtually all aspects of cell structure and function. An extraordinary diversity of cellular activity is possible only because of the versatility inherent in proteins, each of which is specifically tailored to its biological role. The pattern by which each is tailored resides within the genetic information of cells, encoded in a specific sequence of nucleotide bases in DNA. 

The sequence of bases in DNA is recorded as a sequence of complementary bases in a single-stranded mRNA molecule. 

The uracil molecule is one of foe bases in DNA. Estimate foe approximate values of foe indicated bond angles. Its skeleton (not its Lewis structure) is gfven below. 

C13-0086. There are four different bases in DNA strands. How many different 12-base combinations are there ... 

Gajewski, E., Aruoma, O.L, Dizdaroglu, M. and Halliwell, B. (1991). Bleomycin-dependent damage to the bases in DNA is only a minor side-reaction. Biochemistry 30, 2444-2448. 

Aruoma, O.I., Halliwell, B. and Dizdarogju, M. (1989a). Iron ion-dependent modification of bases in DNA by the superoxide radical-generating system hypoxanthine/oxidase. J. Biol. Chem. 264, 13024-13028. 

Copper-ion-dependent damage to the bases in DNA in the presence of hydrogen peroxide. Biochem. J. 273, 601-604. 

A determine that the sequence of nitrogen bases in DNA is different for every organism... 

GG8, the radical cation must traverse five A/T base pairs. Electrochemical measurements in solution have shown that the purine bases (A and G) have considerably lower Eox than the pyrimidines (C and T), with the Eox of G estimated to be about 0.25 V below that of A [20]. It is not very likely that the Eox of bases in DNA will be the same as they are in solution, but it is generally assumed that the order of Eox will remain the same. Consequently, the radical cation at Gi of AQ-DNA(l) must traverse a bridge of five A bases to reach GG8. The process whereby the radical cation crosses such bridges has been a major point of debate in consideration of long distance radical cation migration mechanisms in DNA this issue will be discussed fully below. 

Fig. 10. The formulae of some of the bases in DNA and RNA. The acid dissociation constants and the methylmercury constants and binding centres axe shown (after R. B. Simpson)...

A genetic linear coded molecule of four bases in DNA, the genome... 

The cation 18 did not show any DNA cleavage, due probably to its inherent stability (18 would be more stable than a benzyl cation [66], relatively stable ions that do not alkylate the heterocyclic bases in DNA). The 9-diazofluorene 19 would not undergo reduction like the corresponding diazonium salts (17) because of the presence of a negative charge on the fluorenyl carbon. 

Basic to molecular biology is the concept that DNA and RNA are macromolecules that convey information. The sequence of purine and pyrimidine bases in DNA encodes all the information needed to form and direct the chemical reactions within cells. This information thus encodes all catalytic, regulatory, and structural proteins contained within an organism. The flow of information from DNA to RNA to proteins is... 

There are four bases in DNA guanine, thymine, cytosine and adenine. Each has a ketone C=0 group in which the oxygen is quite electronegative and bears an excess negative charge <5 , and an amine in which the electropositive hydrogen atoms bear an excess... 

Recent experiments have demonstrated the operation of the hole hopping mechanism between G bases in DNA.145,481 In these experiments, Norrish I photocleavage of an acylated nucleoside in a syn-... 

Here are the key points, (a) DNA is the stuff of genes, (b) DNA is a sequence of nucleotides, each of which carries one of four possible symbols, (c) DNA is orgaiuzed into a sequence of genes, (d) Genes determine the sequence of amino acids in proteins, (e) The sequence of amino acids determines the three-dimensional structure of proteins, which, in turn (f) determines their biological properties. These, in turn (g) determine the nature of the cell. It follows that the sequence of bases in DNA is the ultimate repository of the information required to specify the uifique biochemical personality of the cell. 

The Watson-Crick double helix is the outcome of three lines of work. The first is the discovery by Erwin Chargaff of Chargaff s rules." Specifically, for all normal DNAs, A = T, G = C and A + G = C + T. The actual content of each base in DNA varies from species to species over a wide range. Despite this variation, the content... 

The seqnence of amino acids in proteins is nltimately encoded in the sequence of bases in DNA. Transcription encodes this information in mRNA molecules. Each RNA polymerase transcribes a very small part of the total DNA base sequence. It follows that RNA polymerases need specific places on DNA molecules to start and to stop transcription. Getting the amino acid seqnence right is critical for protein function. It follows that getting transcription started at precisely the right place is also critical. If the mRNA base sequence is not right, the amino acid sequence in the protein will not be right. 

Codon a triplet of bases in DNA or mRNA that specifies a specific amino acid in proteins or a termination signal. 

A constant number of chromosomes is present in each cell. The somatic cells (i.e. not sperm or egg) are described as diploid because they contain two complete sets of chromosomes. There are 23 pairs of chromosomes in each cell, 22 pairs of somatic chromosomes (one of each pair derived from each parent) and one pair of sex chromosomes, either two Xs in the female or an X and Y in the male. Together, the 23 chromosomes contain about two metres of linear DNA or about three billion pairs of nucleotides. The linear structure of bases in DNA strands is called the primary structure of the chromosome. The secondary structure is the double heUx, in which the two complementary strands of DNA twist about each other. One turn of the helix is called a pitch and consists of ten nucleotides. 

Small methyl groups are important in the stractnre of some small compounds, nucleotides, some bases in DNA mole-cnles and in postranslational modification of amino acids in proteins. The transfer of a single carbon atom is important in the synthesis of purine nncleotides. The componnds involved in the whole process of methyl gronp transfer, and are carbon metolism, are methionine, homocysteine, serine and the vitamins, folic acid and B12. 

Figure 15.4 Four compounds that are methylated either by SAM or methyl FH4 (CH3 FH4). The processes are (i) cytidine bases in DNA (11) methylatlon of deoxyUMP to produce deoxythymidine monophosphate (111) formation of phosphatidylcholine from phos-phatldylethanolamlne (Chapter 17) (Iv) methylatlon of a protein In myelin. The base cytidine Is methylated In DNA to produce methylcytidine which. If deamlnated, produces methylthymidine In DNA. Methylatlon of the bases can modify gene transcription (see text). (PR 5 -phosphor1bose).

Methionine, which is involved in methyl group donation for nucleotide synthesis, methylation of bases in DNA (Chapter 20) and conversion of choline to ethanolamine for membrane synthesis (Chapter 11). 

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