Why nucleic acid is called acid

A space-filling molecular model of a short segment is displayed in part c on the right. The helix shown here has ten base pairs per turn, and rises 3. This right-handed helix is the favored conformation in aqueous systems, and has been termed the B-helix. As the DNA strands wind around each other, they leave gaps between each set of phosphate backbones. Two alternating grooves result, a wide and deep major groove ca. Other molecules, including polypeptides, may insert into these grooves, and in so doing perturb the chemistry of DNA.

Other helical structures of DNA have also been observed, and are designated by letters e. A and Z. A model of a short DNA segment may be examined by. Click Here. Frieda Reichsman, Univ. In their announcement of a double helix structure for DNA, Watson and Crick stated, "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material. The essence of this suggestion is that, if separated, each strand of the molecule might act as a template on which a new complementary strand might be assembled, leading finally to two identical DNA molecules.

Indeed, replication does take place in this fashion when cells divide, but the events leading up to the actual synthesis of complementary DNA strands are sufficiently complex that they will not be described in any detail. As depicted in the following drawing, the DNA of a cell is tightly packed into chromosomes. First, the DNA is wrapped around small proteins called histones colored pink below. These bead-like structures are then further organized and folded into chromatin aggregates that make up the chromosomes.

An overall packing efficiency of 7, or more is thus achieved. Clearly a sequence of unfolding events must take place before the information encoded in the DNA can be used or replicated.

Once the double stranded DNA is exposed, a group of enzymes act to accomplish its replication. These are described briefly here:. Topoisomerase : This enzyme initiates unwinding of the double helix by cutting one of the strands. Helicase : This enzyme assists the unwinding. Note that many hydrogen bonds must be broken if the strands are to be separated..

SSB : A single-strand binding-protein stabilizes the separated strands, and prevents them from recombining, so that the polymerization chemistry can function on the individual strands. DNA Polymerase : This family of enzymes link together nucleotide triphosphate monomers as they hydrogen bond to complementary bases.

These enzymes also check for errors roughly ten per billion , and make corrections. Ligase : Small unattached DNA segments on a strand are united by this enzyme. Polymerization of nucleotides takes place by the phosphorylation reaction described by the following equation. Di- and triphosphate esters have anhydride-like structures and are consequently reactive phosphorylating reagents, just as carboxylic anhydrides are acylating reagents. Since the pyrophosphate anion is a better leaving group than phosphate, triphosphates are more powerful phosphorylating agents than are diphosphates.

Formulas for the corresponding 5'-derivatives of adenosine will be displayed by Clicking Here , and similar derivatives exist for the other three common nucleosides. The DNA polymerization process that builds the complementary strands in replication, could in principle take place in two ways.

Referring to the general equation above, R 1 could represent the next nucleotide unit to be attached to the growing DNA strand, with R 2 being this strand. Alternatively, these assignments could be reversed. In practice, the former proves to be the best arrangement. Since triphosphates are very reactive, the lifetime of such derivatives in an aqueous environment is relatively short.

However, such derivatives of the individual nucleosides are repeatedly synthesized by the cell for a variety of purposes, providing a steady supply of these reagents. In contrast, the growing DNA segment must maintain its functionality over the entire replication process, and can not afford to be changed by a spontaneous hydrolysis event. As a result, these chemical properties are best accommodated by a polymerization process that proceeds at the 3'-end of the growing strand by 5'-phosphorylation involving a nucleotide triphosphate.

This process is illustrated by the following animation, which may be activated by clicking on the diagram or reloading the page. The polymerization mechanism described here is constant. It always extends the developing DNA segment toward the 3'-end i.

There is sometimes confusion on this point, because the original DNA strand that serves as a template is read from the 3'-end toward the 5'-end, and authors may not be completely clear as to which terminology is used. Because of the directional demand of the polymerization, one of the DNA strands is easily replicated in a continuous fashion, whereas the other strand can only be replicated in short segmental pieces.

This is illustrated in the following diagram. Separation of a portion of the double helix takes place at a site called the replication fork. As replication of the separate strands occurs, the replication fork moves away to the left in the diagram , unwinding additional lengths of DNA. Since the fork in the diagram is moving toward the 5'-end of the red-colored strand, replication of this strand may take place in a continuous fashion building the new green strand in a 5' to 3' direction.

This continuously formed new strand is called the leading strand. In contrast, the replication fork moves toward the 3'-end of the original green strand, preventing continuous polymerization of a complementary new red strand. Short segments of complementary DNA, called Okazaki fragments, are produced, and these are linked together later by the enzyme ligase. This new DNA strand is called the lagging strand. When you consider that a human cell has roughly 10 9 base pairs in its DNA, and may divide into identical daughter cells in 14 to 24 hours, the efficiency of DNA replication must be extraordinary.

The procedure described above will replicate about 50 nucleotides per second, so there must be many thousand such replication sites in action during cell division. A given length of double stranded DNA may undergo strand unwinding at numerous sites in response to promoter actions.

The unraveled "bubble" of single stranded DNA has two replication forks, so assembly of new complementary strands may proceed in two directions. The polymerizations associated with several such bubbles fuse together to achieve full replication of the entire DNA double helix. A cartoon illustrating these concerted replications will appear by clicking on the above diagram. Note that the events shown proceed from top to bottom in the diagram.

One of the benefits of the double stranded DNA structure is that it lends itself to repair, when structural damage or replication errors occur. Several kinds of chemical change may cause damage to DNA:. All these transformations disrupt base pairing at the site of the change, and this produces a structural deformation in the double helix..

Inspection-repair enzymes detect such deformations, and use the undamaged nucleotide at that site as a template for replacing the damaged unit. These repairs reduce errors in DNA structure from about one in ten million to one per trillion. The genetic information stored in DNA molecules is used as a blueprint for making proteins.

Why proteins? Because these macromolecules have diverse primary, secondary and tertiary structures that equip them to carry out the numerous functions necessary to maintain a living organism. As noted in the protein chapter , these functions include:. The critical importance of proteins in life processes is demonstrated by numerous genetic diseases, in which small modifications in primary structure produce debilitating and often disastrous consequences. Such genetic diseases include Tay-Sachs, phenylketonuria PKU , sickel cell anemia, achondroplasia, and Parkinson disease.

The unavoidable conclusion is that proteins are of central importance in living cells, and that proteins must therefore be continuously prepared with high structural fidelity by appropriate cellular chemistry.

We now define genes as sequences of DNA that occupy specific locations on a chromosome. The intriguing question of how the information encoded in DNA is converted to the actual construction of a specific polypeptide has been the subject of numerous studies, which have created the modern field of Molecular Biology. Francis Crick proposed that information flows from DNA to RNA in a process called transcription , and is then used to synthesize polypeptides by a process called translation.

Transcription takes place in a manner similar to DNA replication. A characteristic sequence of nucleotides marks the beginning of a gene on the DNA strand, and this region binds to a promoter protein that initiates RNA synthesis. The double stranded structure unwinds at the promoter site. The RNA molecule thus formed is single stranded, and serves to carry information from DNA to the protein synthesis machinery called ribosomes.

To summarize: a gene is a stretch of DNA that contains a pattern for the amino acid sequence of a protein. The cell then synthesizes the protein, using the mRNA as a template. An important distinction must be made here.

One of the DNA strands in the double helix holds the genetic information used for protein synthesis. This is called the sense strand , or information strand colored red above. World No Tobacco Day. Drugs side effects and their interactions. Herb and their interaction.

Related Books Free with a 30 day trial from Scribd. Related Audiobooks Free with a 30 day trial from Scribd. Views Total views. Actions Shares. No notes for slide.

Total views 1, On Slideshare 0. From embeds 0. Number of embeds 0. This leaves only one remaining proton, which is very acidic. That easily-lost proton is what causes nucleic acids to be so acidic. Why is nucleic acid called an acid? Ethan B. Nov 20, So the sequence of these molecules in the polymer can convey "make a protein", "please replicate me", "transfer me to the nucleus And so if you think about the need to convey genetic information from one cell to another, you would want a molecule that is very stable and doesn't fall apart on its own, and that's a major feature of nucleic acids.

The name "nucleic acid" comes from the fact that they were first described because they actually had acidic properties, much like the acids that you know. And the nucleic part comes from the fact that they were first isolated because they were found in the nucleus.