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Theory of Intelligent Design, the best explanation of Origins » Origin of life »  Nucleotide Biosynthesis

Nucleotide Biosynthesis

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1 Nucleotide Biosynthesis on Sun Jan 26, 2014 4:13 pm

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http://www.wisegeek.com/what-is-nucleotide-biosynthesis.htm

Nucleotide biosynthesis is the process whereby nucleotides are created or synthesized.
This process can occur both within living organisms, as well as within a lab. If occurring within living cells, the process takes place in the cytoplasm of the cell and not within a particular organelle. Nucleotides are particularly important molecules within the cells of all living organisms because they are the molecules that are used to produce DNA and RNA. Also, nucleotides are used to form energy storage molecules and molecules that are necessary for passing signals between cells and between organelles within cells.

There are five different nucleotides; adenine, cytosine, and guanine are found in both DNA and RNA, thymine is found solely within DNA molecules, and uracil is only in RNA. All nucleotides have a similar basic structure, which is a nitrogenous base attached to a sugar molecule and a phosphate group. They are categorized into two groups based on the structure of this base. The nitrogenous base for purines — adenine and guarnine — contains a double ring structure, while the base found in pyrimidines — cytosine, thymine and uracil — has only a single ring structure.

Nucleobase

Nucleobases are nitrogen-containing biological compounds (nitrogenous bases) found within deoxyribonucleic acid (DNA), ribonucleic acid (RNA), nucleotides, and nucleosides. Often simply called bases in genetics, their ability to form base-pairs and to stack upon one another lead directly to the helical structure of DNA and RNA.


Two different methods of nucleotide biosynthesis occur within cells.

If a nucleotide is created from simpler compounds, it is considered de novo nucleotide biosynthesis. De novo is Latin and basically means from the beginning, or from scratch. The other way that nucleotides are formed is through salvage pathways. In this situation, parts of nucleotides that have been broken down are recycled and reused to form new nucleotides.

Each group of nucleotides undergoes de novo nucleotide biosynthesis differently. With pyrimidine nucleotides, the base structure is formed from its components and then attached to a ribose sugar molecule. In contrast, purine nucleotides are created by attaching the simpler compounds directly onto the ribose molecule. During salvage biosynthesis, a base that has already been formed is recycled and reattached to a ribose unit.

Nucleotide biosynthesis results in the creation of ribonucleotides, which are nucleotides that contain a ribose sugar ( Ribose is an organic compound with the formula C5H10O5; specifiifically, a monosaccharide (simple sugar)They are carbohydrates, composed of carbon, hydrogen and oxygen.     ). Ribonucleotides (  In biochemistry, a ribonucleotide or ribotide is a nucleotide containing D-ribose as its pentose component. Nucleotides ( nucleotides are composed of a nitrogenous base, a five-carbon sugar (ribose or deoxyribose), and at least one phosphate group ).




are organic molecules that serve as the monomers, or subunits, of nucleic acids like DNA and RNA.   are used to create strands of RNA, while DNA is created from deoxyribonucleotides ( Deoxyribose, or more precisely 2-deoxyribose, is a monosaccharide . Monosaccharides  are the most basic units of carbohydrates. They are the simplest form of sugar and are usually colorless, water-soluble, crystalline solids Examples of monosaccharides include glucose (dextrose) )  . As such, all nucleotides that are used for DNA must undergo further synthesis.

To form deoxyribonucleotides from ribonucleotides, the ribose sugar loses an oxygen molecule, or undergoes a reduction reaction. To convert uracil to thymine, for example, an additional methyl group is added to the uracil nucleotide. The reduction of the ribonucleotides occurs only after they have been fully formed.

http://dwb.unl.edu/Teacher/NSF/C11/C11Links/www.bact.wisc.edu/microtextbook/metabolism/nucleotidesyn.html

Nucleotides are some of the largest monomers that have to be made by the cell and understandably their synthesis involves many steps and large amounts of energy.
Biosynthesis of nucleotides is under tight regulatory control in the cell. Organisms need to make just the right amount of each base; if too much is made, energy is wasted, if too little, DNA replication and cellular metabolism come to a halt. Also, the cell is sensitive to the presence of any premade nucleotides in its environment and will down regulate their de novo synthesis pathways in favor of using what is already present in the surroundings. Bacteria are capable of interconverting purines (adenine and guanine) and interconverting pyrimidines (thymidine, cytidine and uracil). If a growth medium provides a purine and a pyrimidine, many microbes are capable of synthesizing the other needed nucleotides from them.

All nucleotides contain a ribose sugar and phosphate that form the backbone of DNA and RNA. These are synthesized from ribose 5-phosphate, a central metabolite of the pentose phosphate pathway.

http://en.wikipedia.org/wiki/Pentose_phosphate_pathway

The pentose phosphate pathway (also called the phosphogluconate pathway and the hexose monophosphate shunt) is a process that generates NADPH and pentoses (5-carbon sugars). There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of 5-carbon sugars. This pathway is an alternative to glycolysis. While it does involve oxidation of glucose, its primary role is anabolic rather than catabolic. For most organisms, it takes place in the cytosol; in plants, most steps take place in plastids

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