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2.3.4. What is nucleotides. Primary structure of nucleic acids

Nucleotides are chemical compounds, the building blocks of the nucleic acids RNA and DNA.

A nucleotide is composed of a nucleobase (nitrogenous base), a five-carbon sugar (either ribose or 2-deoxyribose), and one phosphate group.  Nucleotides contain either a purineor a pyrimidine base. Ribonucleotides are nucleotides in which the sugar is ribose. Deoxyribonucleotides are nucleotides in which the sugar is deoxyribose.

In DNA, the purine bases are adenine and guanine, while the pyrimidines are thymine and cytosine. RNA uses uracil in place of thymine. Adenine always pairs with thymine by 2 hydrogen bonds, while guanine pairs with cytosine through 3 hydrogen bonds, each due to their unique structures.

A nucleotide is made of a nucleobase (also termed a nitrogenous base), a five-carbon sugar (either ribose or 2-deoxyribose, depending on if it is RNA or DNA), and one or, depending on the definition, more than one phosphate groups.

Primary Structure of Nucleic Acids

The primary structure of a nucleic acid is the nucleotide sequence

The nucleotides in nucleic acids are joined by phosphodiester bonds

The 3’-OH group of the sugar in one nucleotide forms an ester bond to the phosphate group on the 5’-carbon of the sugar of the next nucleotide

A nucleic acid polymer has a free 5’-phosphate group at one end and a free 3’-OH group at the other end

The sequence is read from the free 5’-end using the letters of the bases

This example reads 5’—A—C—G—T—3’

2.3.5. Describe the function of dna, biological role of dna

Deoxyribonucleic acid or DNA is a molecule that contains the instructions an organism needs to develop, live and reproduce. These instructions are found inside every cell, and are passed down from parents to their children.DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA's instructions, or genetic code. Similar to the way the order of letters in the alphabet can be used to form a word, the order of nitrogen bases in a DNA sequence forms genes, which in the language of the cell, tells cells how to make proteins. Another type of nucleic acid, ribonucleic acid, or RNA, translates genetic information from DNA into proteins.

The entire human genome contains about3 billion bases and about 20,000 genes.

Nucleotides are attached together to form two long strands that spiral to create a structure called a double helix. If you think of the double helix structure as a ladder, the phosphate and sugar molecules would be the sides, while the bases would be the rungs. The bases on one strand pair with the bases on another strand: adenine pairs with thymine, and guanine pairs with cytosine.

DNA molecules are long — so long, in fact, that they can't fit into cells without the right packaging. To fit inside cells, DNA is coiled tightly to form structures we call chromosomes. Each chromosome contains a single DNA molecule. Humans have 23 pairs of chromosomes, which are found inside the cell's nucleus.

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