What component within a dna molecule holds the nitrogen bases together

DNA is one of the nucleic acids, information-containing molecules in the cell (ribonucleic acid, or RNA, is the other nucleic acid). DNA is found in the nucleus of every human cell. The information in DNA:

• guides the cell (along with RNA) in making new proteins that determine all our biological traits
• gets passed (copied) from one generation to the next

The key to all of these functions is found in the molecular structure of DNA, as described by Watson and Crick.

Although it may look complicated, the DNA in a cell is just a pattern made up of four different parts called nucleotides. Imagine a set of blocks that has only four shapes, or an alphabet that has only four letters. DNA is a long string of these blocks or letters. Each nucleotide consists of a sugar (deoxyribose) bound on one side to a phosphate group and bound on the other side to a nitrogenous base.

There are two classes of nitrogen bases called purines (double-ringed structures) and pyrimidines (single-ringed structures). The four bases in DNA's alphabet are:

• adenine (A): a purine
• cytosine(C): a pyrimidine
• guanine (G): a purine
• thymine (T): a pyrimidine

Watson and Crick discovered that DNA had two sides or strands, and that these strands were twisted together like a twisted ladder — the double helix. The sides of the ladder comprise the sugar-phosphate portions of adjacent nucleotides bonded together.

The phosphate of one nucleotide is covalently bound (a bond in which one or more pairs of electrons are shared by two atoms) to the sugar of the next nucleotide. The hydrogen bonds between phosphates cause the DNA strand to twist. The nitrogenous bases point inward on the ladder and form pairs with bases on the other side, like rungs. Each base pair is formed from two complementary nucleotides (purine with pyrimidine) bound together by hydrogen bonds. The base pairs in DNA are adenine with thymine and cytosine with guanine.

Component 1: Nucleic acids

Deoxyribonucleic acid (DNA)

There are two types of nucleic acid: Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA). Both are built up of units called nucleotides. Individual nucleotides are made up of three parts that combine by condensation reactions. These are:
1.  Phosphoric acid (phosphate H3PO4). This has the same structure in all nucleotides.
2.  Pentose sugar, of which there are two types: in RNA the sugar is ribose; in DNA the sugar is deoxyribose
3.  Organic base which contains nitrogen (which can also be called a nitrogenous base).

There are five different nitrogenous bases which are divided into two groups:

• Pyrimidine bases (single ring structures) are thymine, cytosine and uracil
• Purine bases (double ring structures) are adenine and guanine

A single nucleotide subunit, made from 3 different components linked via condensation reactions. The components include: a phosphate group, a pentose sugar (either deoxyribose in DNA or ribose in RNA) and a nitrogenous base (adenine, thymine, guanine, cytosine or uracil).

In DNA there are four possible types of nitrogenous base. Adenine (A) and Guanine (G) both have a double ring structure and are called purines. Thymine (T) and Cytosine (C) both have a single ring structure and are called pyrimidines (*remember the word pyrimidine has the letter Y in it as do the words thymine and cytosine). DNA never has the nitrogenous base Uracil (U), rather this is found in RNA instead of the Thymine (T) nitrogenous base. You DO NOT need to be able to draw these molecular structures, they are here for reference only.

BY1:  Nucleic acids
Deoxyribonucleic acid (DNA)

The structure of DNA:

• DNA is a double stranded polymer of nucleotides (each strand is called a polynucleotide chain)
• Each polynucleotide chain may contain many millions of nucleotide units.
• It is in the form of a double helix, the shape of which is maintained by hydrogen bonding between organic bases
• DNA can contain four types of nitrogenous base: adenine, guanine, cytosine, and thymine.
• Each strand is linked to the other strand by complementary pairs of organic bases.
• Cytosine always pairs with guanine,  and adenine always pairs with thymine
• The complementary base pairs are held together by weak hydrogen bonds.
• DNA is like a coiled ladder with the "uprights of the ladder" being made up of alternating sugars and phosphate groups (called the sugar-phosphate backbone) and the "rungs  of the ladder" are made up of the complementary base pairs.


• Between cytosine and guanine bases there are three hydrogen bonds
• Between adenine and thymine bases there are only two hydrogen bonds
• The pentose sugar is always deoxyribose

A double stranded DNA "double helix". Each polynucleotide strand is made from many nucleotide subunits with nitrogenous bases pointing to the inside of the double helix. Here complementary nitrogenous bases hydrogen bond with one another forming the "rungs" of the ladder. In DNA, the nitrogenous base Adenine (A) forms a complementary pair with Thymine (T) on the other strand and Guanine (G) forms a complementary pair with Cytosine (C). Each polynucelotide strand has a sugar-phosphate backbone formed by phosphodiester bonds.

Draw a part of a DNA chain showing a polynucleotide consisting of three base pairs.

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DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA). Mitochondria

The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.

DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.

An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.