Double Strand
2011
Nucleic Acid: The Molecular Basis of Inheritance
Nucleic Acid: The Molecular Basis of Inheritance
Article summary – This article provides an overview about the components of nucleic acids. It gives an idea about the formation of a polynucleotide chain. In the last part the article gives an idea about the double helical model of the DNA.
1. What determines inheritance?
We inherit properties and some characters from our parents. Many times you must have thought how is this possible? What makes us different from other animals? Among the human beings why are we different from our friends? These are some questions which keep rising in out mind. The answer for all this is the genetic material which is unique for each individual.
2. What is genetic material made up of?
Genetic material consists of Nucleic Acid which exists in two different kinds which are RNA and DNA.
DNA is the most widely found genetic material in the living world. It is known as Deoxyribonucleic acid and is a long polymer of deoxyribonucleotides. It was first identified by Friedrich Meischer in 1869. This is located within the nucleus.
RNA, which is a long polymer of ribonucleotides, is found as a genetic material in some viruses known as retroviruses.
3. Major components of Nucleic acids
Three major components of a nucleic acid are
- Nitrogenous Base
- Pentose Sugar
- Phosphate group
3.1. Nitrogenous bases
There are two different kinds of nitrogenous bases which are Purines (Adenine and Guanine) and Pyrimidines (Cytosine, Thymine and Uracil). Purines are larger nitrogenous bases and are made up of two rings whereas Pyrimidines are smaller bases made up of a single ring.
Nitrogenous bases in DNA are:
- Adenine
- Guanine
- Cytosine
- Thymine
Nitrogenous bases in RNA are:
- Adenine
- Guanine
- Cytosine
- Uracil.
3.2. Pentose sugar
A five-carbon containing monosaccharide is termed as a pentose sugar. The numbering of the five carbon atoms is done clockwise. Different kinds of pentose sugars are present in different nucleic acids. DNA has deoxyribose sugar and RNA has ribose sugar. The ribose sugar has a hydroxyl group at the second position which is lacking in the deoxyribose sugar. Instead, in the deoxyribose sugar the hydroxyl group is replaced with the hydrogen group.
3.2.1. Nucleoside formation
Nitrogenous base + pentose sugar = nucleoside
The nitrogenous base is linked to the pentose sugar via N-glycosidic bond to form a nucleoside. A glycosidic bond is a covalent bond which links the amino or nitrogen containing group to the carbohydrate or sugar. In the figure below the base adenine is linked to ribose sugar to form adenosine and to deoxyribose sugar to form deoxyadenosine. Similarly other bases also get linked to sugars via N- glycosidic linkage to form nucleosides like guanosine or deoxyguanosine, cytidine or deoxycytidine and uridine or deoxythymidine.
3.3. Phosphate group
A phosphate group is attached to the nucleoside at the 5′ position of the sugar via a phosphoester linkage.
Nucleoside + phosphate = Nucleotide
Image reference – http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect02.htm
Depending on the number of phosphate groups attached to the nucleosides the naming of nucleotides is done as
Adenosine 5′ – monophosphate (AMP)
Adenosine 5′ – diphosphate (ADP)
3.3.1. Formation of a dinucleotide
A dinucleotide is formed when two nucleotides are joined through 3′-5′ phospho diester linkage. The two hydroxyl groups attached to the carbon atoms at the 3′ and 5′ positions of the sugar molecules form strong covalent bonds (ester linkages) with the phosphate groups resulting into a phosphodiester linkage.
Similarly when a number of nucleotides are joined with the help of phosphodiester linkages it results into a polynucleotide which has a free phosphate group at the 5′ position and a free hydroxyl group at the 3′ position. The free hydroxyl group at the 3′ position is meant for the chain extension.
Thus a polynucleotide chain made up of bases A, T, G, C, G, T, A, C in sequence is represented as 5′ ATGCGTAC 3′.
4. Structure of DNA
The double helical model of DNA was proposed by James Watson and Francis Crick in 1953. They utilized the X – ray diffraction data produced by Maurice Wilkins and Rosalind Franklin. The length of DNA is different in different organisms and is the characteristic of a species. The length of DNA is determined by the number of base pairs present in the DNA. For example the Bacteriophage lambda has 48502 base pairs, Bacteria E.coli has 4.6 × 106 bp and the haploid content of human DNA has 3.3 × 109 bp.
4.1. Characteristic features of the double helical structure of DNA
- DNA is made up of two polynucleotide chains whose backbone is made up of sugar phosphate linkages and the nitrogenous bases project outside. These two chains are coiled around each other like a spiral stair case and the bases projecting out from the chain pair with their counterparts to form the steps of the stair case. The phosphate and the sugars form the uprights of the staircase.
- Base pairing between the two polynucleotides was proposed based on the proposition made by Erwin Chargaff. According to his proposition within a double stranded DNA the ratios between bases Adenine and Thymine and Guanine and Cytosine remains always constant and equals unity. This led to the fact that the base adenine always pairs with thymine and base Guanine pairs with Cytosine. The bases are paired with the help of hydrogen bonds. Two hydrogen bonds are involved in the pairing between adenine and thymine and three hydrogen bonds are involved in the pairing between Guanine and Cytosine. Thus a purine gets always paired to a pyrimidine and this gives uniformity in the distance between two strands.
- The two chains are anti parallel in polarity which means that if one stand runs in a 5‘ – 3‘ direction the other strand runs in a 3‘-5‘ direction.
Image reference – http://www.pinkmonkey.com/studyguides/subjects/biology-edited/chap8/b0808202.asp
- The two chains are coiled around each other in a right handed fashion. The distance between the two chains is 20A0. Gyre is one full turn of a helix and it is 34A0 or 3.4nm in length. There are 10 base pairs present within each turn and hence the distance between two base pairs is 3.4A0or .34nm.
- The two stands in the double helix are complementary to each other and are not identical. This means if one stand has adenine in a particular position the other strand will have thymine at that position. Hence if we know the sequence of one strand we can predict the sequence of other strand also.
- The plane of one base pair stacks over the other in a double helix. This arrangement along with the hydrogen bonds imparts stability to the structure.
Uniformity in the distance between two poly-nucleotide chains is maintained by the presence of purine on one side and pyrimidine on the other nucleotide chain. Ultimately, all the above features provide optimal stability to the double-helical structure of the DNA.
About the Author
Post Graduate in Bio-Chemistry and PG Diploma in Bio-informatics. Worked as a Bio-informatics professional for about 2.5 years and moved on to content-writing and online teaching since two years. Webpage – http://purnasrinivas.webs.com
Homologous Recombination of Double Strand Breaks.mpg
|
|
Hb Stand/hand Mixer $47.94 Powerful Hamilton Beach® Hand Mixers focus on versatility and ergonomics. You’ll see evidence of Good Thinking┢ throughout their thoughtful design. Most hand mixers have convenient snap-on storage cases, which keep attachments (and sometimes cords) together so you don’t have to search for them each time. A variety of attachments are available with different hand mixers, from traditional bea… |
|
|
DNA double helix structure Photo Mugs DNA double helix structure. Computer artworkof the atomic structure of a DNA( deoxyribonucleic acid ) double helix.Atoms are shown as spheres. The backbone of thedouble helix is composed of two twistingsugar-phosphate strands (blue/green andpink/green). Nucleotide bases on thestrands bond in complementary pairs (diagonallines) to hold the double helix molecule together.It is the sequence of the fo… |
|
|
Dna Photo Mugs DNA, computer artwork. DNA ( deoxyribonucleic acid) consists of two strands (blue) of sugarphosphates forming a double helix. Stretchedbetween these are the nucleotide bases(multicoloured), consisting of guanine, cytosine, thymine and adenine. DNA encodes the bodysgenetic information….. |
|
|
Southwest Chamber Music: Cage, Carter, Harrison, Partch, etc. $109.50 All products are BRAND NEW and factory sealed. Fast shipping and 100% Satisfaction Guaranteed…. |
|
|
Poolside With Gilly $18.99 CD-R. 31 tracks recorded live at the Strand in Hermosa Beach, CA, during the Partyball tour in 1991. Redfly…. |
|
|
Stan Ridgway: Live!1991 Poolside With Gilly @ the Strand, Hermosa Beach, Calif. – Double Cd $8.99 … |
|
|
Thomas Breaks the Rules [VHS] $12.98 … |
|
|
G P Ltd. DBX02-300002 Christmas Icicle Lights, Set of 300 $15.99 300 count clear, white wire, icicle lights. 2 x 150 light sets with end connector. 27 drops per set, 10.15′ lighted length, 17.7′ total length. Spacing is 12″ x (4″ + 3″) x 3″. 7 4 6 7 4 6 7 4 5 per 50 lights. Indoor outdoor use…. |
|
|
Good Tidings SBC60205 G.E. String-A-Long Miniature Christmas Lights, Multi-Colored $9.84 GE, String A Long, 100 Count, Multi Mini Light Set 3″ Lead Wire, 4.5″ Spacing, 3″ End Connector, 37.6′ Lighted Length, With A Lighted Length Of 41.25′…. |
|
|
Hinged Handcuff, #301, Nickel $38.99 Provides additional restraint by more effectively restricting hand and arm movements. All carbon steel construction with a nickel finish. Spun rivets, machined edges and smooth single strand action. Folds flat for compact storage. Weighs 12 ounces…. |
|
|
La Preciosa Sterling Silver Double-Strand Center Love Knot Bracelet $41.49 This pretty double-strand mesh bracelet features a pretty center love knot. Crafted in Italy of sterling silver, this bracelet secures with a lobster claw |
|
|
La Preciosa Sterling Silver Double-Strand Center Love Knot Necklace $69.99 This pretty double-strand mesh necklace features a pretty center love knot. Crafted in Italy of sterling silver, this bracelet secures with a lobster claw |
|
|
La Preciosa Sterling Silver Double-strand Center Knot Necklace $63.99 This double-strand mesh necklace features a pretty center knot. Crafted in Italy of sterling silver, this necklace secures with a lobster claw. |
|
|
La Preciosa Sterling Silver Double-strand Center CZ Snowflake Bracelet $26.99 This La Preciosa bracelet features a snowflake design in the center set with shimmering clear cubic zirconia stones. The bracelet offers a double-strand chain attached to a spring ring clasp. |
|
|
Charming Life Silver Paua Shell and Pearl Double-strand Bracelet (4-9 mm) $51.99 Paua shell and pearl double-strand bracelet features pearls, paua shell, and Swarovski crystalsJewelry is handcrafted of fine sterling silverLustrous paua shell and cultured freshwater pearl bracelet is an excellent accessory |
|
|
La Preciosa Sterling Silver GP Double-Strand Chain w/ Center CZ Snowflake Bracelet $23.99 This cute double-strand bracelet features gold plating over sterling silver. The center snowflake sparkles with over 35 cubic zirconia. Secures with a spring ring. |
|
|
Silvertone Double-strand Green Plastic Bead Necklace $7.59 A 2-strand design is decorated with green glass beads on this fashion necklace. This fine jewelry is crafted of silvertone base metal in a polished finish. |
|
|
Sterling Silver Double-strand Spiral Earrings $18.99 These earrings feature a double strand spiral with a highly polished finish. |
|
|
Charming Life Sterling Silver Double-strand Pearl Bracelet (8 mm) $58.99 This elegant bracelet features two strands of white cultured freshwater pearls accented with Swarovski crystals. The Charming Life jewelry piece is handcrafted of fine sterling silver in the United States. |
|
|
La Preciosa Silver Double-strand Circles Cubic Zirconia Bracelet $57.99 This stunning bracelet shines with a high polish silver finish and is set with round-cut cubic zirconia. Made of sterling silver, this jewelry piece features a lobster claw closure. |
|
|
Double-strand Albutra Vine Necklace and Earring Set (Philippines) $38.49 Organic elements make up this handmade necklace and earring set. An Albutra vine pendant hangs from double strands of glass beads with paper-wrapped wood elements. The neckline is 12 inches, the earrings are on French wire. |
|
|
Sterling Silver Black Jade Double-strand Necklace (U.S.A.) $31.49 Adorn yourself with lovely handmade jewelry. This gorgeous two-strand necklace features green buri tube beads and black wood rondells spaced by red Swarovksi crystals with a black jade flower that holds the strands together. |
|
|
La Preciosa Sterling Silver Double-strand Knotted Earrings $28.99 Perfect for any occasion, these dangling earrings showcase a beautiful knotted design. These earrings are constructed of sterling silver with fishhook backs. |
|
|
DaVonna 14k Gold Black Cultured FW Pearl Double-strand Bracelet (5.5-6 mm/ 7 in) $104.99 Shimmering pearl bracelet adds a classic look to any outfitJewelry clasp is fashioned of 14-karat white gold Bracelet features a double-row of black freshwater pearls |
|
|
Silver Garnet Necklace (Thailand) $30.29 Accentuate your look with the deep hues of a double-strand garnet necklaceWorld jewelry is handmade by artisans in northern ThailandNecklace is completed with silver tone beads |
|
|
La Preciosa Sterling Silver Two-Strand Center Knot Bracelet $38.99 This pretty double-strand mesh bracelet features a center knot. Crafted in Italy of sterling silver, this bracelet secures with a lobster claw |
|
|
La Preciosa Sterling Silver Rose-Gold Double Strand Heart-Link Necklace $72.99 This beautiful Italian-made two-tone necklace features a double-strand heart link design and a center floating heart. Features a toggle clasp |
|
|
DaVonna 14k Gold Cultured Freshwater Pearl Bracelet (5-5.5 mm/ 7 in) $109.99 Pretty double-strand pearl bracelet is appropriate for any occasionJewelry clasp is fashioned of 14-karat yellow goldBracelet features two rows of cultured freshwater pearls |
|
|
Sterling Silver 1ct TDW Round Diamond Bracelet (H-I, I2-I3) $231.99 This attractive bracelet features square-shaped links set with round white diamonds that alternate with double-strand milligrain links. The bracelet is crafted of sterling silver with a box clasp and safety catch. |
|
|
Pearlz Ocean FW Pearl and Multi-gemstone 29-inch Necklace $27.19 This beautiful necklace features an exotic combination of black onyx, obsidian, garnet and freshwater pearls. The double-strand necklace secures with a silvertone copper spring ring clasp. |
|
|
Charming Life 22k Gold-plated Pewter Pearl and Crystal Bracelet (4-8.5 mm) $42.99 Bracelet features a double-strand design of lustrous cultured freshwater pearls and Swarovski crystalsJewelry is crafted of 22 karat gold plated pewterPearl and Swarovski crystal bracelet adds a splash of elegance to any outfit |
|
|
Silvertone Double Graduated Crystal Heart 2-strand Necklace $14.99 This sparkling double-strand necklace features two crystal-laden hearts with over 20 clear crystals. The necklace includes two ball chains attached to a single lobster claw clasp and a 2-inch extender chain. |
|
|
Silver Coral 2-strand Necklace (Thailand) $47.99 Imbue your outfit with tropical passion with this sensuous coral necklace Handmade jewelry features six double-strand circlets of eye-catching coral nuggets Necklace also features silvertone accents that enliven and invigorate |
|
|
La Preciosa Sterling Silver CZ Necklace $111.99 Crafted of sterling silver, this necklace features an elegant design complete with a cubic zirconia stone. This necklace features a double-strand rolo chain and secures with a lobster claw clasp. |
|
|
Sterling Silver Rainbow Moonstone, Amethyst and Citrine Earrings $24.49 These double-strand shepherd’s hook earrings have a strand with an oval amethyst and another strand with an oval citrine. Both strands are completed with rainbow moonstone rondelles. This jewelry was handcrafted in the United States of sterling silver. |
|
|
La Preciosa Silvertone 36-inch Cubic Zirconia Necklace $28.99 This beautiful necklace is set with dazzling, bezel set, round-cut cubic zirconia. Crafted from sterling silver, this stylish necklace can be worn as single or double strand. |
|
|
La Preciosa Goldtone 36-inch Cubic Zirconia Necklace $27.99 This beautiful necklace is set with dazzling, bezel set, round-cut cubic zirconia. Crafted with gold overlay, this stylish necklace can be worn as single or double strand. |
|
|
Elegant 10k Gold Two-tone Lacy Style Necklace $336.99 Gorgeous lacy necklace is a perfect addition to your ensembleJewelry is crafted of 10k yellow and white gold with a beaded designSparkling yellow and white gold beads decorate a double-strand white gold chain necklace |
|
|
Pearl and Green Aventurine Necklace (China) $70.49 This exotic necklace is handcrafted of freshwater pearls and green aventurine This unique necklace features an eye-catching aventurine wheelThe ornate double-strand design of this necklace is adorned with baubles |
|
|
Silver Accent Golden Agate Necklace (Thailand) $31.84 Harness the sweet vitality of the saffron sun with this gorgeous handcrafted necklace. This carefree piece of jewelry features six double-strand sections of tumbled agate nuggets in shades of yellow, accented by antiquated silver links. |
|
|
Valenza Brass 650ct TGW Red and Brown Agate and Crystal Strand Necklace $44.99 This attractive strand necklace is made with multi-shaped mixed agate and crystal beads with brown resin roses set in brass metal. The double-strand necklace is secured with a spring ring clasp and delights with a highly polished accent. |
|
|
Silver White FW Pearl, Yellow Quartz and Smokey Quartz Necklace (7-8 mm) $47.99 This elegant jewelry features white freshwater pearl with cushion-cut smoky quartz and yellow quartz. Crafted of sterling silver with a rhodium-plated on a link chain, this stunning necklace can be worn as a single or double strand. |
|
|
Goldplated Sterling Silver and White Enamel Necklace $170.99 Instantly update your look with this uniquely designed fine sterling silver necklaceItalian-made jewelry features double strands, fancy links, and yellow goldplated beadsStylish necklace is further enhanced with creamy white enamel accent |
|
|
14k Yellow Gold 2-strand Tab Link Lariat Necklace $590.99 This gleaming 14-karat yellow gold necklace features a dangling ball from a tab link chain that has both diamond-cut and sandblasted finishes. Crafted in Italy, this double-strand lariat necklace secures with a lobster claw clasp. |
|
|
Valenza Goldtone 650ct TGW Multi-colored Agate and Crystal Necklace $42.99 This marvelous strand necklace is made with multi-shaped mixed multi-colored agate and crystal beads with black resin roses set on brass metal. The double-strand necklace is secured with a spring ring clasp and delights with a highly polished accent. |
|
|
Antiviral Resistance in Plants (Hardcover) $114.47 Studies related to pathogen-mediated virus resistance in plants were instrumental in providing some of the historical observations which ultimately led to the vital discovery of double-stranded RNA (dsRNA)-induced gene silencing or RNA interference (RN… |
|
|
Single-stranded DNA Binding Proteins (Hardcover) $105.07 The genomes of cellular organisms are organized as double-stranded DNA, a structure that must be unwound to provide DNA replication, recombination, and repair machinery access to genomic information. However, DNA unwinding comes with inherent risks to… |
Comment