3S2+Bio+essay+by+Cao+Yu,+Jie+Hui,+James+and+Keng+Liang

**__ Tasks: __ 1. You will be required to work in groups (of 3s or 4s) to write an essay describing DNA structure .**  1. Create a new page **__on this wikispace__**. At the top of your page, list your group members, with each name in a different colour

2. In a group, write a 300-word essay describing the **components of DNA** and **how these associate** with each other to generate the **overall, 3-dimensional structure** of DNA

3. Any member of the group can start writing the essay, with each member adding/ editing over these 3 weeks. Pls note that each member should use a different colour so everyone can track everyone else's contribution

4. At the bottom of your page/ essay, please include yopur references (again, colour coded to track contributions). ** Cao Y u

Keng Liang

<span style="color: rgb(192, 192, 192);"> <span style="color: rgb(0, 0, 128);">Jie Hui

<span style="color: rgb(192, 192, 192);"> <span style="color: rgb(0, 128, 0);">James- ** <span style="color: rgb(0, 128, 0);"> <span style="color: rgb(255, 0, 0);">The role of DNA molecules is the long-term storage of information. DNA contains the instructions needed to construct other components of cells, such as proteins. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information. Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases (adenine, thymine, cytosine and guanine a.k.a nucleotides) along the backbone that encodes information, which is read using the genetic code (set of rules by which information encoded in genetic material is translated into amino acid sequences by living cells), which specifies the sequence of the amino acids within proteins. This code is read using transcription DNA contains two main strands, one being the "sense strand", one being the "anti-sense strand", which both are wound around each other, giving the shape of a double helix. These strands of DNA are considered as building blocks of genetic information, called nucleotides, arranged in a spiral staircase. <span style="color: rgb(0, 128, 0);"> <span style="color: rgb(0, 0, 128);">The sequence of the sense strand is the same to that of the mRNA's sequence. The antisense strand of DNA usually codes for the mRNA to be translated into protein. <span style="color: rgb(0, 128, 0);"> --The outer longitudinal structure consists of alternating sugars and phosphate groups, otherwise on the sides of the ladder, alternating sugars and phosphate groups are twisted in a spiral fashion and make a complete turn every ten-based pairs. --The inner longitudinal structure consists of nucleotides.



<span style="color: rgb(0, 128, 0);">Features of the DNA Double Helix
<span style="color: rgb(0, 128, 0);"> Each nucleotides includes 3 parts, a phosphate group, a sugar molecule, and one of four bases ( adenine, guanine, cytosine, thymine), the sugar phosphate bonds form the handrails of the staircase, but we find the genetic key to DNA in the steps of the DNA, the nitrogen containing bases. These bases link up using hydrogen bonds, in a very specific way, adenine only binds with thymine, A-T, cytosine also binds to guanine, C-G. While these basic pairings never change, the order of the pairs vary greatly from one spieces to the next. <span style="color: rgb(0, 0, 128);"> The base pairings are bind together by hydrogen bonding. Due to this, as the bond is much weaker than a covalent bond, the bases can be puuled apart very easily, correspondingly, the antisense and the sense strand of DNA can be pulled apart very easily by a mechanic force or high temperature which will overcome the hydrogen bonds.
 * <span style="color: rgb(0, 128, 0);"> Two DNA strands form a helical spiral, winding around a helix axis in a right-handed spiral
 * <span style="color: rgb(0, 128, 0);"> The two polynucleotide chains run in opposite directions
 * <span style="color: rgb(0, 128, 0);"> The sugar-phosphate backbones of the two DNA strands wind around the helix axis like the railing of a sprial staircase, or sides of the ladder.
 * <span style="color: rgb(0, 128, 0);"> The bases of the individual nucleotides are on the inside of the helix, stacked on top of each other like the steps of a spiral staircase.

Andenine and Thymine (A-T) forms a base pair as they require two hydrogen bonds to make them bind together, while Guanine and Cytosine (G-C) requires three hydrogen bonds to bind them together. This explains why A only binds with T and G only binds with C.

<span style="line-height: 115%; color: rgb(255, 0, 0); font-size: 90%; font-family: Tahoma,Geneva,sans-serif;">Transcription is the synthesis of RNA under the direction of DNA. It is the process of transcribing DNA nucleotide sequence information into RNA sequence information. Both nucleic acid sequences use complementary codes (one difference between RNA and DNA sequence is the presence of U, or uracil in RNA instead of the T, or thymine of DNA), and the information is simply transcribed, from one molecule to the other. DNA sequence is transcribed by RNA polymers to produce a complementary nucleotide RNA strand, called messenger RNA (mRNA, which looks like the vertical half of DNA strand), because it carries a genetic message from the DNA to the protein-synthesizing machinery of the cell.
 * ** <span style="color: rgb(128, 0, 128);">Composed of three components
 * <span style="color: rgb(128, 0, 128);">Phosphoric acid
 * <span style="color: rgb(128, 0, 128);">provides negative charge to backbone
 * <span style="color: rgb(128, 0, 128);">participates in phosphodiester bonds
 * <span style="color: rgb(128, 0, 128);">Pentose (furanose) sugar
 * <span style="color: rgb(128, 0, 128);">ribose for RNA, deoxyribose for DNA
 * <span style="color: rgb(128, 0, 128);">numbering of carbons, and important groups on 1', 2', 3', and 5' carbons
 * <span style="color: rgb(128, 0, 128);">Nitrogenous bases
 * <span style="color: rgb(128, 0, 128);">purines and pyrimidines:generic structures
 * <span style="color: rgb(128, 0, 128);">numbering of atoms
 * <span style="color: rgb(128, 0, 128);">N-glycosidic bonds
 * <span style="color: rgb(128, 0, 128);">Adenine, guanine, cytosine, thymine, uracil
 * <span style="color: rgb(128, 0, 128);">nomenclature
 * <span style="color: rgb(128, 0, 128);">bases, nucleosides, nucleotides
 * <span style="color: rgb(128, 0, 128);">adenine vs. adenosine vs. adenylate, e.g.
 * <span style="color: rgb(128, 0, 128);">base pairs form by H-bonding between bases on opposite strands
 * <span style="color: rgb(128, 0, 128);">The double helix
 * <span style="color: rgb(128, 0, 128);">General features
 * <span style="color: rgb(128, 0, 128);">Pentose-P backbone winds around the outside of the cylinder
 * <span style="color: rgb(128, 0, 128);">protects the bases buried within
 * <span style="color: rgb(128, 0, 128);">coats helix with uniform negative charge
 * <span style="color: rgb(128, 0, 128);">Bases are stacked inside the helix cylinder
 * <span style="color: rgb(128, 0, 128);">numerous weak interactions hold strands together
 * <span style="color: rgb(128, 0, 128);">positions of N-glycosidic bonds creates major and minor grooves
 * <span style="color: rgb(0, 0, 128);">Deoxyribose
 * <span style="color: rgb(0, 0, 128);">A a monosaccharide containing five carbon atoms, and including an aldehyde functional group in its linear structure.
 * <span style="color: rgb(0, 0, 128);">Derived from ribose, with the replacement of a hydroxyl group at the second position with hydrogen, resulting in a net loss of an oxygen atom, hence the name "deoxyribose".



Start of the essay
<span style="color: rgb(128, 0, 128);">DNA is a complex molecule which carries the genetic code. The backbone of DNA is based on a repeated pattern of a sugar group and a phosphate group in the shape of a double helix. The full name of DNA, deoxyribonucleic acid, gives the name of the sugar present - deoxyribose, a monosaccharide containing five carbon atoms, and derived from ribose, with the replacement of a hydroxyl group at the second position with hydrogen, resulting in a net loss of an oxygen atom, hence the name "deoxyribose".

<span style="color: rgb(0, 0, 128);">The reason why DNA exists in a helical shape is that firstly, the twisted form of DNA is able to allow both strands of DNA occupy less space in the cell nucleus, thus is an adaptation of DNA. Secondly, the helical strand of DNA is twisted by the process of supercoiling, which are introduced by enzymes called topoisomerases. Hence the helical shape of DNA is a way of space conservation, as the DNA has to contain a large amount of information.

<span style="color: rgb(0, 128, 0);"><span style="color: rgb(0, 128, 0);">Zooming into the DNA double helix structure, there are two DNA strands, one being the "sense" strand, one being the "antisense strand". These two DNA strands form a helical<span style="color: rgb(0, 128, 0);"> spiral, winding around a helix axis in a right-handed spira, with the respective polynucleotide chains running in opposite directions. Focusing on the "backbone or sides" of the two DNA strands, they are composed of sugar molecules and phosphate gorups which wind around the helix axis like the railing of a spiral staircase, or sides of a ladder. Within the railings of the "spiral staircase", bases of the individual nucleotides are in the middle of the helix, stacked on top of each other like the steps of a "spiral staircase", or the "rungs of a ladder". Concerning the individual nucleotides, <span style="color: rgb(0, 128, 0);">each nucleotides includes 3 parts, a phosphate group, a sugar molecule, and one of four bases ( adenine, guanine, cytosine, thymine), the sugar phosphate bonds form the handrails of the staircase, but we find the genetic key to DNA in the steps of the DNA, the nitrogen containing bases. These bases link up using hydrogen bonds, in a very specific way, adenine only binds with thymine, (A-T), cytosine only binds to guanine, (C-G) .While these basic pairings never change, the order of the pairs vary greatly from one spieces to the next. <span style="color: rgb(0, 0, 128);">The reason why andenine only bonds with thymine is due to them being able to form only two hydrogen bonds, while cytosine and guanine are bonded together by three hydrogen bonds. However, in some mutated DNA, the base pairs do not follow the A-T and G-C format, and instead it is possible for andenine to bind with guanine.

<span style="color: rgb(0, 128, 0);"> Resource: "[|DNA Structure [1 ]]", "[|DNA Structure [2 ]]" Resouce: "[|Introduction to DNA Structure]" <span style="color: rgb(128, 0, 128);">Resouce: <span style="color: rgb(0, 128, 0);"> [|"DNA Structure] "