![]() The DNA must be stained with before it can be visualised in the gel.Deoxyribonucleic acid is a molecule that encodes the genome used in the development and functioning of all known living organisms and many viruses. The longer the piece of DNA, the harder it is for it to move through the gel – so the larger fragments are found nearer the wells, whilst the smaller fragments move faster and are located nearer the positive electrode (anode) at the opposite side from the wells. The current is switched on and the DNA is attracted to the positive electrode (anode). The DNA is placed in small wells at the top of an agarose gel, and an electric field applied. It utilises the fact that DNA is a negatively charged molecule. Gel electrophoresis is a technique used to spearate DNA strands of different lengths. The bases which pair up on opposite strands are said to be complementary with:. The bases will only join up according to DNA base-pairing rules: This means they are easy to break apart, an important feature for DNA replication (). The two strands are held together by weak hydrogen bonds between the bases. įigure 4: Formation of the DNA strand and double helix conformation (shape). With the strands running in opposite directions in this way, the DNA molecule is said to be antiparallel. In the diagram, the left hand strand has a phosphate group uppermost (hence carbon 5’), and the right hand strand has the other end uppermost (carbon number 3, which contains an OH, 3’) remind yourself of 3’ and 5’ using the diagram above (Figure 2, page 3 ). If you examine the diagram (Figure 4 ) closely you will see that the strands on either side of the DNA molecule run in opposite directions. The shape of the molecule is known as a double helix. Two DNA strands then wind around each other to form a DNA molecule. Many nucleotides are joined together to form a DNA strand. With many DNA nucleotides joined together a sugar-phosphate backbone is formed.įigure 3: Formation of the sugar phosphate backbone The bond formed is a strong, covalent bond and is known as a sugar phosphate bond (Figure 3 ). (5’).įigure 2 : Detailed structure of a nucleotide, showing the numbering and arrangement of the carbon atoms in the deoxyribose sugar ring.ĭNA nucleotides can be joined together by attaching them between the phosphate group (5’) and the OH group (3’). The base of the nucleotide is attached at carbon number 1 and carbon number 3 (3’) contains an “OH” group.Īs you can see in the diagram below, the phosphate group is attached to carbon number 5. Examine the diagram below (Figure 2 ) The pentagon is closed at the top by an oxygen which isn’t numbered carbon number 5 sits out of the pentagon ring, attached on to carbon number 4. The deoxyribose sugar is a pentagon (5-sided), and each carbon in the pentagon is given a number. A DNA strand is made up of tiny units called nucleotides (Figure 1 ), each consisting of a deoxyribose sugar, base and phosphate. (note at time 3:11, where the arrangement of the polymer is being shown, the authors have incorrectly labelled the 3′ carbon on this section)ĭNA stands for D eoxyribo N ucleic A cid). First a review of the basics.ĭNA Structure: The following video will help you understand this area. In addition an understanding of the form in which DNA is stored is included. At Higher level, a more detailed understanding of the structure of the DNA molecule and its replication is required. It is the DNA base sequence (order of the bases) which ultimately determines the phenotype of an organism.įrom your National 5 studies, you will know something of the structure of DNA, and should be aware of the way in which this information is held in the molecule. Many viruses, which are not made of cells also use DNA, although some carry genetic information as RNA. Revision Resources:Īll cells, bacterial (prokaryotic) or more complex cells such as animal, plant or fungal cells (eukaryotic) store their genetic information in the form of DNA. (a) Structure of DNA -nucleotides (deoxyribose sugar, phosphate and base), sugar–phosphate backbone, base pairing (adenine – thymine and guanine – cytosine), by hydrogen bonds and double stranded antiparallel structure, with deoxyribose and phosphate at 3′ and 5′ ends of each strand respectively, forming a double helix.
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