In humans, 23 chromosomes are passed on from the mother and 23 chromosomes are passed on from the father, giving the child 46 chromosomes.Ĭhromosomes carry genes from the parents, but not all the genes of a parent are sent along.įor each child, different sets of genes are passed on from the parents, resulting in unique DNA for each child. How DNA Is UsedĪll living things – plants, animals, and humans – pass DNA from parents to offspring in the form of chromosomes. New strands attach to both sides of the original DNA, making two identical DNA double helices composed of one original and one new strand. Please note that the above explanation of DNA replication is highly simplified. (The sugar-phosphate backbone comes with the new bases.) It reads the original strand and matches complementary bases to the original strand. Each half of the original DNA still has a base attached to its sugar-phosphate backbone.Ī new strand of DNA is made by an enzyme called DNA polymerase. The specific base pairing provides a way for DNA to make exact copies of itself. When it is time to replicate, the hydrogen bonds holding the base pairs together break, allowing the two DNA strands to unwind and separate. DNA Replicates Itselfīefore a cell can divide and make a new cell, it must first duplicate its DNA. In fact, if you lined up each molecule of DNA in one cell end to end, the strand would be six feet in length. This shape allows for a large amount of genetic information to be ‘stuffed’ into a very small space. It is twisted to the right, making the shape of the DNA molecule a right-handed double helix. Its complementary side would then have to be TTTAAAGGGCCCTAG.Įven though the shape of DNA is often described as a ladder, it is not a straight ladder. For example, one side of DNA could have the genetic code of AAATTTCCCGGGATC. The arrangement of these bases is very important as this determines what the organism will be – a plant, an animal, or a fungus. The chemical bases are connected to each other by hydrogen bonds, but the bases can only connect to a specific base partner – adenine and thymine connect to each other and cytosine and guanine connect to each other. These bases make up the ‘rungs’ of the ladder, and are attached to the backbone where the deoxyribose (sugar) molecules are located. (A grouping like this of a phosphate, a sugar, and a base makes up a subunit of DNA called a nucleotide.) In between the two sides of this sugar-phosphate backbone are four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). (Deoxyribose is the name of the sugar found in the backbone of DNA.) It has an alternating chemical phosphate and sugar backbone, making the ‘sides’ of the ladder. Stryer L.The structure of DNA can be compared to a ladder. Kilpatrick S.T 2011 Lewin's Genes X, 10th Edition, Jones and Bartlett Publishers: London These two sugars only differ by one -OH group being changed to an -H, but provides different capabilities for each molecule. On on the other hand, the sugar in the backbone of RNA is called ribose. In DNA, the sugar involved is deoxyribose. However, their sugar phosphate backbone differs slightly. RNA and DNA are both examples of phosphodiesters and have a very similar structure. One turn of this helix is 34nm long, the diameter of it is 2nm, and there are ten bases attached per turn at 0.34nm. These features make DNA can repel water and would not hydrolysed and breakdown by the aqueous environment. DNA is very stable due to rungs of “ladder” is hydrophobic and phosphate sugar backbone of DNA is negatively charged. The purpose of this twisting is to protect the bases inside it, and prevent them from being damaged by the environment. one runs 3' to 5', the other run 5' to 3'. This is done by the sugar phosphate backbone twisting around itself in a coil. Figure 1 Diagram showing the sugar phosphate backbone of DNA, and the nitrogenous bases attached to it, forming a nucleotide Structure of DNAĭNA is wound into an right-handed double helix.
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