DNA Deoxyribonucleic Acid General information Genetic code of

DNA (Deoxyribonucleic Acid) General information: �Genetic code of life determining how an organism looks and acts �Determines the structure of proteins �Packaged into chromosomes (each chromosome is made up of DNA tightly coiled �Structure first constructed by J. H. Watson and F. H. C. Crick.

Structure DNA consists of three basic building blocks or units: �phosphoric acid �a sugar �a nitrogen based molecule

�The phosphoric acid is the simplest part. It consists of hydrogen, oxygen, and phosphorus. Its chemical formula is H 3 PO 4. When attached to other molecules, this part is commonly called a phosphate group.

�The sugar molecule is a deoxyribose sugar. This sugar has five carbon atoms and, as the name suggests, it lacks an oxygen that is normally part of a sugar molecule. �The molecular shapes of deoxyribose and phosphates are such that they fit together. Fitting together means that after a chemical reaction, they combine to form a bond

�The variable part of DNA consists of molecules called nitrogen bases. There actually four different nitrogen bases: adenine and guanine are chemicals called purines, whereas cytosine and thymine are pyrimidines. (These are similar chemical structures but purines are double-ring structures and pyrimidines are single rings. The difference is important because it results in the way that the base pairs combine. )

�After chemical reactions, adenine and thymine bond together, and cytosine and guanine make a bonded pair. Adenine and thymine are shown as a pair, abbreviated as A-T. The cytosine and guanine make a pair, indicated by C-G. �The largest human chromosome, chromosome number 1, is approximately 220 million base pairs long.

�Adenine Guanine �Thymine Cytosine

�The three main parts of DNA--the sugar, phosphate, and nitrogen base, form structures called nucleotides. Nucleotides are the basic building blocks of DNA and RNA.

Single Stranded DNA �A chain of nitrogen bases can be represented as in the following diagram: �The diagram represents a single strand of DNA and it is only a fragment of a segment of DNA.

�This single strand of DNA can also be written as: -A-C-A-T-T-G-C-T�The nitrogen bases can be in any sequence, but they always pair the same way. �Genes are specific segments of DNA. Genes differ in the number and pattern of base pairs. There are endless possibilities for the patterns and sequences of base pairs. It is the vast number of possibilities of patterns of base pairs that explains how it is possible that a single molecule can hold the code for so many different living

Double-Stranded DNA �DNA is actually made of two strands and a double-stranded DNA looks like:

�Notice that the strand on the right is shown as a mirror image of the left strand. Also notice that adenine bonds with thymine, and cytosine bonds with guanine. This is always true. �In real cells, the two strands actually turn around each other. Think of a ladder that was held at each end and twisted. This spiral shape is called a helix, and because DNA has two strands, it is often called a doublehelix structure. The base pairs form the rungs of the ladder.

Fun Fact �If the DNA in a single human cell were stretched out and laid end-to-end, it would measure approximately 6. 5 feet (2 meters). �The average human body contains 10 to 20 billion miles (16 to 32 billion kilometers) of DNA distributed among trillions of cells �How does DNA fit into tiny cells? ?

�DNA Packaging! �DNA wrapped around special proteins called Histone Proteins several times so it can fit inside the nucleus of cells �Animation: http: //www. youtube. com/watch? v=9 k. Q p. Yd. Cn. U 14&feature=related �Assignment on DNA