 A deoxyribose sugar  A phosphate group (that is negatively charged)  A nitrogenous base

 Adenine  Thymine  Cytosine  Guanine  Adenine and Guanine are grouped as Purines (see diagram pg.210) Purines are a double ring structure  Cytosine and Thymine are Pyrimidines & are a single ring structure

DOUBLE RING SINGLE RING

 Deoxyribose contain 5 carbon atoms and they are numbered clockwise 1 to 5 beginning with the carbon atom to the immediate right of the oxygen atom.  The first carbon atom is named 1’(1 prime) and so on.

 So a nucleotide is a deoxyribose sugar attached to a phosphate group and a nitrogenous base (A, T, G, C)  The phosphate is always attached to the 5’carbon  The nitrogenous base is always attached to the 1’carbon  These repeating units of nucleotides form a simple polymer

DNA Structure Questions Section 4.2 & 4.3  Use the concept of complementary base pairing to explain how if you know the sequence of one strand of DNA you also know the opposite or complementary strand. Use and example in your explanation.  What keeps the bases together in the middle of the DNA strand?  Fully explain how two DNA strands run anti- parallel. Use an example in your explanation.  Which strand is customarily written when writing one strand of DNA? Why is this?  What is the difference between mitosis and cytokinesis?  What does it mean when DNA replication is referred to as semi- conservative?  What begins the process of DNA replication?  What is the function of DNA helicase?  What keeps the complementary bases apart during DNA replication?  What is the function of DNA gyrase?  Can DNA be fully unwound? Explain.

DNA polymerase adds nucleotides at a rate of 50 per second in humans. The whole replication of the entire human genome takes 5 to 10 hours.