2.  Genes carry information from one generation to the next  Genes determine the heritable characteristics of organisms  Genes can be replicated or copied exactly

3.  DNA is a nucleic acid ◦ It has monomers called  nucleotides  Each nucleotide is composed of three basic parts:  5 carbon sugar – deoxyribose  A phosphate group  A nitrogenous base

5.  There are four nitrogenous bases categorized into two groups  Purines: (two rings)  Adenine (A)  Guanine (G)  Pyrimidines: (one ring)  Cytosine (C)  Thymine (T)

6.  DNA can be considered to be like a ladder  The sugar and phosphate groups make up the backbone of the molecule, or the sides of the ladder ◦ They alternate along the sides sugar  The nitrogenous bases stick out of the sides of the sugar ◦ They make up the rungs of the ladder

8.  Realized the number of A’s equals the number of T’s and that the number of G’s equals the number of C’s  Base pairing rule A = TG = C Purines Pyrimidines

9.  Used x-ray diffraction to gather information about DNA structure ◦ Revealed that DNA is in helix form (coil or twisted ladder)

10.  Made 1 st 3-D model of a DNA molecule ◦ Used the work of Chargaff and Franklin to create this model  DNA structure is called a double helix, in which two strands are wound around each other  The two strands are connected by hydrogen bonds

12.  Chromosomes are tightly wound up DNA strands  Increased organization allows for the tremendous length of DNA to fit into the nucleus of the cell

13.  DNA is tightly wound around proteins called histones  8 histones + DNA = nucleosome ◦ These form chromatin  Chromatin tightly wound up makes a chromosome  http://www.youtube.com/watch?v=yqESR7E4b_8&feature=related http://www.youtube.com/watch?v=yqESR7E4b_8&feature=related

14.  Prokaryotic chromosomes are located floating in the cytoplasm of the cell (not in the nucleus)  They are circular in shape (not “X shape” like in eukaryotes)

16.  Replication occurs during interphase (S phase) of the cell cycle ◦ Same in prokaryotes and eukaryotes within  Occurs within the nucleus of the eukaryotic cell or in the cytoplasm of the prokaryotic cell

17.  Watson and Crick  Hypothesized that each strand of the original DNA molecule acted as a template for the creation of a new DNA molecule. Should work because of the base pairing rules

18.  DNA replication begins at a single point in the chromosome and proceeds in two directions

19.  DNA replication begins at hundreds of different locations on the same molecule ◦ It proceeds in both directions until everything is done  Place where separation of strands occurs and replication begins is called a replication fork

20.  Begins when an enzyme (helicase) binds to specific site on the DNA molecule called the origin  Unwinds DNA molecule to make a straight ladder  Also, unzips DNA strands by breaking hydrogen bonds  Occurs at several spots on the DNA

21.  Once unzipped, another enzyme (DNA polymerase III) binds to DNA strand and adds free DNA nucleotides ◦ DNA winds back up to double helix shape http://www.youtube.com/watch?v=rpwjZX_z5rg

22.  One original DNA strand turns into two identical copies of original ◦ Copies contain one strand of the original and one new strand  Mistakes can be made during this process ◦ Cell has an editor that fixes these mistakes

23. http://www.youtube.com/watch?v=zdDkiRw1 PdU