DNA stands for deoxyribose nucleic acid.

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2 DNA stands for deoxyribose nucleic acid. DNA controls the kind of cell which is formed (i.e. muscle, blood, nerve). DNA controls the type of organism which is produced (i.e. buttercup, giraffe, herring, human).

3 DNA Structure

4 Nucleotide Structure DNA is made up of nucleotides joined into long strands or chains by covalent bonds. Nucleic acids are made up of building blocks called nucleotides. Phosphate group Base Deoxyribose sugar

5 DNA is a polymer made up of a chain of nucleotides Each nucleotide has three parts: simple sugar (deoxyribose) phosphate group Nitrogen base (adenine, guanine, thymine, or cytosine)

6 DNA Nucleotide Structure

7 7 PO 4 PO 4 PO 4 A molecule of DNA is formed by millions of nucleotides joined together in a long chain. PO 4 sugar-phosphate backbone + bases

8 Nitrogenous Bases Adenine Guanine Cytosine Thymine

9 Nucleic Acid Structure One nucleotide Covalent bond between nucleotides

10 Chargaff s Rule [A] = [T] and [C] = [G]

11 DNA is a helix. Franklin s X-rays Likely two strands to the molecule Nitrogenous bases near the center of the molecule

12 The Work of Watson and Crick DNA is a double helix, in which two strands of nucleotide sequences are wound around each other.

13 The Double Helix: Antiparallel Strands The two strands in a DNA molecule run in opposite directions. The sugar-phosphate chains are on the outside and the strands are held together by hydrogen bonds between the bases.

14 The Double Helix: Hydrogen Bonding Hydrogen bonds

15 The Double Helix: Base Pairing The two strands of DNA are held together by hydrogen bonds between the nitrogenous bases adenine and thymine and between guanine and cytosine.

16 Nucleotide Sequence Living organisms are different due to the differences in sequences of bases. For example, the code ATTGAC would code for a different protein than TCCAAA Because the order of these bases is so important, DNA must carefully replicate itself when the cell divides to ensure an exact copy is passed on to each daughter cell

17 How is DNA copied? S phase during interphase of the cell cycle Nucleus of eukaryotes DNA replication takes place in the S phase. copyright cmassengale

18 DNA Replication Begins at Origins of Replication Two strands open forming Replication Forks (Y-shaped region) New strands grow at the forks Parental DNA Molecule Replication Fork copyright cmassengale 18 5

19 DNA Replication As the 2 DNA strands open at the origin, Replication Bubbles form Prokaryotes (bacteria) have a single bubble Eukaryotic chromosomes have MANY bubbles Bubbles Bubbles copyright cmassengale 19

20 DNA Replication DNA is un zipped and unwound by the enzyme helicase The enzyme Polymerase attaches and reads the DNA DNA nucleotides find their compliments on each side of the DNA strand New bases keep attaching until two identical molecules of DNA are completed. Mitosis would then follow where each daughter cell would be given matching copies of the original DNA

21 DNA Replication Before new DNA strands can form, there must be RNA primers present to start the addition of new nucleotides Primase is the enzyme that synthesizes the RNA Primer DNA polymerase can then add the new nucleotides copyright cmassengale 21

22 DNA Replication DNA polymerase can only add nucleotides to the 3 end of the DNA This causes the NEW strand to be built in a 5 to 3 direction 5 3 Nucleotide DNA Polymerase RNA Primer 5 Direction of Replication 22

23 Proofreading New DNA DNA polymerase initially makes about 1 in 10,000 base pairing errors Enzymes proofread and correct these mistakes The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors 23

24 DNA - CrashCourse 0:50-3:42

25 Replication Fork Animation 535::/sites/dl/free/ /120076/micro04.swf::DNA%20Replication %20Fork

26 5-3 WH68

27 Speed of DNA Replication!