2. Y Stock NUCLEIC ACIDS

3. DNA DNADNA is a nucleic acid. Within the nucleus chromosomes are made of DNA. DNA contains instructions controlling protein synthesis in the cell.

4. DNA Discovery of DNA Wilkins and Franklin produced x ray diffraction patterns to work out repeat measurements. The structure of DNA was discovered by Crick and Watson in 1953

5. DNA DNA is a very large molecule Made up of mononucleotides Each mononucleotide has a pentose sugar, phosphate group and nitrogenous base.

6. www.chemsoc.org/.../ nucleotide.jpg

7. The pentose sugars www.layevangelism.com/.../ images/deoxyribose.jpg

8. Four nitrogenous bases Cytosine C Thymine T Adenine A Guanine G DNA has four different bases:

9. Thymine and Cytosine are pyrimidines Pyrimidines are single ring bases.Pyrimidines are single ring bases. Thymine and cytosine each have one ring of carbon and nitrogen atoms.Thymine and cytosine each have one ring of carbon and nitrogen atoms. C C C C N N O N cytosine C C C C N N O O thymine C

10. Adenine and Guanine are purines Purines are double ring bases.Purines are double ring bases. Adenine and guanine each have two rings of carbon and nitrogen atoms.Adenine and guanine each have two rings of carbon and nitrogen atoms. C C C C N N N Adenine N N C C C C C N N O N Guanine N N C

11. One Strand of DNA The backbone of the molecule is alternating phosphate and deoxyribose (sugar) molecules From each sugar arises a nitrogenous base. phosphate deoxyribose bases

12. Two Stranded DNA Remember, DNA has two strands that fit together something like a ladder. The rungs are the nitrogenous bases held together by hydrogen bonds.

13. DNA CONT The chains run in opposite directions and are said to be antiparallel.

14. C C C C N N O N C C C C N N O N N N C Hydrogen Bonds The bases attract each other because of hydrogen bonds. Hydrogen bonds are weak but there are lots of them in a single molecule of DNA. (The 3 bonds between cytosine and guanine are shown here.)

15. Hydrogen Bonds, Hydrogen Bonds, cont. When making hydrogen bonds, cytosine always pairs up with guanine, And adenine always pairs up with thymine. (Adenine and thymine are shown here-2 bonds.) C C C C N N N N N C C C C C N N O O C

16. Important: Adenine and Thymine always join together A T Cytosine and Guanine always join together C = G

17. The Shape of the Molecule DNA is a very long polymer. The double strand is twisted. This is called a double helix. Held in place by hydrogen bonds

18. RNA This is made from a single strand The nitrogenous base uracil is present –not thymine The pentose sugar is ribose There are several different types

19. mRNA www.biologycorner.com/ resources/mRNA-colored.gif

20. Role of mRNA Is built up following the code on DNA RNA is used as a template to synthesise proteins

21. tRNA www.bmb.psu.edu/.../ bchmovie/txn_tln/trna.jpg

22. Role of tRNA Picks up amino acids and carries them to mRNA during protein synthesis

23. DNA Replication Special enzymes move along the DNA ladder, unzipping it. New nucleotides move in to each side of the unzipped ladder. Cytosine pairs with guanine and adenine with thymine. When the enzyme has reached the end of the DNA 2 identical DNA molecules are left

24. Replication cont. Each new DNA molecule has one original DNA strand and one which is newly synthesised. This is called semi conservative replication

25. Replication cont. The arrangement of bases on these nucleotides forms the genetic code. If mistakes are made during replication it would cause a mutation

27. members.tripod.com/ beckysroom/dnareplication.jpg

28. DNA Replication summary Occurs in interphase DNA copied exactly DNA unzips Free nucleotides take up position using complementary base pairing. Called semiconservative replication Enzyme DNA polymerase