1. Brain Pop What bases pairs up with Cytosine?

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3. DNA stands for deoxyribose nucleic acid This chemical substance is present in the nucleus of all cells in all living organisms DNA controls all the chemical changes which take place in cell. *** The kind of organism which is produced (butter-cup,giraffe, herring, human etc.) is controlled by DNADNA 2

4. DNA is a very large molecule made up of a long chain of sub-units The sub-units are called nucleotides Each nucleotide is made up of 1.a sugar called deoxyribose 2. a phosphate group -PO 4 and 3. an organic nitrogen base DNA molecule 3

5. Ribose is a sugar, like glucose, but with only five carbon atoms in its molecule Deoxyribose is almost the same but lacks one oxygen atom Both molecules may be represented by the symbol Ribose & deoxyribose 4

6. The most common organic bases are Adenine (Purines) (A) Thymine (Pyrimidines) (T) Cytosine (Pyrimidines) (C) Guanine (Purines) (G) The bases 5

7. The deoxyribose, the phosphate and one of the bases adenine deoxyribose PO 4 Combine to form a nucleotide Nucleotides 6

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

9. In fact, the DNA usually consists of a double strand of nucleotides The sugar-phosphate chains are on the outside and the strands are held together by chemical bonds between the bases 8

10. PO 4 2-stranded DNA 9 Sugar Phosphate bonds Chemical Bonds

11. The bases ALWAYS pair up in the same way Adenine (A) forms a bond with Thymine (T) and Cytosine (C ) bonds with Guanine (G) Bonding 1 10 Adenine Thymine Cytosine Guanine

12. PO 4 thymine PO 4 adenine cytosine PO 4 guanine Bonding 2 11

13. The paired strands are coiled into a spiral called A DOUBLE HELIX 13

14. sugar-phosphate chain bases THE DOUBLE HELIX 14

15. Before a cell divides, the DNA strands 1.Unwind and separate 2.Makes a new partner by adding the appropriate nucleotides 3.Resulting in two double-stranded DNA molecules in the nucleus So that when the cell divides, each nucleus contains identical DNA This process is called Replication Replication 16

16. Question 1 Which of the following are components of nucleotides? (a) deoxyribose (b) amino acids (c) phosphate (d) enzymes (e) organic bases

17. Question 2 Which of the following represents a correct pairing of bases? (a) adenine with thymine (b) adenine with guanine (c) thymine with adenine (d) guanine with cytosine (e) thymine with thymine

18. Question 3 DNA molecules are formed from (a) organic bases (b) amino acids (c) deoxyribose (d) nucleotides

19. Question 4 Which of the following are organic bases? (a) Valine (b) Guanine (c) Thymine (d) Serine

20. Question 5 Replication of DNA occurs (a) During cell division (b) before cell division (c) at any time

21. Answer CORRECT

22. Answer INCORRECT