1. Polynucleotides: DNA and RNA
Structure and function

2. State that DNA is a polynucleotide, usually double-stranded, made up of nucleotides containing the bases adenine, thymine, cytosine and guanine.
State that RNA is a polynucleotide, usually single-stranded, made up of nucleotides containing the bases adenine, uracil, cytosine and guanine.

4. Structure diagrams of phosphate, ribose and deoxyribose sugars attached to nitrogenous bases

5. Structure of DNA and RNA
Basic Unit =
NUCLEOTIDE
A nucleotide consists of:-
PENTOSE sugar molecule In DNA this is DEOXYRIBOSE
In RNA the pentose sugar is RIBOSE
PHOSPHATE
Nitrogen-containing BASE: a purine or pyrimidine

6. There are FOUR different bases in DNA
Making four different types of NUCLEOTIDE :

7. Purine and pyrimidine molecules

8. POLYNUCLEOTIDES Within a DNA or RNA Molecule
Nucleotides join together, to form polymers, called
POLYNUCLEOTIDES
Bases ‘sticking out’ to one side
Sugar-phosphate backbone

10. Nitrogenous bases in DNA and RNA
Purines
Pyrimidines
Number of rings
Names of bases
Found in DNA?
Found in RNA?

11. State that DNA is a double-stranded polynucleotide.
Describe how a DNA molecule is formed by hydrogen bonding between complementary base pairs on two antiparallel DNA strands.
Explain how twisting of the DNA molecule produces the double helix shape.

14. TWO Polynucleotide strands
Each DNA Molecule actually contains
TWO Polynucleotide strands
NOTE :
‘Base-pairing’ rule
A - T
G - C
Hydrogen bonds
Strands are ‘anti-parallel’

17. So, a section of a DNA molecule

18. Furthermore,
The two strands are wound into a HELIX
The famous ‘DOUBLE HELIX’

19. Outline how DNA replicates semi-conservatively, with reference to the role of DNA polymerase.

20. DNA REPLICATION DNA-HELICASE Step 1 Double helix unwinds
Hydrogen bonds break and strands separate
Step 2
Under control of the enzyme :
DNA-HELICASE

21. Nucleotides in the cell are activated, by combining with TWO PHOSPHATES :
Step 3

22. Activated nucleotides attach to ‘spare’ bases on each strand of DNA - according to the ‘base-pairing’ rule.
Step 4
Under the control of the enzyme :
DNA-POLYMERASE
Result :
TWO DNA molecules identical to each other and the original.

23. SEMI-CONSERVATIVE What does this mean?
This type of replication is described as :
SEMI-CONSERVATIVE
What does this mean?

24. Would act as a template to make a complete copy
If replication was CONSERVATIVE
The original molecule
Would act as a template to make a complete copy

25. However, SEMI-CONSERVATIVE
Means only HALF the original molecule appears in each of the new molecules
>>>>>>>>>>>

26. State that a gene is a sequence of DNA nucleotides that codes for a polypeptide.
Outline the roles of DNA and RNA in the cells of living organisms.