1. Nucleic Acid Structure

2. Imagine you had an old recipe book stored in a secure library
Imagine you had an old recipe book stored in a secure library. You want to follow a recipe in the kitchen. What would you do?

3. Imagine you had an old recipe book stored in a library
Imagine you had an old recipe book stored in a library. You want to follow a recipe in the kitchen. What would you do?
Library = Nucleus
Kitchen = Ribosome
Old book = DNA
Photocopy = RNA
Process of photocopying = Transcription
Process of following the recipe = Translation

4. The function of nucleic acids
Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are important information-carrying molecules.
In all living cells, DNA holds genetic information and RNA transfers genetic information from DNA to the ribosomes.
Ribosomes are formed from RNA and proteins.

5. The structure of nucleic acids
Monomer = a nucleotide
Polymer = polynucleotide (DNA or RNA)

6. The structure of nucleic acids – what does the specification say?
Both DNA and RNA are polymers of nucleotides. Each nucleotide is formed from a pentose, a nitrogen-containing organic base and a phosphate group:
• The components of a DNA nucleotide are deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine.
• The components of an RNA nucleotide are ribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or uracil.

7. Making a polynucleotide
Mononucleotide > Dinucleotide > Polynucleotide
Condensation reactions
Phosphodiester bond

8. DNA Structure: Double stranded Long Base pairing Hydrogen bonds
Specific
Complementary
Ratios
Hydrogen bonds

9. The double helix:

10. The double helix:

11. How is the structure of DNA adapted to its function?
Sequence of bases determines sequence of amino acids
3 bases code for one amino acid
Sugar phosphate backbone for stability
Many hydrogen bonds provide strength but can be broken to replicate DNA

12. Triplet code
Degenerate code
Non-overlapping code
Universal code
Start and stop triplet codes

13. Students should be able to appreciate that the relative simplicity of DNA led many scientists to doubt that it carried the genetic code.
Video
Read – “Unravelling the role of DNA” page 39/40

14. RNA – Ribonucleic Acid A nucleic acid Exists in many different forms:
Messenger RNA (mRNA) – makes a complementary copy of the DNA and travels through the nuclear pores to the ribosomes
Transfer RNA (tRNA) – carries amino acids from the cytoplasm to the ribosomes to form a polypeptide

15. RNA Structure mRNA and tRNA Polynucleotide Single stranded
Made of nucleotides:
Pentose sugar – Ribose
Phosphate group
An N-containing organic base:
Adenine (A)
Cytosine (C)
Guanine (G)
Uracil (U)

16. mRNA Long strand Single strand
Complementary to gene (apart from U replaces T)
Made in nucleus, travels out of nuclear pore to ribosomes
Sequence of 3 mRNA nucleotides = a CODON

17. mRNA codons

18. tRNA Small (~80 nucleotides) Single stranded
Folded into ‘clover leaf’ shape
Several types – each can attach to a different amino acid
Anticodon on tRNA pairs up with codon on mRNA at the ribosome, bringing the correct sequence of amino acids together to form a polypeptide