Summary: Nucleic Acids (Grade 11/12 Biology)
Nucleic acids are biological macromolecules essential for the storage, transmission, and expression of genetic information. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
🔹 Structure of Nucleic Acids
- Monomer: The basic unit of nucleic acids is the nucleotide, composed of three parts:
- A nitrogenous base (adenine, guanine, cytosine, thymine [DNA only], or uracil [RNA only])
- A pentose sugar (ribose in RNA, deoxyribose in DNA)
- A phosphate group
- Nucleotides are joined together by phosphodiester bonds, forming the sugar-phosphate backbone of DNA and RNA.
- Nitrogenous bases pair using hydrogen bonds:
- In DNA: Adenine pairs with Thymine (2 hydrogen bonds), and Guanine pairs with Cytosine (3 hydrogen bonds)
- In RNA: Uracil replaces thymine and pairs with adenine
- Purines: Adenine and Guanine (2-ring structure)
- Pyrimidines: Cytosine, Thymine, and Uracil (1-ring structure)
🔹 DNA vs RNA
| Feature | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose | Ribose |
| Bases | A, T, C, G | A, U, C, G |
| Strands | Double-stranded | Single-stranded |
| Location | Nucleus | Cytoplasm and nucleus |
| Function | Stores genetic info | Carries out protein synthesis |
🔹 Functions
- DNA stores and transmits hereditary information and undergoes semiconservative replication before cell division.
- RNA plays multiple roles in protein synthesis:
- mRNA (messenger RNA): Carries genetic code from DNA to ribosomes
- tRNA (transfer RNA): Brings amino acids to the ribosome
- rRNA (ribosomal RNA): Forms part of the ribosome’s structure
🔹 Processes Involving Nucleic Acids
- Replication: DNA makes an identical copy of itself using DNA polymerase
- Transcription: DNA is transcribed into RNA using RNA polymerase
- Translation: The RNA sequence is used to build proteins at the ribosome, involving tRNA and rRNA
🔹 Additional Key Points
- Uracil is found only in RNA; thymine is found only in DNA
- DNA’s double helix structure was discovered by Watson and Crick
- Nucleic acids do not act as enzymes; that function is reserved for proteins
