VCE Biology Unit 3 – AOS 1 – lecture summary: nucleic acids, proteins, gene expression and biotechnology exam notes

🧬 VCE Biology Unit 3 – AOS 1 Notes
What is the role of nucleic acids and proteins in maintaining life?


🔹 1. Nucleic acids as information molecules
🧪 DNA structure
DNA (deoxyribonucleic acid) stores genetic information.
Key features:
 Double helix structure
 Made of nucleotides, each containing:
o Phosphate group
o Deoxyribose sugar
o Nitrogenous base
Bases:
 Adenine (A)
 Thymine (T)
 Cytosine (C)
 Guanine (G)
Base pairing:
 A pairs with T
 C pairs with G
→ held by hydrogen bonds
Important properties:
 Antiparallel strands (run in opposite directions)
 Sequence of bases = genetic code


🧬 RNA types
RNA is single-stranded and uses uracil (U) instead of thymine.
1. mRNA (messenger RNA)
 Carries genetic code from DNA → ribosome
 Contains codons (triplets of bases)
2. tRNA (transfer RNA)

,  Brings specific amino acids to ribosome
 Has anticodon (complementary to mRNA codon)
3. rRNA (ribosomal RNA)
 Forms part of ribosome
 Catalyses peptide bond formation


🔍 Comparison of DNA vs RNA nucleotides
Featur
DNA RNA
e

Sugar Deoxyribose Ribose

Strands Double Single

Bases A, T, C, G A, U, C, G

Functio Long-term Protein
n storage synthesis


🔹 2. The genetic code
🧾 Key properties:
 Triplet code → 3 bases = 1 codon
 Universal → same across almost all organisms
 Degenerate → multiple codons code for same amino acid
Example:
 UUU and UUC both code for phenylalanine


🔹 3. Gene expression
🧪 Step 1: Transcription (DNA → mRNA)
Occurs in nucleus (eukaryotes)
Process:
1. DNA unwinds
2. RNA polymerase binds to promoter
3. Complementary RNA nucleotides added
4. mRNA strand formed