Structure and function of genetic materials — A/L Biology

What must I remember about Structure and function of genetic materials?

• DNA secondary structure: Double-stranded, antiparallel polynucleotide chains (5' to 3' opposite 3' to 5') forming a right-handed double helix (Watson-Crick model).
• Complementary base pairing rule: Adenine forms two hydrogen bonds with Thymine (A = T); Guanine forms three hydrogen bonds with Cytosine (G ≡ C) (Chargaff's rules: A+G = T+C).
• DNA packaging in eukaryotes: Double helix wraps around octamers of basic histone proteins to form nucleosomes (10 nm fiber), coiling into chromatin fibers, looped domains, and metaphase chromosomes.
• Semi-conservative DNA replication model: Each daughter DNA duplex retains one intact parental strand and one newly synthesized complementary strand (Meselson-Stahl experiment).
• Replication machinery: Helicase (unwinds helix), Primase (RNA primer synthesis), DNA Polymerase III (5' to 3' elongation), DNA Polymerase I (primer removal/repair), and DNA Ligase (seals Okazaki fragments on lagging strand).

Test yourself (1 minute)

1. Leading vs Lagging strand synthesis

   Leading strand is synthesized continuously towards the replication fork (5' to 3'); Lagging strand is synthesized discontinuously away from the fork as Okazaki fragments.

2. Directionality of DNA polymerase

   DNA polymerases can ONLY add new nucleotides to the free 3'-OH end of an existing strand; synthesis is strictly in the 5' to 3' direction.

3. Hydrogen bond thermal stability

   DNA sequences rich in G-C pairs require higher denaturation temperatures than A-T rich sequences due to three hydrogen bonds versus two.

Practise Structure and function of genetic materials questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 6

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Where does Structure and function of genetic materials fit in the syllabus?

Year 1 · Term 2