Biology Made Easy- Semi Conservative DNA Replication for AS/A-Level students.

AQA Biology AS/A-Level Revision Notes


DNA replication 🧬
Semi-Conservative DNA Replication: Each daughter DNA molecule contains one original
(parental) strand and one newly synthesised strand, producing two genetically identical DNA
molecules.




es
●​ DNA helicase unwinds the DNA double helix and breaks the hydrogen bonds between
complementary bases, causing the two strands to separate.




ot
●​ Each strand acts as a template.
●​ Free DNA nucleotides are attracted to the exposed bases on each template strand and pair by
complementary base pairing (A-T and C-G).




N
●​ DNA polymerase catalyses the formation of phosphodiester bonds between adjacent nucleotides by
a condensation reaction.
y
●​ Two genetically identical DNA molecules are produced.
ud
St
YK




💡Exam Tips
●​ Always mention DNA helicase and DNA polymerase by name in 4-6-mark questions (+ essay).
●​ Always use the term template strand in exam answers.


🚨 Common Mistakes

●​ Saying DNA polymerase breaks hydrogen bonds.
●​ Forgetting to mention the template strands.
●​ Writing "DNA polymerase joins bases together. ”
●​ Confusing hydrogen bonds with phosphodiester bonds.
●​ Describing DNA replication as "conservative".




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