Role of helicase and DNA polymerase in DNA replication
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Question
What is DNA replication?
Answer
Copying a DNA molecule to make **two identical molecules**, each with **one old (template) strand and one new strand**.
Question
What does helicase do?
Answer
It **unwinds and unzips** the double helix by **breaking the hydrogen bonds** between the paired bases.
Question
Which bonds does helicase break?
Answer
The **hydrogen bonds** between the paired bases (A–T, G–C) that hold the two strands together.
Question
What is the role of DNA polymerase?
Answer
It **adds complementary nucleotides** to a template strand, **building the new strand** and joining the nucleotides with covalent bonds.
Question
Which bonds does DNA polymerase form?
Answer
**Covalent bonds** that join the nucleotides along the sugar-phosphate backbone of the new strand.
Question
In which direction does DNA polymerase build the new strand?
Answer
In the **5'->3' direction** — it adds new nucleotides only to the 3' end of the growing strand.
Question
Which enzyme works first, helicase or DNA polymerase?
Answer
**Helicase** works first to open the helix; **DNA polymerase** follows to build the new strands.
Question
What is a template strand?
Answer
An original (parental) strand whose base sequence is **read** to decide which nucleotides go into the new strand.
Question
What rule decides which nucleotide is added to the new strand?
Answer
**Complementary base pairing**: A pairs with T, and G pairs with C.
Question
Helicase breaks bonds — which kind, and where?
Answer
**Hydrogen** bonds, **between** the two strands (between the paired bases).
Question
DNA polymerase forms bonds — which kind, and where?
Answer
**Covalent** bonds, **along** a strand (the sugar-phosphate backbone of the new strand).
Question
Why is replication called 'semi-conservative'?
Answer
Because each new DNA molecule keeps **one old strand and one new strand** — half of the original is conserved.
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DNA replication
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