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Flip to reveal answersWhat shape is a DNA molecule?
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All 12 Flashcards — The double helix & base pairing
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Question
What shape is a DNA molecule?
Answer
A **double helix** — two strands twisted around each other.
Question
Define complementary base pairing.
Answer
The rule that **A pairs only with T**, and **G pairs only with C**, on the two DNA strands.
Question
Which base pairs with adenine?
Answer
**Thymine (T)**.
Question
Which base pairs with guanine?
Answer
**Cytosine (C)**.
Question
What kind of bond holds a base pair together?
Answer
**Hydrogen bonds** (between the two bases).
Question
How many hydrogen bonds hold an A–T pair? A G–C pair?
Answer
**A–T has 2**; **G–C has 3**.
Question
Which parts of DNA are joined across the helix — bases or backbones?
Answer
The **bases** (by hydrogen bonds). The sugar–phosphate backbones are not joined to each other.
Question
What does 'antiparallel' mean for DNA strands?
Answer
The two strands run in **opposite directions** to each other.
Question
State Chargaff's rule.
Answer
In DNA, **%A = %T** and **%G = %C**.
Question
If a DNA sample is 22% cytosine, what % is guanine?
Answer
**22%** — because %G = %C.
Question
If A is 30%, what is the combined % of G and C?
Answer
A = T = 30%, so A+T = 60%, leaving **40%** shared by G and C (20% each).
Question
Who proposed the double-helix model, and using whose data?
Answer
**Watson and Crick**, using X-ray data from **Rosalind Franklin**.
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Topic 1.2 hub
Nucleic acids
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