Biology · Rung 1 of 4

DNA & genes

DNA stores information in a sequence of bases. Genes are regions whose expression produces functional RNA or contributes to making proteins. Variants of a sequence at the same genomic location are called alleles. Changing a base can have different effects depending on context.

Where this sits

Comes after
The cell
Opens up
Inheritance, Gene expression

Exercises from this rung

Generated by the app, from easiest to hardest

  1. One DNA strand reads 5'-CCC GCA-3'. What is its complementary strand?

    • GGG CGT
    • GGG TGT
    • GGG CGU
    • CCC GCA

    Why GGG CGT: T faces every A and G faces every C, base by base. With U it would be RNA, not DNA; and the same strand repeated pairs with nothing. It is the rule that makes replication possible: each strand carries the other written inside it.

    easier

  2. In standard DNA base pairing, which base pairs with adenine (A)?

    • Guanine (G)
    • Cytosine (C)
    • Thymine (T)

    Why In DNA, A pairs with T and C with G. This complementarity lets each strand serve as a template when genetic material is copied. In RNA, uracil takes the place of thymine.

    in between

  3. After DNA is copied, one base has changed and is not repaired. What has happened?

    • A mutation in the sequence
    • A necessarily beneficial adaptation
    • The automatic loss of every gene

    Why A mutation is a change in the sequence of genetic material. Its effects depend on location and context: it can be neutral, harmful or beneficial. Its occurrence does not guarantee that it helps the organism.

    harder