Question

The sequence below represents one side of a DNA strand.

Answer 1

Answer:

GAA TTC GCA    Original strand

CTT AAG CGT    Complimentary strand

Explanation:

The original strand is already given.  It is GAA TTC GCA

Now we need to recognize the complementary strand from the pool of options and pair their bases. Names are written with their letters.

Nitrogenated bases that form nucleic acids correspond to purines and pyrimidines.

• Adenine (A) and guanine (G) derive from purines,
• Thymine (T) and Cytosine (C) derive from Pyrimidines.  

In the DNA molecule, Adenine (Purine) forms pairs with Timine (Pyrimidine), while Guanine (Purin) pairs with Cytosine. Two hydrogen bonds join the A-T pair, and three hydrogen bonds join the G-C.

Knowing this, we need to find the correct option, which will pair A with T and C with G.

• 1st Strand → CUU AAG CGU → You can eliminate this option because it includes Uracil, which is a base of RNA. Uracil complements with Adenine, but only in RNA, and now we are looking for a DNA complementary strand.
• 2nd Strand → GAA CCT CAT → None of the triplets pair correctly the original strand. It is not complementary
• 4rth Strand  → GAA TTC GCA  → This is equal to the original strand. It does not complement it.
• 3rd Strand → CTT AAG CGT → The three triples complement the ones of the original strand. This is the correct option.

G ⇔C

A ⇔ T

A ⇔ T

T ⇔ A

T ⇔ A

C ⇔ G

G ⇔ C

C ⇔ G

A⇔ T