A DNA strand with sequence 5' CGATTC 3' would be complementary to the sequence
Show Hint
Always double-check the direction of the strands.
A common error is to write the complement in the $3'$ to $5'$ direction but label it as $5'$ to $3'$.
Always reverse your complement to present it in the standard $5'$ to $3'$ direction.
Step 1: Understanding the Concept:
Double-stranded DNA is held together by hydrogen bonds between complementary nitrogenous bases on opposite strands.
The two strands run antiparallel to each other, meaning one strand runs in the $5'$ to $3'$ direction while its complementary partner runs in the $3'$ to $5'$ direction. Key Formula or Approach:
According to Watson-Crick base pairing rules:
- Adenine (A) pairs with Thymine (T) via two hydrogen bonds.
- Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.
To find the complementary sequence:
Write the template sequence in the $5'$ to $3'$ direction.
Determine the complementary base for each nucleotide.
Write the resulting sequence in the $3'$ to $5'$ direction.
Reverse the sequence to present it in the standard $5'$ to $3'$ direction. Step 2: Detailed Explanation:
Let us apply these steps to the given sequence:
The given template strand is:
\[ 5'\text{-C-G-A-T-T-C-}3' \]
Find the complementary base for each position:
- Complement of C is G
- Complement of G is C
- Complement of A is T
- Complement of T is A
- Complement of T is A
- Complement of C is G
Aligning these base pairs gives the complementary strand in the antiparallel ($3'$ to $5'$) direction:
\[ 3'\text{-G-C-T-A-A-G-}5' \]
To match the standard formatting used in the options, we reverse this sequence to write it in the $5'$ to $3'$ direction:
\[ 5'\text{-G-A-A-T-C-G-}3' \]
Comparing this result with the options, we find it matches Option D.
Option A is incorrect because it contains Uracil (U), which is found in RNA, not DNA. Step 3: Final Answer:
The complementary sequence to the $5'\text{-CGATTC-}3'$ strand is $5'\text{-GAATCG-}3'$.
