Problem 8 - Campbell Biology

Question

Which of the following sequences in double-stranded DNA is most likely to be recognized as a cutting site for a restriction enzyme? (A) AAGG TTCC (B) GGCC CCGG (C) ACCA TGGT (D) AAAA TTTT

Step-by-Step Solution

Answer

Option (B) GGCCCCGG is the most likely restriction enzyme recognition site.

Step 1: Understand restriction enzyme recognition sites

Restriction enzymes typically recognize specific palindromic sequences in DNA. A palindromic sequence reads the same forwards and backwards on opposite strands.

Step 2: Analyze option (A)

Check if AAGGTTCC is palindromic. The sequence on the complementary strand TTCC is not the reverse of AAGG.

Step 3: Analyze option (B)

Check if GGCCCCGG is palindromic. The sequence on the complementary strand CCGG is the reverse of GGCC, meeting the criteria for a restriction enzyme recognition site.

Step 4: Analyze option (C)

Check if ACCATGGT is palindromic. The sequence on the complementary strand TGGT is not the reverse of ACCA.

Step 5: Analyze option (D)

Check if AAAATTTT is palindromic. While TTTT is the reverse of AAAA, it is generally not a typical restriction enzyme recognition site due to lack of complexity.

Step 6: Identify the most likely recognition site

Among the options, GGCCCCGG is the only palindromic sequence commonly recognized by restriction enzymes.

Key Concepts

palindromic sequences

Palindromic sequences are a key concept when studying the recognition sites for restriction enzymes in DNA. A palindromic sequence is a sequence of nucleotides that reads the same forwards and backwards on complementary strands of DNA.
This unique feature makes them easily recognizable for certain molecular processes.
For example, in a palindromic sequence, a 5' to 3' direction of one strand matches the 3' to 5' direction of the complementary strand.
Think of it like a word that reads the same backward and forward, such as 'radar' or 'level'.
This symmetry is essential for restriction enzymes to identify their specific cutting sites within the DNA sequence.

DNA sequences

DNA sequences consist of strings of nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G).
The order of these nucleotides in a DNA strand is significant because it determines the instructions available for building proteins.
In double-stranded DNA, adenine pairs with thymine, and cytosine pairs with guanine.
This complementary base pairing holds the two strands of the DNA double helix together.
Sequences can be very long and complex, but specific short sequences can have important biological roles, such as being recognized by restriction enzymes.

restriction enzymes

Restriction enzymes, also known as restriction endonucleases, are proteins that cut DNA at or near specific recognition sites.
These enzymes are essential tools in molecular biology for gene cloning, DNA mapping, and genetic engineering.
Each restriction enzyme has a specific recognition site, most often a palindromic sequence.
When they encounter their specific recognition sequence in a DNA molecule, they make a cut, which can create sticky or blunt ends.
For example, the enzyme EcoRI cuts at the palindromic sequence GAATTC, making a staggered cut between G and A on each strand.

biotechnology

Biotechnology involves the use of living organisms or biological systems to develop useful products and technologies.
Restriction enzymes are fundamental to many biotechnology applications.
They allow scientists to cut DNA at precise locations to manipulate genes and produce recombinant DNA.
This technology has paved the way for advancements in genetic engineering, such as inserting new genes into a genome, creating genetically modified organisms (GMOs), and developing gene therapies.
Biotech industries leverage these methods for innovations in medicine, agriculture, and environmental sustainability.