Problem 8 - AP Biology Premium Prep 2021

Question

BamHI is a restriction enzyme derived from Bacillus amyloliquefaciens that recognizes short palindromic sequences in DNA. When the enzyme recognizes these sequences, it cleaves the DNA. What purpose would restriction enzymes have in a bacterium like Bacillus? (A) They are enzymes that no longer have a purpose because evolution has produced better enzymes. (B) They destroy extra DNA that results from errors in binary fission. (C) They protect Bacillus from invading DNA due to viruses. (D) They prevent, or restrict, DNA replication when the cell isn't ready to copy its DNA.

Step-by-Step Solution

Answer

(C) They protect Bacillus from invading DNA due to viruses.

Step 1: Understand the role of restriction enzymes

Restriction enzymes are proteins that can recognize and cleave specific DNA sequences. BamHI is a restriction enzyme that recognizes short palindromic sequences in DNA. It is important to understand that restriction enzymes protect bacteria against invading foreign DNA, such as DNA from viruses.

Step 2: Evaluate each answer option

Now, let's evaluate each answer option. (A) They are enzymes that no longer have a purpose because evolution has produced better enzymes. - This option is incorrect because restriction enzymes still serve an important role in the defense mechanism of bacteria. (B) They destroy extra DNA that results from errors in binary fission. - This option is incorrect because restriction enzymes do not specifically target extra DNA that results from errors in binary fission. Their main purpose is to protect the bacterium against foreign DNA. (C) They protect Bacillus from invading DNA due to viruses. - This option is correct because restriction enzymes, like BamHI, recognize foreign DNA (such as viral DNA) and cleave it to protect the bacterium. (D) They prevent, or restrict, DNA replication when the cell isn't ready to copy its DNA. - This option is incorrect because restriction enzymes do not control or regulate the replication process in bacterial cells. Their main purpose is protecting the bacterium against foreign DNA.

Step 3: Select the correct answer

Based on the analysis of each option, the correct answer is: (C) They protect Bacillus from invading DNA due to viruses.

Key Concepts

BamHI

BamHI is a type of restriction enzyme commonly used in molecular biology. This enzyme is derived from the bacterium Bacillus amyloliquefaciens. Its primary function is to recognize and cut specific DNA sequences, particularly palindromic sequences. BamHI plays a significant role in the natural defense mechanisms of bacteria. In research laboratories, BamHI is widely utilized to cut DNA at precise locations, facilitating genetic engineering and other molecular biology applications. This enzyme is quite precise, making it invaluable for scientists working with DNA sequences in genetic research.

bacterial defense mechanism

Bacteria utilize various methods to protect themselves from threats, and one critical method is the use of restriction enzymes. These enzymes, including BamHI, serve as a defense mechanism to protect bacteria from invading viruses. When foreign DNA from a virus enters a bacterial cell, the restriction enzyme recognizes the invader by detecting specific DNA sequences.

• Recognition of foreign DNA prevents the virus from hijacking the bacterium's cellular machinery.
• Cleavage of viral DNA essentially neutralizes the threat, thus protecting the bacterium.

This enzymatic action demonstrates an evolutionary adaptation by bacteria, resulting in an effective means to safeguard against viral infections.

DNA cleavage

DNA cleavage is a critical process in molecular biology, particularly with restriction enzymes like BamHI. These enzymes precisely cut DNA strands at specific sequences. The main purpose of DNA cleavage is to help the organism defend against foreign DNA by permanently altering or destroying the invasive genetic material.

• BamHI recognizes the specific DNA sequence, binds to it, and then cleaves the DNA strand.
• The cleavage is specific and predictable, making it a vital tool in molecular cloning and map sequencing.

Through DNA cleavage, biological researchers can also manipulate genetic materials for studying gene function and developing gene therapies.

palindromic DNA sequences

Palindromic DNA sequences are segments of DNA that have a symmetrical structure, similar to a palindrome in language. This means the sequence reads the same forward and backward. This structural property is precisely what restriction enzymes like BamHI recognize and bind to. Palindromic sequences act as distinct markers for these enzymes.

• These sequences ensure that the enzyme only acts on the desired sections of DNA.
• The ability to recognize these sequences allows restriction enzymes to cut DNA at specific sites without disrupting the entire DNA strand.

Understanding these sequences is crucial for genetic engineering as well as for the natural processes bacteria use to protect against viral DNA.