Problem 5 - Campbell Biology Concepts & Connections

Question

Scientists have discovered how to put together a bacteriophage with the protein coat of phage \(T 2\) and the DNA of phage lambda. If this composite phage were allowed to infect a bacterium, the phages produced in the host cell would have _______. (Explain your answer.) a. the protein of \(\mathrm{T} 2\) and the DNA of lambda b. the protein of lambda and the DNA of T2 c. the protein and DNA of T2 d. the protein and DNA of lambda

Step-by-Step Solution

Answer

d. the protein and DNA of lambda

Step 1 - Understand the Question

The question is about a composite bacteriophage with a protein coat of phage T2 and the DNA of phage lambda infecting a bacterium. We need to determine the characteristics of the phages produced in the host cell.

Step 2 - Recognize Phage Components and Function

Phages consist of a protein coat (capsid) and an inner core of DNA. When a phage infects a bacterium, it injects its DNA into the host cell. The host cell's machinery replicates this DNA and produces new phage proteins.

Step 3 - Identify DNA's Role

The DNA injected by the phage dictates the genetic information used to produce new phages. Therefore, the DNA of phage lambda will instruct the bacterium to produce more phages with lambda DNA.

Step 4 - Identify Protein Coat Source

Since the composite phage has the protein coat of phage T2, the initial infection is mediated using T2's protein coat. However, the production of new phage particles will be determined by the DNA of phage lambda.

Step 5 - Conclusion Based on Genetic Information

The phages produced in the host cell will have the protein and DNA of lambda because the genetic information (DNA) directs the production of both the DNA and protein components of new phages.

Key Concepts

Phage Protein Coat

Phage protein coats, also known as capsids, are the protective shells that enclose the phage's genetic material. These coats are made up of protein subunits that assemble into a structured, often geometric shape. The protein coat serves several important functions:
- It provides physical protection for the phage DNA or RNA.
- It facilitates the attachment of the phage to the host bacterium.
- It aids in the injection of the phage genetic material into the host.
In the composite bacteriophage created by combining the protein coat of phage T2 with the DNA of phage lambda, the T2 protein coat is responsible for the initial attachment and infection process. However, it's the DNA inside that determines the production of new phages.

Phage DNA

Phage DNA is the genetic material that carries instructions for creating new phages. DNA can be double-stranded or single-stranded, and in bacteriophages, it is typically double-stranded. This genetic material plays a crucial role in:
- Dictating the synthesis of new phage components.
- Producing proteins necessary for phage assembly.
- Ensuring the replication of the phage's genetic material.
In the example of the composite phage with T2's protein coat and lambda's DNA, it is lambda's DNA that will dictate the production of new phages within the infected bacterial cell. This means that all instructions for making new phages, including their proteins and genetic material, come from the lambda DNA.

Bacterial Infection by Phages

When bacteriophages infect bacteria, they attach to the surface of the bacterial cell and inject their genetic material into the host. This process involves several steps:
- **Attachment**: The phage attaches to specific receptor sites on the bacterial cell wall using its protein coat.
- **Penetration**: The phage injects its DNA into the bacterial cell, leaving the empty protein coat outside.
- **Replication and Assembly**: The phage DNA takes over the bacterial machinery to replicate itself and produce new phage proteins.
- **Lysis and Release**: Newly assembled phages burst out of the bacterial cell, ready to infect new hosts.
In the case of our composite phage with T2's protein coat and lambda's DNA, the initial infection will be similar to how T2 would normally infect a bacterium, but the subsequent replication and assembly of new phages will follow lambda's genetic instructions.

Genetic Replication in Phages

Phage genetic replication involves creating multiple copies of the phage DNA within the host bacterium. This process is tightly regulated and happens in several steps:
- **Replication**: The phage DNA is replicated using the host's cellular machinery. Phage enzymes may assist in this process.
- **Transcription and Translation**: Genes within the phage DNA are transcribed into mRNA, which is then translated into phage proteins.
- **Assembly**: Phage proteins and replicated DNA assemble into new phage particles.
- **Maturation and Lysis**: Mature phages are formed, and the bacterial cell eventually lyses, releasing the new phages.
For our composite phage with the protein coat of T2 and the DNA of lambda, the replication process will produce phages with lambda DNA and lambda-specified proteins. This proves that the genetic information in the phage DNA is crucial for determining the characteristics of the offspring phages.