Problem 7 - AP Biology Premium Prep 2021

Question

Taq polymerase, a DNA polymerase derived from thermophilic bacteria, is used in polymerase chain reactions (PCR) in the laboratory. During PCR, Taq catalyzes DNA polymerization, similar to how it would in bacteria. A normal PCR cycle is as follows: 1\. Melting/Denaturing \(95^{\circ} \mathrm{C}\) 2\. Primer Annealing \(50^{\circ} \mathrm{C}\) 3\. Elongation of DNA (repeat \(20-30\), \(72^{\circ} \mathrm{C}\) cycles) Which of the following conditions likely describes the living environment of Taq bacteria? (A) Freshwater with acidic pH (B) Hydrothermal vents reaching temperatures between \(70-75^{\circ} \mathrm{C}\) (C) Hot springs of \(40^{\circ} \mathrm{C}\) (D) Tide pools with high salinity 3\. Elongation of DNA (repeat \(20-3072^{\circ} \mathrm{C}\) cycles)

Step-by-Step Solution

Answer

The most likely living environment for Taq bacteria is (B) Hydrothermal vents reaching temperatures between \(70-75^{\circ} \mathrm{C}\), as it matches Taq polymerase's temperature tolerance seen during PCR.

Step 1: Analyze the PCR process involving Taq polymerase

The polymerase chain reaction (PCR) uses Taq polymerase to replicate DNA through cycles of denaturing, annealing, and elongating. In these cycles, the enzyme must withstand high temperatures like \(95^{\circ} \mathrm{C}\).

Step 2: Compare the PCR process to the given living conditions

We need to consider which of the provided conditions best suits Taq polymerase's ability to function at high temperatures. (A) Freshwater with acidic pH: This information does not mention temperature, so we cannot determine its suitability. (B) Hydrothermal vents reaching temperatures between \(70-75^{\circ} \mathrm{C}\): Taq polymerase functioning well at high temperatures during PCR suggests it might originate from a high-temperature environment such as hydrothermal vents. (C) Hot springs of \(40^{\circ} \mathrm{C}\): Even though hot springs have an elevated temperature, \(40^{\circ} \mathrm{C}\) is not as high as the temperatures that Taq polymerase can withstand during PCR. (D) Tide pools with high salinity: This information also does not mention temperature, so we cannot determine its suitability.

Step 3: Choose the most likely living environment for Taq bacteria

Based on the comparison in Step 2, we can see that the most likely living environment is the one with high temperatures that match Taq polymerase's temperature tolerance seen in PCR. Thus, the correct answer is: (B) Hydrothermal vents reaching temperatures between \(70-75^{\circ} \mathrm{C}\).

Key Concepts

Taq polymerase

Taq polymerase is a type of DNA polymerase which is essential in the process of copying DNA strands. It's named after the bacterium from which it was originally isolated, Thermus aquaticus. This enzyme is a key component in the lab technique called the polymerase chain reaction (PCR), which is used to make millions of copies of a specific DNA segment. The special property of Taq polymerase is its ability to withstand the high temperatures used in PCR to separate the DNA strands, known as denaturation, which typically occurs at about 95 degrees Celsius.

DNA polymerases like Taq are responsible for binding to single-stranded DNA and adding nucleotides to form a complementary strand. Because it is heat-stable, Taq polymerase does not denature at these high temperatures. This quality makes it incredibly useful for PCR, where multiple cycles of heating and cooling would denature most other enzymes. Taq polymerase's role in PCR is to extend the DNA primers added to the single-strands of DNA during the annealing step, creating new strands during the elongation step at 72 degrees Celsius.

DNA polymerization

DNA polymerization is a fundamental process of DNA synthesis where enzymes called DNA polymerases create DNA strands by adding nucleotides, the building blocks of DNA, to an existing strand. During PCR, DNA polymerization is carried out by Taq polymerase, which adds nucleotides one by one to a DNA template strand.

The steps involved in the polymerization during PCR are highly synchronized. First, high heat is applied to separate the double-stranded DNA. Next, the temperature is lowered to allow primers to bind or anneal to the template strands. Finally, at an intermediate temperature, Taq polymerase synthesizes the new DNA strand by extending the primer. This three-step process is repeated 20-30 times to amplify the desired DNA segment. Each cycle doubles the amount of DNA, leading to exponential amplification.

Thermophilic bacteria

Thermophilic bacteria are a type of extremophile that thrives at high temperatures, often between 45 and 80 degrees Celsius. These organisms are found in environments such as hot springs and hydrothermal vents, where temperatures are significantly higher than what is typical for most life on Earth. Taq polymerase is derived from Thermus aquaticus, a species of thermophilic bacteria.

Lifestyle of Thermophilic Bacteria

Thermophiles have developed unique adaptations that enable not just their survival but also biological functioning in such extreme conditions. Their proteins, including enzymes like DNA polymerases, are remarkably stable at temperatures that would denature proteins from non-thermophilic organisms. The enzymes retain a stable configuration, allowing them to catalyze chemical reactions efficiently at high temperatures.

Understanding thermophilic organisms helps researchers develop various biotechnological applications, such as PCR, by utilizing their heat-stable enzymes.

Enzyme temperature tolerance

Enzyme temperature tolerance refers to the range of temperatures within which an enzyme can function effectively. Most enzymes have an optimal temperature at which their activity is at its peak, and beyond this range, their efficiency can decrease. If the temperature gets too high, enzymes can denature, meaning they lose their three-dimensional structure necessary for their function.

Taq polymerase stands out due to its exceptionally high temperature tolerance, which allows it to catalyze DNA synthesis during the strenuous conditions of PCR. This property can be attributed to the thermophilic bacteria's habitat, such as the hydrothermal vents that have temperatures reaching about 70-75 degrees Celsius, thus enabling the enzyme to operate efficiently during the DNA denaturation and annealing phases of PCR without denaturing itself.