Question

Suppose that \(22 \%\) of the nucleotides of a DNA molecule are deoxyadenosine and during replication the relative amounts of available deoxynucleoside triphosphates are \(22 \%\) dATP, \(22 \%\) dCTP, \(28 \%\) dGTP, and \(28 \%\) dTTP. What deoxynucleoside triphosphate is limiting to the replication? Explain.

Short answer

dCTP is limiting because its availability (22%) is less than required (28%).

Step-by-step solution

Determine Base Pairing

DNA is composed of paired bases, where adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G). This means if a molecule of DNA is 22% adenine, it will also be 22% thymine, and the remaining 56% will be equally split between guanine and cytosine.

Calculate Required Nucleotide Percentages

Given that 22% of the DNA is adenine, the same percentage, 22%, will be thymine. Hence, the other bases, cytosine and guanine, will share the remaining (100% - 22% - 22%) = 56% equally, thus each will be 28%.

Compare with Available dNTPs

Now compare these required percentages with the available deoxynucleoside triphosphates (dNTPs): 22% dATP, 22% dCTP, 28% dGTP, and 28% dTTP. Notice that the percentages for dATP and dTTP match the required percentages (22% each). However, dCTP is only available at 22% while it should be 28%.

Identify the Limiting Nucleotide

Since dCTP is available at 22%, which is less than the required 28%, it will be the limiting factor in replication as there is not enough available to match its required percentage for pairing with the available guanine (28%).

Key concepts

Nucleotide Base Pairing

DNA, or deoxyribonucleic acid, is the blueprint of life. It is structured as a double helix, comprising two strands that coil around each other. The stability of this helix is owed to the specific pairing of four nucleotide bases: adenine (A), thymine (T), cytosine (C), and guanine (G). Each of these bases pairs in a specific way, a concept known as base pairing.

- Adenine always pairs with Thymine, forming two hydrogen bonds.
- Cytosine pairs with Guanine, with three hydrogen bonds connecting them.

This complementary nature ensures that the DNA strands are exact mirrors of each other. For instance, if 22% of nucleotides in a DNA strand are adenine, then 22% will also be thymine. This precise nucleotide base pairing is essential in DNA replication, letting the cell accurately duplicate its genetic material. Understanding this pairing is crucial to grasp biological processes such as transcription and mutation.

Limiting Reagents

In chemistry, a limiting reagent is the reactant that is entirely consumed in a reaction, thereby halting the process. Similarly, in biological chemistry, during DNA replication, the availability of nucleotide triphosphates can 'limit' the replication.

When we replicate DNA, each base pairs with its complement, necessitating an equal and specific amount of each type of base. If any one of the nucleotide bases, such as deoxynucleoside triphosphates (dNTPs), is less available than required, it becomes the limiting reagent, stopping further replication until additional amounts are provided. Consider a scenario where there's 22% available dCTP, but 28% is needed. Since the required amount cannot be matched, dCTP becomes the limitation, hindering complete DNA synthesis. By ensuring proper balance and availability, efficient replication is supported.

Deoxynucleoside Triphosphates

Deoxynucleoside triphosphates (dNTPs) are the building blocks for DNA synthesis. They are comprised of a nitrogenous base, a deoxyribose sugar, and three phosphate groups. These components are crucial during DNA replication as they extend the growing DNA chain.

Each dNTP corresponds to one of the DNA bases:

• dATP for adenine
• dTTP for thymine
• dGTP for guanine
• dCTP for cytosine

These molecules supply the energy needed for the formation of phosphodiester bonds, linking nucleotides in a new DNA strand. As the replication machinery progresses, enzymes incorporate the appropriate dNTP to pair with the base on the template strand. It's essential to maintain correct levels of each dNTP to ensure smooth, error-free replication. An imbalance, such as insufficient dCTP, could lead to interruptions, highlighting the intricate regulation required.

Biological Chemistry

Biological chemistry involves the study of chemical processes within and related to living organisms, making it a foundational area of science. At its core are intricate molecular interactions like DNA replication, where specific molecules align in precise sequences.

DNA replication is not just a mechanical process but a well-orchestrated series of chemical reactions, driven by molecular stability and availability. It involves the seamless coordination of nucleotide base pairing, accurate synthesis via dNTPs, and control over limiting reagents. This synergy exemplifies biological chemistry's complexity and precision.

By understanding these processes, we gain insight into how cells replicate their genetic information, manifesting in growth, development, and maintenance of life. Keeping a balance of components like dNTPs is crucial, as even minor disruptions can lead to significant biological consequences. Hence, exploring these chemical foundations improves our comprehension of life's molecular machinery.