Practice - Nucleic Acids 2 - Online Tutor, Practice Problems & Exam Prep

According to Chargaff's rules, the amounts of purines and pyrimidines in double-stranded DNA are equal, with adenine pairing with thymine and cytosine pairing with guanine. The Watson-Crick model features a major groove, where proteins typically bind, and a minor groove. A palindromic sequence reads the same forwards and backwards, exemplified by the sequence ggatcc. Understanding the structure of nucleotides, including deoxycytidine triphosphate (dCTP), is essential, highlighting the significance of the phosphate groups and the anti-parallel nature of DNA strands.

Practice - Nucleic Acids 2

Chargaff's rules tell us that the amount of purines in double-stranded DNA is going to be equal to the amount of pyrimidines, and that's because there's 50% of each. Additionally, they tell us that the amount of adenine is going to be equal to the amount of thymine, because they're always bound together. And, the amount of cytosine is equal to the amount of guanine because, again, they're always bound together. These are basically summed up by answer choice e. Now, the Watson-Crick model of DNA does not include two equally sized grooves running up the helix. You might recall that there is actually a major groove that is larger than the minor groove, as the names imply. Recall also that the major groove is generally where proteins bind to DNA, though some do interact with the minor groove.

Question 8, which of the following is a palindromic sequence? This relies on you knowing what the term palindrome means, which is something that is the same written backward and forward. Like the word "kayak" or "radar", you could write it backward and forward, and it would be exactly the same. Looking at our answer choices, answer choice d is the correct answer here. If you look at those two sequences, ggatcc and ggatcc, you'll probably notice that they are the same sequence written backward and forward. Actually, I hope you noticed that the 5' end is the same on both, and the 3' end is the same on both because remember, DNA's structure is antiparallel.

Take a moment, pause the video, do number 9. I've already drawn the structure out because it is quite large, and I don't want to spend a lot of time drawing the structure out in front of you because that's boring. I do want to quickly go over the numbering here on the molecule. Let's start with our base. This is our base molecule, and it is numbered starting at this nitrogen 1, 2, 3, 4, 5, and 6. Now let's take a look at our sugar. Since this is deoxy, we don't have an O on the 2'. So there's our 4', 5'. That is where the phosphates are attached, and CTP, that is T for tri. Triphosphate, 3 phosphates, and we have them 1α, 2β, and 3γ here. Alright. So that is our deoxycytidinetriphosphate. Let's flip the page.

Here’s what students ask on this topic:

What are Chargaff's rules and how do they apply to DNA structure?

Chargaff's rules state that in double-stranded DNA, the amount of purines (adenine and guanine) is equal to the amount of pyrimidines (thymine and cytosine). Specifically, the amount of adenine (A) is equal to thymine (T), and the amount of cytosine (C) is equal to guanine (G). This is because A pairs with T and C pairs with G through hydrogen bonds, maintaining a consistent structure. These rules are crucial for the double-helix structure of DNA, ensuring that the two strands are complementary and can accurately replicate during cell division.

What is the significance of the major and minor grooves in the Watson-Crick model of DNA?

The Watson-Crick model of DNA features two grooves: the major groove and the minor groove. The major groove is wider and provides a binding site for many DNA-binding proteins, which can recognize specific base sequences. The minor groove, although narrower, can also interact with certain proteins. These grooves are essential for the regulation of gene expression and the overall functionality of DNA, as they allow proteins to access the genetic information encoded within the DNA strands.

What is a palindromic sequence in DNA, and why is it important?

A palindromic sequence in DNA is a sequence of nucleotides that reads the same forwards and backwards on complementary strands. For example, the sequence GGATCC is palindromic because its reverse complement is also GGATCC. Palindromic sequences are important in molecular biology because they are often recognition sites for restriction enzymes, which cut DNA at specific locations. This property is widely used in genetic engineering and molecular cloning.

How is the structure of deoxycytidine triphosphate (dCTP) organized?

Deoxycytidine triphosphate (dCTP) consists of three main components: a nitrogenous base (cytosine), a deoxyribose sugar, and three phosphate groups. The cytosine base is attached to the 1' carbon of the deoxyribose sugar. The sugar lacks an OH group at the 2' position, distinguishing it from ribose. The three phosphate groups are attached to the 5' carbon of the sugar and are labeled alpha, beta, and gamma. dCTP is a building block of DNA, providing the cytosine nucleotide during DNA synthesis.

Why is the anti-parallel nature of DNA strands important?

The anti-parallel nature of DNA strands means that the two strands run in opposite directions: one strand runs 5' to 3', and the other runs 3' to 5'. This orientation is crucial for the replication and transcription processes. DNA polymerases, the enzymes responsible for DNA synthesis, can only add nucleotides to the 3' end of a growing strand. This anti-parallel arrangement ensures that the complementary base pairing is maintained, allowing for accurate replication and transcription of genetic information.