A. The nucleotide sequence of one DNA strand of a DNA double helix is 5^' -GGATTTTTGTCCACAATCA-3

A. The nucleotide sequence of one DNA strand of a DNA double...

A. The nucleotide sequence of one DNA strand of a DNA double helix is $5^{\prime}$ -GGATTTTTGTCCACAATCA-3'. What is the sequence of the complementary strand? B. In the DNA of certain bacterial cells, $13 \%$ of the nucleotides contain adenine. What are the percentages of the other nucleotides? C. How many possible nucleotide sequences are there for a stretch of single-stranded DNA that is $N$ nucleotides long? D. Suppose you had a method of cutting DNA at specific sequences of nucleotides. How many nucleotides long (on average) would such a sequence have to be in order to make just one cut in a bacterial genome of $3 \times 10^{6}$ nucleotide pairs? How would the answer differ for the genome of an animal cell that contains $3 \times 10^{9}$ nucleotide pairs?

A. The nucleotide sequence of one DNA strand of a DNA double helix is $5^{\prime}$ -GGATTTTTGTCCACAATCA-3'.
What is the sequence of the complementary strand?
B. In the DNA of certain bacterial cells, $13 \%$ of the nucleotides contain adenine. What are the percentages of the other nucleotides?
C. How many possible nucleotide sequences are there for a stretch of single-stranded DNA that is $N$ nucleotides long?
D. Suppose you had a method of cutting DNA at specific sequences of nucleotides. How many nucleotides long (on average) would such a sequence have to be in order to make just one cut in a bacterial genome of $3 \times 10^{6}$ nucleotide pairs? How would the answer differ for the genome of an animal cell that contains $3 \times 10^{9}$ nucleotide pairs?

Key Concepts

Probability and Restriction Site Frequency

The occurrence of a specific nucleotide sequence within a large genome can be determined by probability. For any sequence of n nucleotides, the chance of its occurrence at a random location is 1 in 4^n. This concept is particularly important when predicting how frequently a particular sequence will appear as a potential restriction enzyme recognition site within genomes of various sizes.

Combinatorics of Nucleotide Sequences

Because there are four types of nucleotides (A, T, C, and G), the total number of possible nucleotide sequences for a single-stranded DNA segment of a given length is calculated as 4 raised to the power of the number of nucleotides (i.e., 4^N). This principle of exponential growth in possibilities is fundamental in understanding genetic diversity and complexity.

Chargaff's Rules

Chargaff's rules describe the observation that in double-stranded DNA, the amount of adenine equals the amount of thymine, and the amount of cytosine equals the amount of guanine. This concept is crucial when calculating nucleotide percentages in a DNA sample, as knowing the percentage of one base allows you to infer the percentage of its complement.

Complementary Base Pairing

This principle states that in a DNA double helix, each nucleotide on one strand pairs specifically with a complementary nucleotide on the other strand: adenine pairs with thymine, and cytosine pairs with guanine. This rule is fundamental for accurately replicating and transcribing genetic information and is used to determine the sequence of one strand based on its partner.

Transcript

00:01 Because dna uses complementary base pairing, we can learn a lot about a sequence by comparing just one strand.

00:07 For example, if this sequence is our 5 prime to 3 prime strand, we could find the complementary strand in the 3 prime to 5 prime direction by using complementary base pairing.

00:23 So in complementary base pairing, a pairs with t and c with g.

00:29 So we can go through g pairs with c.

00:33 Pairs with t, t pairs of a, c again, g pairs with c, t with a, c with g with g, a with t, a with t, c with g, a with t again, t with a, c with a, c with g.

00:56 And then if we were to write this as test answer, or to write it up in a paper or anything, you would always rewrite this in the 5 prime to 3 prime direction, because that's a standard convention.

01:10 And so you would just start 5 prime, go t, g, a, t, and so forth.

01:15 I'm not going to rewrite that now.

01:17 But this isn't the only thing that we can do with a sequence.

01:24 So we also know because of complementary base pairing that say we have bacterial cells and 13 % of the nucleotides are adenine.

01:35 So if we have 13 % adenine, what does that tell us? about our percentage of vining, guernicine, and then side of zine.

01:52 Well, we know that a pairs with t, and so that'll give us an equal percentage here.

02:01 And if we add our 2 times 13 % to 2 times whatever c and g are, because we know they'll be the same, we're going to get 100 % because there are no other options.

02:23 And so we do this math, and we can just solve for x with some quick algebra, and that is going to give us 13 % thymine, which is going to be 74 % remaining for our c and g, which if we solve that, we're going to get 74 over 2, which should be 37 % each for both guanine and space z.

02:58 So complementary base pairing can actually tell us even more about this.

03:06 If we think about the number of possibilities for sequences, for any given sequence, at any place, we can have a, t, c, or g.

03:25 So if i want to estimate what this is, it's either going to be a, t, c, or g.

03:33 What that means is that for any given sequence that is n nucleotides long, the number of possible sequences is going to be 4 to the n.

04:06 Again, n being the length...

Please give Ace some feedback