A) What is the assumed directionality of the nucleotide sequence below? Label the ends of the molecule. A C G T C T A A A C G G C T A B) Is the sequence above from a DNA or RNA molecule? How do you know? C) Write the complementary sequence to the strand below (include the directionality). A C G T C T A A A C G G C T A

So here's the 3 part practice problem on nucleic acids. And part a asks, what is the assumed directionality of the nucleotide sequence below? Label the ends of the molecule. So recall from our previous videos that if you're given the nucleotide sequence and the, directionality is not provided, then you always assume it's from the 5 prime end to the 3 prime end. And so the left side here will be the 5 prime end and the right can be the 3 prime end. Now for part b, is the sequence above from a DNA or an RNA molecule? And how do you know? So recall that DNA molecules contain thymine nitrogenous bases whereas RNA molecules contain uracil nitrogenous bases instead of having thymines. So if we analyze the, sequence above, what we'll notice is that there are an abundance of thymines and the lack of uracils. And so that's an indication that this is a DNA molecule. So the answer here is DNA. And for how do we know, it's because we have the presence of thymines and the lack of uracil nitrogenous bases. Now for part c, it asks, write the complementary sequence of the strand below and include the directionality. So notice that the strand below has the exact same sequence of the strand above. And so we can take part a and apply the directionality to part c. Now to complete this problem, we're going to have to recall the base pairing rules. And recall that adenines always base pair with thymines and guanines pair with cytosines. And so when we apply that to this sequence, we're able to reveal the sequence of the complementary strand. A's always base pair with t's, c's with g's, g's with c's, t's with a's, c's with g's, t's with a's. A's base pair with t's, c's with g's, g's with c's, g's with c's, c's with g's, t's with a's, and a's with t's. And so, the next part is to recall that in a DNA molecule, the strands go into opposite directions, and recall that's called antiparallel strands. And so what that means is that if the top strand is going from 5 prime to 3 prime, from left to right, the bottom strand needs to go from 5 prime to 3 prime in the opposite direction from right to left. So that means that the right side is the 5 prime end and the left side is the 3 prime end. And so the answer to part C is just this green highlighted portion here. And so, I'll see you guys in the next practice problem.