DNA Structure - Video Tutorials & Practice Problems

DNA Structure

Hi in this video I'm gonna be talking about DNA structure. So most of this is gonna be a review from bio from your intro bio classes. But I do just want to go over in case you've forgotten or you know just you know, don't necessarily want to go back and review yourself which is totally fine. So um first DNA stands for deoxyribonucleic acid and has three main components. These components include a phosphate, a sugar which for D. N. A. Is deoxyribonucleic. And this is different from RNA, which has ribose. And the difference between the two sugars is the what is that? The two carbon positions. So when de oxy ribose it's a hydrogen and in ribose it's a hydroxyl group, these are present at the two carbon. And actually this is what gives D. N. A. And R. N. A. Very different qualities. It's just the sugar here and then finally there's a nitrogenous base. So these are the three components 123 and the base could be adding guanine cytosine timing. And you may see there are two names for these. For different combinations of these three components, you may see nuclear sides and nuclear ties and wonder how they're different nuclear sides contain the base and the sugar where nucleotides contain the base sugar and phosphate group. So in case you run across these two different names, that's what makes them different. So here's an example of a uh a nucleotide you have your phosphate group, you have your sugar and you have your base and those are the three components that make up a nucleotide. Now the nitrogenous basis. So this part here Um fall into two categories, you have pure ING's these are bases with double rings. So this is what's shown here. Pure ng you have one ring to two rings here and this is adnan are guanine. And then the second classes prior meetings. And these have a single ring and includes seducing and timing. And it's important to know that pure rings always pair with pi remedying. So you have one double ring and one single ring in every nucleotide base pair. And then there was this fancy guy named Shar off. Had he studied the ratio of all of these nitrogenous bases in organisms. And he found that the ratios were that a pairs with T. And C. Pairs of G. And these are the correct pairings. So here we have add ning and timing and these pair together and we have guangming inside of seeing these pair together. These two are the pairings. These two are the permitting and appearing always pairs with the permitting. Now there are two types of bonds that create D. N. A. The first is the fossil di ester bonds and these connect the nucleotides together in a single strand. So this is the backbone. This is one strand, how everything is connected together through these possible diaspora bonds, hydrogen bonds are the second type of bond. And these connect the complementary strands together. And that's what is referred to the second strand that has the inverted nucleotide sequence on it. Right? Because if you have A. T. T. C. G. Then you have, in order for these two pair you have to have the opposite right? So here you have hydrogen bonds, you have your first strand, you have your complementary strand over here. And phosphor di ester bonds are water. Here, phosphoric ester bonds connect this train together. Now hydrogen bonds actually differ depending on what pairing it is. So if it's A G. C pairing, there are three hydrogen bonds and if it's an 80 pairing there are two and this actually makes uh D. N. A. With more G. C. Bands actually stronger than D. N. A. With more 80 bands because there's an extra hydrogen bond for every G. C pairing. Now we say that the complementary strands here are anti parallel, right? Because that means that the nucleotides are inverted. So we give them sides based on the position of the carbon. So here we have the five prime and three prime side. And this pairs of the five prime and three prime side over here. And this refers to the position of the carbon on the sugar. This five prime or three prime five prime carbon, or the three prime. And this is the orientation. So if the one strand is five prime, 23 prime, the second complementary strand will be inverted. And that makes it anti parallel, it'll run three prime to five prime. And when they come together like this these two strands they form a double helix and the double helix has a major groove which has more base pairings in it and a smaller minor groove. So here we have our double helix. The hydrogen bonds here are forming between the bases. You can see them here with A. T. And A. There's 212 with A. G. And A. C. There's 3123. Now the backbone that's curling around here, these are the fosse bobo di ester bonds. I'm not gonna spell that out but possible di ester bonds. And um you have your major group which is bigger, you have your minor group which is smaller and I'm trying to think any of these differences. If you have one going five prime, five prime, let's follow this around to three prime. Then you have five prime, 23 prime. And that makes them anti parallel. And the complementary is the recurring to the, you know the actual nucleotides being complementary to each other and allowing them to bind together. So that's the overview of D. N. A. What it consists of its structure, how it all binds together and what we all call the different sides of everything. So with that let's now move on

Which of the following is not a component of a nucleotide?

• A. Phosphate
• B. Pentose Sugar
• C. Starch sugar
• D. Nitrogenous base

Chargoff's rules states that which nucleotide pairings occurred?

• A. A and G, C and T
• B. T and U, C and G
• C. G and U, C and A
• D. A and T, C and G

Which of the following is NOT true regarding the structure of the DNA double helix?

• A. The two strands run parallel
• B. The two strands are complementary
• C. The nucleotides are held together via Phosphodiester bonds
• D. There is a major groove and minor groove