One common feature of all DNA polymerases is that they a. synthesize DNA in the 3^'- to- 5^' dir

One common feature of all DNA polymerases is that they a....

Key Concepts

Directionality of DNA Synthesis

DNA synthesis by polymerases occurs in a unidirectional manner, specifically from the 5' end toward the 3' end. This is due to the chemical structure of nucleotides, where the free 3'-OH group serves as the attachment point for the next nucleotide, establishing an intrinsic directionality in the formation of the DNA chain.

Primer Requirement

DNA polymerases cannot initiate DNA synthesis de novo; they require a primer with a free 3'-OH group to begin adding nucleotides. Typically, this primer is an RNA segment synthesized by primase, ensuring that DNA polymerases can start the replication process.

DNA Polymerases

DNA polymerases are enzymes responsible for assembling DNA by adding nucleotides to a growing strand, using a pre-existing strand as a template. They play a crucial role in DNA replication and repair by ensuring that the genetic code is accurately copied and maintained.

Transcript

0:00 All right.

00:01 So in order to help you with your question, let's talk about dna polymerase a little bit and try and eliminate some of the multiple choices that were given to you as answers.

00:12 We'll try and narrow it down to the correct answer.

00:15 So first, does dna polymerase require a primer? and the answer there is going to lie within comparing rna versus dna.

00:25 When we're talking about rna, we don't always require a primer.

00:30 But dna always, always requires a primer, and that is going to eliminate that option right then and there for you.

00:39 Secondly, does dna polymerize synthesize in both directions or switch strands? and this is going to come down to maybe something that you've heard about if you're familiar with okasaki fragments.

00:52 These are created on the lagging strand because the dna polymerase cannot more.

01:00 Move in both directions.

01:01 It only moves in one direction and it creates these okasaki fragments as it moves in the direction that it has to, which means that it's kind of working backwards on this lagging strand, okay? but on the leading strand, it does not have to work backwards and it does not create okosaki fragments.

01:23 So that right there might tell you, or indicate that it does not switch strands it never switched strands it has two separate strands and it moves in one direction so that would eliminate that choice as well and of course now we're going to have to figure out which direction does it move in and in order to do that we're going to have to determine the direction of the strand we're looking at is it a five prime to three prime orientation or is it a three prime to five prime orientation.

01:59 We're also going to examine the bond linkage and then we're going to think in terms of biochemistry as well as genetics because biochemistry often is going to be able to explain some of the behaviors that occur in genetics.

02:14 So here we're looking at a little piece of dna here.

02:20 And the important thing to first remember is number your carbons.

02:26 So, our prime carbon 1, 2, this is your 3 prime, prime prime carbon 4, and this is your 5 prime, the carbon that hangs off of that sugar.

02:38 So here i've tried to give you a little example of how they look linked, quite simplified.

02:45 This would be your base.

02:47 These are your 5 carbon sugars.

02:50 We have them labeled.

02:51 Here is your 3 prime and your 5 prime.

02:54 And then we have your phosphate group here.

02:57 Now, we have the same one here, and you can tell this is the 5 prime, this is the 3 prime.

03:08 So we're moving in a 5 to 3 prime direction on this strand.

03:13 Now, what if it looked maybe, and this is going to be rough because i'm just really flipping it here, but what if we had something that looked more like this.

03:27 Now we have a hydroxyl group up at the top, and your 3 prime carbon is right here, and your 5 prime is here, you know, so we have 3, 5, 3, 5, 3, 5, and so it's moving now in a 3 prime to 5 prime direction.

03:49 And that is how you would determine which direction the strand is.

03:53 In this case, what we're looking at again five to three prime and hopefully you can now quickly spot that the bond linkage right here how these sugars are linked together how that phosphate and sugars are linked are involving ester bonds this is an ester bond and can you spot the ester bonds below so here we have one ester bond and here we have the second and that is on the same exact molecule, if you look at these, their mirror images of each other.

04:32 And so dna, 5 prime, and 3 primons are linked via phospho -diester bonds, right? because there are two of these bonds in each.

04:44 So here is an ester bond, and here.

04:49 There's the other ester bond.

04:50 And so that's a diester.

04:52 And because of that little phosphate, it's a phosphodiaster bond.

05:00 Now, bonds contain and use energy.

05:04 They use energy to form a bond and energy is used to break bonds.

05:10 So in terms of biochemistry, when we're talking about any biochemistry, we ask how favorable is this reaction? and that's going to tell us how likely the reaction is to proceed.

05:22 So dna polymerase in your chapter, it is said that dna polymerase requires dntp.

05:32 Dntp might sound familiar to atp...

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