DNA Directionality: 3' to 5' & Bacterial DNA Explained

In summary, DNA has directionality based on the free end of the ribose. Without nicking the DNA, there is no way to tell which strand is going in which direction. The polymerase needs to be able to read from 3' to 5' in order to make new DNA or RNA.
  • #1
at2341
10
0
Hi,

To my understanding, the directionality of DNA (3' to 5') (5' to 3') is based on where the free(unattached) end of the ribose is.

With this idea, how can bacterial DNA (where the ends are joined together) have directionality?
 
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  • #2
Cut it!
 
  • #3
Circular DNA is still DNA. One strand will be 3'-5' and the other 5'-3'. Bases may only be added to the 3' end of any DNA strand, so that it is unidirectional.

To clarify: the 5' end is a phosphate grp and the 3' is a hydroxyl grp
 
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  • #4
I appreciate your replies,

Once the 3' end joins the 5' end to make a circle, you really can't tell where the 3' and 5' ends start. Is this correct? thanks
 
  • #5
at2341 said:
Once the 3' end joins the 5' end to make a circle, you really can't tell where the 3' and 5' ends start. Is this correct? thanks


There is no start or end really, just direction. One strand will be in one direction, and the other complimentary strand in the other. As Matteo said...cut it! :)
 
  • #6
1) Without cutting the DNA, there is no way to tell which strand is going in which direction? Is this correct?

2) If we can't tell which strand is which, how can the polymerase differentiate?

Thanks
 
  • #7
I think what you may be asking about is which is the sense and anti sense strand.
If so then several steps are required for translation of a segment.
Unfolding, attachment of one or more promoters, and an available start codon.
AFAIK both sides of the DNA molecule can satisfy these conditions.
So the sense strand is the one that satisfies the requirements.
 
  • #8
at2341 said:
1) Without cutting the DNA, there is no way to tell which strand is going in which direction? Is this correct?

2) If we can't tell which strand is which, how can the polymerase differentiate?

It depends on whether you are talking about replication (DNA polymerase) or transcription (RNA polymerase).

In replication, I believe there is an enzyme that "nicks" the DNA strand at a certain location (based on sequence) making a 3' and a 5' end. In transcription, the RNA polymerase binds to a promoter sequence which is aligned in a certain direction. Polymerase reads from 3' to 5' direction so that the new DNA or RNA it makes is building in the 5' to 3' direction.
 
  • #9
thank you guys for replying.

BoomBoom, that's exactly what I wanted to know... how do the enzymes differentiate which way to go. thanks
 
  • #10
Consider a strand of DNA from the perspective of the middle of the ribose ring. The 3' direction is toward where the oxygen of a phosphate group hooks directly to the ring. The 5' direction is toward the extracyclic methylene which is bound to another phosphate. You don't need to cut the strand to see this directionality. Let's arbitrarily call one end of an enzyme's binding site the front; the enzyme would encounter a very different shape of substrate surface if it binds a strand of DNA with its front in the 3' direction as opposed to binding with its front in the 5' direction. No nick of the strand is needed, the shape of the ribose ring is enough to determine directions on the strand.
 
  • #11
JonMoulton said:
No nick of the strand is needed, the shape of the ribose ring is enough to determine directions on the strand.

Good point...I didn't think of that. Thanks Jon!
 

Related to DNA Directionality: 3' to 5' & Bacterial DNA Explained

What is the significance of DNA directionality?

The directionality of DNA refers to the arrangement of nucleotides in a DNA strand. This is important because it determines how DNA is replicated and read by cells. In most organisms, DNA is read in the 3' to 5' direction, meaning that the 3' end of the DNA strand is read first and the 5' end is read last. This directionality is important for the accurate copying and translation of genetic information.

What does 3' to 5' mean in terms of DNA directionality?

The numbers 3' and 5' refer to the carbon atoms in the sugar molecule of each nucleotide in a DNA strand. The 3' carbon has a hydroxyl group attached to it, while the 5' carbon has a phosphate group attached to it. This arrangement causes the DNA strand to have a directionality, with the 3' end being the "start" and the 5' end being the "end".

Why is bacterial DNA different from eukaryotic DNA?

Bacterial DNA is different from eukaryotic DNA in several ways. First, bacterial DNA is usually found in a circular form, while eukaryotic DNA is linear. Additionally, bacterial DNA does not have introns (non-coding regions), unlike eukaryotic DNA. Also, the DNA replication process in bacteria is simpler and faster compared to eukaryotes.

Can DNA directionality change?

No, DNA directionality is determined by the arrangement of nucleotides in the DNA strand and cannot be changed. However, mutations can occur in the DNA sequence, which can affect the direction of genetic information being read. Additionally, some viruses have the ability to change the directionality of DNA during their life cycle.

How is the directionality of DNA important in bacterial genetics?

The directionality of DNA is critical in bacterial genetics because it determines how genes are transcribed and translated into proteins. The 3' to 5' directionality ensures that the genetic information is read and copied accurately, leading to the production of functional proteins. This is essential for bacterial survival and reproduction.

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