4
$\begingroup$

I am confused about the term DNA-binding domain. Does it mean that there are some parts of the DNA that tend to coil up? Does it happen because some proteins tend to stick around that area? Also it is my understanding that with some proteins DNA (say for bacteria like E. coli) tends to coil up. Do we know what is the approximately the size of these coils? What is a ‘motif’ in this context.

$\endgroup$
6
$\begingroup$

Welcome to Biology.SE!

The term "domain" in biochemistry and molecular biology is usually used to refer to a part of a protein that has a conserved structure and function, is similar between related proteins, and can generally exist or function on its own if it was separated from the rest of the protein. A DNA-binding domain is a protein structure that has a high affinity for DNA, and so binds to it when the two molecules are in the same vicinity. An example is a type of protein called a transcription factor, which binds to DNA in the nucleus of the cell (in Eukaryotes, bacteria and Archaea don't have nuclei - the DNA just floats free) and causes changes in the transcription of genes. The following image from WikiMedia shows how transcription factors work in general.

transcription factors

"DNA coiling" is a very generic term that describes many different things. The basic structure of DNA itself is a coil, with two sugar chains (the deoxyribose in DeoxyriboNucleic Acid or DNA) coiling around each other, and attached by nucleic acid bases. In the eukaryotic cell, individual strands of DNA are associated with structural proteins to create chromatin, which is what makes up chromosomes in the nucleus of each cell. In the first stage, naked DNA is wrapped or coiled around structural proteins called histones into a structure called a nucleosome. These then stack into a "solenoid" or fiber structure, which makes up so-called "relaxed" chromatin - regions of the genome where active transcription is taking place. If a part of a chromosome has been marked as inactive, or during certain steps in the cell cycle when one cell splits into two (mitosis), the fibers further coil into condensed chromatin, forming the typical structure many people associate with chromosomes. This image, from Wikipedia, visualizes each step in the process.

chromatin structure

The word "motif" can sometimes mean the same thing as domain - for example, someone might refer to a "DNA-binding motif" in a protein. However, a motif is typically smaller than a domain, can occur in DNA, RNA, and proteins, and has to do with the specific sequence. A "structural motif" in a protein is something like a helix-loop-helix or a beta-hairpin turn that can appear in multiple different kinds of protein domains, and doesn't necessarily have the same exact function in those different domains, but typically has a fairly conserved sequence that is very similar. As an example, the zinc finger motif is found in protein domains that bind DNA, RNA, and other proteins.

All of this terminology can be very confusing at first, but if you stick with it it'll get easier over time. Biochemistry and molecular biology are fascinating fields, so keep up your studies!

$\endgroup$
  • $\begingroup$ Does "binding" mean the protein attaches to the DNA? In the figure the pink protein seems to attach to the DNA. $\endgroup$ – anvSnMusater Aug 17 '13 at 20:54
  • $\begingroup$ @anvSnMusater yes, binding means that the protein and the DNA are attached to each other, but they can separate later. $\endgroup$ – MattDMo Aug 17 '13 at 20:55
  • $\begingroup$ Thanks, finally, I want to ask you, does the binded protein fold the DNA? $\endgroup$ – anvSnMusater Aug 17 '13 at 21:27
  • $\begingroup$ It can, especially if it is part of a large complex of proteins, like those involved in replication or DNA damage repair. $\endgroup$ – MattDMo Aug 17 '13 at 23:50
  • $\begingroup$ This answer is vastly overweight. You should use your discretion in choosing illustrations. The first is especially incomprehensible. Do you really expect the poster to be able to follow it? $\endgroup$ – David Jan 29 '17 at 19:16
0
$\begingroup$

Domain and motif are indeed related, but I would think that domain indicates the region in a protein (or DNA) involved in the function (be it DNA binding, catalytic etc for protein / transcription factor binding etc for nucleic acids), while motif is used to describe the particular sequence of building blocks in that domain / region. Motif is used to indicate the particular amino acids that one typically finds in the protein domain, but also to indicate the particular nucleotides in a DNA/RNA strand.

$\endgroup$
  • 1
    $\begingroup$ can you add some references to back up your answer? it would definitely add strength and credibility. $\endgroup$ – Vance L Albaugh Jan 29 '17 at 18:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.