What are genes, chromosome and DNA?

[n.karthick]

Hi I am not from biological background and I seek simple explanations for the above (genes, chromosome and DNA)
I know plenty of material are available in net, but if some one explains me what they are and how they are connected in essence I would be grateful to him.
These terms are repeatedly being discussed everywhere even in common conversations.
One guy was telling me that gene is like software and chromosome is like hardware. Is this analogy correct? I got confused how there could be software like thing in a tiny living organism.
Please explain, thanks.

 

[mishrashubham]

1) All living organisms contain DNA. (We don't know about any organism till date that does not contain DNA and viruses are not yet classified as full fledged organisms)
2) DNA is a very long molecule.
3) It consists of two parts: (a) a sugar backbone and (b) base pairs

http://2.bp.blogspot.com/_cWcuJM9QI...uble_Helix%2Bwallpapers%2Bimages%2Brna+45.jpg

4) It can be visualised as having the shape of a ladder where the sugar backbone forms the vertical side and the base pairs the rungs.
5) There are four different nucleobases (a) Adenine (b) Thymine (c) Guanine and (d) Cytosine
6) The order of arrangement of these base pairs in the DNA molecule acts like a code to produce proteins.
7) There are discreet parts of this DNA molecule which code for a certain protein. These parts are called genes.
8) Every gene codes for a single protein.
9) These proteins do some work which can be building and repairing, catalyzing reactions etc.
10) There are thousands of such genes in a DNA molecule.
11) The combination of these genes and in turn the proteins they produce make us what we are.
12) Each and every cell of out body contains this DNA in its dense central portion called the nucleus.
13) In the nucleus there is not one but many unique molecules of DNA each containing different information.
14) The number may vary among different species (Humans have 23 chromosome pairs).
15) Each such DNA molecule is called a chromosome. We have two copies of every chromosome which are identical to each other apart from the sex chromosomes. more info
http://en.wikipedia.org/wiki/Chromosome
16) The entire set of the chromosomes is called the genome.

Well that is about as concise as I can put it. There are a couple of loose ends there but I think they are unavoidable.

One guy was telling me that gene is like software and chromosome is like hardware. Is this analogy correct? I got confused how there could be software like thing in a tiny living organism.
Please explain, thanks.

Well I cannot relate to that analogy. A better one would be

Imagine that the genome is a book.
There are twenty-three chapters, called CHROMOSOMES.
Each chapter contains several thousand stories, called GENES.
Each story is made up of paragraphs, called EXONS, which are interrupted
by advertisements called INTRONS.
Each paragraph is made up of words, called CODONS.
Each word is written in letters called BASES.

This one's from the book "Genome" by Matt Ridley. I highly recommend it if you really want to learn about genetics.

 

[n.karthick]

Thanks for your reply. What I understood is, many genes form DNA, many DNA molecules form chromosome and many such chromosomes are called as Genome.
I will refer to the book you have mentioned.
Thanks

 

[Pythagorean]

neat interactive visuals for seeing the whole picture:
http://www.johnkyrk.com/

 

[Ryan_m_b]

Thanks for your reply. What I understood is, many genes form DNA, many DNA molecules form chromosome and many such chromosomes are called as Genome.
I will refer to the book you have mentioned.
Thanks

Close but not quite. Chromosomes are large molecules of DNA that have coiled up on themselves like a scrunched up ball of string. DNA is made from base pairs, a section of base pairs that codes for a protein is called a gene

 

[mishrashubham]

neat interactive visuals for seeing the whole picture:
http://www.johnkyrk.com/

While I absolutely love that website (it was one of the things that got me interested in cell biology a few years back), I don't think it would be suitable for someone who is not from a biological background. Anyways it is very interesting you may have a look.

 

[mishrashubham]

...many DNA molecules form chromosome and many such chromosomes are called as Genome.

Each chromosome is a single long molecule of DNA not that a chromosome is made up of many DNA molecules. And it is not merely many chromosomes but instead the set comprising of the complete genetic information of an organism is what is called the Genome.

 

[Pythagorean]

While I absolutely love that website (it was one of the things that got me interested in cell biology a few years back), I don't think it would be suitable for someone who is not from a biological background. Anyways it is very interesting you may have a look.

My backgroud isn't in biology. I supplement with other materials. But this site gives you an overall view. That's what I had been lacking since most other educational materials you find online go into specific details and are really wordy and reduced and focused.

 

[mishrashubham]

My backgroud isn't in biology. I supplement with other materials. But this site gives you an overall view. That's what I had been lacking since most other educational materials you find online go into specific details and are really wordy and reduced and focused.

Sorry my mistake. What I meant was that it would be better to study about genetics at the macroscopic level (sorry couldn't find a better word) i.e. its effects on organisms and the environment before going into the molecular level. Appreciation of genes and their importance should precede the knowledge about their working.

 

[Pythagorean]

Sorry my mistake. What I meant was that it would be better to study about genetics at the macroscopic level (sorry couldn't find a better word) i.e. its effects on organisms and the environment before going into the molecular level. Appreciation of genes and their importance should precede the knowledge about their working.

Hrm, I didn't see any mention of environment in your reply to the OP. I agree that evolution is important too, but the OP asked about how genes work.

 

[mishrashubham]

Hrm, I didn't see any mention of environment in your reply to the OP. I agree that evolution is important too, but the OP asked about how genes work.

Well this is a complex topic as there are so many interactions happening between the genes and various other things such as the organism itself, the environment through the organisms, other organisms of the same species, other organisms of a different species. And which is why I recommended the book as it gives a very good idea about genes and covers many of its aspects.

Also another book that I recommend is "Genetics for Dummies". It is specifically made for people with little knowledge of genetics.

 

[Pythagorean]

Actually, come to think of it, Sapolsky's lectures on human behavioral biology go into the environmental details. I posted it in the main tutorials forum.

 

[mishrashubham]

The main tutorials forum? I am not aware of it, could you just give the link to your post.

 

[Ken Natton]

I too like those animations you provided a link to Pythagorean. I don’t pretend for one moment to fully ‘understand’ everything that they portray, but they do provide some degree of insight even at a superficial level. And I can see how, if you are studying the deeper technicalities of some aspect of cell biology, those animations could be very helpful in establishing the point in your mind.

That book you mentioned mishrashubham looks superb. I shall be looking to obtain a copy and spend some time trying to understand what it has to teach me.

Thanks guys.

 

[Pythagorean]

No problem, I'm going to check out mishra's reference sometime myself.

@mishrashubham:

https://www.physicsforums.com/showthread.php?t=487385

 

[mishrashubham]

Thanks Pythagorean