Naked Science Forum

Life Sciences => Cells, Microbes & Viruses => Topic started by: mphutchy on 28/11/2009 23:58:59

Title: Is the DNA "code" one long complete chain or broken and packaged into chromsomes
Post by: mphutchy on 28/11/2009 23:58:59

Hi  - this is my first post here, so go easy, as I have a casual interest in science, so my understanding of most things is a fuzzy!

I need some help understanding DNA?  I have read or been told that DNA is bundled (wound tightly) into Chromosomes. What I am trying to get my head around is when you read about DNA it is always described as this single long double helix structure containing the genetic coding for all humans. However, I also know that humans have 23 pairs of chromosomes. So my questions are as follows:

1. Does each Chromosome contain the exact same DNA (i.e a complete sequence) or just portions of the DNA and hence you can only have the full sequence if you look at all the chromosomes?

2. Does every cell in the body contain exactly the same DNA sequence arranged in to Chromosomes? If so, how does the cell "know" what it is supposed to do?

My second question might highlight my naivety on this, but I am interested in this aspect of science, but do struggle to understand it, so any guidance would be appreciated.

Cheers

Michael

Title: Is the DNA "code" one long complete chain or broken and packaged into chromsomes
Post by: Nizzle on 01/12/2009 09:00:58

1. The complete collection of our DNA in one single copy is called a "genome". Double helix DNA is in fact two copies of your genome (sense and antisense). The double helix DNA in humans is divided in 23 chromosomes (so each chromosome is a part of your entire DNA collection and are thus not the same), which are present twice in each cell. Every gene is therefore present twice, once from your mother, once from your father.

2.) Every  living cell in the body has exactly the same DNA sequence in the chromosomes (except red blood cells that don't have a nucleus). But every type of cell "knows" what to do and what not to do because it receives specific instructions from outside the cell, which sometimes results in an entire cascade of secondary instructions.

I've tried to explain in layman's terms. If you have any further questions please ask..

Title: Is the DNA "code" one long complete chain or broken and packaged into chromsomes
Post by: mphutchy on 03/12/2009 14:08:39

Many thanks Nizzle. You have explained it very clearly.