DNA in Chromosomes

one_raven

one_raven

God is a Chinese Whisper
Valued Senior Member
It is a little unclear to me how the DNA strand is organized in a human cell.

Are the chromosomes made of DNA broken up into 23 distinct sections that, if combined would make a single complete DNA strand?

Are the chromosomes actually broken, or is it just easier to visualize that way?
If they are broken, when cell division happens, does each chromosome pair divide and seperate?

Or, is each chromosome pair made from an entire strand of DNA?
If that's the case, does that mean we have 23 entire DNA strands in each (other than the sperm and egg) cell?

Please help me understand this more clearly.

Thank you
 
dagaz said:
Each chromosome is made up of one long strand of a DNA molecule. So Humans have 46 DNA molecules in their 46 chromosomes.
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Your link (http://blairgenealogy.com/dna/dna101.html) stated:
Chromosomes are paired threadlike "packages" of long segments of DNA contained within the nucleus of each cell. In humans there are 23 pairs of chromosomes. In 22 pairs, both members are essentially identical, one deriving from the individual's mother, the other from the father. The 23rd pair is different. In females this pair has two like chromosomes called "X". In males it comprises one "X" and one "Y," two very dissimilar chromosomes. It is these chromosome differences which determine sex.
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Thank you for your response, dagaz.
Let me re-phrase the question, because your answer did not address what I was looking for.
I think either you misunderstood me, or I misunderstood you.


OK, let's say there is a single complete strand of human DNA.
I read that it is about 6 feet long and has something like 3 billion base pairs.
There are 23 pairs of chromosomes in every cell (except reproductive cells).
What I am unclear on is whether each chromosome has a full six-foot strand of 3 billion base pairs, or if each chromosome has its own "section" of the full strand and if you add them all together you get a full strand (or, actually one maternal strand and one paternal strand).

I think each chromosome has it's own "section" of the full strand, but I can't find a definitive answer that says this.
If that is the case, are the chromosomes each their own individual piece as they are illustrated, or is that only done for illustration purposes and it is two long pieces in actuality?

If each chromosome has it's own seperate section of the DNA strand, is there any place in the body (or any of our cells) that has a complete unbroken strand, or does it simply not come that way? Is the six-foot long 3 billion rung "ladder" just a visualization tool, rather DNA is actually 46 seperate and distinct DNA molecules never actually being attached to each other?

I hope I was more clear (I think I may have actually muddled my questions up more :p).
 
Each chromosome is a section of the genome. If you unravelled each of the 23 chromosomes and lined them up end on end you would have a 3 billion base pair strand (only one copy of them). I don't think this is 6 feet long (Chromosome # 1, the largest weighing in at 260 million base pairs, is 8 cm long when stretched out). They are actually separated in the cell.

You will not find a 3 billion base pair strand anywhere in the human body.
 
Thank you.
That's what I was looking for.

Idle Mind said:
If you unravelled each of the 23 chromosomes and lined them up end on end you would have a 3 billion base pair strand (only one copy of them).
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23 chromosomes make up one 3 billion base pair strand, but there are 23 pairs so, each cell has the equivalent of 2 full strands, right?

Can we determine which parent each individual chromosome came from?

Where does mitochondrial come into play? Is that part of the 23 chromosomes? Is it part of the 3 billion pairs?
 
23 chromosomes make up one 3 billion base pair strand, but there are 23 pairs so, each cell has the equivalent of 2 full strands, right?
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That's correct.
Can we determine which parent each individual chromosome came from?
Click to expand...
We sure can. Quite easily at that.
Where does mitochondrial come into play? Is that part of the 23 chromosomes? Is it part of the 3 billion pairs?
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Mitochondrial DNA is not included as part of the chromosomal DNA, nor part of the roughly 3 billion base pairs. The chromosomal DNA refers to the DNA that is found within the nucleus. mtDNA is strictly maternal, and only has genes that code for proteins found in the mitchondria themselves as far as I'm aware.
 
Yes, thanks for the clarification Paul. I realize I wasn't as clear as I meant to be, so my apologies.
 
one_raven said:
It is a little unclear to me how the DNA strand is organized in a human cell.
Click to expand...

Have a look at <a href="http://www.dnaftb.org/dnaftb/">DNA from the Beginning</a>, particularly the section: <a href="http://www.dnaftb.org/dnaftb/29/concept/index.html">DNA is packaged in a chromosome</a>. :D
 
one_raven said:
OK, let's say there is a single complete strand of human DNA.
I read that it is about 6 feet long and has something like 3 billion base pairs.
There are 23 pairs of chromosomes in every cell (except reproductive cells).
What I am unclear on is whether each chromosome has a full six-foot strand of 3 billion base pairs, or if each chromosome has its own "section" of the full strand and if you add them all together you get a full strand (or, actually one maternal strand and one paternal strand).

I think each chromosome has it's own "section" of the full strand, but I can't find a definitive answer that says this.
If that is the case, are the chromosomes each their own individual piece as they are illustrated, or is that only done for illustration purposes and it is two long pieces in actuality?

If each chromosome has it's own seperate section of the DNA strand, is there any place in the body (or any of our cells) that has a complete unbroken strand, or does it simply not come that way? Is the six-foot long 3 billion rung "ladder" just a visualization tool, rather DNA is actually 46 seperate and distinct DNA molecules never actually being attached to each other?

I hope I was more clear (I think I may have actually muddled my questions up more :p).
Click to expand...

OK a basic misunderstanding that has crept into your thinking is that DNA can be separated. DNA is a molecule in the same way that water or methane is a molecule. The difference is that DNA is a long and complex molecule and not every DNA molecule is the same - they are all built from the same stuff but they are not all in the same order (i.e. the base pairs) - if that makes sense.

So in the nucleus of each cell you have 46 chromosomes each made up of a tightly wound DNA molecule. Those 46 chromosomes (or 46 DNA molecules) make up our genome - our complete genetic code.
 
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