These terms were not in the ciriculum when I went to school, except for cell and chromosomes, and I have great difficulty in understanding the relationship between several of these entities.** For example am I correct in assuming cells are made up of DNA double helix strands which in turn are comprised of chromosomes laid out along the DNA strand and these chromosomes are themselves comprised of genes laid out along the stretch of DNA?** I’m thinking that a gene is a short stretch of DNA, but wondering how one determines when a gene begins and ends. And is the genome just a map of one strand of DNA?
Every organism has a genome. The genome includes all the DNA of that organism. This DNA has segments (called genes) which act as the “templates” for producing the biomolecules necessary for life (ie proteins). DNA is made up of nucleic acids and the sequence of these nucleic acids determine where a gene begins and where it ends (more complicated than this but sufficient for your understanding). Because the DNA of larger organisms is so large, it is compacted into chromosomes so that it can all fit within a cell. So the sequence of structures from simplest to most complex is:
nucleic acids->DNA->chromosomes->genome
Beer, does that mean that there is more than one distinctly identifiable DNA strand in a chromosome, or a mass of identicle DNA strands?
Each chromosome is composed of only one DNA strand (or two ‘mirror-image’ strands locked together if you want to get picky) It’s very long, twisted and convoluted but when it is pulled straight it remains only one strand.
So each chromosome is a discrete length of DNA. Each length of DNA contains numerous functional segments called genes. Together all the DNA from all the chromosomes comprises the genome.
I often hear that cloning involves the process of DNA substitution and that each DNA contains the blueprint for the organism that possesses it. Would it be correct then to say that cloning actually involves the substitution of an entire genome which essentially is a book of blueprints?
Oy. That hurt.
OK, here goes. This from a microbiology/genetics student.
Ever cell of every organism has one or more chromosomes. Each chromosome consists of one double-stranded piece of DNA, which is made up of nucleotides - A,G,C,T.
A gene is a section of DNA that codes for a functional product, usually a protein. The DNA is transcribed into RNA - which consists of similar nucleotide, which is then translated into a protein, which is made of amino acids.
Markers are unique pieces of DNA used by geneticists as landmarks on the chromosome. For instance, the sequence AGGCTTTGAAACGATTAGC may occur only once in the entire genome (which is the word for all of the DNA in all of the chromosomes), so you can make a molecule which will bind that sequence, which allows you to tell how far away other things are. Basically.
As for cloning, you’re a little confused there. Clones are cells - or organisms - that have exactly the same genome. I’m growing some clones right now by isolating a single cell and allowing it to grow into thousands. Because they all came from one original cell, they’re all genetically identical and therefore clones.
Genetic engineering often involves inserting a piece of foreign DNA into a cell - bacterial, usually - so that it then expresses a protein not ususally found in that cell type. An example is inserting the human insulin gene into bacteria. This is sometimes called cloning a gene because you’re making more copies of that gene, and because once you insert the gene into one cell, you need to clone that one cell into many in order to get enough of the protein you’re interested in.
This has been thoroughly discussed a couple of months back, if you search for it. DNA is composed of ribonucleotides, ribose sugar, and phosphates. The ribonucleotides (bases) are A, T, G, and C (abbreviations for the names, adenine, etc.) which are hydrogen-bonded as rungs on the DNA helix, with the sugars and phosphates being the sides. Three bases code for an amino acid. That is called a gene for that amino acid. The whole complicated process was set forth in the prior post. (The actual production of amino acids occurs outside the nucleus by RNA. I’m not going to repeat what has already been said in the other post.)
Cloning is accomplished by inserting a somatic cell inside an egg. Every cell has the blueprint for every molecule in the body (the entire genome). Once a cell is specified to be a part of an arm, for example, only those DNA that code for the arm part are expressed. But all the instructions are still there. By inserting a cell before it has been differentiated into a specific type into a nucleus, a clone can be produced. This is similar to the research being done on stem cells, which have also not been differentiated.
I was writing my post while you posted yours, Smeghead. You’re the expert here and I wouldn’t have posted if I had seen yours. However, there are two types of cloning. Dolly and these other animals were cloned by inserting a somatic cell into an egg of an animal and reinserting the combo back into the female animal. Your description of cloning is for more elementary life: bacteria, etc.
Well I suppose you could say cloning (as the word has come to be used in the past 5 years or so) involves substitution of DNA.
More correctly the DNA from a donor cell is removed and replaced with the DNA from the animal you want to clone. Replacement is substitution I guess.
Yes DNA contains the blueprint for an organism. Since cloning involves replacing all the genetic material in a cell (please nobody mention mitochondria), then yes cloning involves substitutiong the entire genome.
Just a slight nitpick, ignore it if you like. Referring to ‘each DNA’ is probably technically incorrect. Used in this sense DNA is essentially a plural noun in that it’s referring to a whole string of little peices of DNA joined together in a chain to form one big DNA strand. Kind of like saying pants. Saying ‘each DNA contains a blueprint’ is a bit like saying ‘each pants contains a pair of hairy legs’. Not actually incorrect it just sounds kind of strange. ‘Each DNA strand/complement contains…’ (like ‘each pair of trousers’) or just ‘DNA contains’ is probably more correct.
English is so much fun when you start mixing it with scientific acronyms that have largely lost their original chemical meaning even to most scientists. Hee hee.
I’m surprised, Gaspode, that you did not correct my definition of “gene,” when I said that three bases code for an amino acid, and that constitutes a gene. Another inaccuracy on my part. The three bases form a codon, which codes for an amino acid. The entire sequences of bases, coding for an entire protein, is the gene. I had to correct myself before somebody else does.
barbitu8–just to nitpick (since you caught the codon thing), but you missed this: DNA is made up of deoxyribose nucleotides, not ribose (the sugar in RNA). 
Well, I know that. Deoxyribose is a form of ribose. And the RNA, which does the actual translation, is ribose.
Well, except it’s the ribosome that does the actual translation, not the RNA. The RNA is just the message.
Just messing with you, barbitu8.
Fair enough, my friend.
I hoped I was just pointing out a discrepancy. Deoxy vs ribose can make a big difference if you are doing molecular biology and maybe your probe ain’t working because it’s the wrong probe or it’s was made wrong. The sense thing to do-- takes on lingual conatations. Pun intended.
DNA v RNA. I don’t think we differ. This thread should just die as as a matter of fact.
Just to nitpick.
“Cloning” as a verb (or I guess a gerund in this case) used in molecular biology very rarely means the whole nuclear transfer business. Cloning usually refers to isolating a copy of a gene and getting it in an easily accessible form, for instance a bacteria plasmid or a phage.
So, for instance, I have found a new gene. I want to clone it. In fruit flies, the way I would do this is first cytologically map and then genetically isolate the gene. I would then look for genes expressed from a particular segment of DNA to which I have mapped my gene of interest. I would then probe a library of phages or bacteria containing chunks of the fly genome. At the end of this process, I would have my gene ready to copy. This is cloning in the molecular biology world.
This causes a lot of confusion. While the definition of cloning mentioned in the above paragraph doesn’t leak out into the popular press so often, you will hear that people have “cloned” the gene responsible for a human disease, or for extending the life of fruit flies. This only means that they have identified and isolated those genes (and doesn’t involved sheep named Dolly).
I’ll just second edwino–cloning in molecular biology rarely refers to the type of stuff invovled with ‘Dolly the Sheep’.
For lay people: Insulin production in bacteria is more like what is going on when a cloned gene is talked about.
Actually Smeghead, there’s a lot of evidence that the ribosomal RNA does the translation in the ribosome. (See Science, Aug 2000, IIRC, I think the second week)
It might be that the protein in the ribosome just provides the physical scaffold for the catalytic rRNA. But this is beyond the OP and, I admit, something I don’t fully understand.
Probably there’s a lot of funding out there there for ribozymes.
But yeah, you get the difference between mRNA and rRNA (which again is probably beyond the OP).
Yeah, I know. I just felt like berating barbitu8. Hey, that rhymed!
That didn’t rhyme. It had to be " I just felt like berating barbitu8ing" to rhyme.
Curses. You’re right. I originally wrote “berate barbitu8” then changed it. I guess we’re even.