Hi everyone,

 

Just started my A-level in biology and am confused about how DNA replicates

 

Unfortunately what I have been taught seems to go against the biology I previously learnt from GCSE- e.g. is DNA not found in the nucleus after all?

 

Any help would be appreciated

 

Cheers

Perhaps your confusion stems in part from major differences between eukaryotes vs prokaryotes.

Eukaryotes have complex chromosomal DNA structures contained in a nucleus.

Unlike eukaryotes, prokaryotes do not have a nucleus.

Prokayotes do have a nucleoid that has very little DNA in it. Most of their DNA is contained in plasmids....which are circular pieces of DNA that are found throughout the cytoplasm.

Yeast, which are eukaryotes, also have plasmids (in addition to a nucleus). I hope that helps to clear it up for you.

It is in the nucleus of the animal cells, yet it does travel around when it is being made.

 

Look up the work done by George Pavade. You can do the same experiment using radioactive phosphorus.

Prokayotes do have a nucleoid that has very little DNA in it. Most of their DNA is contained in plasmids....which are circular pieces of DNA that are found throughout the cytoplasm.

 

Uh, not quite correct. The majority of prokaryotic DNA is contained in the nucleoid area in which the chromosome is located. Usually only high copy plasmids may have a higher DNA yield than the chromosome, but they are not that common. Even then one has to keep in mind that in any case the majority of the genes is located on the chromosome whereas plasmids usually only have accessory functions. Some larger plasmids (megaplasmids) are found to be essential, but they are also usually present as single copy.

 

Also what about RNA? It is in the title but not in the OP?

hey

 

DNA is mostly found in the chromosomes. RNA (ribonucleic acid) is found throughout the cell.

 

Procaryotic cells contain no membrane-bound organelles. They therefore have no nucleus as such, and the nuclear material is one long DNA strand.

 

Eucaryotic contain membran-bound organelles and have nuclei which contain more than one chromosome.

 

i hope this helps

btw, what do u mean by 'A-level biology'?

Cheers everyone, this has helped a lot

 

Oh a by the way, A level stands for 'Advanced' level, the stage after the standard level for 16 year olds