All UK Exam Boards included

DNA and Chromosomes

This is a legacy topic. View the most up to date content by selecting the exam board in the dropdown to the left.

 

 

This is a legacy topic. View the most up to date content by clicking an exam board tab above or visiting the home page.

 

DNA and chromosomes may seem like completely separate things. Well, they’re not. In fact, all chromosomes are individual DNA molecules coiled and twisted around, because DNA is huge. At least in eukaryotes it is. That’s one of the first differences between eukaryotes and prokaryotes in their DNA – prokaryotes have less DNA.

 

Eukaryotic DNA is stored within the nucleus of each cell (apart from cells without one, e.g. red blood cells). Because of its sheer size, it must be organised well. Proteins called histones help do just that:

 

 

This is the second difference: eukaryotes have histones around which the DNA coils, while prokaryotes don’t. So what does prokaryotic DNA look like?

 

 

The DNA above is stored as a small loop (the bacterial chromosome), and as a plasmid. A plasmid is even smaller, and may be copied and transferred to another bacterium of the same or different species by a process called conjugation (or, more colloquially, bacteria sex).

 

Eukaryotic DNA is linear, rather than circular. That means the DNA, despite being coiled numerous times, has a distinguishable start point and end point, while prokaryotic DNA is a continuous circle (see above picture).

 

The Differences between Eukaryotic and Prokaryotic DNA

 

Size large small

Shape linear circular

Histones present absent

 

Sorry! There are no posts.

Sorry! There are no posts.

Your Reviews

I bookmarked the site 

translucent The Student Room

OFF TOPIC : I just want to say that your website is brilliant, thank you!!

Anonymous YouTube

I got A* in A-level biology (Cambridge), thanks! I love your videos

Sherif Negm Facebook

wow just checked out your website and think it’s pretty cool.

Eager bug The Student Room

OMG that’s great! Actually just helped me with my homework

mabelbarc The Student Room