1. DNA and the Genome
Key Area 1b
Organisation of DNA

2. Organisation of DNA in Prokaryotic & Eukaryotic Cells

3. Learning Intentions By the end of this topic you should be able to:
Identify prokaryotes and eukaryote cells from diagrams
Describe the key similarities and differences between prokaryote and eukaryote cells
Describe structure of a plasmid and can name the types of cells where they are found
Describe structure of circular chromosomes and identify the location and types of cells where they are found
Compare the DNA found in mitochondria and nucleus of eukaryote cells
Describe the DNA in linear chromosomes found in nucleus of eukaryote cells

4. You should already know:
DNA is the genetic material of living things
DNA structure.
Difference between a prokaryote and eukaryote.

5. Cell Size Remember 1m = 1000mm 1mm (10-3m) = 1000µm
1µm (10-6m)= 1000nm
1nm (10-9m) = 1000pm

6. There are two main classifications of cells
Prokaryotic – bacteria
Eukaryotic – fungi, green plants and animal cells

7. Prokaryotic Cell Structure (Bacteria)

8. Prokaryotic DNA
Prokaryotic DNA is different to eukaryotic DNA in that:
Prokaryotes have a SINGLE CIRCULAR CHROMOSOME but Eukaryotes have LINEAR CHROMOSOMES in the NUCLEUS
Prokaryotic DNA is not located in a nucleus but is instead found in a nucleoid region

9. Prokaryotic DNA
Prokaryotic DNA is associated with NO PROTEINS but Eukaryotic DNA is associated with PROTEINS called HISTONES.
Remember – bacterial cells also have extra genetic material in the form of small circular PLASMIDS
Yeast is a special example of a eukaryote as it also has plasmids

10. Eukaryotic Cells May be unicellular or multicellular
DNA is enclosed in a double nuclear membrane
They contain numerous membrane-bound organelles
They can be divided into fungi, animal or plant cells

11. Circular chromosomes in the mitochondria and chloroplasts
Eukaryotic Cells
These cells have DNA in their nucleus but also have…
Circular chromosomes in the mitochondria and chloroplasts

12. The packaging of DNA in eukaryotic chromosomes
4 cm
Too small to show the real size, but you could fit 10,000 along the length of a fingernail!
The length of DNA in one chromosome
into this...

13. DNA is thousands of times longer than the cell it is going into so it must be arranged in such a way that it fits into the nucleus.
To do this, the DNA is tightly coiled and packaged around a series of proteins called HISTONES
Every 8 of these histones further coil together to make NUCLEOSOMES

14. Nucleosomes
DNA double helix is wrapped around histone proteins forming nucleosomes (beads on a string)

15. The pieces of DNA between the nucleosomes is known as linker DNA and is a constant length. The combination of DNA and protein is called chromatin.

16. Thick chromatin fibre
The chain of nucleosomes then folds into a thicker chromatin fibre