Unit 1: 1.1 Structure of DNA Organisation of DNA Higher Biology Unit 1: 1.1 Structure of DNA Organisation of DNA

Learning intention Investigate how DNA is organised in various organisms.

Success criteria State what is meant by the term Eukaryotes and Prokaryotes Describe the structure of the DNA in each Explain what is meant by DNA packing and why it is important.

Do all types of cells have nucleus?

Classification Organisms can be divided into 2 groups. Those who have nucleus and those who don’t. Prokaryotes are organisms which are lacking Nucleus Eukaryotes are organisms which contain a Nucleus.

Prokaryotes An example of this which you learnt about in national 5 was Bacteria.

Prokaryotes DNA Prokaryotes usually have a single circular double stranded chromosome. Some prokaryotes have a second chromosome which can carry extra non-essential genes – this is called a plasmid. The DNA is tightly packaged with proteins to form a nucleoid.

Eukaryotes Eukaryotes are organisms with a nucleus containing several linear chromosomes. This is the DNA that you will be familiar with. Eukaryotes also have extra DNA out with the nucleus – mitochondrial and chloroplast DNA.

Mitochondrial DNA This is found in the mitochondria of the cell In both plants and animals This DNA is circular and double stranded This is responsible for coding for tRNA, ribosomal RNA and some proteins in the mitochondria

Chloroplasts DNA This is present in plant cells You may see this also called plastid DNA Like mitochondrial DNA it is circular in shape. This codes for tRNA, rRNA and proteins involved in photosynthesis.

DNA storage Chromosomes are structures of tightly coiled DNA. Why do you think they are stored like this? Think of DNA like a ball of string. Would the string take up more space rolled out or stored in a ball? You have 46 chromosomes in each cell in your body, with each of those containing around 4cm of DNA. That means your body contains enough DNA to stretch it out to the moon and back and still have a little left over!

How to store the lengths of DNA DNA therefore is tightly folded and organised to be packed into the nucleus of cells. To do this, proteins are involved in order to pack the DNA tighter.

Success criteria State what is meant by the term Eukaryotes and Prokaryotes Describe the structure of the DNA in each Explain what is meant by DNA packing and why it is important.