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Organisation of DNA 1.1B - Coggle Diagram
Organisation of DNA 1.1B
Prokaryotes (e.g. bacteria)
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.
Eukaryotic DNA (e.g. green plant cell)
Contain DNA in..
Nucleus
–
linear chromosomes
that are tightly coiled
and packaged with associated proteins.
Mitochondria– circular chromosomes f
ound in plant &
animal cells.
Yeast (
Single cell eukaryotic
)
Their genetic content is
contained within a nucleus
(although they may also possess circular plasmids in the cytoplasm).
Plant cell contains
Linear Chromosome,
Chloroplasts + Mitochondria contain circular
DNA packaging in Eukaryotes
Level 0: Double Helix
DNA forms a double stranded, double helix with antiparallel strands.
The chain links together, running from 5’ to 3’, These bonds are all strong covalent bonds forming the sugar-phosphate backbone
Bases have complementary pairing They link with hydrogen bonds, much weaker than covalent bonds.
Level 1: Nucleosomes
DNA double helix is wrapped around
histone
proteins
forming
nucleosomes
(a bit like beads on a string)
The combination of DNA and protein is called
chromatin
.
The pieces of DNA between the nucleosomes is
known as
linker DNA
and is a constant length.
This level of organisation is seen throughout the
cell cycle and mitosis.
One human chromosome –pulled out– is approximately 4 cm. The cell packages this into a bundle of 1.2 – 2 μm long. But you have 46 chromosomes – this is approximately 1.84 metres of DNA in every cell of your body.
Supercoiling
the process by which a
cell manages to fit in all of its DNA