DNA in chromosomes:
contains DNA in close
association with
histones
Histones: help
support and
protect DNA
DNA diffusely organised in
a form, chromatin
Heterochromatin:
Densely packed (dark
under EM)
Euchromatin: Less
densely packed
(lighter under EM)
Nucleoli
1-3 um
Under EM, appears darker
than chromatin and is a more
discrete structure
Contains DNA that codes
for ribosomal RNA (rRNA)
Makes ribosomes (organelles essential
in the process of protein synthesis
Once produced, these
are transported out
of the nucleolus,
through the nucleus
and into the
cytoplasm
Control centre of the
cell
DNA in chromosomes
codes for the synthesis
of proteins in the
cytoplasm
Islolating chromosomes (DNA)
from cytoplasm and its
reactions, DNA is protected from
damage
‘DNA code’ for protein
synthesis needs to be moved to
cytoplasm where protein
synthesis takes place and other
molecules need to enter
nucleus from cytoplasm (nuclear pores in nuclear envelope)
Nuclear envelope is a double membrane
Outer membrane encrusted with ribosomes (site of RER)
mRNA (carrying genetic code from DNA) passes through nuclear pores into cytoplasm