The nucleus

Recap:

DNA is packaged into chromosomes. The DNA wraps around histone molecules which increases the efficiency of packaging.

The nuclear envelope is composed of two membranes, perforated by pores. The outer membrane is continuous with the ER, supported by lamina - causes many disease that we don’t yet understand

The nucleus contains additional organelles such as the nucleolus, the site of ribosome production.

The Nuclear Pores are a complex arrangement of proteins. The movement of substances into and out of the nucleus is regulated by the pore.

 the essential role of a eukaryotic nucleus

separate transcription from translation which allows both alternative splicing ie a variety of mRNAs and therefore proteins to be made from one pre-mRNA, as well as a time difference between transcription and translation, allowing proteins to be made on demand in response to env. conditions

 the significance of the nuclear pore complex

allows passage of molecules through the nuclear membrane

 aspects of the nuclear transport mechanism

either through simple diffusion for small molecules or active signal dependent transport like the nuclear import/localisation signal (NLS) that allows transport of large molecules through the pores and membrane. These signals are small proteins often made up of charged lysine and tag proteins for transport

 the role of nuclear envelope in nuclear organisation

the nuclear envelope in made up of the protein mesh lamina which allows the bilayer of the membrane, allowing for separate functions and protein compositions of the inner and outer nuclear membranes that make up the nuclear envelope

identity and function of sub-domains of the nucleus

none of them are membrane bound

  • nucleolus - ribosome production

  • speckles - pre mRNA processing

  • cajal bodies: splicing

  • PML bodies: storage depot

the distinction between hetero- and euchromatin

heterochromatin is tightly wrapped around histone proteins = dense = very low transcription activity, further away from the nucleolus so in the periphery within the nucleus

euchromatin is loosely wrapped around histone proteins = less dense = high transcription activity = expression of the gene = RNA synthesis, is found in the centre of nucleus, close to the nucleolus

Illness arising from nuclear structure defects

inherited territories for chromosomes can be modified = modification in expressed genes

mutation of lamina = loss of robust nucleus structure

Illnesses are inherited and can be for example Hutchinson–Gilford progeria syndrome which causes premature aging