Nucleus

• nucleus = repository of genetic information & the cell’s control centre.

  it is also a membrane bound organelle in eukaryotic cells containing DNA
• • Anthony Van Leeuwenhoek was the first to observe the nucleus on the blood cells of birds & amphibians
  • Felice Fontana discovered the nucleus by observing epidermal cells of eels
  • Robert Brow observed the nucleus in plant cells & was the first to name it ‘nuclei’
• • Nucleus contains DNA arranged in chromosomes
  • nucleus is surrounded by nuclear envelope which separates the nucleus from cytoplasm
  • nuclear membrane is supported by meshwork of intermediate filaments (nuclear lamins)
  • outer membrane is continuous with rough endoplasmic reticulum
  • nuclear envelope contains pores which controls the movement of substances in and out of nucleus
• Nucleus separates fragile chromosomes from cell contents for the proper function of cell
• Nucleus is important for DNA replication, transcription & RNA processing
• separates RNA transcription in the nucleus from translocation machinery in cytoplasm
• nuclear envelope allows gene expression to be regulated.

  mRNA undergoes post-transcriptional processing before moving from nucleus to cytoplasm.

  control of gene expression at level of transcription (e.g expression of some eukaryotic genes controlled by regulated transport of transcriptional factors from cytoplasm to nucleus)
• Nucleolus is when one or more nucleoli are found inside the nucleus .

  they are most prominent in cells that are synthesising large amounts of proteins.

  The nucleolus is the sites at which ribosomes are assembles & ribosomal RNA is transcribed
• Nuclear envelope is a double-membrane structure which surrounds the nucleus; it’s outer membrane is continuous with the endoplasmic reticulum and the 2 membranes are perforated by nuclear pore complexes.
• nuclear lamina (lamins) are a fibrous network on the inner surface of the nuclear envelope comprised of lamin intermediates
• lamins are a group of intermediate filament proteins that form a fibrous network known as the nuclear laminate on the inner surface of nuclear envelope.
• nuclear pore complexes are large, multiprotein structures which are composed largely of nucleoporins. They extend across the nuclear envelope.

  ions and small molecules are able to freely difffuse via the nuclear pore complexes.

  large molecules such as proteins and ribonucleoproteins are selectively transported through with aid from soluble proteins
• chromatin is a complex of DNA & proteins that form chromosomes within the nucleus of eukaryotic cells
• perinuclear space is the gap between the inner and outer membrane
• nucleoporins is a large group of proteins that make up the nuclesr pore complexes.
• FG-nucleoporins are proteins on the inner surface of the nuclear pore complex with a globular domain that forms part of the pore structure & a random coil domain o hydrophilic amino acids punctuated by short repeats rich in phenylalanine & glycine.
• cytosol: the unstructured aqueous component of the cytoplasm of a cell, within which various organelles and particles are suspended.
• cytoskeleton is the network of fibrous elements consisting of primarily of microtubules, microfilaments and intermediate filaments found in cytoplasm. it provides organisation and support
• cytosolic protein are proteins in cytosol
• nuclear lamina is the localised nuclear side of the nuclear membrane which contains mesh works of interconnected protein subunits (nuclear lamins).

  nuclear lamina gives shape and stability to the nuclear envelope and is anchored by attachments to NPCs and integral membrane proteins.

  nuclear lamina interacts directly with chromatin