Nucleus

• Nucleus:

  • enclosed in a nuclear envelope with protein channels called nuclear pores. it also contains an important area called the nucleolus.
• The nucleolus is responsible for making ribosomes, which are used to make proteins.
• Nucleus is the biggest component of a cell. The cell’s control centre
• The nucleus stores most of the cell’s gene. Most not all given some are in chloroplast and mitochondria.
• Components of the nucleus:

  • Nuclear Envelope
  • Nuclear Pores
  • Nucleolus
• Nuclear Envelope:

  • surrounds the nucleus
  • has two membrane (inner and outer + perinuclear space in between)
• Inner membrane of the nuclear envelope is lined with lamina which is made out of intermediate filaments (strong). This contributes to the shape of the nucleus.
• Nuclear Pores:

  • protein channels called nucleoporins which helps movement of molecules across the membrane.
  • forms the nuclear pore complex (movement across two membrane + perinuclear space)
• Nuclear pores:

  • Nucleus- Cytoplasm: tRNA, mRNA and ribosomal subunits (made by nucleolus) is transported OUT of the nucleus.
• Nuclear pores:

  • Cytoplasm-Nucleus: control signal, macromolecule and energy move inside the nucleus which is then used in biological processes.
• Nucleolus:

  • responsible for production of ribosomal RNA and ribosomal subunits which are essential outside the nucleus to use in processes like translation (protein synthesis)
• Nucleolus:

  • contains DNA- must be tightly organised but ACCESSIBLE.
  • non-membrane bound region within the nucleus
• DNA Organisation:

  • a thread of DNA interacts with complexes of Histone proteins- gives DNA a more compact shape.
  • DNA wrapping around a histone forms a nuclesome
  • Multiple nucleosome coil together to form a chromatin (30 nm) which is then further packaged forming the chromosome.
• Within the nucleus, euchromatin and heterochromatin are present. However, they differ by how loosely packed or densely packed they are.
• Euchromatin:

  • loosely packed- More Accessible
  • Transcriptionally active
• Heterochromatin:

  • Densely packed
  • silent/ transcriptionally inactive
• Amount of Euchromatin and heterochromatin DOES NOT remain constant throughout the lifetime of a cell.