Richard Webb

• Nucleus is an organelle that protects, copies and transcribes DNA
• The structure of the nucleus consists of a double membrane nuclear envelope that separates the nucleoplasm from the cytosol
• The double membrane nuclear envelope facilitates the passage of macromolecules via the nuclear pore complex
• The nucleoplasm is an aqueous medium that contains proteins and DNA
• Nucleolus is a specialised sub-region where rRNA molecules assemble and synthesise ribosomes
• An amino Acid sequence that targets proteins to the nucleus allowing them to enter nucleoplasm via the nuclear pore complex is called... the nuclear localisation signal.
• The cytoskeletal nuclear lamina is a protein meshwork lining the inner surface of the nuclear envelope and forms part of the cytoskeletal network.
• The cytoskeletal nuclear lamina anchors chromatin.
• Ribosome formation involves the assembly of ribosomal precursor RNA with ribosomal proteins and snRNA
• Nucleolus granules are responsible for pre ribosome assembly and maturing of ribosomes
• Fibrillar centre is responsible for rRNA transcription and where genes for pre-rRNA 45s are expressed
• Heterochromatin is dense and exists when low number of genes or no genes are present
• Euchromatin is less dense and exists when many active genes are present
• Chromatins are DNA strands wrapped around a protein scaffold. They are tightly packed so DNA can fit inside the nucleus.
• DNA double helix makes a complete turn every 10 base pairings
• The diameter of DNA is 20 Angstrom
• There are four bases in DNA, Adenine, Cytosine, Guanine and Thymine
• The four bases are hydrophobic, the sugar backbone is hydrophilic
• Adenine and Thymine are bonded by 2 hydrogen bonds
• Cytosine and Guanine are bonded by 3 hydrogen bonds
• Chromosomes are composed of DNA molecule and a protein
• Chromosomes are located in the nucleus
• Chromatin reduces the length of the chromosomes
• Two ways of packaging DNA is via supercoiling and chromatins wrapping around histones and condensing its size
• Topoisomerases are required to unwire supercoiled DNA
• Helicases are required to unravel two strands of DNA
• Topoisomers are DNA structures that present differently. They are genetically identical yet topologically different.
• During meiosis, the dissolution of the nuclear envelope occurs, a homologous pair of chromosomes migrate to opposite cell poles and the nuclear envelope reforms twice around 2 sets of separated chromosomes.
• Diploid number is the number of chromosomes in a species
• Gametes number is the haploid number of chromosomes
• If DNA was unravelled and extended, it would be over 2 metres long.
• The cytosol contains 200 - 400 mg of protein
• Cytosol protein can be divided into Soluble Globular Protein and Filamentous Protein
• Soluble globular protein is responsible for replication, DNA repair and generation of metabolic energy.
• A detergent can remove the globular proteins from the structure, but has no effect on filamentous proteins
• The cytoskeleton is composed of long polymers of single monomeric proteins that allows cells to adopt non spherical shapes
• The three types of cytoskeletal proteins are actin proteins, intermediate proteins and microtubules.
• Filamentous proteins are arranged into bundles and 3D networks by cross linking proteins
• Bundles are held together by alpha actinin or fimbrin
• 3D networks are held together by filamin, spectrin or dystrophin