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Lecture 3

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Biological Sciences
Bebhinn Treanor

Lecture 3 NUCLEUS o Location of where DNA particle is wrapped around: core particle made up of 8 core histone proteins  ‘True’ Nucleus: Eukaryotes  Function of Nucleus: safe storage site of hereditary materials and is the site where heredityary  Components of core particle: 2 molecules of histone H2a, 2 molecules of histone material is replicated (later in S phase). Also the site where RNA synthesis occurs and where big H2b, 2 molecules of H3 and 2 molecules of histone H4 RNA protein structures are assembled  Shape of core particle: soccer ball o # of times DNA is wrapped around core particle of histone proteins: 2  Organelle which all eukaryotes have: nucleus  # of membranes in a proper nucleus: 2 close membranes that fit together o Each segment of DNA: clamped with histone H1  Double membrane bound: 2 phospholipid bilayers closely together o Result of histones and DNA: histones shorten and fatten DNA o Nucleosomes: bead-like structure of DNA + histones  Nuclear Envelope: pair of membranes together o Charge on histones that are rich in amino acids: positively charged  Membranes of nuclear envelope: outer and inner membrane  Inner membrane: inward facing-side which is associated with a protein meshwork called the o Result of positive charged histones on DNA: Help balance DNA’s net negative charge that are caused by DNA’s phosphate groups. Thus histones neutralize DNA nuclear lamina  Level 2 Packaging:  Nuclear lamina: protein meshwork (associated with inner membrane of every nucleus)  Components of Lamina: intermediate filaments o Organization of ‘beads’ of chromatin: spiralling collection of nucelosomes. o Spiral of nucelusomes: have a hollow centre  Purpose of intermediate filaments: gives strength to the nuclear envelope o Solenoid fiber: spiralling cluster of nucleosomes  Nuclear pore: carefully regulated set of opening that control the movement of large molecules  Diameter of solenoid fibre: 30 nm in and out of the nucleus  Level 3 Packaging:  Components of a single nuclear pore: 8 large protein granules arranged in an octagon o Organization of 30 nm solenoid fiber: organized into looped domains  Relation/Metaphors of Nucleus: secured area o Majority of the chromatin in the G 1ucleus: euchromatin o Nuclear Pores: Area of fence with gates  Gates have security guards which only allow certain molecules that have ID o Euchromatin: has the looped domains as the end-point packaging o Can be used as a template for RNA: Euchromatin, thus can be transcribed  Location of most hereditary material: nucleus o Heterochromatin: some regions of the chromosomes at G tha1 get even more packaged  Other locations with hereditary info: small amounts of DNA in mitochondria and chloroplasts knot a knot-like structure  Organisation of DNA: chromosomes o Can NOT be used as a template for RNA: Heterochromatin thus CANNOT be transcribed  Nucleolus (Nucleoli): factory where a lot of proteins re put together with RNA molecules to o Location of DNA in G 1 nucleus and never leaves the nucleus make riboprotein structures subunits of ribosomes) o Structure of Nucleoli: small dense spherical structure in the nucleus of a cell during TRANSLATION interphase  Requirements for the process of translation: ribosomal proteins that are combined with o Components of Nuceoli: several protein complexes ribosomal RNA to form je ribosomal subunits that are required for the process of translation o Examples of complexes made in the Nucleoli: 2 major ribosomal units  Nucleoplasm: the chromosomes and the nucleioli float in a fluid  Location of Translation: Cytoplasm  Location where ribosomal units can function: cytoplasm  Components of the fluid of Nucleoplasm: suspension of carious particles, fibres, proteins and o Thus, once the ribosomal units are assembled, they move out of the nucleus through the other molecules nuclear pores CELLULAR ACTIVITY IN DNA DNA PACKAGING WITH PROTEINS  DNA does not DIRECTLY control cellular activity but instead acts INDIRECTLY through other  Components of each eukaryotic organism: long, linear double stranded DNA molecule  Packing of each linear DNA molecule of eukaryotes: chromosomal proteins (DNA is never molecules  Template to make RNA: DNA ‘naked’)  Encodes information to make proteins: RNA  Chromatin: association of DNA with its packaging proteins that condense to form chromosomes  Function of chromosomal proteins: serve to protect the DNA from damage, AND to organize it  What directly directs cellular activity? Protein  DNA (transcription) RNA (translation) Protein so it will fir into the nucleus  Location of RNA transcription and protein translation: 1 phase of cell  Length of DNA helix in humans: 2 metres  Diameter of DNA helix in humans: 0.006mm  Significance of proteins: extremely important and workhorses of cell.  Functions of proteins: Some act as enzymes which drive chemical reactions and some form important structural features of cell. Some serve as signals or signal receivers. DNA PACKAGING IN G CYCLE 1  All cells regulate: process of RNA (transcription). NOT all gene products are regulated at each  Level One Packaging: step 1 | P a g e  Important point of the regulation of gene expression: occurs at the point of controlling the  The decision whether or not a particular gene will be transcribed: determined by whether or initiating of transcription not the appropriate transcription factors are bound to that gene’s promoter, and can attract yje o Why? Translation is an energetically expensive process RNA polymerase to the gene  Most important step in regulating gene expression: initiation of transcription 9other steps are  Common feature of ALL promoter regions: for genes that encode protein is a small section of fine tuning)
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