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Nucleus basics

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					           Nucleus basics
• 1. Structure of DNA: 405-408, fig. 10.10
• 2. Components of Chromosomes: origins,
  centromeres, genes, telomeres: pp 507-
  515
• 3. Folding of chromosomes: Beads on a
  string and histones involved, 30 nm
  solenoid loops, folded loops, mitotic
  chromosomes: pp 505-507, Fig. 12.14
  We won’t go into chromatin remodeling by
  covalent modification of histones or by
  remodeling complexes.
• 4. Chromatin, heterochromatin,
  euchromatin : 504
• 5. Replication: Replication is
  semiconservative, bidirectional, and
  semidiscontinuous; (550-560), Fig., 13.9-
  13
• 6. Eukaryotes have multiple origins of
  replication; replication occurs in replication
  units. pp 565-569, Fig. 13.19
Circular bacterial
replication-
semiconservative,
bidirectional
          (For the Exam….)
• We’ll end the material for Exam III after the
  nucleus, maybe a brief review of mitosis-
  some reproduction for the final exam.
• Lab quiz 2 will be during our independent
  lab period, TBA.
• Quiz on Friday!
• Transcription:
• Three main types of RNA’s: mRNA, rRNA,
  tRNA, plus other small RNA types (443)
• 3 types of RNA polymerases & their products,
  use of alpha-amanitin to distinguish between the
  types. (443; my notes)
• Promoters, transcription factors , enhancers,
  (442-456, 528), Figs 11.6, 18
• RNA processing: 5’ caps, Splicing, 3’ polyA
  tails, introns, and exons (454-464), Figs 11.21,
• Ribosomal RNA- multiple copies of rRNA genes,
  rRNA formation from a single transcript by
  nucleolytic processing. (11.12, 14 p. 447, 448)
• Translation:
• Large and small ribosomal subunits; Start
  (met) and stop codons; translation
  beginning at 5’ end; translation beginning
  at the amino end, concluding at the COOH
  end. (479-486)
          Chapter 12- Nucleus
• I. Structure and Function of the Nucleus
•
• A. Functions: 1) Production, in response to
  environmental/ internal signals,of RNA; “the control
  center of the cell”;
•
• 2) Ribosome assembly
•
• 3) Replication & maintenance of the genome; only
  molecule that is repaired is DNA.
•
•
• B. Structure: Complex, membrane-bound
  organelle; Approx. 10% of the
• size of the cell. Membrane prevents the
  coupling of transcription and translation.
  Components: (12.1)
 Transport to and from the nucleus
• In spite of the fact that it’s a characteristic of
  “advanced” cells, the nuclear membrane causes
  problems.
• Proteins are only made in the cytoplasm; RNA's
  are made in the nucleus but used in the
  cyptoplasm; Ribosomes are assembled inside,
  but used outside. LOTS of proteins are needed
  in the nucleus- histones, TFs, polymerases of all
  sorts, etc.
• Karp states that a typical cell, like a
  growing liver cell (he uses the example of
  a HeLa cell), has 10,000,000 ribosomes.
  Every sec it must import 560,000
  ribosomal proteins and export 14K
  ribosomes. Busy, Busy, Busy!
• Most of this coming and going is through
  the nuclear pore complex
Cytoplasmic face
Nuclear face
               Key parts
• Rings on the cytoplasmic and nuclear
  sides, with supporting spokes
• Central transporter- limits diameter to 9
  nm, diffusion to proteins < 60,000
• About 30 protein types
• GREAT BIG THING! 15-30X the mass of a
  ribosome!
• Cytoplasmic filaments
• Nuclear basket
     Getting things in and out
• Simple diffusion of some proteins.
• Others need signals to enter and leave.
• The players: Importins alpha and beta;
  protein with Nuclear Localization Signal
  (NLS); Ran-GTP; exportin.
Cool experiment! ONE AA
change, and it no longer goes to
the nucleus!!!
Note that this is a model-
”proposed steps”




                             It’s not really clear how RAN gets
                             back in; it may simply diffuse in.
                             Once in, it is reconverted to RAN-
                             GTP. And, of course, the exportin
                             needs to get back in as well!
A MAJOR
export is
mRNA! The
splicing
complex is
involved in
export! The
Exon Joining
Complex binds
to TAP, which
allows binding
to the NPC and
export. The
EJC and TAP
must then get
back in.
            Things to Know
• Nuclear functions
• Structure of the nucleus, of the nuclear
  pore complex.
• Why import/export is important
• Importin exportin, RAN-GTP/GDP story
• How splicing, of all things, gets involved in
  mRNA export.
                 The quiz
• Nucleus basics- structure of DNA,
  important terms- histones, nucleosomes,
  telomeres, splice, cap, tail, triplet codon,
  three polymerases, transcription,
  translation
• Structure of the nuclear pore. Examples of
  import and exported items

				
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