Chapter 6 The Cell: Nucleus, Ribosomes 2005-2006

Nucleus Function contains eukaryotic cell’s genetic library Size most genes in nucleus some genes located in mitochondria & chloroplasts Size ~ 5 microns (µm) in diameter 2005-2006

Nucleus structure Structure separated from cytoplasm by a double membrane, nuclear envelope double membrane is fused in spots forming pores allows large macromolecules & particles to pass through What kind of molecules need to pass through? 2005-2006

Nucleus structure Within nucleus, DNA organized into fibrous material, chromatin in normal cell appears as diffuse mass When cell prepares to divide, chromatin fibers coil up as separate structures, chromosomes 2005-2006

Nucleus structure Densely stained region = nucleolus Function production of ribosomal subunits from rRNA & proteins pass through nuclear pores to cytoplasm & combine to form ribosomes 2005-2006

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Ribosomes Function Structure protein production ribosomes contain rRNA & protein composed of 2 subunits that combine to carry out protein synthesis The genes for rRNA have the greatest commonality among all living things. There is very little difference in the DNA sequence of the rRNA genes in a humans vs. a bacteria. Means that this function (building of a ribosome) is so integral to life that every cell does it almost exactly the same way. Change a base and this changes the structure of the RNA which causes it to not function. 2005-2006

Types of Ribosomes Free ribosomes Bound ribosomes suspended in cytosol synthesize proteins that function within cytosol Bound ribosomes attached to outside of endoplasmic reticulum synthesize proteins for export or for membranes 2005-2006

Ribosomes Prokaryotes & eukaryotes have different ribosomes different size subunits different proteins can this difference be useful? 2005-2006

Prokaryote vs. eukaryote ribosomes selective poisons can target the proteins of prokaryotic (bacterial) ribosomes = antibiotics 2005-2006

Any Questions??