Cell Biology Exam III

Cell Biology Exam III - Cell Biology Exam II Review CHAPTER...

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Cell Biology Exam II Review CHAPTER 15 - Eukaryotic Cells Contain a Basic Set of Membrane-Enclosed Organelles – The nucleus is surrounded by a double membrane called the nuclear envelope. It communicates with the cytosol through the nuclear pores. Nuclear membrane is continuous with the endoplasmic reticulum. The ER is the site of most new membrane synthesis. Rough ER makes protein Smooth ER makes steroids and is involved in Detox Golgi Apparatus – Receives ER products, modifies them and then ships them off. Receives membrane from ER. - Membrane Bound Organelles Evolved in Different Ways – Eukaryotic Cells could not have evolved without internal membranes Golgi, ER, Lysosomes all have nuclear membranes. They all evolved from the invagination of the plasma membrane, thus they are all components of the endomembrane system. o Golgi, Er, Lysosome Endomembrane system - Protein Sorting - With mitochondria, chloroplasts, nucleus, peroxisomes and ER, proteins are delivered from the cytosol. With Golgi, lysosomes and endosomes, proteins are delivered from the ER. GEL-ER Chloroplasts and Mitochondria have post-translational translocation of unfolded proteins. Translocation requires ATP chaperone proteins to fold the protein correctly and make it active, after it has entered the choloroplast or Mitochondria. What is actually imported is only a protein precursor. The ER has Co-translational translocation of proteins. Peroxisomes have a really short import sequence with a carboxylic acid end! It is ser-lys-leu-COO- !! - Proteins Are Imported Into Organelles By Three Mechanisms – Proteins moving from cytosol to nucleus do so through gated nuclear pores. Proteins moving from Cytosol (meaning manufactured from free floating ribosomes) ER, Peroxisomes, Chloroplasts, or Mitochondria, do so through Protein Translocators. These require that the protein actually unfold! Everything moving from ER to any other part of the endomembrane system (GEL) do so through vesicle transport. - Signal Sequences Direct Proteins To The Correct Compartment –
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These signal sequences are located on the protein and usually removed after import. They are essential to protein transport. Ex. Removing the signal sequence from an ER protein turns it into a cytosolic protein. It is typically 15-16 amino acids long. Proteins destined for the thylakoid actually have two signal peptidases (one on top of the other) because it has to cross two different bilayers. - Proteins enter the nucleus through Nuclear Pores – Nuclear envelope encloses DNA and is made of 2 layers. One of them has binding sites for chromosomes The other is the nuclear lamina! This provides structural support for the envelope.
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This note was uploaded on 05/04/2008 for the course BIOL 3510 taught by Professor Chapman during the Spring '08 term at North Texas.

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Cell Biology Exam III - Cell Biology Exam II Review CHAPTER...

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