MCB Ch. 15 notes

MCB Ch. 15 notes - Ch 15 – Intracellular Compartments and...

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Unformatted text preview: Ch. 15 – Intracellular Compartments and Transport (October 31 st , November 2 nd , and November 5 th Lecture Notes) • Membrane-Enclosed Organelles o Eukaryotic cells contain a basic set of membrane-enclosed organelles occupy up to half the volume of the cell, expand the total surface area twenty fold (due to membrane invagination) interior of the endomembrane system is the same environment as outside the cell nuclear envelope, endoplasmic reticulumn, Golgi apparatus, mitochondia, chloroplasts, vescicles, endosomes, lysosomes o membrane-enclosed organelles evolved in different ways endosymbiotic theory of mitochondria and chloroplasts (cell engulfed smaller aerobic bacteria) plasma membrane invagination for nuclear envelope and ER • Protein Sorting o protein synthesis free ribosomes form peripheral membrane proteins, nuclear proteins, chloroplast/mitochondrial proteins, and cytosolic proteins ribosomes on the rough ER synthesize most integral membrane proteins, secreted proteins, and lipids o proteins are imported into organelles by three mechanisms determined by the amino acid sequence, can contain a sorting signal each mechanism requires the input of energy 1 st- transport through selective nuclear pores 2 nd- protein translocators allow protein to cross a membrane 3 rd – transport vescicles o signal sequences direct proteins to the correct compartment often a continuous stretch of amino acids (15-60 in length) o proteins enter the nucleus through nuclear pores the nuclear envelope is perforated by pores proteins can cross the membrane from either side nuclear pores are large, elaborate structures act as barriers to lateral diffusion of proteins nuclear localization signals consist of several linear basic amino acids; these sequences bind to importins, which ferry the protein across the nuclear membrane summary: How are nuclear proteins sorted from cytoplasmic proteins? Proteins enter the nucleus through nuclear pore complexes, which consist of over 50 proteins Proteins smaller than 60,000 daltons diffuse freely through nuclear pores. Pore expands to allow the passage of larger proteins and complexes. Nuclear transport proteins (importins) mediate transport of proteins with NLSs, using energy derived from GTP hydrolysis o Proteins unfold to enter mitochondria and chloroplasts signal sequence at N-terminus allows them to enter the organelle are translocated simultaneously across the inner and outer membranes • TOM and TIM complexes facilitate this • additional signals are needed to transport proteins into the membranes or the intermembrane space • requires a lot of energy (approx. 200 mV) TOM complex TIM proteins...
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This note was uploaded on 05/11/2008 for the course BI 304 taught by Professor Oconnorandburgess during the Spring '08 term at BC.

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MCB Ch. 15 notes - Ch 15 – Intracellular Compartments and...

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