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BIOL 3510: CHAPTER 15 INTRACELLULAR COMPARTMENTS & TRANSPORT
Main function of the Endoplasmic Reticulum
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Synthesis of most lipids and proteins for distribution to many organelles and to the plasma membrane
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Main function of Golgi Apparatus
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Modification, sorting, and packaging of proteins and lipids for either secretion or delivery to other organelles
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Main function of Endosomes
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Sorting of endocytosed material
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Main function of Lysosomes
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Intracellular degradation
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% Volume of Cytosol
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54%
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% Volume of Mitochondria
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22 %
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% Volume of Endoplasmic Reticulum
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12%
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% Volume of Nucleus
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6%
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% Volume of Golgi Apparatus
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3%
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Three General Types of Transport
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1. Nuclear pores
2. Across intracellular membranes or the plasma membrane
3.Vesicles to either Golgi or to the Plasma
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What do signal sequences do?
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Direct proteins to various intracellular compartments
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Major AA signal for Import into ER
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NH3-Met-Met-Met-Ser-Phe-Val-Ser-Leu-Leu-Leu-Val-Gly-Ile-Leu-Phe-Trp-Ala-Thr-Glu-Ala-Glu-Gln-Leu-Thr-Lys-Cys-Glu-Val-Phe-Gln
Leu
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Major AA signal for Retention in lumen of ER
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Lys-Asp-Glu-Leu-COO-
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Major AA signal for Mitochondria
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NH3-Met-Leu-Ser-Leu-Arg-Gln-Ser-Ile-Arg-Phe-Phe-Lys-Pro-Ala-Thr-Arg-Thr-Leu-Cys-Ser-Ser-Arg-Tyr-Leu-Leu
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Major AA signal for Nucleus
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Pro-pro-Lys-Lys-Lys-Arg-Lys-Val
Lys
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Proteins destined for the ER have a _________.
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Signal Sequence
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Mutant proteins
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Either don't have the sequence OR have the sequence where it normally doesn't exist
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Is the ER dependent on signal sequence and the type of protein?
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No, ONLY signal sequence.
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Nucleus's outer membrane is ______ with that of the ____.
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contiguous, ER
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This space is analogous to the ER lumen.
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Perinuclear space
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This is a web of proteins that provides support to the inner membrane of the nucleus
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Nuclear lamina
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Transport into the Nucleus
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-Proteins with a nuclear signal sequence binds to a nuclear transport receptor
-Accompanies protein through nuclear pore, then disengages inside nucleus
-Interactions b/w transport receptor and pore "pull' the protein into nucleus
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Is the nuclear transport receptor used again?
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yes, it's recycled and leaves the nucleus
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What does the Cytosolic fibril do?
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Catch proteins that are headed into the nucleus
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Energy transport for Nucleus protein
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GTP |
Process of GTP Energy for Nucleus Protein Transport
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-Receptor binds to cargo protein
-Transport of protein to nucleus
-Ran-GTP binds to transport receptor, cargo protein released
-Receptor and GTP gets transported out
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Transport into the mitochondrion:
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1. Contact between signal sequence and receptor protein - Outer membrane
2. Protein translocator diffuses in the membrane until it reaches contact site
3. Inside: Chaperones pull protein in, refold its, and cleaves off signal sequence
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Transport into ER lumen:
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mRNA or a polyribosome chain bind to ER by many nascent polypeptide chains and insert themselves into membrane.
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Transport into ER Lumen -detailed
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Signal recognition particle (SRP) binds to ER signal sequence on protein
Binds to SRP receptor on ER Membrane
Entire complex passes through the translocation channel
SRP dissociates and is recycled
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Translocation Channel:
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Channel that passes the growing polypeptide chain as a loop
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Signal Peptidase
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Cleaves off signal sequence on a growing polypeptide chain inside the ER
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How are Transmembrane Proteins made:
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a hydrophobic start-transfer sequence binds to the transmembrane channel
a hydrophobic stop-transfer sequence anchors protein in the membrane
Start sequence is at the end and stop is located mid-ventrally
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How are Transmembrane loops made?
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Same features as previous but start-transfer sequence is located midway and not at the end of protein
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Traffic in vesicles are between 3 things
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ER, the Golgi Apparatus, and the Plasma Membrane
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Golgi Apparatus transports vesicles to ________ or ________.
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plasma membrane or lysosome
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What is a lysosome?
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a bag of hydrolytic enzymes that break down stuff
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These pits are on the outer membrane are endocytosed
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Clathrin coated pits
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Detailed mechanism of Clathrin coated pits
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Receptors bind to their ligands > bind to adaptins > bind to clathrin > pinched off by dynamins > INSIDE CELL, uncoating occurs > only ligand-receptor complex remains
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Clathrin + Adaptin 1
Origin:
Destination:
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Origin: Golgi Apparatus
Destination: Lysosomes (Via Endosomes)
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Clathrin + Adaptin 2
Origin:
Destination:
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Origin: Plasma Membrane
Destination: Endosomes
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COP Proteins
Origin:
Destination:
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Origin: ER, Golgi cisterna, Golgi apparatus
Destination: GC, GA, ER
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Delivery of an uncoated vesicle
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Tethering > Docking > Fusion
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Uncoated vesicles are routed to a target membrane by ________
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Rab (family of proteins ) called tethering
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What does Rab do for a uncoated vesicle?
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Rab engages tethering proteins on the target membrane
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What do SNARE proteins do?
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After tethering, vesicle is docked by snare proteins (v-snare and t-snare), which are embedded in the vesicle and target membranes
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What follows after tethering and docking of an uncoated vesicle?
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Membrane fusion and ligand delivery follows
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Where are the v-snares and t-snares located?
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v-snare located on vesicle membrane and fuses with t-snare on membrane and assists in fusion
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What are N-linked oligosaccharides?
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In ER Lumen, a Dolichol (common glycolipid), donates it's oligosaccaride at Asn through a transferase.
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Modification of this common oligosaccardie chain yields proteins with ______ ______ ______ attached.
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specific sugar motifs
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What folds and does a final export of mature proteins out of the ER?
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Chaperone proteins
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Chaperone action inside the ER
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Misfolded proteins inside ER build up into the lumen
Inside, apoptotic programmed cell death can occur.
Mechanism is called "Unfolded Protein Response" (UPR) controls this.
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Does the ER allow immature or misfolded proteins to pass into the cytosol?
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NO
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What is passed in Cystic fibrosis?
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antibodies, chloride channel
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The Golgi Apparatus is arranged in a ______ fashion.
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polar
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Name the compartments of the Golgi starting with the Cis side.
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Cis-Golgi network > cis cisterna > medial cisterna > trans Golgi network
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Define the cis-Golgi.
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Adjacent to the ER, vesicle moves through stacks of cisterna towards trans Golgi or routed back to ER
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Define trans-Golgi.
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Oriented towards the Plasma membrane
vesicles -----> lysosomes
OR to plasma membrane
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