BIOL 3510: CHAPTER 15 INTRACELLULAR COMPARTMENTS & TRANSPORT

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

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