Topic 8 Flashcards by Allyssa L

ribosomes are located in…

the cytosol; either free or on membrane bound organelles

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synthesis of ALL proteins start on…

free ribosomes; then can continue membrane bound

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two major branches of protein sorting

cytosolic and secretory

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targets of cytosolic pathways

nucleus, mitochondria, chloroplasts, peroxisome

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in cytosolic pathway, protein synthesis starts in ________ and finishes in _________.

cytosol, cytosol

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targets of secretory pathway

nuclear membrane proteins, ER proteins, golgi proteins, endoscopes, lysosomes, secretory vesicles, plasma membrane

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secretory pathway protein synthesis starts in ________ and finishes in ________.

cytosol, ER

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cytosolic pathways moved to final destination through recognition of…

specific targeting amino acid sequences (signal sequences) within the protein

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most cellular compartment have their own….

chaperones

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What replaces cytosolic chaperones?

mitochondrial chaperones

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endoplasmic reticulum with ribosomes

rough ER

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rough ER

involved in protein metabolism

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smooth ER

involved in lipid metabolism and not associated with ribosomes

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The ________ is the entry point for most proteins into the secretory pathway.

rough ER

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co-translational transport

when majority of proteins destined for secretory pathway are translocated into ER during synthesis on membrane-bound ribosomes

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how does co-translational transport occur?

signal hypothesis

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C terminus

carboxyl terminus; end of peptide

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N terminus

amino terminus; start of peptide

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signal recognition particles, SRPs

recognize and bind to signal sequences in the growing protein while it’s still being translated

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signal sequences

specific amino acid sequences

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SRPs are composed of..

small, cytoplasmic non-coding RNA and proteins

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SRP receptors

proteins on the membrane of the ER that bind the SRP

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translocon

a membrane channel through which polypeptide chains with a signal sequence are transported into the ER

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Why is the term “secretory pathway” misleading?

It’s not just for secretion of proteins, but carries out sorting of both free and membrane-bound proteins to some intracellular destinations

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Players in "Signal Hypothesis"

- signal sequence - SRP - signal recognition particle receptor - translocon - signal peptidase enzyme (cleave off signal sequence)

When ribosome sits over translocon channel...

protein is synthesized into the channel

After proteins are translocated to ER as unfolded polypeptide chains,....

they fold into their 3D conformations

passage into ER lumen and ER membranes involve....

chaperones (BiP is one in the ER)

Intergral membrane proteins must be inserted in the correct orientation in the ER because....

they cannot be flipped within the membrane

transmembrane sequence

stops the polypeptide from entering the lumen of ER and changes conformation of translocon channel so that it opens and releases polypeptide chain to ER membrane

Describe Smooth ER and membrane assembly

due to hydrophobicity... membrane lipids are synthesized with already existing cellular membranes of the smooth ER

flippases

enzymes that facilitate translocation of newly synthesized phospholipids to opposite side of bilayer

cis face of Golgi

closest to ER where proteins enter

trans face of the Golgi

from ER where proteins exit

Sorting off proteins starts in the Golgi... why?

ER proteins (BiP) first go to Golgi before they are sent back to the ER

mannose-6-phosphate

specialized form of oligosaccharide †ha† target proteins for lysosomes

_______ of vesicular transport is key to maintaining the functional organization of the cell

selectivity

2 steps to ensure correct proteins get to their correct final destination

- get correct protein into correct vesicle | - get vesicle to correct final destination

Most transport vesicles that carry secretory proteins from the ER to the Golgi and from the Golgi to other targets are coated with cytosolic coat proteins and are called..

coated vesicles

play a key role in ensuring the vesicles reach their correct targets within the cell following exit from Golgi

different kinds of protein coats

cathrin, COPI, COPII

lysosomes

membrane-enclosed organelles that contain enzymes capable of breaking down all types of polymers at acidic pH

cathrin-coated vesicle

sort through lysosomal proteins

most lysosomal enzymes are...

acid hydrolases

active at acidic pH that is maintain within lysosomes, but not at neutral pH in rest of cytoplasm

proton pumps

maintain acidity of lysosome

snare hypothesis of vesicle fusion

proposal for mechanism of fusion for transport and secretion

two stages of snare hypothesis

- transport vesicle must recognize the correct target | - vesicle and target must fuse for purpose of delivering the cargo

tethering factors

stimulate formation of SNARE complexes between vesicles and target membrane, beginning process of membrane fusion.

SNARE-SNARE paring

provides energy to drive membrane fusion

Rab protein

recognize and bind tethering factors on target; forming initial interactions between vesicle and target membrane

Nuclear pore complex consists of ...

a structure with eight-fold symmetry organized around a large central channel

nuclear pore complex is composed of ....... different nucleoporins

30-50

Depending on their size, small polar molecules, ions, and macromolecules can travel through the nuclear pore complex by...

passive and energy dependent

nuclear localization signals

specific amino acid sequences that are recognized by transport receptors and direct the transport of proteins from the cytoplasm through the nuclear pore complex into the nucleus.

nuclear transport receptors

proteins that recognize nuclear localization signals and mediate transport across the nuclear envelope

karyopherins

family of nuclear transport receptors

importins

karypherins that direct nuclear import

Ran

a GTP-binding protein that regulates movement of importing/cargo complex into nucleus

What drives importing movement across th pore?

unequal distribution of Ran/GTP

nuclear export signals (NES)

specific amino acid sequences that target proteins for export from nucleus

exportins

member of karyopherin family that interact with NES; similar mechnanism as importing

RNA transport across nuclear envelope as..

ribonucleoprotein complexes (RNPs)

rRNAs transport across nuclear envelope as..

ribosomal subunits

mRNAs transport across nuclear envelope as..

in association with two proteins known as mRNA exporter complex

tRNAs transport across nuclear envelope as..

associated with exporting-t

snRNAs transport across nuclear envelope as..

assembled into snRNPs and then back into nucleus as splice some complex