Final 2 Flashcards
Where do proteins without a sorting signal end up?
Stay in cytosol
Gated transport of the nucleus through what?
Nuclear pore complexes
3 types of intracellular transport
Gated, transmembrane, vesicular
2 types of sorting signals
Signal sequences, signal patches
How long are sorting signals?
15-60 continuous residues
How are signal sequences removed from a protein?
Signal pepidases
Proteins that make up a NPC
Nucleoporins
About how many NPCs does a mammalian cell contain?
3000-4000
True or false: nuclear proteins can be transported through a pore complex while folded
True
Binding sites for nuclear import receptors
F-G repeats
Provides energy for concentration of particular proteins on one side of the nuclear envelope
Ran
What kind of molecule is Ran
GTPase
Triggers hydrolysis of ATP, converting Ran-GTP to Ran-GDP in the cytosol
GAP (GTPase-activating protein)
Promotes the exchange of GDP for GTP, converting Ran-GDP to Ran-GTP
GEF (Guanine exchange factor)
Ran-____ is primarily in the cytosol; Ran-____ is primarily inside the nucleus
GDP, GTP
Where are mitochondrial signal sequences?
Amino-terminus
Completes mitchondrial import by repeated cycles of ATP hydrolysis
HSP70
Helps insert membrane proteins into outer membrane
TOM (translocase of outer membrane)
Spans both mitochondrial membranes and mediates translocation of proteins in to the matrix space
TIm23
Mediates the insertion of a subclass of inner membrane proteins
TIM22
Mediates the insertion of inner membrane proteins synthesized in the mitochondrial matrix
OXA complex
Keeps mitochondrial precursors in their unfolded confromation using ATP
HSP70
What acts as a stop-transfer sequences that prevents further translocation across IMM
Hydrophobic signal
True or false: all peroxisome proteins must be imported from the cytosol
True
House oxidative enzymes such as oxidases that produce peroxide
Peroxisomes
How are peroxisomes inolved in lipid metabolism?
Degrade fatty acids by beta oxidation
True or false: proteins imported into peroxisomes can be imported fully-folded
True
Proteins involved in the generation or maintenace of peroxisomes
Peroxins
helps insert and fold beta-barrels in the OMM
SAM
Protein that binds to emergent signal sequences, halts translation, and targets the complex to the ER
Signal recognition particle (SRP)
How are SRPs recognized on the ER membrane?
SRP receptor
Protein translocation channel of the ER
Sec61 complex
ER chaperone that binds and releases proteins to maintain directionality
BiP
Protease that removes signal sequences in the ER membrane
Signal peptidase
-COOH-terminus in the cytoplasm
Type I membrane protein
-NH3-terminus in the cytoplasm
Type II membrane protein
What protein charges typically remain in the cytosol?
Positive
An ER lumenal Hsp70 homolog that binds to unfolded proteins and prevents aggregation
BiP
Calcium-binding proteins that are lectins that bind to oligosaccharides on incompletely folded proteins and prevents aggregation
Calnexin, calreticulin
Enzyme that aids in folding by helping correct disulfide bond formation in newly synthesized proteins
Protein disulfide isomerase (PDI)
Covalent addition of sugars to proteins
Glycosylation
Attachment of sugar to the hydroxyl group of serine on threonine
O-linked glycosylation
Attachment of sugar ot the amide nitrogen of asparagine
N-linked glycoslyation
Enzyme that transfers an oligosaccharide to the Asn residue
Oligosaccharyl transferase (OST)
Lipid scaffold that helps transfer sugars to proteins
Dolichol
Why are sugars added to proteins in the ER
As a tag to mark the state of protein folding
ER resident enymze that removes glucose in order to allow a protein to continue folding
Glucosidase
Adds a single terminal glucose to a protein that is not properly folded
Glucosyl transferase
Cytoslic degradation machinery
Proteasome
ER resident protein sequence
HDEL or KDEL
Protein coat used for Golgi -> PM and endocytosis
Clathrin
Protein coast used for intragolgi and retrograde Golgi -> ER
COPI
Protein coat for ER -> Golgi
COPII
Coat subunit that has enzymatic activity for COPI
ARF
Coat subunit that has enzymatic acitivty for COPII
SAR1
Stimulate GTPase activity and make it go faster
GAP (GTPase activating protein)
Molecule that initiates the formation of vescile budding on the ER membrane
SAR1
When SAR1 is off, where is its helix?
Tucked away
When SAR1 is on, where is its helix?
Exposed and inserted into phopholipid bilayer
How does SAR1 initiate budding?
Nucleates the binding of coat proteins
Two dimeric subunits of COPII coat
Sec23/Sec24
Interacts with integral membrane proteins that aids in the selection of membrane integral cargo receptors
Sec24
Forms a cage structure to deform the membrane and form a vesicle
Sec13/Sec31
What happens when SAR1 cleaves its GTP to GDP?
Leaves coated vesicle, starting a cascade that uncoats the vesicle
2 addressing systems for vesicles
Tethering, docking
How many proteins are in the complex involved in the tethering process?
5-10
Protein that mediates the communication between a vesicle and a membrane
Rab proteins
What kind of protein are Rab proteins?
G-protein
What does a Rab protein do exactly?
Tells SNARE proteins that a vesicle has been “tethered” and now able to “dock”
Responsible for the merger of two phospholipid bilayers
SNARE proteins
2 proteins involved in recycling SNARE proteins
Adapter SNAP and chaperone NSF
Forward traffic
Anterograde
Backwards traffic
Retrograde
How is the localization of the golgi in perinuclear region maintained?
Microtubules
Some proteins getting packaged into ER vesicles just because they are in the right place at the right time
Bulk Flow
How are ER resident proteins stopped from being packaged into vesicles for transport?
Aggregate themselves into too large of complexes for vesicles
Aggregation of ER proteins
Kin Recognition
Fusion of uncoated vesicles in between ER and cis-Golgi
Vesicular tubular clusters (VTC)
True or false: VTCs are unique to ER to golgi transport
True
Fusion of vesicular membranes
Homotypic fusion
Fusion of vesicular membrane to a organelle membrane
Heterotypic fusion
How are KDEL sequences recognized for retrograde transport?
Golgi membrane bound receptor
Motif for membrane bound residents that end up in the wrong place
KKXX
What is KKXX recognized by?
COPI coat machinery
How do KDEL receptors know when to unbind to its cargo?
Golgi is more acidic than ER, so releases in the more neutral environment of the ER
4 functions of golgi
Glycosylation, production of proteoglycans, protein sorting, sulfation
Specifically, what kind of glycosylation occurs in the golgi?
Modification of existing N-linked sugar, O-linked glycoslyation
4 functions of protein glycosylation
Aid in protein folding, surface coating, specific interactions, ECM
How does surface coating of glycosylated proteins help the protein
Protection from extracellular enivornment
2 classes of N-linked sugars
High mannose, complex
Where are high mannose sugars added?
ER
Where are complex sugars trimmed?
Golgi
What modifies complex sugars?
Glycosyltransferases
Example of a sugar with a negative charge
Sialic acid
What residues does o-linked sugar modification take place on?
Serine or threonine hydryoxyl residues
Primary degradative organelle of the cell
Lysosomes
Besides degradation, what other role does lysosomes play
Osmolyte storage
Role of vacuoles in a plant
OSmotic stability or turgor pressure
Sorting signal of proteins of secretory pathway to lysosomes
Mannose-6-phosphate sorting signal
What kind of singal is the Mannose-6-phosphate signal?
Signal patch
What is the mannose-6-phosphate sorting signal recognized by?
N-acetylglucosamine (GlcNAc) phosphotransferase in the cis-Golgi
How does GlcNAc-P work?
Binds high mannose and a UDP-GlcNAc and catalyzes transfer of GlcNAc phosphate to terminal mannose residue
How are GlcNAc sugars removed?
Glycosidase
What is the mannose 6-P tag recognized by?
Mannose 6-phosphate receptor (M6PR) in TGN
How are lysosome proteins released into the lysosome?
pH sensitivity (lysosome very acidic)
