Exam 3: Ch 13 Targeting of Proteins to Mitochondria, Chloroplasts, Peroxisome Flashcards
structure of mitochondria and chloroplasts
2 phospholipid bilayers
outer membrane, inner mebrane, intermembrane space, internal matrix (lumen)
structure of peroxisome
single membrane and single luminal matrix
proteins encoded by mitochondrial or chloroplast DNA are…
synthesized on ribosomes within the organelles and directed to the correct subcompartment immediately
the majority of proteins in mitochondria and chloroplasts are encoded by genes in the…
nucleus, and imported into the organelles after synthesis in cytosol by free ribosomes
do proteins targeted to the mitochondria, chloroplast, and peroxisome have a signal sequence?
yes, part of the mature protein
cleaved in mitochondria and chloroplast
not cleaved in peroxisome
in mitochondria and chloroplasts, protein import requires ____ and occurs where
energy
occurs at points where the outer and inner membranes are close together
may need 2 targeting sequences and 2 translocon systems
import to matrix requires
a matrix-targeting sequence
goes to outer mitochondrial memb. import receptor –> import pore (outer memb)
simultaneous transport occurs through TIM through the inner membrane into the matrix
are chaperonins found in the matrix?
yes, help final folding of matrix proteins
studies with ______ proteins show important features of mitochondrial import
chimeric
a precursor must be unfolded to enter import pores
_ energy inputs are needed to import proteins into mitochondria
3
ATP hydrolysis by chaperone proteins
molecular motor of chaperone + TIM
proton-motive force (H+ electrochemical gradient)
targeting of proteins to areas other than the matrix of the mitochondria require..
more than 1 signal sequence
targeting to inner membrane
3 pathways
1: same as targeting to matrix + stop-transfer sequence
2: insertion into inner membrane
3: incorporates multiple segments into inner membrane
targeting to intermembrane space
2 pathways
1: matrix targeting sequence + sequence that blocks translocation of protein across inner membrane
2: direct transport to intermembrane space without a matrix targeting sequence
targeting to outer-membrane
beta barrel structure
interact with general import pore
transfer to SAM
targeting of chloroplast _____ proteins is similar to import of mitochondrial matrix proteins
stromal
ex. enzymes of calvin cycle (rubisco)
stromal import sequence
similar to matrix import sequence
transport entirely ATP hydrolysis dependent
involves a receptor and import pore
thylakoid
series of interconnected membranous sacs
proteins in thylakoids carry out photosynthesis
many proteins in thylakoids are synthesized in the…
cytosol as precursors with multiple targeting sequences
stromal import sequence, thylakoid lumen sequence
_ pathways for transporting proteins from the stroma to the thylakoid have been identified
4
closely related to translocation across bacterial membrane
4 pathays of thylakoid transport
1: involves an SRP with a translocon
2: ATP hydrolysis
3: related to Oxa1 protein
4: metal-containing cofactors, H+ electrochemical gradient
as peroxisomes are enlarged by addition of protein and lipid, they eventually…
divide to form new ones
peroxisomes use what types of enzymes
ones that use molecular oxygen to oxidize substates
generates hydrogen peroxide
abundant in liver cells
what sequence targets proteins to the peroxisome (matrix)
SKL at the c terminus
peroxisomal targeting sequence 1 (PTS1)
peroxisomal protein import mechanism
protein with PTS1 binds to soluble carrier protein in cytosol
carried and binds to receptor in peroxisome matrix
protein imported
carrier protein recycled
is a different set of proteins required to embed proteins into the peroxisomal membrane?
yes
nuclear envelope
two membranes that separate the nucleus from the cytoplasm
continuous with ER membrane
nuclear pores
span both membranes of nuclear envelope
allow transport of proteins and other molecules into and out of the nucleus
made of nuclear pore complex made from nucleoporins
imported nuclear proteins have what sequence
nuclear localization sequence
do proteins enter the nucleus in a folded state?
yes
environment of the nuclear pore
aqueous pore
3 types of nuclearporins
structural: form scaffold
membrane: highly curved region
FG: line channel of NPC
what receptor is needed for nuclear transport
a nuclear transport receptor
two required cytosolic components for nuclear transport
Ran
nuclear transport receptor
Ran
small monomeric G protein (GTP/GDP)
nuclear transport receptor
binds the NLS on a cargo protein and to FG nucleoporins
in nucleoplasm, interacts with Ran-GTP which goes back to the cytoplasm
then Ran turns GTP –> GDP and releases the nuclear transport receptor back into cytoplasm
what is exported from the nucleus to cytoplasm
proteins
tRNA
ribosomal subunits
nuclear export requires what signal
a nuclear export signal (NES)
what receptor is needed for nuclear export
exportin 1
interacts with Ran-GTP and NES
most mRNAs are exported from the nucleus by a ___-independent mechanism
Ran-independnt
mRNA export from nucleus
mRNA associated with an hnRNP forming an mRNP
uses mRNP exporter that interacts with FG nucleoporins
uses ATP hydrolysis
driven by a concentration gradient
