Lecture 14 - Peroxisomes, Mitochondria, Chloroplasts & Nucleus Flashcards
_____ _______ _______ allows polypeptide to enter organelles after they’ve been synthesized
post-translational import
where are proteins destined for peroxisome, mitcohondrion, chloroplast or nuclear interior synthesized?
on free ribosomes and released into the cytosol
in the rough ER, proteins that are imported by organelles need what?
- a sorting signal (amino acid sequence)
- a receptor (recognizes the sorting signal, and transports the protein to the membrane)
- a membrane transporter (facilitates passaged into the organelle, through the bilayer
def: spherical organelles, defining characteristic is the presence of catalase, H2O2 metabolism
perioxisome
what are the essential roles of peroxisomes?
- H2O2 metabolism
- detoxification of harmful compounds
- oxidation of fatty acids
- metabolism of nitrogen-containing compounds
- catabolism of unusual substances
def: enzymes that degrade H2O2 into water and oxygen
catalases
def: enzymes that oxidize organic substances and produce H2O2 in the process
oxidases
membrane lipids are either synthesized by ________ ______ or transported there by ______ _____ ______
peroxisomal enzymes, lipid transfer proteins
where are most peroxisomal proteins are synthesized and then translated?
on free cytosolic ribosomes, the post-translationally imported via a C-terminal peroxisomal target signal (PTS-1)
def: in mitochondria, contains porins, which allow free movement of small molecules and ions across the outer membrane
outer membrane
def: in mitochondria, acts as a permeability barrier to most solutes
inner membrane
def: within the inner membrane; contains most of the enzymes associated with mitochondria function, in addition to DNA and ribosomes
matrix
def: area between the outer and inner membranes
inter membrane space
def: localized regions where protons can accumulate during the electron transport process
intracistal space
where are most mitochondrial and polypeptides synthesized
on cytoplasmic ribosome
what kind of molecules can pass through the porins in the outer membrane of mitochondria?
ATP, ADP
CoA, NAD
ions
what is the DNA composition of mitochondrial proteins?
99% nuclear genes
1% mitochondrial genome
where are most of the mitochondrial proteins found?
mitochondrial matrix or inner mitochondrial membrane
what state are the proteins that enter the mitochondria
unfolded state and contain a pre sequence or “internal targeting sequence”
where does translocation occur simultaneously in the mitochondria?
where the inner and outer membrane are close together
what are TOMs
Translocase of the Outer Mitochondrial Membrane
what are TIMs
Translocase of the Inner Mitochondrial Membrane
how are cytosolic proteins kept in an unfolded state?
bound by molecular chaperones
__________ encoded by an N-terminal alpha-helix binds the receptor component of ____ on the outer mitochondria membrane, and is positioned into the TOM channel on the outer mitochondrial membrane
“presequences”, TOM
what happens during transport of proteins destined for the matrix?
TOM and TIM23 channels are brought together
what powers the movement into the matrix for mitochondrial matrix proteins?
electrical potential
what are the 2 hypothesis for how mitochondrial proteins are pulled into the matrix?
- chaperones, using ATP hydrolysis
- random diffusion allowing the peptide to poke the N-terminus through the channel
what happens once the protein is brough into the mitochondrial matrix?
pre sequence is cleaved by peptidase and the protein folds into its native conformation
what happens during transport of proteins destined for the inner membrane of the mitochondria?
TOM and TIM22 channels are brought together
what signals the TIM22 channel to allow the protein to pass into the lipid bilayer
the internal targeting sequence
chloroplasts are the site of __________
photosynthesis
chloroplasts are surrounded by which membranes?
inner and outer
def: system of flattened membranous sacs founding chloroplasts
thylakoids
def: stacks of thylakoids
grana
the _______ contains a larger circular genome in chloroplasts
stroma
all chloroplast proteins have a _____ ________ _________ which is removed by a peptidase upon transport
stroma targeting domain
a ____________ __________ __________ is needed for entry into the thylakoid though some thylakoid membranes proteins are _______ __________ __________
thylakoid transfer domain, co-translationally inserted
where are enzymes and proteins needed in the nucleus imported from?
the cytoplasm
where are messenger RNA and ribosome components needed in the cytoplasm exported from?
the nucleus
what are the 2 membranes of the nuclear envelope?
- the inner membrane defines the nucleus
- the outer membrane is contiguous with the ER
def: fuse the two membranes of the nucleus and serve as a conduit for transport between the cytoplasm and nucleoplasm
nuclear pores
what travels through nuclear pores from the cytosol to the nucleus?
- histones
- DNA and RNA polymerase
- transcription factors
- RNA processing proteins
- ribosomal proteins
what travels through nuclear pores from the nucleus to the cytosol?
- tRNA
- mRNA
- RNP complexes
nuclear pores are composed of ~30 different proteins called _________
nucleoporins
def: the central granule in a nuclear pore, likely involved in moving molecules across the nuclear envelope
transporter
do NPC allow passive transport of particles?
yes, if they are smaller than 10 nm in diameter, they can pass through aqueous diffusion channels that particles can move freely within
def: enable proteins to be recognized and transported by nuclear pore complex
nuclear localization signals(NLS) and nuclear export signals(NES)
what is the composition of an NLS?
- 8-30 amino acids
- contains proline and positively-charged amino acids (arginine and lysine)
def: regulates nuclear import/export
Ran
def: mediate the tethering of transport vesicles to target membranes
Rab
def: crucial for assembling coat proteins during vesicle formation
ARF
def: linked to G-protein coupled receptors, can influence cell cycle, well-characterized oncogene
Ras
def: actin binding protein regulator
Rho
where does the energy needed to import proteins through nuclear pores come from?
hydrolysis of GTP by the GTPase Ran
where is Ran found?
in the nucleus and cytoplasm
what form is GTP found in the cytoplasm?
GDP-bound because the Ran-GAP is localized in the cytoplasm
why is GTP-bound form found in the nucleus?
presence of Ran-GEF
what does the importin do to the cytoplasmic protein when it binds to the NLS?
it mediates the movement of the protein towards a nuclear pore
once the importing-protein complex has docked with the NPC and transported into the nucleus, how does the protein get released?
the importin associates with a GTP-binding protein RAN, causing release
where does the GTP-Ran-importin complex go after release?
travels back to the cytoplasm through an NPC and is released as GTP is hydrolyzed
adaptor proteins also involved in RNA export have _______ _______ _______
nuclear export signal sequences
