Cell and molec membrane enclosed organelles

cells

signal recognition particle

What does SRP stand for?

ER signal sequence, ribosome

SRP binds to exposed __________ and __________.

SRP

causes the slowing of protein synthesis (translation) done by the ribosome

protein translocator

SRP-ribosome complex then binds to a SRP receptor in the ER membrane, and the SRP is released and the ribosome passes from the SRP receptor to a_______________ in the ER membrane. Protein synthesis then resumes and the translocator starts to transfer the growing polypeptide across the lipid bilayer

What happens when SRP dissociates from the ER signal sequence and the ribosome?

SRP binding

initiates targeting of ribosomes synthesizing inner-membrane proteins to the translocation pore of the membrane

the SRP arrests protein synthesis to prevent protein synthesis being finished before targeting is complete and is responsible for targeting signal peptide-bearing proteins to be transported to the ER for secretion or to be used in the plasma membrane

Why is the SRP so important?

ER

makes up more than half of the membrane of an average cell

ER

consists of tubules and flattened sacs that extend throughout the cytosol (inside the membrane)

interconnecting the ER

Tubules are responsible for _______________

single internal space

The ER lumen is a __________

ER lumen

an extensive network of membrane tubules, vesicles and flattened cisternae (sac-like structures)

Making lipids for the mitochondria, peroxisomes, and membranes.

What are the main roles of the ER?

ER

What makes transmembrane proteins and sequesters Ca++ from the cytosol?

co-translational translocation

proteins are imported prior to the polypeptide chain being completed

ER

ribosomes that synthesize proteins are attached directly to the _________

ribosomes

What coats the surface of the ER?

post-translational translocation

import proteins to other organelles or ER after synthesis of polypeptide chain is complete

glycosylation, phosphorylation, and proteolysis

What are examples of post-translational modifications?

smooth ER

transport vesicles to the Golgi, contain hepatocytes, and holds the enzymes that are required to make cholesterol

to make lipids, steroid hormones, and detoxify harmful metabolic byproducts. It also acts as a storage facility for Ca++ within the cell.

What are the functions of the smooth ER?

cytosol

Calcium is released into the ________ and the calcium pump then takes it up

ER lumen

Calcium pump transports Ca++ from the cytosol into the _____________.

because the ER serves as a reservoir for fast and specific calcium release

Why does the ER need calcium?

Ca++

Some parts of the ER are designated for ________ only.

sarcoplasmic reticulum

muscle cells that are type of modified ER for Ca++ storage

myofibril contraction and relaxation

the release and uptake of Ca++ is triggered by ______________.

to produce muscle contractions and relaxation

What is the function of myofibril?

transmembrane proteins and water soluble proteins

what are the two types of proteins that go to the ER?

transmembrane proteins are embedded in the lipid bilayer and water soluble proteins are located in the ER lumen

What is the difference between transmembrane proteins and water soluble proteins?

both have ER signal sequence and both can stay in the ER or be transported

What do transmembrane proteins and water soluble proteins have in common?

SRP

goes back and forth between the ER and the cytosol and binds to the signal sequence in the ER

SRP receptor

in the ER membrane and it is able to recognize SRP

SRP

___________ binds to the ER signal sequence and the ribosome.

ribosome

SRP causes a pause in translation, so that the ___________ can bind before the polypeptide chain is completed and released into the cytosol.

SRP-ribosome

bound by ER signal sequence and binds to the SRP receptor protein translocator

translocator

SRP/ SRP receptor released from the ribosome, but the ribosome remains bound to the ___________ and the translocator will then insert the polypeptide chain into the membrane

Translocon or translocator

acts as a channel through the hydrophobic membrane of the ER after the SRP has dissociated and translation is continued.

translocon or translocator

The emerging polypeptide is threaded through the channel as an unfolded string of amino acids by the _________.

in the ER

Where is the translocon or translocator located in the cell?

ER membrane bound ribosomes and free ribosomes

What are the two populations of ribosomes?

they differ in the proteins that they make

How are the two populations of ribosomes different?

Membrane-bound ribosomes or ER bound organelles

are attached to the cytosolic side of the ER membrane and are engaged in the synthesis of proteins that are being concurrently translocated into the ER

Free ribosomes

are unattached to any membrane and synthesize all other proteins encoded by the nuclear genome

ER lumen

Proteins fold and assemble in the _______________, some of them stay in the ER whereas others leave the ER.

they contain an ER retention signal with 4 amino acids at the C-terminus

What are ER resident proteins?

they make sure proteins function properly to help other proteins fold and assemble correctly

What is the main function of ER resident proteins?

protein disulfide isomerase

What is one example of an ER resident protein?

What does protein disulfide isomerase do?

it catalyzes disulfide bonds

ER translocator

polypeptide chain can pass through this aqueous channel with a translocon or translocator bound to it

sec61 complex

a 4 subunit complex that makes up the translocator and generates gated channel

because if it wasn't a gated channel, all of the Ca++ would leak out

Why is it important that the sec61 complex is a gated channel?

a translocator and accessory components

What does a translocon consist of?

polypeptides (it travels from the ribosome to the ER to complete protein synthesis)

What can perform co-translational or posttranslational delivery?

post-translational translocation

_____________ feeds in the polypeptide into the ER.

accessory proteins

What does a translocator require to feed the polypeptide chain into the ER?

ATP hydrolysis (where you break down ATP into ADP)

Therefore, what has to happen for this feeding of the polypeptide chain into the ER to occur?

ER

During each round of hydrolysis, the translocator pushes a portion of the polypeptide chain into the _________.

BIP

accessory protein required to function with the translocator

BIP

plays a major role in chaperoning newly synthesized proteins, and is responsible for maintaining the permeability barrier of the ER during protein translocation, targeting misfolded proteins for retrograde translocation so they can be degraded by the proteasome, contributing to ER calcium stores, and sensing stress in the ER to activate the unfolded protein response (UPR).

ATP dependent

__________ cycles of BIP binding releases and drives unidirectional translocation

peroxisomes

a single membrane organelle that does not contain DNA or ribosomes

in the nucleus

What are all of the proteins encoded for the peroxisome?

peroxisomes

contains oxidative enzymes that remove hydrogen atoms from organic substrates, therefore making them less acidic and harmful

hydrogen peroxide

the oxidation reaction that takes place in the peroxisomes produces ______________.

catalyze

uses H2O2 generated by this reaction to oxidize other substrates

Peroxisomes

oxidize substrates to detoxify harmful molecules that enter the bloodstream

liver and kidney cells

Where can peroxisomes be found in your body?

peroxisomes

can convert excess H2O2 into H2O

to breakdown fatty acids

What is the major function of peroxisomes?

2 carbons

Peroxisomes shortens alkyl fatty acids ________ at a time?

Actetyl CoA

Fatty acids are converted into what?

plasmalogens

Peroxisomes catalyze the first set of reactions that generate _______________.

plays a crucial role as endogenous antioxidants that protecting other phospholipids, lipids and lipoprotein particles from oxidative stress

What is the main function of a plasmalogen?

myelin

Plasmalogens are the most abundant class of phospholipids in ____________.

neuological disorders like Lorenzo's Oil

What do peroxisome disorders often lead to?

Where do proteins enter the peroxisomes from?

cytosol and the ER

peroxins

assist in the formation of peroxisomes by producing the membrane that separates the peroxisome from the rest of the cell and by importing enzymes into the peroxisome

peroxin

soluble receptor protein in peroxisomes that recognize amino acid signal sequence

What is the amino acid sequence that peroxins recognize?

Ser-Lys-Leu at the C-terminus

ATP hydrolysis

What do peroxins require to work?

peroxins

complex of 6 subunits that form a protein translocator in the peroxisome membrane

pore

peroxins form a ________, so that proteins have to unfold to enter the membrane.

delivered via ER-derived vesicles or translocated post-translationally straight from the cytosol

peroxisome proteins are either ....

outer membrane of the mitochondria

transport into the mitochondria that involves the membrane being in contact with the cytosol

inner membrane of the mitochondria

encloses the mitochondrial matrix space that forms extensive invaginations

cristae

What are these extensive invaginations called?

matrix

the inside compartment of the inner membrane

intermembrane space

the space between the outer and inner membrane and is continuous with the cristae space

DNA and ribosomes

the mitochondria has its own _______ and ________.

they need to unfold

Why do proteins need to do to enter the mitochondria?

TOM complex

transfers proteins across the outer membrane of the mitochondria

SAM complex

helps proteins fold properly

TIM complex

has two complexes (TIM23 and TIM 22) that act as receptors and components of channels

TIM 22

transport soluble proteins into the matrix space and insert them into the inner membrane

TIM 23

mediates the insertion of thesubclass of inner membrane proteins and assists them in transport of ADP, ATP, and phosphates in and out of the mitochondria.

OTA complex

mediates insertion of the inner membrane proteins that are synthesized within the mitochondria

No

Do prokaryotes have membrane-bound organelles?

What is the cell membrane system composed of?

nucleus, ER, Golgi and plasma membrane

DNA and ribosomes

Mitochondria and chloroplasts have their own ___________ and ______________.