The System of the Internal Membranes

Endocytosis

import mediated by the formation of endocytic vesicles

Exocytosis

export or secretion

plasma membrane

small vesicles

endoplasmic reticulum

Golgi apparatus

lysosomes

5 organelles involved in the continual exchange of materials with the environment

Peroxisomes

contain enzymes that break down lipids and destroy toxic molecules through oxidation reactions and is one of the digestive organelles of the cell

nuclear envelope

a double membrane

endoplasmic reticulum

what is the outer membrane continuous with?

perinuclear space

the cavity between the two membranes

nuclear pores

allows for both passive and active transport

lamin

proteins that cover the inner membrane

nuclear lamina

a network of lamin protein fibers that lines the inner wall of the nuclear envelope

structural support and attachment sites for the chromatin

what does the nuclear lamina provide for the nucleus

entire nucleus collapses

what happens when the nuclear lamina is destroyed?

cytoskeleton

what is the nuclear laminia a component of?

intermediate filament

what is the nuclear lamina categorized as?

protein complexes

what do nuclear pores contain that allow for transport through the nuclear envelope?

Passive diffusion

used for small molecules and small proteins since this requires no energy

Active transport

required for larger proteins and all RNAs and is energy-dependent

DNA polymerases

RNA polymerases

transcription factors

histones and other chromatin assembly proteins

lamins

5 proteins that are transported through the nuclear envelope

nuclear localization signal (NLS)

a seven amino acid stretch in the middle of the protein that is found on the proteins that can be transported through the nuclear envelope

T antigen

part of the simian vacuolating virus 40 that is an oncogenic protein that is capable of transforming cells by altering the activity of nuclear transcription factors

enter the nuclei of the cells infected by the virus and cause malignancy

the NLS on the T antigen allow it to...

pyruvate kinase

the cytoplasmic enzyme that catalyzes the last step of glycolysis

no

does pyruvate kinase have an NLS?

expression vector

a plasmid that is designed for gene expression in cells

strong viral promoter

what are genes in the plasmid of the virus under the control of?

high levels

where the henes in the plasmid are introduced into the cells, what levels are they expressed in?

construct a chimeric protein

introduce plasmid into cultured cells

observe pyruvate kinase localization in the cells using an anti-pyruvate kinase antibody

experimental approach to determine if a nuclear localization signal is enough to transport a cytoplasmic protein to the nucleus

chimeric protein

the pyruvate protein with the nuclear localization signal of the SV40 T-antigen by constructing it in an expression vector

energy-dependent

The process of transporting large proteins into the nucleus is...

the prospective nuclear protein with a nuclear localization signal

a nuclear transport receptor protein that recognizes and binds to the NLSs in the cargo protein

a transport complex forms what two things?

the nuclear transport receptor protein and cargo protein

what makes up the transport complex?

nuclear pore

where is the transport complex translocated through?

nuclear pore proteins

what proteins does the transport complex interact with to translocate the transport complex through the nuclear pore?

Ran-GTP

binds to the nuclear transport receptor protein, causing the dissociation and release of the cargo protein inside the nucleus

nuclear transport protein

what does Ran-GTP bind to and goes to the cytoplasm?

Ran GTPase activating protein

removes Pi from GTP on Ran

returns to the cycle

where does the nuclear transport receptor protein go to after dissociating from Ran-GDP

nucleus

where is Ran-GTP most abundant?

cytoplasm

since Ran-GTP is mainly in the nuclus, where does it tend to go?

hydrolyzed to GDP by Ran GTPase-activating protein

what happens to GTP when it enters the cytoplasm?

its diffusion drives the nuclear import cycle

what does the Ran-GTP gradient across the nuclear envelope cause?

GTP hydrolysis

what is required for the Ran-GTP gradient since it is energy dependent?

nucleus following its own concentration gradient

where does the Ran-GDP produced in the cytoplasm go back to?

GTP

what is the GDP on the Ran protein exchanged for?

Ran-GEF

what catalyzes the exchange of GDP for GTP?

NF-kB

a transcription factor that is dormant in the cytoplasm with IkB (inhibitor kB) bound to it

NLS of NF-kB

what does IkB mask?

prevents Importin to bind NF-kB

what does the masking of NLS on the NF-kB by the IkB cause?

IkB is phosphorylated and destroyed

what causes IkB to detach from NF-kB?

Importin

when IkB releases NF-kB, what binds to it?

transolcates it to the nucleus where it can activate transcription

when importin binds to NF-kB, what happens?

regulating immune response to infection

what key role does NF-kB play?

Pho4

a transcription factor that exist in the cytoplasm in an inactive phosphorylated state

phosphate group

what blocks the NLS of Pho4?

dephosphorylated

what must happen to Pho4 in order for importin to bind to it and take it to the nucleus?

regulation of cell division cycle

what is Pho4 involved in?

smooth endoplasmic reticulum

the site of lipid synthesis and processing

builds membranes and membrane systems for the cells

what is one of the main functions of the smooth ER?

rough endoplasmic reticulum

the site of protein synthesis and processing

site of protein folding

addition of cofactors, lipids and carbohydrate groups

what are two functions of the rough endoplasmic reticulum?

Translation

the synthesis of polypeptides by ribosomes in the cytoplasm

free ribosome

where does translation occur ifbthe synthesized protein is to stay in the cytoplasm or go into the nucleus, the chloroplast, the mitochondria, or the peroxisome?

ribosomes associated with the rough ER

where does translation occur if the synthesized protein is a membrane protein, lysosomal, or secreted?

lumen of the ER

where is the newly syntheised protein translocated if the synthesized protein is a membrane protein, lysosomal, or secreted?

ER signal sequence

what do all secreted proteins contain in their amino terminal?

ER signal sequence

a signal necessary for translocation into the ER and removed after translocation

signal recognition particle (SRP)

recignizes the ER signal sequence in the growing polypeptide

SRP recepetor

where does the SRP dock on the ER membrane?

translocation channel

where does the growing polypeptide move through?

signal peptidase

removes the translocation signal from the new polypeptide

secretion pathway

the pathway proteins synthesized on the rough ER take

ER for protein processing

ER-Golgi intermediate complex for retrieval of ER-resident proteins

Golgi apparatus for protein sorting

out of cell OR plasma membrane OR lysosome

what are the 4 steps of the secretion pathway?

The pulse-chase experiment

what is the experiment done to track the secretion pathway?

Incubate cultured pancreatic cells with radioactive amino acids for 3 minutes

Remove radioactive medium

Observe movement of radioactive proteins by periodic autoradiography

what are the 3 steps of the pulse-chase experiment?

step 1

which step of the pulse-chase experiment is the pulse?

step 3

which step in the pulse-chase experiment is the chase?

ER-Golgi intermediate complex

a system pf membrane stacks located between the ER and the Golgi

a check point that ensures that proteins that should stay in the ER do not reach the Golgi apparatus

what is the function of the ER-Golgi intermediate complex?

traffic from the ER to the Golgi is non-selective

what is the reason for the ER-Golgi intermediate complex?

retention signal (KDEL)

a signal on ER-resident proteins that allow for the ERGIC to recognize it and send back to the ER

Golgi

where do proteins lacking the KDEL continue through?

Golgi apparatus

the protein sorting center of the cell

cis face of Golgi network

where do protein-containing vesicles coming from the ER enter at the Golgi?

through medial and trans Golgi stacks

where do proteins move through once entering the Golgi network?

trans face of Golgi network

where are the proteins released from the Golgi network?

protein modification, sorting and packaging for wither secretion or delivery to other organelles

what are the functions of the Golgi apparatus?

Constitutive

Regulated

Lysosomal proteins

3 types of transport form the Golgi appartus

constitutive transport

operates in all cells via unregulated secretion and also includes the delivery of membrane proteins and lipids

Regulated transported

operates only in specialized cells

external signal

what makes the specialized cells in regulated transport release their secreted products?

endocrine cells secrete hormones

neurons secrete neurotransmitters

2 examples of regulated secretions

special large vesicles that wait in cell until the signal is received

where are the regulated secretion products sorted?

calcium

what is exocytosis dependent on?

Ca2+

what induces the fusion of secretory vesicles to the cell membrane for the release of products in regulated secretion?

simple endocrine cells

signals from where cause the opening of Ca2+ stores in the endoplasmic reticulum?

axon terminials of neurons

where is the extracellular Ca2+ inflow observed?

Golgi

where is the disulfide bond formed?

C segment

what is removed in the secretory vesicle?

lysomsomal protein transport

the transport of digetsive proteins to the lysosome

clathrin coated

what are all vesicles that target the lysosome coated with?