intracellular compartments and protein transport

in our cells we have a lot of different _ happening at the same time

chemical reactions

at any one time a typical eukaryotic cell carriers out thousands of

different chemical reactions, many of which are mutually incompatible

at any one time a typical eukaryotic cell carriers out thousands of different chemical reactions, many of which are

mutually incompatible

For a cell to operate effectively, the different intracellular processes that occur simultaneously must somehow

be segregated

two strategies for isolating and organizing different chemical reactions include

-Both prokaryotic and eukaryotic cells aggregate different enzymes required to catalyze a particular sequence of reactions into large multicomponent complexes, such as synthesis of DNA, RNA, and proteins

-Most highly developed in eukaryotic cells, it is to confine different metabolic processes and the proteins required to perform them, within different membrane-enclosed compartments

intracellular compartments and transport slide

there needs a way in the cells to organize the pathways so they are not

“butting heads“

often enzymes are organized into

complexes

eukaryotes put different enzymes for different processes into

different organelles

the nucleus shares a double membrane with the

endoplasmic reticulum

what type of membrane does the nucleus have

a double membrane

intracellular compartments/organelles slide

intestinal cell organelles diagram slide

main function of nucleus :

surrounded by a double membrane(nuclear envelope) and communicates with the cytosol via nuclear pores

Two types of endoplasmic reticulum

smooth and rough

endoplasmic reticulum function

major side for synthesis of new membranes

rough ER -

ribosomes attached to its cytosolic surface

smooth ER -

lacking ribosomes

golgi apparatus -

receives proteins and lipids from the ER, modifies them, and then dispatches them to other destinations in the cells

lysosomes:

sacs of digestive enzymes degrade worn-out organelles, macromolecules, and particles taken into the cell by endocytosis

endosomes:

compartments containing endocytosed materials

peroxisomes

single membrane and contains enzymes used in variety of oxidative reactions

mitochondria

pyruvate oxidation, TCA cycle, oxidative phosphorylation

chloroplasts

photosynthesis

main function of membrane bound organelles slide

relative volumes of membrane enclosed organelles slide

people how exercise more typically have more of this organelle

mitochondria

endosymbiotic theory-

nuclear membranes and ER may have evolved through invagination of the plasma membrane

endosymbiotic theory slide

mitochondria and cell symbiotic relationship

mitochondria provide energy, cell provide food and protection

endosymbiotic theory slide 2

synthesis of all proteins begins in the (there are a few exceptions)

cytosol

proteins where their synthesis does not begin in the cytosol

a few mitochondrial and chloroplast proteins

sorting signal:

directs protein to the organelle in which is it is required

3 ways that membrane enclosed organelles can import proteins

1.transport through nuclear pores:from the cytosol into the nucleus

2.Transport across membranes: cytosol into ER, mitochondria or chloroplast for example

3.Transport by vesicles: loaded from the lumen of 1 compartment of the endomembrane system and discharge into the 2nd compartment

membrane enclosed organelles importing proteins slide

signal sequences slide

signal sequences direct proteins to the correct organelle slide

proteins destined for the ER possess a __ sequence that directs them to that organelle, those destined to remain in the cytososl lack the sequence

N-Terminal

the outer nuclear membrane is continuous with the

ER

double membrane of the nuclear envelope is penetrated by

nuclear pores

which direction does traffic occur in through nuclear pores

both

what passes through nuclear pores

newly made proteins, RNA molecules, Ribosomal subunits

nuclear membrane slide

the nuclear pore complex forms a

gate through which molecules enter or exit from the nucleus

nuclear pore complexes are filled with

water

the nuclear pore complex forms the binding site for

chromosomes and provide anchorage for the nuclear lamina

Many proteins that line the nuclear pore contain

extensive and unstructured regions, preventing the passage of large molecules

nuclear pore complex slide

proteins bound for the nucleus are actively transported through

nuclear pores

Nuclear Localization Signal

the signal sequence that directs a protein from the cytosol into the nucleus

Nuclear Transport Receptors

bind to the NLS on newly synthesized proteins destined for the nucleus

proteins bound for the nucleus slide

_ match up with the nuclear import receptor bound to the prospective nuclear protein and bring them towards the nuclear pore

cytosolic fibril

nuclear import receptor arrives in nucleus then

releases protein, then decycles back out to be used again

where does nuclear protein bind to nuclear import receptor

in the cytosol

when nuclear proteins bind to _ they can be transported through nuclear pore

nuclear import receptor

When the nuclear import receptor bound to the nuclear protein enters the cell what happens

Ran GTP binds changing the shape of the protein allowing it to pop-off

step 1 of proteins being brought into the nucleus

nuclear transport receptor picks up its cargo protein in the cytosol and enters the nucleus

step 2 of proteins being brought into the nucleus

in the nucleus, Ran-GTP bind to the nuclear transport receptor, causing it to release its cargo

step 3 of proteins being brought into the nucleus

the nuclear transport receptor-still carrying the Ran-GTP is transported back through the pore to the cytosol

step 4 of proteins being brought into the nucleus

in the cytosol an accessory protein triggers Ran to hydrolyze its bound GTP to GDP

Ran-GDP falls off the nuclear transport receptor, which is then free to bind another cargo protein destined for the nucleus

GTP hydrolysis slide

the energy supplied by _ drives nuclear transport

GTP hydrolysis

do membrane-enclosed organelles import proteins

yes

proteins are imported into mitochondria in _ form

unfolded

the same ribosomes are floating cytosol as are attached to

rough ER

the mitochondrial signal sequence of a precursor protein is recognized by

a receptor in the outer mitochondrial membrane

the complex of receptor and attached protein diffuses _ in the membrane to a contact site, where teh protein is translocated across both the outer and inner membranes by a —

laterally, protein translocator

the signal sequence is cleaved off by a _ inside the mitochondrion

signal peptidase

_ help to pull the protein across the membranes

chaperone proteins

proteins imported into mitochondria slide

the ER is the most extensive _ in eukaryotic cells

membrane network

ER slide

the common pool of _ is used to synthesize both the proteins that stay in the cytosol and the ER

ribsomes

membrane bound ribosomes

attached to the cytosolic side of the ER membrane

free ribosomes

unattached to any membrane

at the end of each round of protein synthesis what happens to the membrane bound ribosomes

they are released to rejoin the common pool in the cytosol

ribosomes slide

— and — direct a ribosome to the ER membrane

ER signal and a SRP

Signal-Recognition Particle (SRP) first step

binds to the exposed ER signal sequence and to the ribosome, thereby slowing protein synthesis by the ribosome

Signal-Recognition Particle (SRP) binds to the exposed ER signal sequence and to the ribosome, thereby slowing protein synthesis by the ribosome. the SRP-ribosome complex then

binds to an SRP receptor in the ER membrane

After the SRP-ribosome complex binds to an SRP receptor in the ER membrane what happens

SRP is released, passing the ribosome to a translocation channel in the ER membrane

When the ribosome is passed to teh translocation channel what happens

Translocation channel inserts the polypeptide chain into the membrane and starts to transfer it across the lipid bilayer

ER signal sequence slide

A translocation channel binds the —- and actively transfers the rest of the polypeptide ——

signal sequence,across the lipid bilayer as a loop

During the translocation process, the signal peptide is —

cleaved from the growing protein by a signal peptidase

During the translocation process, the signal peptide is cleaved from the growing protein by

a signal peptidase

The cleaved signal is —-

ejected into the bilayer, where it’s degraded, and the translocated polypeptide is released as soluble protein into the ER lumen

protein crossing the ER membrane slide

A single-pass transmembrane protein is

integrated into the ER membrane

An —- ER signal sequence initiates transfer of the protein

N-terminal

An N-terminal ER signal sequence initiates transfer of the protein
• When this sequence enters the translocation channel, the
channel

discharges the protein sideways into the lipid bilayer

An N-terminal ER signal sequence initiates transfer of the protein
• When this sequence enters the translocation channel, the
channel discharges the protein sideways into the lipid bilayer
• N-terminal signal sequence

is cleaved off, leaving the
transmembrane protein anchored in the membrane

single pass trans-membrane protein slide

A —- transmembrane protein uses an internal start- transfer sequence to integrate into the ER membrane

double-pass

Like the N-terminal ER signal sequence, the internal start-transfer signal

is recognized by an SRP that brings the ribosome to the ER membrane.

(double pass transmembrane protein) A ——- ER signal sequence acts as a start-transfer signal and initiates the transfer of the polypeptide chain

internal

(double pass transmembrane protein) When a stop transfer sequence enters the translocation channel—-

the channel discharges both sequences into the membrane