ZIMA Lecture 4

Question 1

Which compartment takes up the most volume/ is the largest in the cell?

What compartment is present in the greatest number?

Answer 1

Cytosol is the largest compartment/ takes up the most volume in the cell

Mitochondria are present in the greatest number

Question 2

What is the fate of a protein with no sorting signal?

Answer 2

A protein with no sorting signal remains in the cytosol

Question 3

Which organelles receive proteins via gated transport?

Which organelles receive proteins via transmembrane transport?

Which organelles receive proteins via vesicular transport?

Answer 3

Gated transport: nucleus

Transmembrane transport: Mitochondria, ER, peroxisomes and plasmids

Vesicular transport: Golgi, Lysosome Endosomes, Cell Exterior

Question 4

Can you create an ER in a cell without an ER?

AKA can you create an organelle de novo?

Answer 4

NO, a new organelle cannot be made without an existing organelle. These organelles contain infor that is required for their construction.

Question 5

What is the difference between the inner and outer membrane of the nucleus?

What is synthesized in the nucleus and sent out to the cytosol

vs

What is synthesized in the cytosol and brought into the nucleus?

Answer 5

Inner nuclear membrane contains specific proteins that act as anchoring sites for chromatin and nuclear lamina.

Outer membrane is continous with the ER.

tRNAs and mRNAs are made in the nucleus and sent out to cytosol

Histones, gene regulators, DNA and RNA Poly are made in cytosol and brought into nucleus

Question 6

What structure is reponsible for the traffic of proteins and RNA between the nucleus and the cytosol?

What kind of molecules can get through?

Answer 6

The NUCLEAR PORE COMPLEX

Small molecules can freely diffuse through NPC, large proteins can;t oass NPC by passive diffucion they have special mechainism

Question 7

Is transport of proteins in the nucleus pre translational, pretranscriptional, post transcriptional, post translational?

Answer 7

NUCLEUS: post translational

(fully folded proteins can be transported into the nucleus)

Question 8

What is responsible for the selectivity of the nuclear import proces?

What structures recognize those specific signals?

Answer 8

Nuclear localization signals are responsible for the selectivity of the nuclear import process

Nuclear Import or Export Receptors bind to those localization signals

Question 9

Where does the nucleus get the energy for transporting proteins in and out?

Answer 9

The energy for nuclear transport is obtained from GTP hydrolysis by Ran GTPase.

Question 10

Where are Ran GAP and Ran GEF located?

Answer 10

Ran GAP is located in cytosol, it hydrolyses GTP to GDP and causes Ran-GDP to enter nucleus

Ran GEF is located in the nucleus, phosphorlyates the GDP into GTP and then causes RAN GTP to leave the nucleus

Question 11

How does the Ran GTPase mechanism work

Answer 11

In the cytosol, RAN GDP binds to a nuclear import receptor. (remember ran gap converts gtp to gdp)

It then enters the nucleus, where Ran GTP binds to the nuclear imort receptor and the cargo protein is delievered to nucleus. (ran gef converts gdp to gtp)

It then leaves the nucleus and goes back into the cytosol.

Question 12

Where do most of the proteins used in the mitichondria come from?

Answer 12

Most of the proteins come from the cytosol even though mitochondria have their own machinery to make proteins.

Question 13

Can fully folded proteins enter the mitochondria?

Answer 13

No, mitochondrial proteins are first fully synthesized as precursor proteins in the cytosol ( a post translational mechanism). Then chaperon proteins bind to them as they enter the mitochondria. (not fully folded)

Question 14

Define the role of the following structures:

TOM

SAM

TIM23

TIM22

OXA

Answer 14

TOM: protein transport through the outer membrane into the intermembrane space

SAM: folding of porin channels in the outer membrane (beta barrels)

TIM23: protein transport into matrix space and insertion of proteins into inner membrane

TIM22: insertion of proteins responsible for ATP-ADP transport of inner membrane

OXA: insertion of proteins that are synthesized into the inner membrane

Question 15

Explain the mechanism of how proteins enter the mitochondria

Answer 15

Transport of Proteins into Mitochondria:

1. The signal sequence on precursor protein binds to receptor on TOM complex
2. Chaperone proteins Hsp70 are stripped off and then the protein chain is fed into translocation of TOM complex
3. Protein first binds to the TIM 23 complex and passes through it
4. Signal sequence removed by peptidases

Question 16

What energy source is used in nuclear protein transport?

What energy source is used in mitochondrial protein transport?

Answer 16

Nucleus: GTP

Mitochondria: ATP

Question 17

What two things fuel mitochondrial protein importation?

Answer 17

ATP hydrolysis both outside and in the matrix,

and the membrane potential (on inner memebrane) fuel mitochondrial protein import.

ATP gets hydrolyzed to pop off the chaperone proteins.

Question 18

How are porins (pore forming proteins on the outermembrane of the mitochondria) transported into the mitochondria?

Answer 18

Porins are first transported through the TOM complex into the intermembrane space.

The SAM complex then inserts the porin proteins into the outer membrane and then helps to fold it properly

Question 19

The ER is in charge of ____ & ____ synthesis and ___ storage

The ER membrane is continous with _____

Answer 19

The ER is in charge of protein and lipid synthesis and also calcium storage.

The ER membrane is continous with the outer nuclear membrane.

Question 20

Rough ER vs Smooth ER

Proteins begin import into the ER before complete synthesis of the polypeptide chain - a _________ mechanism.

Answer 20

Rough ER: coated by ribosomes (protein synthesis)

Smooth ER: Lipid synthesis and calcium storage

Protein begin to import into the ER before complete synthesis of the polypeptide chain- a co-translational mechanism.

Question 21

All proteins are directed to the ER membrane by a ________.

That ______ is cleaved off by a _____ in the ER membrane.

Answer 21

All proteins are directed to the ER membrane by an ER signal sequence.

The ER signal sequence is cleaved by a signal peptidase in the ER membrane.

Question 22

What is SRP? What does it do?

Answer 22

SRP: made up of polypeptides and RNA
SRP guides signal sequence of a protein into the ER

SRP stops the process of protein synthesis, which gives the ribosome time to bind to the ER membrane before completion of the polypeptide chain,

Question 23

Polypeptide chains are transferred across the ER membrane through a ______.

At rest that ____ is closed by a short helix

The growing polypeptide chain can remove that plug allowing a protein to transfer across the ER membrane

Answer 23

Polypeptide chains are transferred across the ER membrane through a translocator.

At rest, that translocator is closed by a short helix/”plug”

The growing polypeptide chain can remove the plug allowing a protein to go across

Question 24

What does a protein need to have to become a transmembrane protein in the ER?

Answer 24

A start-transfer sequence is necessary for a protein to become a transmembrane protein in the ER

Question 25

Where do proteins get glycosylated?

What is the functional role of protein glycosylation?

Answer 25

Proteins get glycosylated in the lumen of the ER

The functional role of protein glycosylation is PROPER PROTEIN FOLDING.

Question 26

Where are the proteins that have a lot of sugars located?

Answer 26

Majority of glycolipids are inside lumen of ER, Golgi, or outside of plasma membrane

Cytosolic proteins have VERY few sugars