Cell Compartments and Protein Targeting Day 10

Do prokaryotes have a nucleus?

no, they do not have a nucleoid region

do eurkaryotes have a nucleus?

yes, they have a nucleoid region

where is transcription located in prokaryotes?


where is transcription located in eukaryotes?


where is translation located in prokaryotes?


where is translation located in eukaryotes?


what is the size of prokaryotes?

small (1-2) micrometers

what is the size of eukaryotes?

larger (10-100 micrometers)

ratio of surface area to volume in prokaryotes?

high (compared to eukaryotic cells)

ratio of surface area to volume in eukaryotes?

low (compared to prokaryotic cells)

internal organization of prokaryotes

no organelles

Internal Organization of eukaryotes

contains organelles

total membrane in prokaryotes

much lower than eukaryotic cells

total membrane in eukaryotes

much higher than prokaryotic cells

eukaryotes membranes of organelles inside cells are either physically connected by membrane "bridges" or transiently connected by......

vesicles, which are small membrane-enclosed sacs that transport substances w/in a cell or interior to exterior of cell

interconnected membranes make up the...

endomembrane system

endomembrane system includes..

a system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, the plasma membrane, and the vesicles in between them.

How are proteins sorted?

Proteins have function all over the cell
-Signal sorting peptides
-Signal sequences specific for different organelles
-ER/Golgi apparatus (endomembrane system)

what are the three primary roles of Golgi apparatus?

it further modifies proteins & lipids produces by ER, it acts as a sorting station as these proteins & lipids more to their final destination, its site of synthesis of most of cells carbohydrates

What would happen if a sodium/potassium pump lost its ER signal peptide?

No longer targeted to ER, instead of translated in the cytosol

What would happen if a sodium/potassium pump lost its signal anchor sequence?

Lost its signal anchor sequence, it's going to be in the ER lumen with the same sorting process as a protein secreted of cell. Just trafficked to the plasma membrane and secreted to extracellular space.

What effect would this have on the cell's energy metabolism?

Mess up sodium concentration gradient so it would not take glucose into the cell

Explain why compartmentalization is advantageous for eukaryotic cells

More efficient for the cell.
Separation of the processes transcription and translation occurring in different locations, the benefit of the regulation(what if something goes wrong, gives the cell opportunity to fix mistakes)


provide a way for a vesicle to empty its contents to extracellular space or to deliver proteins embedded in vesicle membrane to plasma membrane


a vesicle bud off from plasma membrane, enclosing material from outside cell & bringing it into cell interior

The endomembrane system regulates...

protein traffic and performs metabolic functions in the cell

nucelar envelope

a double membrane perforated by pores that regulate the movement of materials between the nucleus and the cytoplasm

After mRNA exits the nucleus thru pores, mRNA bonds to....

free ribosomes in cytosol or ribosomes associated in endoplasmic reticulum (ER)

Ribosomes are...

sites of protein synthesis, in which amino acids are assembled into polypeptides guided by info stored in mRNA
THIS WAY nuclear envelope & its associated protein pores regulate which molecules move in & out of nucleus

Endoplasmic Reticulum (ER) is..

an organelle bounded by a single membrane

ER interior is called

its interior is continuous throughout and is called lumen

ER produces ad transports...

many proteins and lipids used inside and outside the cell, including all transmembrane proteins, as well as, proteins destined for Golgi apparatus, lysosomes, or export out of cell.

Rough ER is..

rough bc studded w/ ribosomes;
makes alterations to proteins

Smooth ER is...

smooth bc it lacks ribosomes;
helps move lipids within the cell , regulates calcium levels, breaks down toxic substances

Golgi Apparatus

stacked flat sacs, receives vesicle bound proteins from Rough ER and distributes them to other organelles or out of cell, receiving, processing, packaging, shipping.


membrane bound sacs that store, help w waste disposal, transport

Plasma Membrane

surrounding every cell must provide sufficient surface area for exchange of oxygen, nutrients, and wastes relative to the volume of the cell.

Explain how a protein travels through the endomembrane system

-Proteins are made on the ribosomes bound to the RER.
-The proteins enter the cis face of the golgi apparatus and packages the protein into vesicles.
-They exit through through the trans face and move through the cytoplasm.
-They then fuse with the plasma

An example of compartmentalization in eukaryotic cells:

the lysosome;
-The major processes occurring in the lysosome involve: Hydrolysis of macromolecules
-In order for this to occur, lysosomes need: Enzymes that catalyze hydrolysis reactions

Having the molecules to specific process a shared location increases the efficiency of the cell

-Molecules involved in DNA replication and transcription are located in nucleus
-Molecules involved in the majority of ATP production are located in mitochondria
-Molecules involved with photosynthesis are located in chloroplasts

Mitochondria and Chloroplasts:

Specialized compartments allow these organelles to harness energy for the cell

What protein determines where it will be sorted to in a cell?

Signal sequences- specific amino acids in the protein;
Absent in certain proteins

What could disrupt the sorting process?

- Loss/change of a signal sequence

What cellular functions are dependent on the sorting process?

Everything, if a protein is not its correct location the cell loses the function of the protein

Where does protein sorting begin?

Ribosomes associated with ER;
Free ribosomes
Both determined by signal sequence on proteins

Which proteins ribosomes in the cytosol?

No signal sequence
The signal sequence that is NOT an ER sequence

explain why pH is important for lysosomal function

Lysosomes function at certain pH levels and will not function if this pH changes

Which proteins are translated by ribosomes associated with the endoplasmic reticulum membrane?

Proteins with ER signal sequence
Binds to signal recognition particle (SRP)

As a free ribosome translates the protein in cytosol, this sequence is recognized by an RNA-protein complex know as....

a signal-recognition particle (SRP)

The SRP binds to ...

both the signal sequence and free ribosomes and brings about a pause in translation
then binds w/ receptor on RER so that the ribosome becomes associated w/ RER

Where are proteins sorted after entering the ER?

-Depends on the additional signal sequence
-Endomembrane system
-Secreted protein leaves the cell

What determines whether proteins are soluble or transmembrane?

-No signal anchor sequence(soluble)
-Protein with signal anchor sequence (transmembrane protein)

signal-anchor sequence are ...

N-terminal extensions of newly synthesized secretory and membrane proteins.

Where do proteins go after the ER?

They go to the Golgi apparatus

Where do proteins go after the Golgi if there is not additional signal sequences (other than ER sequence)?

Plasma membrane secreted out of the cell

Where do proteins go after the Golgi, If additional signal sequences?

Lysosome stay in Golgi go back to ER;
Enzymes that attach sugars to proteins (glycosylation)

What type of proteins would sort to the lysosomes?

Digestive enzymes(acid hydrolases), Proton pumps (hydrogen ions that keeps pH low), and Transporter proteins (macromolecules in Monomers out)


organelles that harness energy from chemical compounds such as sugars and converts it into ATP

Which organelle receives proteins from the endoplasmic reticulum, and sorts them to other organelles?

Golgi apparatus

Proteins with no signal peptide will end up in:

The cytosol

In prokaryotic cells, transcription and translation take place:

In the cytoplasm

Which of the following is a feature of eukaryotic cells, but NOT prokaryotic cells:

membrane enclosed organelles

In a typical animal cell, which organelle is involved in the synthesis of proteins?

Endoplasmic reticulum

Which of the following is not part of the endomembrane system?


If the glycosylation function of the Golgi were disrupted, which of the following could be observed?

Proteins on the cell surface would not have the correct sugars attached

Review your model of protein sorting. Glycosyltransferase enzymes are normally targeted to the lumen of the Golgi. If the ER signal sequence of this protein is mutated such that it can no longer bind to the SRP, predict where the protein would end up.

It would likely be targeted to the cytosol because proteins without an ER sequence are translated in the cytosol .

Review your model of protein sorting. What can happen to a protein that is translated and then incorporated into the endoplasmic reticulum membrane as a transmembrane protein?

It can be added to the plasma membrane of the cell

Review your model of protein sorting. Proteins such as insulin are secreted from the cell through exocytosis. On its way to the plasma membrane, insulin must travel through what organelle?

Endoplasmic reticulum

prokaryotic cell has RNA, ribosomes and plasma membrane BUT DOES NOT HAVE

does not have Mitochondria