Endomembrane System in Eukaryotic Cells

32 Questions

Which statement best describes the endomembrane system?

It is present only in eukaryotic cells and is made up of compartments like the endoplasmic reticulum and Golgi apparatus.

Which organelle is linked to the nuclear envelope?

Endoplasmic reticulum

What is the chemical composition of the endoplasmic reticulum?

It may be isolated from the 3rd pellet of the UCD in the form of rough or smooth microsomes.

What distinguishes the smooth endoplasmic reticulum (SER) from the rough endoplasmic reticulum (RER)?

Presence of ribosomes on the membrane

What is the ultrastucture of ER membrane as seen in TEM?

Trilamellar and thinner than plasma membrane

What is used to separate rough from smooth microsomes?

Centrifugation in a sucrose density gradient

What type of fatty acids are present in the phospholipid bilayer of the smooth microsome membrane?

High percentage of unsaturated fatty acids

What is the main purpose of centrifugation of the smooth microsomes in a sucrose concentration gradient?

To separate microsomes based on their density and origin

What is the approximate protein content in the membrane of the smooth microsomes?

70%

Where are carbohydrates found in relation to proteins and lipids in the smooth microsome membrane?

Towards the luminal surface

What is the specific content of the cavity in the smooth endoplasmic reticulum (SER) dependent on?

Cell type

Where does protein synthesis for luminal proteins in the rough endoplasmic reticulum (RER) begin?

Cytosol

What is the function of the signal sequence in protein synthesis for luminal proteins in the RER?

Enables the protein to be addressed for translocation

What is the role of Signal Recognition Particle (SRP) in protein synthesis for luminal proteins in the RER?

Binds to the signal sequence and causes a temporary halt in translation

What happens after the protein enters the lumen of the RER during protein synthesis for luminal proteins?

'The protein is taken up by chaperone proteins involved in translocation and post-translational modifications'

What types of proteins can be synthesized in the rough endoplasmic reticulum (RER)?

Soluble or luminal proteins and hydrophobic proteins

What represents 50 to 60% of the cell volume and is the fundamental substance of the cell in which organelles are immersed?

Hyaloplasm

What comprises a network of protein filaments and a complex aqueous solution within the cell?

Hyaloplasm

What is the pH range of hyaloplasm in plant cells?

pH 5.5 to 6

In which cell part can hyaloplasm be found in the form of a gel or fluid?

Hyaloplasm itself

Which part of the cell is specifically criss-crossed by fibrous or tubular structures contributing to its architecture and dynamics?

Cytoskeleton

Which organelle is linked to the nuclear envelope and plays a role in the architecture and dynamics of the cell?

Cytoskeleton

What is the main component of microtubules?

Globular protein of 50 kDa

What is the diameter of the microtubules?

25 nm

What stabilizes the structure of microtubules?

Microtubule-associated proteins (MAPs)

What are the permanent cellular elements made up of stable microtubules?

Centrioles and cilia/flagella

What are centrioles composed of?

9 parallel triplets of short microtubules

What are the characteristics of cilia and flagella?

Fine digitiform structures carried by the cell surface

What types of microtubules are preserved regardless of the fixative and fixation temperature?

Stable microtubules

What proteins are associated with the transport of vesicles along microtubules?

Kinesin and dynein

What is the specific structure that makes up centrioles?