Membrane Enclosed Organelles and Cellular Processes

A set of flashcards designed to help review key concepts regarding membrane-enclosed organelles, their functions, transport mechanisms, and cellular processes.

What are membrane-enclosed organelles?

Organelles surrounded by a lipid bilayer, containing unique molecules and carrying out specific functions.

Which structures are considered membrane-enclosed organelles?

Nucleus, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, peroxisomes, mitochondria, and chloroplasts.

What is the primary role of the endoplasmic reticulum (ER)?

Major site of membrane synthesis and protein processing.

What distinguishes rough ER from smooth ER?

Rough ER has ribosomes attached, which synthesize proteins, whereas smooth ER is involved in lipid synthesis and detoxification.

What key functions do lysosomes perform?

Digest worn-out organelles and macromolecules taken into the cell via endocytosis.

What are peroxisomes responsible for?

Contain enzymes that break down lipids and toxic molecules, producing hydrogen peroxide.

How do mitochondria and chloroplasts differ from other organelles?

They evolved from engulfed bacteria and contain their own DNA and ribosomes.

What is the mechanism by which proteins are sorted and delivered to organelles?

Proteins contain sorting signals, which direct them to their proper destinations.

What is the function of signal sequences in proteins?

They direct proteins to their correct organelle or location within the cell.

How do proteins move from the cytosol to the nucleus?

Through nuclear pores, which actively transport specific macromolecules.

What are transport vesicles and their role?

Small membrane-bound packages that transport proteins and lipids between organelles.

What is the difference between constitutive and regulated exocytosis?

Constitutive exocytosis occurs continuously in all cells, while regulated exocytosis occurs in specialized cells in response to specific signals.

Which organelles are involved in the endomembrane system?

Nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and endosomes.

How do integral membrane proteins enter the ER?

They are synthesized on ribosomes bound to the ER and directly translocate into the ER membrane.

What happens to signal sequences after a protein reaches its destination?

They are often removed by peptidases.

What role do chaperone proteins play in organelles?

Help proteins fold correctly and assist in the transport of proteins across membranes.

Why is the nuclear envelope significant?

It includes nuclear pores that regulate movement of substances in and out of the nucleus.

What occurs during vesicle docking?

Vesicles recognize and bind to specific target membranes to deliver their cargo.

What are Rab proteins?

Molecular markers on vesicles that help in the targeting and docking of transport vesicles.

What triggers the fusion of vesicles with their target membranes?

Interactions between SNARE proteins on vesicles and target membranes.

What is the function of the Golgi apparatus in protein processing?

It modifies, sorts, and packages proteins for delivery to their destinations.

What is the unfolded protein response?

A cellular response to misfolded proteins in the ER that enhances protein folding capacity.

How does receptor-mediated endocytosis differ from pinocytosis?

Receptor-mediated endocytosis is selective, capturing specific molecules, while pinocytosis is non-specific.

What is autophagy?

The process where cells degrade obsolete parts of themselves, such as damaged organelles.

What cellular function does the cytoskeleton support?

It provides structural support and pathways for the movement of organelles.

What is the main role of endosomes?

Sort and transport substances ingested by endocytosis to lysosomes for degradation.

How do cells maintain their membrane composition during endocytosis?

By balancing vesicle budding (exocytosis) and internalization (endocytosis) processes.

What is the significance of glycosylation in the ER?

It helps stabilize proteins and directs them to their destinations.

What occurs to proteins that do not fold correctly in the ER?

They are retained, degraded, or transported back to the cytosol for degradation.

What happens to lysosomal enzymes during their transport route?

They are tagged with mannose 6-phosphate for sorting into lysosomes.

What characterizes the trans Golgi network?

It is the sorting station where proteins are directed to final destinations.

How do specialized secretory cells utilize regulated exocytosis?

They store and secrete proteins in response to stimuli.

What happens to excess cholesterol in the cytosol?

It is used for membrane synthesis after being released from lysosomes.

What structure provides mechanical support to the nucleus?

Nuclear lamina.

How do cells uptake cholesterol from the bloodstream?

Through receptor-mediated endocytosis of LDL particles.

What is pinocytosis commonly referred to as?

Cellular drinking.

What are the two main pathways for proteins once they enter the endosome?

Return to the plasma membrane or degradation in lysosomes.

How does the cell respond to an overload of misfolded proteins?

By triggering the unfolded protein response to manage and reduce the protein load.

How do endocytic vesicles maintain their orientation?

The cytosolic side always faces the cytosol after budding from the membrane.

What is the role of acidification in endosomes?

It triggers the release of bound cargo from their receptors.

What is necessary for the production of ATP in mitochondria?

High specialization of their internal membranes.

What is the relationship between the ER and the Golgi apparatus?

Proteins synthesized in the ER are sent to the Golgi for processing and sorting.