Cellular Organelles and membrane trafficking - week 21

Question 1

what do eukaryotic cells contain

Answer 1

Eukaryotic cells are cells that contain a nucleus and membrane-bound organelles

Question 2

what are organelles and what is there function

Answer 2

Eukaryotic cells have evolved various membrane-bounded compartments called organelles that have specialized functions. These organelles work together to carry out essential cellular processes, such as energy production, lipid/carbohydrate/protein/nucleic acid synthesis, and cellular waste degradation.

Question 3

where did mitochondria and chloroplasts originate from

Answer 3

Mitochondria and chloroplasts are believed to have originated from endosymbiotic events where ancestral eukaryotic cells engulfed and established symbiotic relationships with prokaryotic cells. Over time, these prokaryotic cells evolved into mitochondria and chloroplasts, which are now essential organelles in eukaryotic cells.

Question 4

what is the key evidence that supports the endosymbiotic theory and what does that suggest

Answer 4

One key evidence supporting the endosymbiotic theory is that mitochondria and chloroplasts have their own DNA, which is distinct from the nuclear DNA of the host eukaryotic cell. This suggests that they retain remnants of their prokaryotic genomes, supporting the idea that they were once free-living bacteria that were engulfed by ancestral eukaryotic cells.

Question 5

how does mitochondria acquire energy

Answer 5

Mitochondria acquires energy from oxidative phosphorylation, which is the process by which energy from the breakdown of nutrients, such as glucose is used to generate ATP (adenosine triphosphate), which is the primary energy currency of the cell.

Question 6

how does chloroplast acquire energy

Answer 6

Chloroplasts acquires energy from photosynthesis, a process by which energy from absorbed photons is used to synthesize organic molecules, such as sugars, using carbon dioxide and water.

Question 7

how has the evolution of mitochondria and chloroplasts caused significant changes in energy metabolism in eukaryotic cells

Answer 7

The evolution of mitochondria and chloroplasts brought about significant changes in the energy metabolism of eukaryotic cells as it allows them to acquire and use energy more efficiently. This symbiotic relationship has played a crucial role in the evolution of complex life forms on Earth, as it provided eukaryotic cells with a significant advantage in terms of energy acquisition and utilization.

Question 8

what kind of structure does mitochondria have

Answer 8

Mitochondria has a complex double membrane structure that consists of an outer membrane and an inner membrane, which enclose two distinct compartments known as the intermembrane space and the matrix.

Question 9

where does oxidative phosphorylation occur, what happens during the process and what is the end result

Answer 9

The oxidative phosphorylation process occurs in the inner mitochondrial membrane.
During this process, energy is extracted from the transfer of electrons through the electron transport chain, creating proton gradients across the inner mitochondrial membrane. These proton gradients are then used to drive the enzyme ATP synthase, which synthesizes ATP from ADP and inorganic phosphate. This process is known as chemiosmosis and its end result is ATP production in mitochondria.

Question 10

what does the outer and inner mitochondrial membranes surround

Answer 10

The outer mitochondrial membrane surrounds the intermembrane space, which is the space between the outer and inner mitochondrial membranes. The inner mitochondrial membrane surrounds the matrix, which is the innermost compartment of the mitochondria where many of the metabolic reactions take place.

Question 11

what functions occur in the outer and inner mitochondrial membranes

Answer 11

Both the outer and inner mitochondrial membranes have distinct protein compositions and functions.
The outer membrane contains porin channels that allow for the exchange of small molecules between the cytoplasm and the intermembrane space. While the inner membrane contains various transporters and enzymes that are involved in oxidative phosphorylation and other metabolic processes.

Question 12

what is mitochondrial DNA, how many copies of mtDNA is present in a single vertebrate cell and where is mtDNA inherited from

Answer 12

Mitochondria also contain their own DNA, which is a circular DNA molecule that is separate from the nuclear DNA of the host cell. This mitochondrial DNA (mtDNA) is unique in its structure and function, and it is believed to have originated from the ancestral bacteria.
Mitochondria typically have multiple copies of mtDNA, with estimates of around 1000 copies in a single vertebrate cell, and mtDNA is inherited only from the mother.

Question 13

where does mitochondria receive energy-yielding chemical intermediates from

Answer 13

Mitochondria receive energy-yielding chemical intermediates from glycolysis and fatty acid oxidation, which are two ancient metabolic pathways that occur in the cytoplasm of cells.

Question 14

what happens during glycolysis and where is the end product of glycolysis transported to

Answer 14

Glycolysis is the process by which glucose which is a common sugar molecule is broken down into two molecules of pyruvate, along with the production of ATP and NADH which is a high-energy electron carrier.
Pyruvate, along with ATP and NADH which are end products of glycolysis, can then be transported into the mitochondria where it enters the citric acid cycle, also known as the Krebs cycle.

Question 15

what happens during fatty acid production process and where is the end product of this process transported to

Answer 15

Fatty acid oxidation (also known as beta-oxidation) is the process by which fatty acids which are stored forms of energy in the form of triglycerides, are broken down into acetyl-CoA molecules in the cytoplasm.
Acetyl-CoA, which is a high-energy molecule, can then be transported into the mitochondria and enter the citric acid cycle.

Question 16

what happens once acetyl-coA enter the mitochondrial matrix and where is the end product of citric acid cycle of acetyl-coA be used

Answer 16

Once acetyl-CoA enters the mitochondrial matrix, it becomes a substrate for the citric acid cycle. citric acid cycle is a series of chemical reactions that occurs in the inner mitochondrial membrane and the matrix.
During the citric acid cycle, acetyl-CoA is further oxidized, generating ATP, NADH, and FADH2 (another high-energy electron carrier), which are then used in the electron transport chain and oxidative phosphorylation to produce ATP.

Question 17

what is the citric acid cycle and why is it important

Answer 17

The citric acid cycle is an ancient and highly conserved metabolic pathway and is important for energy production in eukaryotic cells, including the energy-producing organelles like mitochondria.

Question 18

During 1 turn of the citric acid acid, 1 molecule of acetyl-coA is broken down to generate what

Answer 18

During one turn of the citric acid cycle, the breakdown of one molecule of acetyl-CoA generates three molecules of NADH and one molecule of FADH2 and two molecules of carbon dioxide, and the 2 molecules of carbon dioxide are waste products.

Question 19

what are NADH and FADH2, what do they carry and where can it be used

Answer 19

NADH and FADH2 are high-energy electron carriers that carry energetic electrons generated during the citric acid cycle and other metabolic pathways. These energetic electrons are then used in the electron transport chain which is a series of protein complexes located in the inner mitochondrial membrane.

Question 20

where is the respiratory chain located and what is it

Answer 20

The respiratory chain (also known as the electron transport chain) is located in the inner mitochondrial membrane of eukaryotic cells.
It is a series of protein complexes that facilitate the transfer of electrons from high-energy electron carriers, such as NADH and FADH2, to molecular oxygen (O2) through a series of redox reactions.

Question 21

how is a proton gradient created and formed

Answer 21

As electrons are transferred along the electron transport chain, energy is used to pump protons (H+) across the inner mitochondrial membrane creating a proton gradient.
This proton gradient (also known as a chemiosmotic gradient) is formed by the accumulation of protons on one side of the inner mitochondrial membrane, creating a higher concentration of protons in the intermembrane space compared to the mitochondrial matrix.

Question 22

what is the proton gradient used for

Answer 22

The proton gradient created by the respiratory chain is used to drive the synthesis of ATP through ATP synthase.

Question 23

how is ATP produced from ADP

Answer 23

As protons flow back into the mitochondrial matrix through ATP synthase, the energy released from this process is used to phosphorylate ADP to ATP, producing ATP.
This process is known as oxidative phosphorylation because it couples the transfer of electrons along the respiratory chain with the phosphorylation of ADP to ATP.

Question 24

what are thylakoids and where are they found

Answer 24

Thylakoids are membrane-bound compartments found inside chloroplasts in plants and cyanobacteria.

Question 25

what do thylakoids contain and what are thylakoid membranes organised into

Answer 25

Thylakoids contain the chlorophyll pigments that are responsible for capturing light energy during photosynthesis.
The thylakoid membranes are organized into stacks called grana, which are connected by stroma lamellae.

Question 26

what is stroma and what do they contain that is needed for the calvin cycle and what is calvin cycle

Answer 26

The stroma is the internal cellular compartment of chloroplasts and cyanobacteria that surrounds the thylakoid membranes.
It contains enzymes necessary for the Calvin cycle, which is the second stage of photosynthesis where carbon fixation occurs.

Question 27

what is periplasm

Answer 27

Periplasm is a term used in bacteria to refer to the space between the inner and outer membranes of the cell wall.

Question 28

where is chlorophyll found, what is chlorophyll able to do and why is it essential

Answer 28

Chlorophyll is a pigment molecule found in algae and plants that is responsible for absorbing light energy during photosynthesis.
It is capable of changing its state upon contact with photons, which allows it to boost electrons to an excited state and initiate the process of photosynthesis.
Chlorophyll is what gives plants their green color and is essential for their ability to convert light energy into chemical energy through photosynthesis.

Question 29

why does the thylakoid membranes contain photosynthetic machinery and what does the thylakoid membranes enclose

Answer 29

Thylakoid membranes contain the photosynthetic machinery which is needed for capturing light energy and carrying out the electron transport chain during photosynthesis.
These membranes enclose the thylakoid lumen, which is a space inside the thylakoid where protons accumulate during the light-dependent reactions of photosynthesis.

Question 30

How does the inner membrane of chloroplasts resemble the plasma membrane of bacteria in terms of function and structure, and what is its relationship with the stroma in chloroplasts?

Answer 30

Similar to the plasma membrane of bacteria, the inner membrane of chloroplasts acts as a permeability barrier and contains carriers for transporting metabolites. It surrounds the stroma, which is the cytoplasmic compartment of the original symbiotic bacterium that was engulfed by the ancestral eukaryotic cell and gave rise to chloroplasts.

Question 31

What are the key functions of the chloroplast stroma, including biochemical reactions, metabolic products, and cellular processes?

Answer 31

The stroma is a protein-rich compartment where various biochemical reactions occur, including the synthesis of three-carbon sugar phosphates, chloroplast proteins, and plant fatty acids. It also houses the chloroplast genomes and serves as a site for starch storage.

Question 32

what does the outer membrane of chloroplasts contain and what do they faciliate

Answer 32

The outer membrane of chloroplasts, similar to bacterial and mitochondrial membranes, contains large pore channels that allow for the free passage of metabolites in and out of the chloroplast. This facilitates and allows them to the exchange of molecules between the chloroplast and the surrounding cytoplasm of the cell.

Question 33

what are reaction centers and what are they responsible for

Answer 33

Reaction centers are protein complexes that contain chlorophyll and other pigments, and they are responsible for absorbing light energy during photosynthesis.

Question 34

what happens when reaction centers absorb light and what is generated

Answer 34

When reaction centers absorb light, they initiate an electron transport pathway that generates a proton gradient across the thylakoid membrane, pumping protons from the stroma into the thylakoid lumen.
This proton gradient is then used to generate ATP as well as to produce NADPH which is a reducing agent used in the Calvin cycle for carbon fixation.

Question 35

What is the estimated efficiency of photosystems in converting sunlight into energy, and when did they emerge in the history of life?

Answer 35

Photosystems are protein complexes that absorb light during photosynthesis. They have remarkable efficiency (estimated at around 40%) in converting sunlight into energy. They emerged early in the history of life, just a few hundred million years after the origin of life itself. This efficiency and complexity of photosystems highlight the remarkable ability of natural systems to harness energy from sunlight, surpassing the efficiency of many human-made photovoltaic cells.

Question 36

what is a reaction center in a Type ll photosystem

Answer 36

The transmembrane complex of proteins, pigments, and oxidation/reduction cofactors is called a reaction center in a Type II photosystem.

Question 37

what do they reaction centers of purple and green fiamentous bacteria use as their electron acceptors and what is similar to

Answer 37

The reaction centers of purple bacteria and green filamentous bacteria like photosystem II of cyanobacteria and chloroplasts use pheophytin as the primary electron acceptor and a quinone as the secondary electron acceptor. This is a common feature of Type II photosystems, which are found in these bacteria as well as in cyanobacteria and chloroplasts.

Question 38

what do the reaction centers of green sulfur bacteria and helibacteria use as their electron acceptors and what is it similar to

Answer 38

The reaction centers of green sulfur bacteria and heliobacteria, similar to photosystem I of cyanobacteria and chloroplasts, utilize iron-sulfur (Fe-S) centers as electron acceptors.

Question 39

why does Fe-S centers have lower energy levels compared to the electron acceptors in photosystem II

Answer 39

The Fe-S centers have lower energy levels compared to the electron acceptors in photosystem II, which allows for the capture of light energy at longer wavelengths.

Question 40

what is the role of photosystem l in the photosynthetic machinery of plants, algae and some bacteria

Answer 40

Photosystem I (PSI) is a key component of the photosynthetic machinery in plants, algae, and some bacteria. It is responsible for capturing light energy and converting it into chemical energy through a series of electron transfer reactions.

Question 41

How are special-pair chlorophylls in PSI excited and what happens to the excited electrons in terms of electron transport and transfer to iron-sulfur centers?

Answer 41

The excitation of special-pair chlorophylls in PSI can occur through direct absorption of light or resonance energy transfer from surrounding light-harvesting complexes. The excited electrons then move within the reaction center and are transferred to iron-sulfur centers, which act as electron carriers for further electron transport in the photosynthetic process.

Question 42

what are peroxisomes and what is there function

Answer 42

Peroxisomes are membrane-bound organelles found in eukaryotic cells. They are typically small, spherical organelles surrounded by a single membrane.
They are involved in various metabolic processes, particularly lipid metabolism.

Question 43

what is one of the main functions of peroxisomes

Answer 43

One of the main functions of peroxisomes is the metabolism of lipids and other metabolites.

Question 44

What are the key functions of peroxisomes in cellular metabolism, including fatty acid breakdown, acetyl-CoA production, and their role in lipid digestion and metabolism in the liver?

Answer 44

Peroxisomes contain a variety of enzymes that are responsible for breaking down fatty acids through a process called β-oxidation. This generates energy and produces acetyl-CoA, which can be further utilized in various cellular processes. Peroxisomes are also involved in the oxidation of bile acids and cholesterol, which are important for lipid digestion and metabolism in the liver.

Question 45

what are the 2 ways peroxisomes form

Answer 45

Peroxisomes can form in two different ways.
Peroxisomes form via de novo synthesis by budding from the ER or through growth and division of preexisting peroxisomes.

Question 46

why do eukaryotic cells have specialized membrane-bound compartments

Answer 46

Eukaryotic cells have specialized membrane-bound compartments to provide energy and synthesize lipids, carbohydrates, proteins, and nucleic acids, and degrade cellular components through specialized organelles.

Question 47

what is the functions of endoplasmic reticulum (ER)

Answer 47

The ER (endoplasmic reticulum) is a crucial organelle in eukaryotic cells with multiple essential functions. These include protein synthesis and processing, lipid synthesis, compartmentalization of the nucleus, storage and release of calcium (Ca2+), detoxification of compounds, lipid transfer and signaling to other organelles.
The ER is also involved in the biogenesis of the Golgi apparatus, peroxisomes, and lipid droplets, and plays a role in mitochondrial division.

Question 48

what is the function of rough ER and smooth ER

Answer 48

The rough ER (rER) is covered with ribosomes on its cytoplasmic surface and is responsible for protein synthesis, folding, and degradation.
The smooth ER, consisting of ribosome-free tubular elements, is specialized for drug metabolism (in hepatocytes), steroid synthesis (in endocrine cells), or calcium uptake and release.

Question 49

what is the nuclear envelope in ER

Answer 49

The ER also forms a double membrane bilayer barrier around the cell nucleus, known as the nuclear envelope.

Question 50

what does the ER form with other membranes and with whats help

Answer 50

The ER forms various types of contacts with other membranes in the cell, facilitated by specific proteins.

Question 51

Proteins and Processes in ER Domains: Functions and Associations Table

Answer 51

Proteins and Processes in ER Domains: Functions and Associations Table

Question 52

How is protein glycosylation accomplished in the endoplasmic reticulum (ER), including the synthesis of core oligosaccharides via the dolichol pathway and the transfer of completed oligosaccharides to nascent protein chains in the ER lumen?

Answer 52

1. Protein Glycosylation in ER: Proteins synthesized in association with the ER are often glycoproteins, with carbohydrates covalently attached to them.
2. Dolichol Pathway: The dolichol pathway is involved in the synthesis of the core oligosaccharide, consisting of mannose and N-acetylglucosamine. This occurs in the cytoplasm and the core oligosaccharide is attached to dolichol in the ER membrane through high-energy pyrophosphate bonds.
3. Oligosaccharide Completion: The core structure is completed by adding sugars imported into the ER, and the oligosaccharide-transferase complex transfers the completed oligosaccharide to the consensus Asn-X-Ser/Thr motif of a nascent protein chain as it enters the lumen of the ER.

Question 53

what type of structure does golgi apparatus have in most cells

Answer 53

The Golgi apparatus, in most cells, has a ribbon-like structure that surrounds the centrosome located on one side of the nucleus.

Question 54

what does the electron micrograpbs of cells show in term of the golgi apparatus

Answer 54

In electron micrographs of cells, it appears as a single stack of cisternae that are cut transversely. The cis and trans faces of the Golgi are located at opposite sides of the stack, with the trans-Golgi network (TGN) extending from the trans face.

Question 55

what does golgi apparatus for support and transport

Answer 55

The Golgi apparatus utilizes microtubules to provide structural support and facilitate intracellular transport.

Question 56

what are vesicular tubular carriers

Answer 56

Vesicular tubular carriers (VTCs) are vesicles that bud from the endoplasmic reticulum (ER) and are destined for fusion with the membranes of the Golgi apparatus.

Question 57

what are the 3 primary functions of golgi apparatus within the secretory membrane system

Answer 57

1. Carbohydrate synthesis: The Golgi apparatus acts as a factory for synthesizing the carbohydrate chains of glycoproteins, proteoglycans, and polysaccharides that are secreted by cells, including plants. These carbohydrates are essential for the biological functions of these molecules at the cell surface.
2. Protein sorting: The Golgi apparatus serves as a protein-sorting station, directing proteins to various cellular destinations, such as transport to the plasma membrane, secretion to the cell exterior, sorting to the endosome/lysosomal system, or retrieval back to the endoplasmic reticulum (ER). This ensures proper localization and function of proteins within the cell.
3. Lipid synthesis: The Golgi apparatus is also involved in the synthesis of sphingomyelin and glycosphingolipids, which are important lipids that associate with cholesterol and influence protein sorting in the Golgi apparatus and plasma membrane. These lipids play a role in maintaining membrane integrity and organization.

Question 58

what are the 3 proposed models for cargo movement through the golgi apparatus and what happens in each model

Answer 58

There are three proposed models for cargo movement through the Golgi apparatus:
vesicle budding and fusion, cisternal progression, and lipid partitioning mechanism.

In the vesicle budding and fusion model, cargo is packaged into vesicles that bud off from one Golgi compartment and fuse with the next.
In the cisternal progression model, new cisternae with cargo form at the cis side of the Golgi and mature as Golgi enzymes move back through the stack.
The lipid partitioning mechanism suggests that cargo moves through the Golgi by partitioning into specific lipid domains.

Question 59

what are the 3 primary functions carried out by the golgi apparatus within the secretory membrane system and why are these functions important

Answer 59

The Golgi apparatus, a vital organelle in the cell, carries out three primary functions within the secretory membrane system.
Firstly, it facilitates sorting of proteins and lipids from the Trans-Golgi Network (TGN) to different destinations within the cell or for secretion outside the cell. Secondly, it mediates a continuous transport process to the cell surface through tubular carriers that bud out from the TGN, without the involvement of known coat proteins.
Lastly, it plays a role in the partitioning of cargo proteins into specialized lipid domains containing sphingolipids and cholesterol, which are important for membrane organization, trafficking, and signaling. Together, these functions of the Golgi apparatus are important for maintaining cellular homeostasis and ensuring proper cellular function.

Question 60

other than the constitutive transport pathway, which pathway does endocrine, exocrine and neuronal cells utilize and why

Answer 60

In addition to the constitutive transport pathway, endocrine, exocrine, and neuronal cells utilize a specialized sorting pathway from the TGN to concentrate and package selected proteins in storage granules. This is because this regulated secretory pathway allows for the storage and controlled release of proteins in response to hormonal or neural stimulation.

Question 61

where are proteins such as polypeptide hormones and digestive enzymes stored

Answer 61

Proteins such as polypeptide hormones and digestive enzymes which are needed intermittently are stored in secretory granules until they are discharged from the cell upon command.

Question 62

why is the regulated secretory pathway different from the constitutive pathway

Answer 62

The difference between the 2 pathways is unlike the constitutive pathway, the regulated secretory pathway does not rely on a universal sorting signal for cargo proteins.

Question 63

in the regulated pathway what does the process of secretory granule formation involve and how can the process occur

Answer 63

In the regulated pathway, the process of secretory granule formation involves physical sorting, selective retention, and condensation of the secretory proteins. This secretory granule formation can occur through mechanisms such as charge neutralization, protein aggregation, and active extrusion of ions.

Question 64

why does the constitutive pathway and regulated secretory pathway work together

Answer 64

The constitutive pathway and regulated secretory pathway work together to ensure that the proteins are properly sorted, stored, and released in response to specific signals, allowing for precise control of cellular secretion in these specialized cells.

Question 65

How do clathrin and retromer coats facilitate cargo sorting for transport to the endosome/lysosomal system

Answer 65

The sorting of cargo to the endosome/lysosomal system involves the capture of cargo molecules, including acid hydrolases, in carrier vesicles from the TGN by coats. These coats, such as clathrin or retromer, play a crucial role in packaging the cargo into vesicles.

Question 66

How does mannose 6-phosphate (M6P) prevent the secretion or misdirection of acid hydrolases during sorting into vesicles for the endosome/lysosomal system?

Answer 66

The cargo, which includes approximately 50 different acid hydrolases with diverse cellular functions, is marked with mannose 6-phosphate (M6P) in the cis-Golgi to divert it from the default secretory pathway. M6P acts as a signal for the enzymes to be sorted into vesicles destined for the endosomes/lysosomes, preventing their secretion or misdirection to other compartments.

Question 67

How do TGN vesicles transport cargo to endosomes, and how does late endosomes and lysosomes maintain cellular homeostasis?

Answer 67

Carrier vesicles from the TGN transport cargo to early endosomes, which mature into late endosomes. Acid hydrolases in late endosomes and lysosomes digest and recycle the cargo, maintaining cellular homeostasis and function.

Question 68

How does macropinocytosis facilitate bulk nutrient uptake through the formation of macropinosomes and their transport along microtubules

Answer 68

Macropinocytosis is a cellular process where protrusions close around extracellular fluid, forming a macropinosome. This vesicle is then transported along microtubules towards the center of the cell, allowing for the internalization of unconcentrated extracellular fluid. This process is beneficial for bulk nutrient uptake.

Question 69

What are caveolae, their size, composition, and coat proteins on the cytoplasmic surface

Answer 69

Caveolae are small patches of plasma membrane, about 50 nm wide, enriched in cholesterol and coated with caveolin and cavin proteins on the cytoplasmic surface.

Question 70

what is phagocytosis and does it involve actin cytoskeleton in the ingestion of large particles

Answer 70

Phagocytosis is the process of ingesting large particles like bacteria, foreign bodies, and remnants of dead cells. Cells use the actin cytoskeleton to push a protrusion of the plasma membrane that surrounds these particles.

Question 71

What are the key steps and proteins involved in clathrin-mediated endocytosis, including the role of AP2 complexes, clathrin, amphiphysin, dynamin, auxilin, and Hsc70 in cargo sorting, vesicle formation, and fusion with endosomes

Answer 71

Clathrin-mediated endocytosis involves AP2 complexes that target the plasma membrane and interact with tyrosine-based sorting motifs in transmembrane proteins.
AP2 also initiates the assembly of a clathrin lattice, which concentrates cargo molecules in coated pits.
AP2 and clathrin interact with amphiphysin which is a BAR-domain protein that attracts the GTPase dynamin. Once a coated pit is assembled and a coated vesicle is formed through fission from the plasma membrane, auxilin and the ATPase Hsc70 dissociate clathrin and release the cargo-carrying vesicle into the cell for fusion with endosomes.

Question 72

How is cargo and membrane sorted along the endocytic pathway, including the role of clathrin-mediated endocytosis, endosomal maturation, lysosomes, and recycling pathways

Answer 72

The sorting of cargo and membrane along the endocytic pathway involves several steps. Cargo and membrane taken up by clathrin-mediated endocytosis are delivered to tubulovesicular early endosomes, which then mature into multivesicular bodies and late endosomes before eventually fusing with lysosomes. Each compartment along this pathway sorts membrane-containing receptors and other proteins into tubules and vesicles that can be recycled back to the plasma membrane, either directly or indirectly through perinuclear recycling endosomes or the trans-Golgi network (TGN).

Question 73

What processes are involved in endosome maturation and how do they impact cargo and membrane sorting and trafficking in the endocytic pathway

Answer 73

The maturation of endosomes involves several processes, including the accumulation of internal membranes, delivery of lysosomal hydrolases from the TGN, and acquisition of targeting and fusion machinery. These steps are crucial for the proper sorting and trafficking of cargo and membrane within the endocytic pathway, allowing for recycling of membrane components and delivery of cargo to the appropriate cellular destinations, such as lysosomes for degradation or back to the plasma membrane for reuse.

Question 74

How do lysosomes and proteasomes regulate proteolysis to maintain cellular homeostasis

Answer 74

Two distinct ways in which cells compartmentalize intracellular proteolytic activity are through lysosomes and proteasomes.
Cells compartmentalize intracellular proteolytic activity to prevent unregulated proteolysis. Lysosomes are membrane-bound compartments with acidic environment that sequester hydrolases, including proteases, for targeted degradation of cellular components. Proteasomes, located in the cytoplasm and nucleus, selectively degrade proteins marked with ubiquitin.
Both lysosomes and proteasomes play crucial roles in regulating proteolysis to maintain cellular homeostasis.

Question 75

what would be lethal in a cell if it is unregulated

Answer 75

Unregulated proteolysis within a cell would be lethal.