Week 4 Seminar Endomembrane System and Endoplasmic Reticulum 1 Quiz

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Questions and Answers

What is the primary function of the Golgi apparatus?

Calcium storage

Lipid biosynthesis

Protein synthesis

Modification and sorting of proteins (correct)

The smooth ER is involved in storing calcium ions for muscle contraction.

True

What enzyme is important for cholesterol biosynthesis in the smooth ER?

Hydroxymethylglutaryl-CoA reductase (HMG-CoA reductase)

The Golgi apparatus is made up of a series of flattened membrane-bound ______.

cisternae Signup and view all the answers

Match the Golgi networks to their positions within the Golgi apparatus.

Cis-Golgi network (CGN) = Closest to ER Medial Golgi network = Middle of the Golgi Trans-Golgi network (TGN) = Farthest from ER, closest to cell surface Cisternae = Stacked membrane-bound sacs Signup and view all the answers

Which model describes the concept that cisternae gradually change in composition as they move forward?

Cisternal maturation model Signup and view all the answers

In the stationary cisternae model, the Golgi compartments move forward.

False Signup and view all the answers

What is the term used for the process in which lipids and proteins move from the ER toward the plasma membrane?

Anterograde transport Signup and view all the answers

The addition of carbohydrate side chains forming glycoproteins is known as __________.

glycosylation Signup and view all the answers

Which type of glycosylation involves adding a glycan to a nitrogen atom?

N-linked glycosylation Signup and view all the answers

Retrograde transport refers to the movement from Golgi cisternae back toward the ER.

True Signup and view all the answers

Match the types of transport with their definitions:

Anterograde transport = Movement toward the plasma membrane Retrograde transport = Movement back toward the ER Signup and view all the answers

What happens to membrane material when a secretory granule fuses with the plasma membrane?

It becomes part of the plasma membrane. Signup and view all the answers

What is the primary function of the Golgi apparatus?

Modification and packaging of proteins Signup and view all the answers

Exocytosis is the process by which cells internalize external materials.

False Signup and view all the answers

What type of cell are both exocytosis and endocytosis unique to?

Eukaryotic cells Signup and view all the answers

The process by which amino sugars are added to proteins is called __________.

glycosylation Signup and view all the answers

Match the following terms with their definitions:

Exocytosis = Release of substances from the cell Endocytosis = Ingestion of external materials by the cell Golgi apparatus = Modifies and packages proteins Endoplasmic reticulum = Synthesizes proteins Signup and view all the answers

Which of the following processes involves the formation of an endocytic vesicle?

Endocytosis Signup and view all the answers

The Golgi apparatus is involved in protein trafficking and lipid modification.

True Signup and view all the answers

Describe the role of the endoplasmic reticulum in protein synthesis.

The endoplasmic reticulum is responsible for the synthesis of proteins, which are then transported to the Golgi apparatus for further processing. Signup and view all the answers

Cells transport proteins and lipids through specialized pathways involving the __________ and the Golgi apparatus.

endoplasmic reticulum Signup and view all the answers

Which process specifically refers to the packaging and movement of proteins from the ER to the Golgi?

Vesicular transport Signup and view all the answers

What is a primary role of the ribosomes attached to the rough ER?

Synthesis of membrane-bound and soluble proteins Signup and view all the answers

Glycosylation refers to the process of adding carbohydrates to proteins.

True Signup and view all the answers

What process is responsible for degrading improperly folded proteins in the ER?

ER-associated degradation (ERAD) Signup and view all the answers

The membranes of the smooth ER form ______ structures.

tubular Signup and view all the answers

Match the following functions with the correct type of endoplasmic reticulum:

Rough ER = Glycosylation of proteins Smooth ER = Carbohydrate metabolism Signup and view all the answers

Which of the following statements is true regarding the Golgi apparatus?

The Golgi receives transition vesicles from the rough ER. Signup and view all the answers

Smooth ER aids in the enzymatic breakdown of stored glycogen.

True Signup and view all the answers

What is the function of glucose-6-phosphatase in smooth ER?

Breakdown of glucose-6-phosphate into free glucose and inorganic phosphate. Signup and view all the answers

In the rough ER, proteins undergo ______ modifications.

posttranslational Signup and view all the answers

Which disease is associated with defects in the processes occurring in the rough ER?

Familial hypercholesterolemia Signup and view all the answers

What is the main function of transport vesicles in the endomembrane system?

Transport vesicles carry membrane lipids and membrane-bound proteins to their proper destinations in the cell or for secretion. Signup and view all the answers

Explain the structural characteristics of the endoplasmic reticulum (ER).

The ER is a continuous network of flattened sacs, tubules, and vesicles that stretches throughout the cytoplasm, consisting of membrane-bounded sacs called ER cisternae. Signup and view all the answers

Describe the significance of the ER lumen in the endoplasmic reticulum.

The ER lumen is the space enclosed by the ER cisternae, where protein folding and modification occur. Signup and view all the answers

What roles do the different types of endoplasmic reticulum (rough and smooth) play in a eukaryotic cell?

Rough ER is primarily involved in protein synthesis due to ribosomes, while smooth ER is involved in lipid synthesis and detoxification processes. Signup and view all the answers

How does the endomembrane system connect the nuclear envelope and plasma membrane?

The endomembrane system is associated with both the nuclear envelope and the plasma membrane, forming a continuous network that facilitates communication and material exchange. Signup and view all the answers

What role do ribosomes play in the rough endoplasmic reticulum?

Ribosomes attached to the rough ER synthesize both membrane-bound and soluble proteins. Signup and view all the answers

What is the significance of ER-associated degradation (ERAD)?

ERAD eliminates misfolded proteins from the ER to maintain cellular homeostasis. Signup and view all the answers

How does the smooth ER contribute to drug detoxification?

The smooth ER facilitates drug detoxification through enzyme-catalyzed hydroxylation. Signup and view all the answers

What modifications occur to proteins in the rough ER?

In the rough ER, proteins undergo co-translational and posttranslational modifications, such as glycosylation and folding. Signup and view all the answers

What is the function of glucose-6-phosphatase in the smooth ER?

Glucose-6-phosphatase breaks down glucose-6-phosphate into free glucose and inorganic phosphate. Signup and view all the answers

What effect does the addition of hydroxyl groups have on hydrophobic drugs?

It increases their solubility and facilitates excretion from the body. Signup and view all the answers

Which enzymes are involved in the process of hydroxylation?

Cytochrome P-450 enzymes are responsible for this process. Signup and view all the answers

Describe the role of ATP in the calcium storage function of the smooth ER.

ATP powers calcium ATPases that pump calcium ions into the ER. Signup and view all the answers

What is the primary function of the smooth ER in steroid hormone production?

It synthesizes cholesterol and steroid hormones such as cortisol and testosterone. Signup and view all the answers

How thick are the membranes of the endoplasmic reticulum compared to cell membranes?

ER membranes are about 5 nm thick, while cell membranes are about 8 nm thick. Signup and view all the answers

What is the structural organization of the Golgi apparatus?

It consists of a series of stacked, flattened membrane-bound cisternae. Signup and view all the answers

Identify the three networks of the Golgi apparatus and their positions.

The Cis-Golgi network (CGN) is closest to the ER, the Medial Golgi network is in the middle, and the Trans-Golgi network (TGN) is farthest from the ER. Signup and view all the answers

What is the primary role of hydroxymethylglutaryl-CoA reductase in the smooth ER?

It plays a critical role in cholesterol biosynthesis. Signup and view all the answers

Explain the significance of the Golgi apparatus in relation to proteins.

The Golgi apparatus modifies, sorts, and packages proteins for secretion or use within the cell. Signup and view all the answers

What type of cargo does the smooth ER primarily produce?

It primarily produces lipids, including phospholipids and cholesterol. Signup and view all the answers

What is the primary role of the endomembrane system in eukaryotic cells?

The endomembrane system is responsible for the synthesis, modification, transport, and degradation of proteins and lipids within the cell. Signup and view all the answers

Describe the difference between rough and smooth endoplasmic reticulum (ER).

Rough ER is studded with ribosomes and is primarily involved in protein synthesis, while smooth ER lacks ribosomes and is involved in lipid synthesis and detoxification. Signup and view all the answers

Explain how transport vesicles contribute to the function of the endomembrane system.

Transport vesicles carry proteins and lipids between organelles, ensuring they reach their specific destinations within the cell. Signup and view all the answers

What is the significance of the ER lumen in the endoplasmic reticulum?

The ER lumen serves as the site for protein folding and modification, as well as for the synthesis of certain lipids. Signup and view all the answers

How does the endomembrane system interact with the nuclear envelope?

The endomembrane system is interconnected with the nuclear envelope, facilitating the exchange of materials and communication between the nucleus and the cytoplasm. Signup and view all the answers

What roles do chaperones play in the endoplasmic reticulum?

Chaperones help in recognizing and folding proteins properly, and they assist in eliminating misfolded proteins through ER-associated degradation (ERAD). Signup and view all the answers

What is the significance of glycosylation in rough ER protein synthesis?

Glycosylation modifies proteins by adding carbohydrates, which is crucial for protein folding, stability, and cell signaling. Signup and view all the answers

How does the rough ER ensure the quality of proteins before they reach the Golgi apparatus?

The rough ER utilizes a quality control system, specifically ERAD, to degrade improperly folded or assembled proteins, preventing their transport to the Golgi. Signup and view all the answers

What is the primary function of smooth ER in liver cells regarding glucose metabolism?

The smooth ER in liver cells contains glucose-6-phosphatase, which converts glucose-6-phosphate into free glucose for export into the bloodstream. Signup and view all the answers

Explain the structural difference between rough ER and smooth ER.

Rough ER has ribosomes attached to its cytosolic side, while smooth ER lacks ribosomes and is structured as tubular membranes. Signup and view all the answers

How does the addition of hydroxyl groups affect the solubility of hydrophobic drugs?

The addition of hydroxyl groups makes hydrophobic drugs more soluble, facilitating easier excretion from the body. Signup and view all the answers

What is the significance of ATP-dependent calcium ATPases in muscle cells?

They pump calcium ions into the smooth ER, crucial for releasing calcium during muscle contraction. Signup and view all the answers

What role does Hydroxymethylglutaryl-CoA reductase play in the smooth ER?

It is important for cholesterol biosynthesis within the smooth ER. Signup and view all the answers

Why is the composition of the ER membrane significant compared to other cellular membranes?

The ER membrane's composition differs notably, influencing its specific functions in lipid synthesis and protein processing. Signup and view all the answers

Describe the organization of the Golgi apparatus?

The Golgi apparatus consists of 3−8 stacked, flattened membrane-bound cisternae, which include the cis-Golgi network, medial Golgi network, and trans-Golgi network. Signup and view all the answers

Study Notes

The Endomembrane System

The endomembrane system is an interconnected network of membrane-enclosed organelles in eukaryotic cells.
The endomembrane system includes the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vacuoles, and plasma membrane.
The endomembrane system is responsible for synthesizing, modifying, transporting, and sorting proteins and lipids.

The Endoplasmic Reticulum (ER)

There are two types of ER: rough ER and smooth ER.
Rough ER (RER) is studded with ribosomes and is involved in protein synthesis and modification.
Smooth ER (SER) lacks ribosomes and is involved in lipid synthesis, detoxification, calcium storage, and steroid hormone synthesis.

Rough ER

Ribosomes attached to the cytosolic side of rough ER synthesize both membrane-bound and soluble proteins.
Rough ER carries out co-translational and posttranslational modifications, including glycosylation, protein folding, and assembly of multimeric proteins.
Rough ER operates a quality control system: improperly folded, assembled, or modified proteins are degraded by cytosolic proteasomes via ER-associated degradation (ERAD).

Smooth ER

The smooth ER lacks ribosomes and forms a tubular structure.
Smooth ER is involved in carbohydrate metabolism, particularly glycogen breakdown.
Smooth ER in liver cells contains glucose-6-phosphatase, an enzyme that breaks down glucose-6-phosphate to free glucose and inorganic phosphate (Pi).
Smooth ER plays a role in detoxification by adding hydroxyl groups to hydrophobic drugs, making them more soluble and easier to excrete.
Smooth ER is involved in calcium storage, particularly in muscle cells.
Smooth ER is the site of cholesterol and steroid hormone biosynthesis.
The ER is the primary source of membrane lipids, including phospholipids and cholesterol.

The ER Membrane

The ER membrane is about 5 nm thick, whereas cell membranes are about 8 nm thick.
The ER membrane is the source of most membrane lipids, but other cellular membranes have different compositions from the ER membrane.

The Golgi Apparatus

The Golgi apparatus is a series of flattened membrane-bound cisternae stacked together (Golgi complex).
The Golgi apparatus is involved in modifying, sorting, and packaging proteins and lipids.
The Golgi apparatus consists of three main regions: the cis-Golgi network (CGN), the medial Golgi network, and the trans-Golgi network (TGN).

Trafficking of Lipids and Proteins Through the Golgi

Two models have been proposed for the movement of lipids and proteins from the CGN to the TGN: the stationary cisternae model and the cisternal maturation model.
The stationary cisternae model suggests that shuttle vesicles carry material forward from the ER to successive Golgi compartments, which remain in place.
The cisternal maturation model suggests that the cisternae themselves move forward and change in composition as they do.
In both models, enzymes and lipids needed in earlier compartments move backward in a retrograde fashion.

Anterograde and Retrograde Transport

Anterograde transport refers to the movement from the ER through the Golgi apparatus toward the plasma membrane.
Retrograde transport refers to the flow of vesicles from Golgi cisternae back toward the ER.

Glycosylation

Glycosylation is the addition of carbohydrate side chains (glycans) to specific amino acid residues of proteins, forming glycoproteins.
Much of the protein processing carried out within the ER and Golgi apparatus involves glycosylation.
There are two general kinds of glycosylation: N-linked glycosylation (or N-glycosylation) and O-linked glycosylation.
In N-linked glycosylation, the glycan is added to a nitrogen atom.
In O-linked glycosylation, the glycan is added to an oxygen atom.

Transporting Materials Across Membranes

There are two methods of transporting materials across the plasma membrane: exocytosis and endocytosis.
Exocytosis is the process by which secretory granules release their contents to the exterior of the cell; this is the mechanism for moving proteins from the ER through the Golgi apparatus to secretory vesicles, and it ultimately results in the release of material from the cell.
Endocytosis is the process by which cells internalize external materials. In this process, a small segment of the plasma membrane progressively folds inward and pinches off to form an endocytic vesicle containing ingested substances or particles.

Exocytosis and Endocytosis

Both exocytosis and endocytosis are unique to eukaryotic cells and are involved in the delivery, recycling, and turnover of membrane proteins.

The Endomembrane System

The endomembrane system of eukaryotic cells is comprised of the endoplasmic reticulum (ER), Golgi apparatus, endosomes, and lysosomes.
It is associated with both the nuclear envelope and plasma membrane.
Material flows through the endomembrane system via transport vesicles.
These vesicles transport membrane lipids and proteins to their destination within the cell or for secretion.

Endoplasmic Reticulum

The endoplasmic reticulum (ER) is a continuous network of flattened sacs (cisternae), tubules, and vesicles that extend throughout the cytoplasm of eukaryotic cells.
The ER is responsible for protein synthesis, folding, modification, and transport; lipid synthesis, and detoxification.
The space enclosed by ER cisternae is called the ER lumen.

Types of ER

Rough ER: contains ribosomes attached to its cytosolic side, synthesizes both membrane-bound and soluble proteins, and carries out protein modification, folding, and quality control.
Smooth ER: lacks ribosomes, is involved in carbohydrate metabolism, detoxification, calcium storage, and steroid biosynthesis.

ER-Associated Degradation (ERAD)

Misfolded proteins are recognized by chaperone proteins for degradation in ERAD.
ERAD eliminates misfolded proteins from the ER and prevents their transport to the Golgi.

Golgi Apparatus

The Golgi apparatus is a series of flattened, membrane-bound cisternae stacked together known as a Golgi complex.
The Golgi processes, sorts, and packages proteins and lipids received from the ER.
It can be divided into three functional compartments:
- Cis-Golgi Network (CGN): The compartment closest to the ER.
- Medial Golgi Network: The middle compartment.
- Trans-Golgi Network (TGN): The compartment farthest from the ER, closest to the cell surface, where transport vesicles bud off to deliver lipids and proteins to other parts of the endomembrane system or for secretion.

Transport Through the Golgi

There are two main models for how lipids and proteins move through the Golgi:
- Stationary Cisternae Model: Vesicles transport material from the ER to successive Golgi compartments.
- Cisternal Maturation Model: Cisternae themselves move forward as they change in composition.
Movement from the ER through the Golgi toward the plasma membrane is called anterograde transport; movement back towards the ER is called retrograde transport.

Glycosylation

Glycosylation is the addition of carbohydrate side chains (glycans) to specific amino acids.
It occurs mainly in the ER and Golgi apparatus.
There are two types:
- N-Linked Glycosylation: glycans are added to a nitrogen atom.
- O-Linked Glycosylation: glycans are added to an oxygen atom.

Transport Across the Plasma Membrane

Exocytosis: Secretory granules release their contents to the exterior of the cell.
Endocytosis: Cells internalize external material via the formation of endocytic vesicles.
Both processes are involved in the delivery, recycling, and turnover of membrane proteins.

The Endomembrane System and Peroxisomes

The endomembrane system in eukaryotic cells consists of the endoplasmic reticulum (ER), Golgi apparatus, endosomes, and lysosomes.
It is associated with both the nuclear envelope and the plasma membrane.
Trafficking (movement of proteins and lipids between organelles) is tightly regulated within the endomembrane system.
Materials flow between the ER, Golgi apparatus, endosomes, and lysosomes through transport vesicles.
Membrane lipids and membrane-bound proteins are transported to their appropriate destinations or secreted.

The Endoplasmic Reticulum (ER)

The ER is a continuous network of flattened sacs (cisternae), tubules, and vesicles that extend throughout the eukaryotic cell's cytoplasm.
It is responsible for synthesizing both membrane-bound and soluble proteins.
The rough ER has ribosomes attached to its cytosolic side and is involved in co-translational and post-translational protein modifications, including glycosylation, folding, and assembly of multimeric proteins.
It also has a quality control mechanism known as ER-associated degradation (ERAD), where improperly folded or assembled proteins are degraded by cytosolic proteasomes.

Smooth Endoplasmic Reticulum (Smooth ER)

The smooth ER lacks ribosomes and has a tubular structure.
It plays various roles, including carbohydrate metabolism (glycogen breakdown), drug detoxification (hydroxylation), calcium storage, and steroid biosynthesis.
Smooth ER in liver cells contains glucose-6-phosphatase, an enzyme that breaks down glucose-6-phosphate, releasing free glucose for transport out of the cell.
Cytochrome P-450 enzymes in the smooth ER catalyze hydroxylation, making hydrophobic drugs more soluble for excretion by the body.
Muscle cells use the smooth ER's calcium storage and release mechanism to aid in muscle contraction.
The smooth ER is the primary source of membrane lipids, including phospholipids and cholesterol.

The Golgi Apparatus

The Golgi apparatus is composed of flattened, membrane-bound cisternae stacked together, forming a Golgi complex.
It is organized into three regions: cis-Golgi network (CGN), medial Golgi network, and trans-Golgi network (TGN).
Transport vesicles bud off from the TGN, transporting lipids and proteins to other endomembrane system components.

Trafficking Through the Golgi

Two models describe the movement of lipids and proteins through the Golgi: the stationary cisternae model and the cisternal maturation model (membrane flow).
The stationary cisternae model proposes that shuttle vesicles move material forward from the ER to successive Golgi compartments, while the cisternal maturation model suggests that the cisternae themselves move forward, changing composition as they do.
Anterograde transport refers to the movement of vesicles from the ER towards the plasma membrane, while retrograde transport describes the flow of vesicles back towards the ER.
The cell recycles lipids and proteins during the late stages of this process.

Glycosylation

Glycosylation is the process of adding carbohydrate side chains (glycans) to specific amino acid residues of proteins, forming glycoproteins.
It is a crucial protein processing step occurring in the ER and Golgi apparatus.
Two types of glycosylation exist: N-linked glycosylation (N-glycosylation) and O-linked glycosylation.

Transporting Materials Across Membranes

Exocytosis is the process by which secretory granules release their contents to the exterior of the cell, playing a role in the secretory pathways that move proteins from the ER through the Golgi to secretory vesicles.
Endocytosis is the process by which cells internalize external materials, involving the inward folding and pinching off of the plasma membrane to form endocytic vesicles containing ingested substances.
Both exocytosis and endocytosis are unique to eukaryotic cells and are crucial for the delivery, recycling, and turnover of membrane proteins.

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Description

Test your knowledge on the endomembrane system and the endoplasmic reticulum (ER) in eukaryotic cells. This quiz covers the structure, function, and types of ER, including rough and smooth ER. Assess your understanding of protein and lipid synthesis, modification, and transport processes.