Chapter 8

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Questions and Answers

Which technique involves using a green fluorescent protein to observe protein synthesis and movement within living cells?

Electron microscopy

Biochemical analysis of subcellular fractions

GFP-based protein tracking (correct)

Autoradiography

What type of cells release digestive enzymes in response to a stimulus?

Pancreatic cells (correct)

Fibroblasts

Smooth muscle cells

Neuronal cells

Which method has largely supplanted autoradiography for visualizing biochemical processes?

Biochemical analysis of subcellular fractions

Electron microscopy

GFP-based protein tracking (correct)

Cell-free systems

What did Nobel laureates James Rothman and Randy Schekman use in their research on vesicle trafficking?

Cell-free systems Signup and view all the answers

$\text{What is the main role of the endomembrane system?}$

$\text{Biosynthetic and secretory pathways}$ Signup and view all the answers

$\text{Which method involves techniques to isolate and characterize organelles, such as the use of microsomes for studying the endoplasmic reticulum (ER)?}$

$\text{Biochemical analysis of subcellular fractions}$ Signup and view all the answers

Where are carbohydrates added to proteins in the endoplasmic reticulum?

RER lumen Signup and view all the answers

What aids in protein folding and oligomerization in the RER lumen?

BiP (Binding immunoglobulin protein) Signup and view all the answers

Where is the signal sequence located for directing protein synthesis on membrane-bound ribosomes?

N-terminus Signup and view all the answers

Which portion of the protein is cleaved by a proteolytic enzyme upon entering the RER lumen?

N-terminal portion containing the signal sequence Signup and view all the answers

What is extensively developed in various cell types and functions in steroid hormone synthesis and detoxification?

Smooth endoplasmic reticulum (SER) Signup and view all the answers

Which part of the endoplasmic reticulum contains ribosomes on its cytosolic surface?

(Rough endoplasmic reticulum) RER Signup and view all the answers

Which organelles are part of the endomembrane system?

Endoplasmic reticulum and Golgi complex Signup and view all the answers

Which organelle is involved in lipid manufacture and metabolism?

Smooth endoplasmic reticulum Signup and view all the answers

What is the function of the biosynthetic pathway?

Synthesis, modification, and transport of proteins Signup and view all the answers

Which organelle is studded with ribosomes and involved in protein production?

Rough endoplasmic reticulum Signup and view all the answers

What happens to materials in the endomembrane system?

They are shuttled back and forth between organelles in transport vesicles Signup and view all the answers

Which organelle is part of an integrated network within the endomembrane system?

Rough endoplasmic reticulum Signup and view all the answers

What is the role of lysosomes in cell processes?

They contain acid hydrolases and play a key role in organelle turnover and autophagy. Signup and view all the answers

What can lead to serious human health disorders, such as Tay-Sachs disease?

Lysosomal malfunctions Signup and view all the answers

What process involves the uptake of large particles, which are then digested within a phagolysosome?

Phagocytosis Signup and view all the answers

Which bacterium affects fusion with lysosomes?

$Mycobacterium$ $tuberculosis$ Signup and view all the answers

What drives phagocytosis?

$Actin$-containing microfilaments Signup and view all the answers

What is responsible for the maintenance of proteins in the ER through retention or retrieval mechanisms based on their physical properties?

Golgi apparatus Signup and view all the answers

Which organelle is responsible for synthesizing most membrane lipids?

Endoplasmic Reticulum (ER) Signup and view all the answers

What is the fate of misfolded proteins in the ER?

Destroyed in the cytosol by the ER-associated degradation (ERAD) process Signup and view all the answers

Which pathway is involved in the degradation of misfolded proteins?

Proteasome Pathway Signup and view all the answers

What is the role of the Golgi complex in glycoprotein assembly?

Assembly of carbohydrate components of glycoproteins Signup and view all the answers

Which organelle is involved in membrane biosynthesis and lipid synthesis?

Endoplasmic Reticulum (ER) Signup and view all the answers

What determines the fate of soluble ER proteins from ER to Golgi or their stay in the ER?

Retrieval signal, KDEL, present on soluble ER proteins Signup and view all the answers

Which method has largely replaced autoradiography for visualizing biochemical processes related to protein synthesis and trafficking?

GFP-based protein tracking Signup and view all the answers

Who received the Nobel Prize for their research on vesicle trafficking using cell-free systems?

James Rothman and Randy Schekman Signup and view all the answers

What is the main purpose of using cell-free systems in studying the endomembrane system?

To investigate the proteins involved in membrane trafficking and reconstitute cellular processes in vitro Signup and view all the answers

Which pathway involves upregulation of transcription/translation of factors leading to continuous secretion and exocytosis upon arrival of a stimulus?

Regulated secretion pathway Signup and view all the answers

What is the role of microsomes derived from the endomembrane system?

To investigate the structural and functional aspects of the ER Signup and view all the answers

What is the method used to visualize biochemical processes using radiolabeled materials and to determine where secretory proteins are synthesized?

Autoradiography Signup and view all the answers

Which type of autophagy involves the direct engulfment of cytoplasmic material by lysosomes?

Microautophagy Signup and view all the answers

What is the main cause of Tay-Sachs disease?

Absence of specific lysosomal enzymes Signup and view all the answers

Which process involves the uptake of substances into the cell and can be categorized as 'cell drinking'?

Pinocytosis Signup and view all the answers

What triggers the discharge of a secretory vesicle through exocytosis?

Increase in calcium ions Signup and view all the answers

Which bacteria can hijack the phagocytic machinery for survival within phagocytic cells?

$ ext{Mycobacterium tuberculosis}$ Signup and view all the answers

Which model for the movement of materials through the Golgi complex incorporates both vesicle and cisternal transport?

Cisternal maturation model Signup and view all the answers

What is the fate of misfolded proteins in the ER according to ER-associated degradation (ERAD)?

They are transported into the cytosol for degradation in proteasomes Signup and view all the answers

Which organelle plays a crucial role in assembling carbohydrate components of glycoproteins and synthesizing complex polysaccharides found in plant cell walls?

Golgi complex Signup and view all the answers

Which pathway directs the movement of proteins in the cell for degradation?

$26S$ proteasome pathway Signup and view all the answers

What allows for retrieval of soluble ER proteins from the Golgi complex back to the ER?

$KDEL$ retrieval signal binding to $KDEL$ receptors and $COPI$ proteins Signup and view all the answers

What is primarily responsible for maintaining membrane asymmetry during trafficking within the endoplasmic reticulum?

Phospholipid synthesis Signup and view all the answers

Which organelle comprises the rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER)?

Endoplasmic reticulum Signup and view all the answers

What is the primary role of the smooth endoplasmic reticulum (SER) in various cell types?

Steroid hormone synthesis Signup and view all the answers

What determines the site of protein synthesis in the endoplasmic reticulum?

N-terminus sequence Signup and view all the answers

What is the process called when polypeptides move through the ER membrane during synthesis?

$\delta$-translocation Signup and view all the answers

What is the role of chaperones in the rough endoplasmic reticulum (RER) lumen?

Assist in protein folding Signup and view all the answers

What happens to approximately one-third of polypeptides encoded by the human genome?

Synthesized on ribosomes of RER and released into the ER lumen Signup and view all the answers

Study Notes

Intracellular Membrane Dynamics: ER and Golgi Complex

Membranes in the Endoplasmic Reticulum (ER) arise from preexisting membranes, and lipids are inserted into existing membranes.
Most membrane lipids are synthesized within the ER, and newly synthesized phospholipids are inserted into the cytosolic leaflet and then flipped into the opposite leaflet by flippases.
The ER has quality control mechanisms to ensure misfolded proteins are not transported further, and misfolded proteins are destroyed in the cytosol by the ER-associated degradation (ERAD) process.
The Proteasome Pathway is involved in the degradation of misfolded proteins, where ubiquitin molecules are attached to the protein substrate and recognized by the 26S proteasome.
The Golgi complex is a stack of flattened cisternae divided into cis, medial, and trans compartments, each with distinct functions in sorting and processing proteins.
There are regional differences in membrane composition across the Golgi stack, with specific enzymes and molecules present in different compartments.
The Golgi complex plays a key role in the assembly of carbohydrate components of glycoproteins and is the site of synthesis of complex polysaccharides.
The movement of materials through the Golgi complex is debated, with contrasting views on whether the cisternae are stable or mature as they move from the cis to the trans face.
Different types of coated vesicles, such as COPII, COPI, and Clathrin-coated vesicles, are involved in transporting materials between different membrane compartments of the biosynthetic-secretory pathway.
A retrieval signal, KDEL, present on soluble ER proteins determines their fate from ER to Golgi or their stay in the ER, with KDEL receptors facilitating the retrieval process.
The Golgi complex is involved in the sorting and processing of proteins, and has a role in synthesizing complex polysaccharides and glycolipids.
The ER is involved in membrane biosynthesis and lipid synthesis, and the Golgi complex is responsible for sorting and modifying proteins and lipids.

Intracellular Membrane Biosynthesis and Quality Control

Membranes in the Endoplasmic Reticulum (ER) are formed from preexisting membranes, with proteins and lipids being modified as they move through different compartments.
Most membrane lipids are synthesized within the ER, except for certain unique lipids of mitochondria and chloroplasts.
Misfolded proteins in the ER are not destroyed but are transported into the cytosol for degradation in proteasomes through ER-associated degradation (ERAD).
The ubiquitin-proteasome pathway directs the movement of proteins in the cell, where ubiquitin molecules are attached to the protein substrate and recognized by the 26S proteasome for degradation.
The Golgi complex is a stack of flattened cisternae with distinct compartments, including the cis and trans Golgi networks, involved in sorting proteins for further trafficking.
There are regional differences in membrane composition across the Golgi stack, with specific enzymes and compounds present in different cisternae.
The Golgi complex plays a crucial role in assembling carbohydrate components of glycoproteins and synthesizing complex polysaccharides found in plant cell walls.
Two contrasting models for the movement of materials through the Golgi complex are the vesicular transport model and the cisternal maturation model, with the current model incorporating both vesicle and cisternal transport.
Different types of coated vesicles, including COPII, COPI, and clathrin-coated vesicles, facilitate transport between different membrane compartments of the biosynthetic-secretory pathway.
The KDEL retrieval signal on soluble ER proteins allows for their retrieval from the Golgi complex back to the ER by binding to KDEL receptors and COPI proteins.
The ER is not involved in the synthesis of proteins, but it is the site for the synthesis of lipids for a cell's membrane, including phospholipids and cholesterol.
The ER also ensures the maintenance of membrane asymmetry during trafficking and contains enzymes that modify lipids present within the membrane.

Utility of Genetic Mutants in Studying the Endoplasmic Reticulum

Genetic mutants provide insights into the function of normal gene products.
Isolation of proteins from yeast has led to the identification of homologous proteins in mammals, indicating the conserved nature of endomembrane systems.
The endoplasmic reticulum (ER) is a dynamic network of membranes that extends throughout the cytoplasm, comprising the rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).
The smooth endoplasmic reticulum (SER) is extensively developed in various cell types and is involved in functions such as steroid hormone synthesis, detoxification, and sequestration of calcium ions.
The rough endoplasmic reticulum (RER) is composed of flattened sacs with ribosomes on its cytosolic surface and is involved in the synthesis of proteins, including secreted proteins and integral membrane proteins.
Approximately one-third of polypeptides encoded by the human genome are synthesized on ribosomes of RER and released into the ER lumen in a process called co-translational translocation.
The site of protein synthesis is determined by the sequence of amino acids in the N-terminus, with a signal sequence guiding the proteins and ribosomes to the ER membrane.
The synthesis of a secretory protein on a membrane-bound ribosome involves several steps, including recognition of the signal sequence by a signal recognition particle (SRP) and cleavage by a proteolytic enzyme in the ER lumen.
The RER lumen contains chaperones to assist in protein folding and protein disulfide isomerase to add disulfide bonds to cysteines.
The smooth endoplasmic reticulum (SER) is involved in the synthesis of steroid hormones in endocrine cells, detoxification of organic compounds, and sequestration of calcium ions in muscle cells.
The rough endoplasmic reticulum (RER) is involved in the synthesis of proteins, including secreted proteins, integral membrane proteins, and soluble proteins of organelles within the endomembrane system.
The movement of polypeptides through the ER membrane during synthesis is called cotranslational or post-translational translocation.

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Learn about the utility of genetic mutants in studying the function of normal gene products and the conserved nature of endomembrane systems. Gain insights into how mutations in specific genes can lead to the identification of homologous proteins in different organisms.