85 Questions
What is the function of signal recognition particle (SRP)?
It recognizes and binds to the signal sequence and to the ribosome
What type of proteins are targeted for the ER by cotranslational translocation?
Most ER lumen proteins
What is the function of oligosaccharide transferase in the ER?
It adds glycosyl groups to asparagines in the nascent protein
What is the importance of glycosylation in protein processing?
It plays a critical role in determining protein structure, function and stability
What is the role of chaperones in the ER?
They bind to polypeptides and keep them from interacting with anything until the polypeptide is completely synthesized
What is the consequence of incorrect protein folding in the ER?
The protein could assume incorrect formation or aggregate with other partially made polypeptides
Where do chaperones bind to polypeptides in the mitochondria?
On the inside of the mitochondrial membrane
What is the process by which soluble materials in the extracellular fluid are taken up and incorporated into vesicles for digestion?
Receptor-mediated endocytosis
Where are proteins sorted for transport to lysosomes, plasma membrane, or secretion from the cell?
Golgi Apparatus
What is the function of Nuclear Localization Signal (NLS) in protein sorting?
Direct import of proteins into the nucleus
What is the characteristic of mitochondrial and chloroplast membranes?
Double membrane
What is the process by which proteins are transported to the mitochondrial matrix?
Protein unfolding and translocation
What is the function of the signal sequence in amino acid sequence in protein sorting?
Specifying the final destination of proteins
What is the role of the trans Golgi network in protein sorting?
Sorting proteins according to their final destination
What is the characteristic of proteins that pass through the Golgi apparatus?
They are all except those retained in the Golgi apparatus
What is the primary function of peroxisomes?
To isolate and break down harmful hydrogen peroxide
Which pathway is responsible for the transport of proteins to the extracellular environment?
Secretory pathway
What is the characteristic of the chemical environment in the ER and Golgi apparatus?
Oxidizing
Which proteins are translocated simultaneously into the mitochondrial matrix?
Mitochondrial matrix proteins
What is the purpose of chaperone proteins in protein transport?
To help pull proteins across membranes and refold them
Which organelles are involved in the secretory pathway?
Endoplasmic reticulum, Golgi apparatus, and cell membrane
What is the characteristic of mitochondrial matrix proteins?
They are folded in the cytosol and cross the membrane in their folded conformation
Which proteins are synthesized on free ribosomes?
Co-translationally translocated proteins
What is the term for the process by which cells engulf and internalize external substances through the formation of vesicles?
Phagocytosis
What is the term for the process by which molecules are released from the cell through the fusion of secretory vesicles with the plasma membrane?
Exocytosis
What is the function of the endomembrane system in eukaryotic cells?
To transport molecules across membranes
What is the term for the process by which cells take in fluids and macromolecules through the formation of small vesicles?
Pinocytosis
What is the function of lysosomes in eukaryotic cells?
To digest and recycle cellular waste and foreign substances
What is the term for the movement of molecules across membranes through the use of electrochemical potential?
Active Transport
What is the function of the Golgi apparatus in eukaryotic cells?
To modify and package proteins and lipids for transport
What is the term for the process by which molecules are transported across membranes through selective channels?
Selective Transport
What is the function of calreticulin in the ER?
To bind calcium ions
What happens to misfolded proteins retained in the ER?
They are retro-translocated to the cytosol for degradation
What is the mechanism known as ER-associated degradation (ERAD)?
Retro-translocation of misfolded proteins to the cytosol
How do single-pass transmembrane proteins (TMPs) pass through the phospholipid bilayer?
Only once
What is the characteristic of multipass transmembrane proteins (TMPs)?
They have an N-terminal motif on the cytosolic face
What is the function of the trans-Golgi network?
Processing and sorting of glycoproteins and glycolipids
What is the purpose of the Golgi apparatus?
Processing and modification of proteins and lipids
What is the orientation of ER transmembrane proteins established during?
Biosynthesis on the ER membrane
What is the role of chaperones in the ER during protein synthesis, and how do they prevent incorrect protein folding?
Chaperones in the ER bind to nascent polypeptides and prevent them from interacting with other molecules until they are fully synthesized, preventing incorrect folding and aggregation.
How does the cell respond to misfolded proteins retained in the ER?
Misfolded proteins retained in the ER are degraded through ER-associated degradation (ERAD).
What is the difference between single-pass and multipass transmembrane proteins (TMPs) in terms of their topology?
Single-pass TMPs pass through the phospholipid bilayer once, while multipass TMPs pass through multiple times.
What is the mechanism by which proteins are targeted for the ER by cotranslational translocation?
Signal recognition particle (SRP) recognizes and binds to the signal sequence near the N-terminus of the protein, halting translation.
What is the role of calreticulin in the ER, and how does it relate to calcium binding?
Calreticulin is a calcium-binding protein in the ER that helps regulate calcium levels and protein synthesis.
What is the significance of protein glycosylation in the ER lumen, and how does it relate to protein folding?
Glycosylation adds oligosaccharides to asparagines in the nascent protein, influencing protein structure, function, and stability during folding.
How do chaperones facilitate protein folding in the ER, and what is the consequence of incorrect folding?
Chaperones bind to nascent polypeptides, preventing incorrect folding, which can lead to aggregation and degradation.
What is the purpose of the translocon complex in the ER, and how does it relate to protein synthesis?
The translocon complex adds glycosyl groups to asparagines in the nascent protein, facilitating protein synthesis and folding.
What happens to misfolded proteins retained in the ER?
Misfolded proteins retained in the ER are retro-translocated to the cytosol to be degraded by the proteasome through a mechanism known as ER-associated degradation (ERAD).
What is the role of calreticulin in the ER?
Calreticulin is a calcium binding integral protein that plays a role in protein folding and glycoprotein synthesis in the ER.
How do single-pass transmembrane proteins (TMPs) pass through the phospholipid bilayer?
Single-pass TMPs pass through the phospholipid bilayer only once, characterized by an N-terminal motif on the exoplasmic face and a hydrophilic C-terminal segment on the cytosolic face.
What is the characteristic of multipass transmembrane proteins (TMPs)?
Multipass TMPs pass through the phospholipid bilayer multiple times, characterized by an N-terminal motif on the cytosolic face.
What is the function of the trans-Golgi network?
The trans-Golgi network is involved in the processing and sorting of glycoproteins and glycolipids at the interface of the biosynthetic and endosomal pathways.
When are ER transmembrane proteins' orientation established?
The orientation of ER transmembrane proteins is established during biosynthesis on the ER membrane.
What is the role of chaperones in protein folding, and how do they interact with polypeptides in the ER?
Chaperones assist in protein folding by binding to unfolded polypeptides, preventing aggregation. In the ER, chaperones bind to hydrophobic regions of polypeptides, helping to maintain their unfolded state until they reach their native conformation.
What is the mechanism of ER-associated degradation (ERAD), and how does it contribute to protein quality control?
ERAD is a process in which misfolded or unassembled proteins are retrotranslocated from the ER to the cytosol for proteasomal degradation, maintaining protein homeostasis.
Describe the orientation of ER transmembrane proteins established during translation, and how does this orientation influence their function?
During translation, ER transmembrane proteins are inserted into the ER membrane with their N-terminus in the ER lumen and C-terminus in the cytosol, influencing their function and interaction with other proteins.
What is the role of calreticulin in the ER, and how does it interact with calcium ions?
Calreticulin is a calcium-binding chaperone in the ER that assists in protein folding and quality control, with its calcium-binding activity influencing its chaperone function.
How do proteins synthesized on free ribosomes differ from those translated on ER-bound ribosomes?
Proteins synthesized on free ribosomes are typically cytosolic or nuclear, whereas those translated on ER-bound ribosomes are usually secretory or membrane-bound proteins.
What is the characteristic of multipass transmembrane proteins (TMPs), and how do they interact with the phospholipid bilayer?
Multipass TMPs have multiple transmembrane regions, which span the phospholipid bilayer, allowing them to interact with both the cytosol and the ER lumen.
What is the purpose of the trans-Golgi network (TGN) in protein sorting, and how does it differ from the cis-Golgi network?
The TGN is a region of the Golgi apparatus where proteins are sorted and packaged for transport to lysosomes, plasma membrane, or secretion, differing from the cis-Golgi network, which receives proteins from the ER.
What is the role of signal sequences in protein targeting, and how do they influence protein sorting and localization?
Signal sequences are specific amino acid sequences that direct proteins to their target organelles, influencing protein sorting and localization through interactions with receptors and translocation channels.
What is the primary function of hydrophilic and hydrophobic passageways in solute transport across membranes?
To allow transport of nutrients and other solutes into the cell
What is the role of electron transport proteins in mitochondria?
To generate energy in the mitochondria
What is the characteristic of the cell membrane that allows it to be flexible and fluid?
Its dynamic structure, with ions and organic molecules that can change
What is the role of receptors in intercellular communication?
To trigger an intracellular response to chemical signals
What is the purpose of vesicles in cellular transport?
To store and transport materials within the cell
What is the importance of selective permeability in cell membrane function?
To maintain homeostasis and regulate the flow of molecules into and out of the cell
What is the primary function of membrane transport?
To facilitate the movement of ions and organic molecules across the cell membrane
Which type of receptors bind signaling molecules outside the cell and initiate physiological responses?
G-protein coupled receptors
What is the term for the simultaneous transport of two solutes in the same or opposite directions across the membrane?
Coupled transport
What determines the permeability of a substance through the bilipid layer?
The size and charge of the molecule
Which class of receptors is characterized by the presence of an ion channel that opens and closes in response to chemical or mechanical signals?
Ion channel receptors
What is the role of carrier proteins in membrane transport?
To facilitate the movement of solutes across the membrane
What is the characteristic of Enzyme-linked receptors?
They phosphorylate proteins in response to signaling molecules
What is the term for the protein that binds to GTP or GDP, depending on activation?
Alpha subunit
What is the primary function of the cell membrane?
To facilitate the exchange of materials and energy with the environment
What is the term for the fluid state of the phospholipid bilayer in the cell membrane?
Fluid mosaic model
What is the purpose of membrane enzymes?
To facilitate the breakdown of substances
What is the function of transport proteins in the cell membrane?
To regulate the concentration of ions and molecules
What is the term for the molecules that allow cells to identify and interact with each other?
Cell adhesion molecules
What is the term for the lipids that make up the cell membrane?
Phospholipids
What is the characteristic of the hydrophobic tail of a phospholipid?
It is hydrophobic
What is the term for the type of lipid that has a sugar molecule attached to the glycerol backbone?
Glycolipid
What are the three major classes of Transmembrane receptors?
Ligand-gated ion channels, enzyme-linked receptors, and G-protein coupled receptors
What is the role of an amphipathic lipid in a phospholipid bilayer structure?
To create a hydrophobic (water-fearing) environment
Study Notes
Enzymes and Membrane Function
- Enzymes aid in identifying specific organelles and are involved in energy production in mitochondria, with electron transport proteins like cytochromes and iron sulphur proteins playing a crucial role.
- Solute transport across membranes occurs through hydrophilic and hydrophobic passageways, allowing for the transport of nutrients.
Cell Membrane Properties
- The cell membrane is a dynamic, non-rigid structure that allows for flexibility and fluidity due to its composition of ions and organic molecules.
- Vesicles are structures within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer, and are formed during secretion, uptake, and transport of materials within the plasma membrane.
Dynamism of Cell Membrane
- The fatty acid composition of the cell membrane can change, with unsaturated fatty acids and chain length affecting its properties.
- The cell membrane has selective permeability, allowing certain substances to pass through while restricting others, which is crucial for maintaining homeostasis and proper cellular function.
Membrane Transport
- Membrane transport involves the movement of solutes across the membrane, with a higher concentration of solutes inside organelles than outside.
- The major aspects of membrane transport include permeability of the molecule through the lipid bilayer and the availability of an energy source.
- There are two types of transport: primary active transport, which is directly driven by ATP hydrolysis, and secondary active transport, which is driven by the gradient power of another molecule.
Receptors
- Receptors bind signaling molecules outside the cell and initiate a physiological response, with transmembrane proteins being classified into three main types: ion channel receptors, G-protein coupled receptors, and enzyme-linked receptors.
- Ion channel receptors are multimeric proteins that form a passageway through the membrane, allowing specific ions to pass through.
- G-protein coupled receptors are specialized proteins that bind to GTP or GDP, depending on activation, and dissociate into two parts that interact with other membrane-bound proteins.
- Enzyme-linked receptors, such as receptor tyrosine kinases (RTKs), are the largest class of enzyme-linked receptors and are regulated by protein tyrosine phosphatase (PTP).
Cell Membrane Structure
- The cell membrane is composed of a phospholipid bilayer, embedded proteins, carbohydrates, and cholesterol.
- The fluid mosaic model describes the structure of the cell membrane, with proteins embedded in the lipid bilayer and carbohydrates attached to the surface.
Membrane Lipids
- Phospholipids are amphipathic lipids with a phosphate-based head group and a hydrophobic tail, consisting of phosphoglycerides, sphingolipids, and sterols.
- Glycolipids are composed of monosaccharides attached to glycerol, while sterols are multi-ring molecules related to cholesterol.
This quiz covers protein folding in the ER, including the role of calreticulin, ER-associated degradation, and the processing of ER transmembrane proteins.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
