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Questions and Answers
What is the primary function of the rough ER?
What is the primary function of the rough ER?
Where are proteins synthesized that contain signal sequences?
Where are proteins synthesized that contain signal sequences?
What happens to the signal sequence during protein transfer into the ER?
What happens to the signal sequence during protein transfer into the ER?
What defines a lumen in cell biology?
What defines a lumen in cell biology?
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What is the role of the transitional ER?
What is the role of the transitional ER?
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Proteins synthesized on free ribosomes are likely to:
Proteins synthesized on free ribosomes are likely to:
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Which component is responsible for recognizing the signal sequence during protein synthesis?
Which component is responsible for recognizing the signal sequence during protein synthesis?
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What happens to secretory, ER, Golgi apparatus, and lysosomal proteins after synthesis?
What happens to secretory, ER, Golgi apparatus, and lysosomal proteins after synthesis?
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What determines the orientation of a protein once it is inserted into the endoplasmic reticulum (ER)?
What determines the orientation of a protein once it is inserted into the endoplasmic reticulum (ER)?
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What happens to misfolded proteins in the endoplasmic reticulum?
What happens to misfolded proteins in the endoplasmic reticulum?
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Which of the following is primarily synthesized in the smooth endoplasmic reticulum?
Which of the following is primarily synthesized in the smooth endoplasmic reticulum?
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What is the function of the KDEL sequence in proteins?
What is the function of the KDEL sequence in proteins?
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Which component is important for the folding of proteins inside the ER?
Which component is important for the folding of proteins inside the ER?
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How are proteins and lipids transported from the ER to the Golgi apparatus?
How are proteins and lipids transported from the ER to the Golgi apparatus?
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What is formed to stabilize proteins during post-translational modifications in the ER?
What is formed to stabilize proteins during post-translational modifications in the ER?
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What is the primary role of the rough endoplasmic reticulum?
What is the primary role of the rough endoplasmic reticulum?
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Which of the following organisms is not used to study cell biology?
Which of the following organisms is not used to study cell biology?
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What major component accounts for approximately 50% of the mass of plasma membranes?
What major component accounts for approximately 50% of the mass of plasma membranes?
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Which method is used for DNA replication in cell biology studies?
Which method is used for DNA replication in cell biology studies?
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Which of the following cell components is primarily studied using fluorescence microscopy?
Which of the following cell components is primarily studied using fluorescence microscopy?
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What is the role of cholesterol in animal plasma membranes?
What is the role of cholesterol in animal plasma membranes?
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Which technique helps in the detection and quantification of RNA?
Which technique helps in the detection and quantification of RNA?
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Which organelle is not included in the focus areas of the course outline?
Which organelle is not included in the focus areas of the course outline?
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Which process is primarily associated with the concept of epigenetics?
Which process is primarily associated with the concept of epigenetics?
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Which phospholipid is primarily found in the outer leaflet of the plasma membrane?
Which phospholipid is primarily found in the outer leaflet of the plasma membrane?
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What is the primary role of lipid rafts in the plasma membrane?
What is the primary role of lipid rafts in the plasma membrane?
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Which of the following membrane proteins are loosely associated with the plasma membrane?
Which of the following membrane proteins are loosely associated with the plasma membrane?
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Caveolae play an important role in which cellular activities?
Caveolae play an important role in which cellular activities?
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What is the function of the glycocalyx on the cell surface?
What is the function of the glycocalyx on the cell surface?
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What characteristic differentiates integral membrane proteins from peripheral proteins?
What characteristic differentiates integral membrane proteins from peripheral proteins?
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Which molecules are specifically found on the outer membrane of the plasma membrane?
Which molecules are specifically found on the outer membrane of the plasma membrane?
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How does the mobility of membrane proteins get restricted?
How does the mobility of membrane proteins get restricted?
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Study Notes
Introduction to Cell Biology
- Course taught by Prof. Mamoun Ahram in the School of Medicine
- Office hours are by appointment on Tuesdays from 12-2 pm
- Course is divided into multiple topics, including cell membranes, organelles, and cell signaling
Main Topics Covered
- Biomembranes: Composition, structure, and functions
- Endoplasmic Reticulum (ER): Protein sorting, folding, and degradation, lipid synthesis
- Golgi Apparatus: Protein modifications and packaging
- Vesicular Network: Transport of materials within the cell
- Mitochondria: Energy production and mitochondrial diseases
- Peroxisomes: Specialized metabolic functions
- Nucleus: Genetic information storage and replication
- Cytoskeleton: Structural support and cell movement
- Extracellular Network: Cell-cell interactions and communication
- Cell Signaling: Pathways regulating cellular responses
- Cancer Cells: Aberrant cell growth and proliferation
Research Organisms
- Escherichia coli (E. coli): A common bacterium used in biological research
- Yeast (Saccharomyces cerevisiae): A single-celled eukaryotic organism
- Caenorhabditis elegans: A nematode worm used in developmental biology
- Drosophila melanogaster: A fruit fly used in genetics and developmental biology
- Mice (Mus musculus): A mammalian model organism
- Cultured cells and tissues: Derived from different organisms, allowing for controlled experimentation
Major Molecular Components of Cells
- Nucleic acids: DNA and RNA, carriers of genetic information
- Carbohydrates: Sugars and polysaccharides, energy sources and structural components
- Proteins: Functional molecules involved in almost all cellular processes
- Lipids: Fats, oils, and phospholipids, structural components of membranes and energy storage
Studying Cell Components
- Cell and protein detection: Identifying and quantifying cellular components
-
Microscopy: Visualizing cells and their structures using various techniques:
- Light microscopy
- Fluorescence microscopy (immunofluorescence)
- Electron microscopy
- Scanning electron microscopy
- Cell fractionation: Separating cellular components based on size and density
Plasma Membrane Composition
-
Phospholipids: Asymmetrically distributed across the membrane bilayer
- Outer leaflet: choline, sphingomyelin
- Inner leaflet: ethanolamine, serine, inositol
- Glycolipids: Found exclusively on the outer membrane
- Cholesterol: Essential for animal plasma membranes, not present in bacteria or plant cells
Organelle Lipid Composition
- Cholesterol: Important component of animal cell membranes
- Sterols: Found in plant cells instead of cholesterol
Lipid Rafts
- Specialized membrane regions enriched in cholesterol and sphingolipids
- Involved in signal transduction and vesicular trafficking
Caveolae
- Subsets of lipid rafts requiring cholesterol for their formation
- Caveolin: Protein essential for caveolae formation
- Functions in endocytosis, cell signaling, and lipid transport
Membrane Proteins
- Peripheral membrane proteins: Loosely associate with membranes via protein-protein interactions
-
Integral membrane proteins: Embedded within the membrane bilayer
- Single-pass or multi-pass proteins
- Lipid-anchored membrane proteins: Associated with membranes via lipid modifications
Protein Mobility in Membranes
- Both proteins and lipids can diffuse laterally
- Mobility can be restricted by:
- Association with the cytoskeleton
- Specific membrane domains
- Lipid composition
Glycocalyx
- Carbohydrate coat on the cell surface composed of glycolipids and glycoproteins
-
Functions:
- Cell-cell interactions (e.g., immune cells)
- Protection from ionic and mechanical stress
- Barrier against microorganisms
Endoplasmic Reticulum (ER)
- Network of membrane-enclosed tubules and sacs (cisternae)
- Rough ER: Covered with ribosomes, involved in protein processing
- Smooth ER: Lipid metabolism
- Transitional ER: Exit point for vesicles to the Golgi apparatus
Protein Sorting
- Signal sequences: Short amino acid sequences at the amino terminus of proteins destined for the ER
- Signal sequences are recognized during translation and direct the ribosome to the ER membrane
- The signal sequence is cleaved after translocation into the ER lumen
Pathways of Protein Sorting
- Proteins synthesized on ribosomes bound to the ER:
- Secretory proteins: Released into the ER lumen
- ER, Golgi, and lysosomal proteins: Transported via vesicles
- Membranous proteins: Inserted into the ER membrane
- The ER lumen is topologically equivalent to the exterior of the cell
Insertion of Membrane Proteins
- Internal transmembrane sequences anchor proteins within the membrane
- Transmembrane sequence orientation determines the direction of insertion and protein orientation
Protein Folding and ERAD
- Properly folded proteins move to the next stage of processing
- Misfolded proteins are:
- Targeted for degradation in the proteasome
- Ubiquitylated (addition of ubiquitin proteins)
Synthesis of Phospholipids
- The smooth ER is the main site of synthesis for:
- Membrane glycerophospholipids
- Sphingophospholipids
- Steroids
ER-Golgi Intermediate Compartment (ERGIC)
- Transport vesicles carrying proteins and lipids from the ER fuse with the ERGIC before moving to the Golgi.
Retention of ER Proteins
- The KDEL sequence (Lys-Asp-Glu-Leu) at the C-terminus of many ER proteins helps retain them in the ER lumen.
- Removal of the KDEL sequence allows the protein to move to the Golgi and be secreted.
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Description
Test your knowledge on the fundamental concepts of cell biology. This quiz covers key topics such as biomembranes, organelles, and cell signaling. Brush up on your understanding of cellular structures and functions as well as the role of cells in disease.
