Podcast
Questions and Answers
Which organism is commonly used as a model to study cellular processes and is a prokaryotic organism?
Which organism is commonly used as a model to study cellular processes and is a prokaryotic organism?
What percentage of the mass of plasma membranes is typically composed of lipids?
What percentage of the mass of plasma membranes is typically composed of lipids?
Which of the following techniques is NOT used for studying cell components?
Which of the following techniques is NOT used for studying cell components?
Which of the following is NOT a focus area in the course outline related to the endoplasmic reticulum?
Which of the following is NOT a focus area in the course outline related to the endoplasmic reticulum?
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What is the main structural component of animal plasma membranes that distinguishes them from bacterial and plant cells?
What is the main structural component of animal plasma membranes that distinguishes them from bacterial and plant cells?
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Which of the following is the focus of the course that involves manipulating DNA?
Which of the following is the focus of the course that involves manipulating DNA?
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Which of these organisms is NOT typically used for studying cell biology?
Which of these organisms is NOT typically used for studying cell biology?
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Which type of membrane is comprised of 30% lipids?
Which type of membrane is comprised of 30% lipids?
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Which phospholipid is found in the outer leaflet of the plasma membrane?
Which phospholipid is 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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What type of membrane protein is characterized by being indirectly associated with membranes?
What type of membrane protein is characterized by being indirectly associated with membranes?
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Which of the following is NOT a function of the glycocalyx?
Which of the following is NOT a function of the glycocalyx?
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Which type of membrane protein has parts that are embedded in the lipid bilayer?
Which type of membrane protein has parts that are embedded in the lipid bilayer?
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What structural component is essential for the formation of caveolae?
What structural component is essential for the formation of caveolae?
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Which of the following is primarily involved in maintaining specific protein distribution in the plasma membrane?
Which of the following is primarily involved in maintaining specific protein distribution in the plasma membrane?
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What is the primary function of glycosylphosphatidylinositol (GPI)-anchored proteins in lipid rafts?
What is the primary function of glycosylphosphatidylinositol (GPI)-anchored proteins in lipid rafts?
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What is the primary function of rough ER?
What is the primary function of rough ER?
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What role do signal sequences play in protein synthesis?
What role do signal sequences play in protein synthesis?
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Where are proteins synthesized that will be processed in the rough ER?
Where are proteins synthesized that will be processed in the rough ER?
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Which of the following best describes the transitional ER?
Which of the following best describes the transitional ER?
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What happens to the signal peptide during protein transfer to the ER lumen?
What happens to the signal peptide during protein transfer to the ER lumen?
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What types of proteins are released into the lumen of the ER?
What types of proteins are released into the lumen of the ER?
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What does the term 'lumen' refer to in cell biology?
What does the term 'lumen' refer to in cell biology?
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Which type of ribosomes synthesizes proteins that are released outside of the cell?
Which type of ribosomes synthesizes proteins that are released outside of the cell?
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What determines the direction of insertion and orientation of a membrane protein in the endoplasmic reticulum?
What determines the direction of insertion and orientation of a membrane protein in the endoplasmic reticulum?
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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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Where is the major site of membrane glycerophospholipid synthesis located?
Where is the major site of membrane glycerophospholipid synthesis located?
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What is the role of chaperones in the endoplasmic reticulum?
What is the role of chaperones in the endoplasmic reticulum?
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What sequence allows retention of proteins within the ER lumen?
What sequence allows retention of proteins within the ER lumen?
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What type of cells would contain large amounts of smooth endoplasmic reticulum?
What type of cells would contain large amounts of smooth endoplasmic reticulum?
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What is the function of the ER-Golgi intermediate compartment (ERGIC)?
What is the function of the ER-Golgi intermediate compartment (ERGIC)?
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What type of modification occurs to proteins inside the endoplasmic reticulum after they are synthesized?
What type of modification occurs to proteins inside the endoplasmic reticulum after they are synthesized?
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Study Notes
Course Outline
- The course will cover Introduction/biomembranes, ER/protein sorting, Golgi apparatus, vesicular network, mitochondria/mitochondrial diseases, peroxisomes, nucleus, cytoskeletal networks, extracellular network, cell signalling, proliferation, differentiation, death, and cancer cells
- Introduction and the central dogma of molecular biology, gel electrophoresis, restriction endonucleases, recombinant DNA technology, DNA cloning and RFLP, denaturation/renaturation concepts, dot/Southern blotting, DNA replication, PCR and DNA sequencing, the human genome, transcription, mechanisms of regulation, epigenetics, coding and non-coding RNA, RNA detection/quantification, translation, yeast two-hybrid system, DNA mutations, DNA repair, and CRISPR-Cas9 will also be discussed.
What Organisms are Used to Study Cells?
- Escherichia coli (E. coli)
- Yeast (Saccharomyces cerevisiae)
- Caenorhabditis elegans
- Drosophila melanogaster
- Mice
- Cultured cells and tissues
Major Molecular Components of Cells
- Nucleic acids
- Carbohydrates
- Proteins
- Lipids (50% of plasma membrane mass, 30% of mitochondrial membranes)
How to Study Cell Components
- Cell and protein detection
- Microscopy (light, fluorescence (immunofluorescence), electron, scanning electron)
- Cell fractionation
Biochemical Composition of Plasma Membranes
- Phospholipids are asymmetrically distributed on each side of the membrane bilayer
- Outer leaflet: Choline and sphingomyelin
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Inner leaflet: Ethanolamine, serine, inositol (minor)
- Inositol plays a role in cell signalling
- Glycolipids are exclusively found on the outer membrane.
Lipid Rafts
- Specialized membrane regions with clusters of cholesterol and sphingolipids (sphingomyelin and glycolipids)
- Enriched in glycosylphosphatidylinositol (GPI)-anchored proteins and proteins involved in signal transduction and intracellular vesicular trafficking (transport)
Caveolae
- A subset of lipid rafts that require cholesterol for formation
- Formed by the membrane protein caveolin, which interacts with cholesterol and the cytoplasmic protein cavin
- Important for several cellular activities including endocytosis, cell signalling, regulation of lipid transport, and protection of the plasma membrane against mechanical stress
Types of Membrane Proteins
- Peripheral membrane proteins are indirectly and loosely associated with membranes through protein-protein interactions, mainly ionic bonds.
- Integral membrane proteins have some of their helical parts inserted into the lipid bilayer. They can be single-pass (type I or II) or multi-pass proteins.
- Lipid-anchored membrane proteins (myristoylation, palmitoylation, glycosyl-phosphatidylinositol)
Protein Mobility
- Proteins and lipids are able to diffuse laterally within the membrane.
- The mobility of membrane proteins is restricted by:
- Their association with the cytoskeleton
- Specific membrane domains, which maintain the specific distribution of apical and basolateral proteins
- Specific lipid composition (e.g. lipid rafts).
Glycocalyx
- The surface of the cell is covered by a carbohydrate coat known as the glycocalyx, formed by the oligosaccharides of glycolipids and glycoproteins.
- Functions:
- Cell-cell interactions such as immune cells
- Protection of cell surface from ionic and mechanical stress
- Formation of a barrier for microorganisms
Endoplasmic Reticulum (ER)
- A network of membrane-enclosed tubules and sacs (cisternae) that extends from the nuclear membrane throughout the cytoplasm.
- The largest organelle in most eukaryotic cells.
- Rough ER: Covered by ribosomes on its outer surface and functions in protein processing
- Smooth ER: Lipid metabolism
- Transitional ER: Exit of vesicles to Golgi apparatus
Protein Sorting
- Proteins containing signal sequences are synthesized on membrane-bound ribosomes and translocated directly into the ER
- These proteins may stay within the ER or be transported to nuclear membranes, peroxisomal membranes, or the Golgi apparatus and from there to endosomes, lysosomes, the plasma membrane, or outside the cell via secretory vesicles.
- Lumen: a membrane-defined space found inside several organelles, cellular components, or structures
-
Signal sequence: A sort sequence of amino acids of the polypeptide at the amino terminus. It is then cleaved from the polypeptide chain during its transfer into the ER lumen.
- The signal sequence is recognized as the protein is synthesized and the ribosome is transported to the surface of the RER
- Translation resumes on the surface of RER, the peptide simultaneously translocates into the ER through the translocon, and the signal peptide is cleaved by signal peptidase
- The completed polypeptide chain is released within the ER lumen
Pathways of Protein Sorting
- Secretory, ER, Golgi apparatus, and lysosomal proteins are released into the lumen of the ER.
- Membranous proteins are initially inserted into the ER membrane.
- Considerations: Single vs. multiple membrane-spanning region, orientation of N- and C-termini
- The lumens of the ER and Golgi apparatus are topologically equivalent to the exterior of the cell.
Insertion of Membrane Proteins via Internal Transmembrane Sequences
- Translocation of the polypeptide chain stops when the translocon recognizes a transmembrane sequence allowing the protein to become anchored in the ER membrane.
- The direction of the internal transmembrane sequence determines the direction of insertion and orientation of the protein ends.
Multi-Transmembrane Domain Proteins
- Have multiple transmembrane sequences.
Once Inside the ER, Proteins Are:
- Folded (with the help of chaperones)
- Complexed (quaternary structure)
- Disulfide bond formation by protein disulfide isomerase
- Glycosylated
- Anchored by lipids
Protein Folding and ER-Associated Degradation (ERAD)
- If correctly folded, proteins move on.
- If misfolded, proteins are sent to the cytosol, ubiquitylated (addition of small proteins called ubiquitins), and degraded in the proteasome.
Synthesis of Phospholipids in ER
- The smooth ER is the major site of synthesis of membrane glycerophospholipids, which are then transported from the SER to other membranes.
- Sphingophospholipids (like ceramides and glycolipids) and steroids.
- Large amounts of smooth ER are found in steroid-producing cells, such as in the testis and ovary.
- SER is abundant in the liver, which contains enzymes that metabolize various lipid-soluble compounds.
ER-Golgi Intermediate Compartment (ERGIC)
- Proteins and lipids are carried from the ER to to the Golgi in transport vesicles, which fuse with the ER–Golgi intermediate compartment (ERGIC), and are then carried to the Golgi.
Retention of ER Protein
- Many proteins with the KDEL sequence (Lys-Asp-Glu-Leu) at the C-terminus are retained in the ER lumen.
- If the sequence is deleted, the protein is transported to the Golgi and secreted from the cell.
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Description
This quiz explores fundamental concepts in cell biology, including biomembranes, organelles, and cell signaling. It also delves into the central dogma of molecular biology, DNA technology, and the various model organisms used in cellular studies. Test your knowledge on these essential topics in cellular and molecular biology.
