Final Exam (Material From Last 4 Chapters)
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What are the three major types of cytoskeletal proteins, their basic subunits, their energy usage, and their stability?
Microtubules -alpha and beta tubulin -GTP hydrolysis -dynamic instability Intermediate Filaments -fibrous protein subunits (keratin, vimentin) -does NOT require energy -high stability, dynamic Actin Filaments -actin protein subunits -require ATP hydrolysis -less stable, rapid turnover
Rank the three major types of cytoskeletal proteins from smallest to largest
SMALLEST: Actin Filaments NEXT: Intermediate Filaments LARGEST: Microtubules
What are some functions of Intermediate Filaments and where are they located in a cell?
-stabilize nuclear membrane -help form cell-cell junctions (desmosomes) found throughout the cytoplasm
What types of cells would you expect to have a great deal of intermediate filaments in the cytoskeleton, and why?
-Epithelial cells -Muscle cells these are cells that experience mechanical stress, where structural support and mechanical capabilities are greatly needed
Microtubules can be very dynamic structures. When would you expect cytoskeletal proteins to form stable, relatively permanent structures in a cell vs. transient, temporary structures?
PERMANENT: -when long-term structural support or tissue integrity is required TRANSIENT: -for dynamic cellular processes like cell division, migration, and intracellular transport
Name one disease/problem that may occur in Microtubules, Intermediate Filaments, and Actin Filaments
Microtubules - Kartagener Syndrome (fertility problems, lung infections, cilia are disrupted and unable to function) Intermediate Filaments - Progeria (genetic, impaired cell division and nuclear instability) Actin Filaments - Phalloidins (inhibit depolymerization of actin)
Give some examples of how the cytoskeleton facilitates intracellular transport.
-mitotic spindle formation with cell division (microtubules) -vesicle transport (actin) -kinesin and dyesin transport of cargo
Describe the structure of the nucleus. Include in your description, nuclear pores, nuclear envelope, nuclear lamina, and nucleolus.
Nuclear Envelope = acts as a barrier, separating the contents of the nucleus from the cytoplasm (double membrane that surrounds the nucleus Nuclear Pores = large protein complexes embedded in the nuclear envelope, gateways for the transport of molecules between the nucleus and the cytoplasm, regulate the passage of ions, small molecules, and macromolecules Nuclear Lamina = meshwork of intermediate filaments that lies on the inner surface of the nuclear envelope, structural support to the nucleus and helps maintain its shape Nucleolus = rRNA synthesized, within the nucleus
How does a nuclear pore differ from an ion channel?
-requires energy in the form of GTP -proteins transported in folded state -use nuclear transport receptors that are able to bind to a protein (through signals) and pull them through the pore via their amino acid sequences
How are proteins targeted to the nucleus rather than some other organelle within the cell? Give examples of proteins that you might expect to be targeted to the nucleus
nuclear localization signals (NLS) facilitate their import into the nucleus -transcription factors -histones
Describe how proteins are transported into the nucleus and understand the role that GTP plays in this process.
• NLS binds to cargo protein • Receptor transports cargo protein to nucleus • Cargo protein delivered to nucleus when Ran-GTP bind to transport receptor, releasing the cargo protein • Empty receptor returns to cytosol and Ran-GDP dissociates (GTP is hydrolized)
Describe the three mechanisms by which proteins are imported into organelles
• Transport through Nuclear Pores • Transport across Membranes (STOP-TRANSFER SEQUENCES!) • Transport by Vesicles (inward or outward)
What is the difference between a free and bound ribosome? Are they structurally the same or different? Where do proteins go that are produced by each?
free ribosomes are located in the cytoplasm and synthesize proteins for the cytoplasm itself or organelles within the cytoplasm. Bound ribosomes are associated with the ER membrane and produce proteins that are targeted to secretory pathways or specific organelles.
What are the two types of endoplasmic reticulum (ER)?
Rough and Smooth
What is the role of the signal recognition peptide (SRP) in protein synthesis?
binds to SRP on the ribosome to “pull it to the spot” for which the proteins polypeptide chain can be translocated into the ER lumen
What type of protein modifications can occur in the RER? Give a specific example of two types of modification
-form disulfide bonds (insulin) -glycosylation by glycosyltransferases -protein folding -cleaving by peptidases
How does a transport vesicle get from the RER to the Golgi apparatus?
COP II
How can proteins be further modified in the Golgi apparatus? Give an example.
glycosylation
Define the difference between pinocytosis, phagocytosis, and receptor-mediated endocytosis
Pinocytosis = “drinking,” extracellular fluid Phagocytosis = “eating,” solid particles Receptor-mediated endocytosis = molecules bind to receptors and coated pit engulfs and forms vesicle to bring into the cell
What is a KDEL receptor?
grabs signal sequence
What are the three types of receptors present on the cell surface, and an example for each?
• Ion Channels (Na+) • GPCRs (epinephrine) • Enzyme-coupled receptors (insulin)
Which of the following is true of G-protein coupled receptors (GPCRs)? a. A ligand binds to the alpha subunit of the GPCR, which then hydrolyzes GTP to GDP b. When a ligand binds to the receptor portion of the GPCR, the alpha subunit dissociates and is involved in down-stream signaling events. c. A ligand hydrolyzes GTP to GDP, which activates the receptor portion of the GPCR. d. The beta-gamma subunit does not participate in any down-stream signaling events. e. All of the above are true
b. When a ligand binds to the receptor portion of the GPCR, the alpha subunit dissociates and is involved in down-stream signaling events.
What are three reasons that a cell might divide?
• growth and development • tissue repair • reproduction
What is P53?
induces apoptosis if DNA cannot be repaired (in S phase) “Guardian of the Genome