Cell Molecular Exam 4 Flashcards
(18 cards)
- How is each of the following used to study vesicle trafficking?
a. Temperature-sensitive yeast mutants
RER => Vesicles => golgi => vesicles => plasma membranes
What would various accumulations in areas indicate that the mutation would be
- How is each of the following used to study vesicle trafficking?
b. endoglycosidase D sensitivity
Indicates whether proteins have passed the medial Golgi; resistance means they have advanced, sensitivity means they haven’t.
- What are the 3 types of coated vesicles? For each one
What is its origin and destination? What coat proteins does it have? Does it move in an anterograde or retrograde direction?
COPII -transport newly synthesized proteins containing Golgi-targeting sequences in their cytosolic domain or bound to such proteins from the rough ER to the cis-Golgi (anterograde direction).
COPI - transport vesicles carrying ER/Golgi-resident proteins in the retrograde direction, which supports Golgi cisternal maturation. RETROGRADE
Clathrin - Trans-Golgi, plasma membrane, Endosomes/lysosomes, Clathrin, adaptins (AP1–AP3)
- What is the function of the GTPase, Rab and SNARE proteins in vesicles?
Rab (GTPases): Specify vesicle targeting by recruiting tethering proteins.
SNAREs: Mediate membrane fusion—v-SNAREs on vesicles pair with t-SNAREs on target membranes.
- What is cisternal maturation?
Process for movement of proteins through the Golgi, one cisterna that matures, proteins are modified.
Golgi cisternae themselves move forward (cis to trans), changing composition as they go. Retrograde vesicle traffic (COPI) returns enzymes to earlier compartments.
- How is a a protein in the trans-Golgi network directed to the lysosome, endosome, constitutive secretion, or regulated secretion?
To lysosome: Mannose-6-phosphate tagging → clathrin-coated vesicle.
Endosome: Specific receptors mediate sorting.
Constitutive secretion: Default pathway—continuous transport to membrane.
Regulated secretion: Proteins are stored in vesicles, released upon signal.
- What are multivesicular endosomes? What is their function?
Endosomes with internal vesicles that deliver membrane proteins to lysosomes for degradation. Also exploited by viruses like HIV for budding.
- Describe the structure and function of a G Protein-Coupled Receptor.
Structure: 7 transmembrane helices.
Function: Ligand binding activates G-proteins (trimeric), which then regulate effectors like adenylyl cyclase or phospholipase C.
- Describe the process by which an extracellular signal results in a change in cellular activity. (Key players: ligands, receptors, G-proteins, kinases, phosphatases, effectors)
Ligand → Receptor (e.g., GPCR) → G-protein activation → Effector enzyme (e.g., adenylyl cyclase) → Second messenger (e.g., cAMP) → Protein kinases → Cellular response.
- What is a second messenger? How is each of the following second messengers activated and what does it do?
a. cAMP
Activation: Adenylyl cyclase. Precursor - G-protein activated => enzymes
Function: Activates PKA → gene expression, metabolism
- What is a second messenger? How is each of the following second messengers activated and what does it do?
b. IP3 and DAG
Activation: PLC cleaves PIP2 → IP3 + DAG
Precursor - PIP2, is cleaved
Function: IP3: releases Ca²⁺ from ER; DAG: activates PKC
activates 2 enzymes, then releases Ca2+, which then activates Phospholipase C (PKC)
- What is a second messenger? How is each of the following second messengers activated and what does it do?
c. Ca2+
Activation: Released via IP3; also through channels
Function: Binds calmodulin, activates kinases and signaling cascades
- How can a signal transduction pathway be amplified or repressed?
Amplification: One ligand → many G-proteins → many second messengers → broad effect.
Repression: Feedback inhibition, receptor desensitization (e.g., β-arrestin), phosphodiesterases breaking down cAMP.
Negative feedback loop:
Signal amplification, one component, many targets.
- Describe the general structure of a receptor tyrosine kinase. How are these receptors activated and what happens when they are? What kinds of cellular processes do these receptors regulate?
Structure: Ligand-binding extracellular domain, single transmembrane helix, intracellular tyrosine kinase domain.
Activation: Ligand binding → dimerization → autophosphorylation → recruitment of signaling proteins.
Functions: Cell growth, differentiation, survival
- Outline the steps of each pathway.
a. Ras-MAPK pathway
- RTK binds ligand.
- Grb2 binds phosphorylated RTK.
- SOS activates Ras (GDP → GTP).
- Ras activates Raf → MEK → MAPK.
- MAPK phosphorylates transcription factors → gene expression.
- Outline the steps of each pathway.
b. JAK-STAT pathway
- Cytokine binds receptor → receptor dimerizes.
- JAK phosphorylates the receptor and STAT proteins.
- STATs dimerize and enter the nucleus.
- Activate gene transcription.
- Terminated by SHP1 (short-term) and SOCS (long-term).
- How is each of the following irreversible mechanisms used in signal transduction? Give an example of each.
a. Site-specific protein cleavage
Site-specific protein cleavage: Example: Notch signaling—ligand binding causes proteolysis of the receptor; cleaved segment enters nucleus to alter transcription.
- How is each of the following irreversible mechanisms used in signal transduction? Give an example of each.
b. Proteasomal degradation of signaling components
Proteasomal degradation: Example: Wnt and NF-κB pathways—proteins are ubiquitinated and degraded to regulate signaling duration and strength
