cell signalling 2

• What are the general features of signal transduction?

  Hydrophobic and hydrophilic signals

  
• How is signal transduction amplified?

  Through multiple steps in the signaling pathway

  
• What is the advantage of signal amplification in terms of sensitivity?

  It enhances the detection of weak signals
• Name an important biological example of signal transduction.

  Vision in human rod cells

  
• What is rhodopsin?

  A GPCR that senses light

  
• Where is rhodopsin located in rod cells?

  In the flattened membrane disks
• What happens to cis-retinal when light is absorbed?

  It is converted to all-trans isomer

  
• What triggers the isomerization of retinal in rhodopsin?

  Absorption of energy from a photon

  
• What is the role of activated rhodopsin?

  It activates Gt protein (transducin)

  
• What happens to all-trans-retinal after it dissociates from opsin?

  It is converted back to cis isomer

  
• What is the effect of light activation on cGMP-gated cation channels?

  They close, leading to hyperpolarization

  
• What is the initial effect of light on dark-adapted rod cells?

  High cGMP levels keep channels open

  
• What is the first step in the light activation of rhodopsin?

  Light absorption activates rhodopsin to R*

  
• What does Gαt·GTP bind to in the signaling pathway?

  PDE (cGMP phosphodiesterase)
• What is the result of PDE activation?

  Hydrolysis of cGMP to GMP
• What happens to the cytosolic cGMP concentration when light activates rhodopsin?

  It decreases, closing cation channels

  
• What is the significance of signal termination in vision?

  It allows temporal resolution of vision
• What complex binds to the GTP-γ subunit for signal termination?

  RGS9-Gβ5 GTPase-activating complex
• What is the role of guanylate cyclase in the signaling pathway?

  It generates cGMP when Ca2+ drops
• What is the function of rhodopsin kinase?

  It phosphorylates light-activated rhodopsin

  
• What does arrestin do in the feedback repression process?

  It inhibits rhodopsin activation of Gαt

  
• How quickly does the process of rhodopsin phosphorylation occur?

  Within 50 milliseconds

  
• What is the effect of signal transduction pathways on extracellular signals?

  They amplify the effects of signals

  
• What does low blood levels of epinephrine stimulate?

  Liver glycogenolysis and glucose release
• How many G proteins can a single epinephrine molecule activate?

  Hundreds of G proteins

  
• What does AC catalyze in the signaling pathway?

  Synthesis of cAMP molecules
• What do activated target proteins do in the signaling pathway?

  Phosphorylate and activate multiple proteins

  
• What is gene expression?

  Process of synthesizing a functional gene product
• What is transcription?

  Making mRNA from a DNA template
• What is transcriptional regulation?

  Controlling the rate of gene transcription
• What is a transcription factor?

  A protein that regulates gene expression
• What does upregulation do in gene transcription?

  Increases the rate of gene transcription
• What is a coactivator?

  A protein that increases gene transcription rate
• What is a corepressor?

  A protein that decreases gene transcription rate
• What is a response element?

  A specific DNA sequence for transcription factors
• What is the process of making mRNA from DNA called?

  Transcription
• What role does RNA polymerase play in transcription?

  It synthesizes mRNA from a DNA template
• How do transcription factors affect gene expression?

  They promote or suppress transcription
• What does upregulation do to gene transcription?

  Increases the rate of transcription
• What is downregulation in gene transcription?

  Decreases the rate of transcription