Biochemistry Online: An Approach Based on Chemical Logic

Biochemistry Online





Learning Goals/Objectives for Chapter 9B:
After class and this reading, students will be able to

  • describe how a transmembrane ion gradient and nongated/gated membrane ion channels specific for given ions can give rise to a transmembrane electric potential across membranes
  • given ion concentrations and the electrical potential across a membrane, predict likely changes in the membrane potential and ion concentrations on the opening of specific channnels;
  • use the Goldman equation to predict transmembrane electrical potentials;
  • state difference between the communication across the neuromuscular junction and a synapse between two neurons;
  • state the difference between nongated and gated ion channels;
  • describe different ways to open/close gated ion channels
  • describe the immediate changes in the muscle cells when acetylcholine is released into the neuromuscular junction
  • describe the roles of stimulatory neurotransmitter receptors, voltage-gated Na+and K+ channels and the Na/K-ATPase  in the activation of a neuron;
  • explain the mechanism for selectivity of K+ over the smaller Na+ ion in the K+ channel;
  • briefly explain how membrane protein channels can be gated open by changes in transmembrane potential;

B11.  The Senses

Taste (Gustatory)- There are 5 different types of tastants  perceptible to mammals.  These include sweet, sour, salty, bitter, and umami (taste of monosodium glutamate).  It appears that different cells expressing different tastant receptors (TR) mediate taste.  These receptors could be ligand-gated ion channels, or work through ligand-induced conformational changes in the receptor which are sensed by intracellular proteins (usually G proteins, that are discussed in the next chapter section). 

Sweet -  Cells that recognize and respond to sweet tastants express receptors from the TIR family.  The receptor appears to be active as a heterodimer.  Dimers of T1R2 and T1R3 recognize sucrose and saccharin.  The bound receptor is coupled to intracellular G proteins.

Sour - This sense would protect us from excessively acidic foods.  Huang et recently found an ion channel, PKD1L1 (Polycystic-Kidney-Disease-Like Ion Channel), that is necessary in mice for the sour sensation. Mice breed to lack this gene could not detect sour stimuli.  

Salty - Taste cells with receptors necessary for salt sensation have not yet been identified.

Bitter - Bitter taste perception, required to prevent the ingestion of toxic substances, is mediated by the T2Rs family of receptors, mediated by the G-protein, gustducin.  

Umami - The G-protein coupled receptor for this taste consists of a dimer of TIR1 and T1R3.

Smell (Olfactory) - tba

Sight (Visual)- TBA


Return to Chapter 9B: Neural Signaling Sections

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Archived version of full Chapter 9B:  Neural Signaling


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Biochemistry Online by Henry Jakubowski is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.