Related Concept Videos
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
01:12Synaptic Signaling
Neurons communicate at synapses, or junctions, to excite or inhibit the activity of other neurons or target cells, such as muscles. Synapses may be chemical or electrical.
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
01:22Diversity in Cell Signaling Responses
The physiological function of a cell and cellular communication are outcomes of a range of extrinsic signals, intracellular signaling pathways, and cellular responses. No two cell types express the same repertoire of signaling components. Receptors are highly selective for their cognate ligands, but once activated, they can alter multiple cellular processes such as DNA transcription, protein synthesis, and metabolic activity.
Graded and Abrupt Responses
Some signaling systems generate...
Graded and Abrupt Responses
Some signaling systems generate...
01:19Contact-dependent Signaling
Contact-dependent signaling, as the name suggests, requires that communicating cells be in direct contact with each other. This is achieved either through receptor-ligand interactions or by specialized cytoplasmic channels that allow the flow of small molecules between cells. In animal cells, channels called gap junctions facilitate contact-dependent signaling in certain tissues, whereas, plasmodesmata perform a similar function in plants.
Gap Junctions
In animal cells, gap junctions are formed...
Gap Junctions
In animal cells, gap junctions are formed...
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Related Experiment Video
Updated: Jun 13, 2026
10:44
Translating Extracellular Electron Transfer Activities with Organic Electrochemical Transistors
Published on: January 31, 2025
New perspective in ethylene signaling.
1Division of Plant and Crop Sciences, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, UK.
Plant Signaling & Behavior
|April 21, 2010
Summary
Understanding plant ethylene signaling requires studying mutants. New components complicate ethylene receptor signal output mechanisms, with species-specific differences potentially impacting developmental responses.
Area of Science:
- Plant biology
- Molecular genetics
- Biochemistry
Background:
- Ethylene signaling is crucial for plant development.
- Arabidopsis mutants have advanced understanding, but receptor signal output mechanisms remain unclear.
- Discovery of new components adds complexity to ethylene signaling pathways.
Purpose of the Study:
- To explore the complexity of ethylene signaling pathways.
- To investigate the diverse functions of ethylene receptors.
- To identify potential species-specific differences in ethylene responses.
Main Methods:
- Analysis of Arabidopsis mutants.
- Investigating ethylene receptor function.
- Studying CTR-like proteins in tomato.
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Main Results:
- Ethylene receptors are not equivalent; some possess unique functions.
- Multiple CTR-like proteins in tomato interact with various receptors.
- Focusing solely on Arabidopsis triple response mutants may miss developmental components.
Conclusions:
- Ethylene signaling is complex, involving multiple receptors and interacting proteins.
- Species-specific differences exist in ethylene signaling pathways.
- Further research is needed to fully elucidate ethylene's role in plant development.