operator

Examples of operator in the following topics:

• The trp Operon: A Repressor Operon

  • A DNA sequence called the operator sequence is encoded between the promoter region and the first trp-coding gene.
  • This operator contains the DNA code to which the repressor protein can bind.
  • Because the repressor protein actively binds to the operator to keep the genes turned off, the trp operon is negatively regulated and the proteins that bind to the operator to silence trp expression are negative regulators.
  • When tryptophan is plentiful, two tryptophan molecules bind the repressor protein at the operator sequence.
  • When tryptophan is absent, the repressor protein does not bind to the operator and the genes are transcribed.

• Conditioned Behavior

  • In classical conditioning, a behavior is paired with an unrelated stimulus; in operant conditioning, behaviors are modified by consequences.
  • Two types of conditioning techniques include classical and operant conditioning.
  • In operant conditioning, the conditioned behavior is gradually modified by its consequences as the animal responds to the stimulus.
  • This type of learning is an example of operant conditioning.
  • The training of dolphins by rewarding them with food is an example of positive reinforcement operant conditioning.

• The lac Operon: An Inducer Operon

  • CAP binds to the operator sequence upstream of the promoter that initiates transcription of the lac operon.
  • If glucose is absent, then CAP can bind to the operator sequence to activate transcription.
  • If lactose is absent, then the repressor binds to the operator to prevent transcription.

• Catabolite Activator Protein (CAP): An Activator Regulator

  • Just as the trp operon is negatively regulated by tryptophan molecules, there are proteins that bind to the operator sequences that act as a positive regulator to turn genes on and activate them.
  • This cAMP binds to the CAP protein, a positive regulator that binds to an operator region upstream of the genes required to use other sugar sources.

• Charles Darwin and Natural Selection

  • Charles Darwin and Alfred Wallace independently developed the theories of evolution and its main operating principle: natural selection.
  • Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature.

• Open and Closed Circulatory Systems

  • An open circulatory system does not use as much energy to operate and maintain as a closed system; however, there is a trade-off with the amount of blood that can be moved to metabolically-active organs and tissues that require high levels of oxygen.

• Anatomy of the Eye

  • The lens is operated by muscles that stretch it flat or allow it to thicken, changing the focal length of light coming through to focus it sharply on the retina.
  • However, when looking at a star in the night sky or other object in dim light, the object can be better viewed by the peripheral vision because it is the rods at the edges of the retina, rather than the cones at the center, that operate better in low light.

• The Galapagos Finches and Natural Selection

  • Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature.
  • Peter and Rosemary Grant and their colleagues have studied Galápagos finch populations every year since 1976 and have provided important demonstrations of the operation of natural selection.

• Scientific Reasoning

  • Science (from the Latin scientia, meaning "knowledge") can be defined as knowledge that covers general truths or the operation of general laws, especially when acquired and tested by the scientific method.
  • Scientists seek to understand the world and the way it operates.  

• Denaturation and Protein Folding

  • Pepsin, the enzyme that breaks down protein in the stomach, only operates at a very low pH.