High School Biology : Understanding Receptors and Ligands

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #7 : Transport And Signaling

Which of the following cannot act as a ligand?

Possible Answers:

Integral membrane proteins

Steroids

Calcium ions

Neurotransmitters

Inhibitors

Correct answer:

Integral membrane proteins

Explanation:

Ligands bind to receptors, which cause conformational changes and various effects on the cell. Integral membrane proteins span the lipid bilayer. These proteins commonly act as receptors and bind to ligands to produce conformation changes. They cannot leave the lipid bilayer, and thus are never ligands that can bind to other receptors.

Ligands are generally small ions or molecules, such as glucose or triglycerides. Calcium ions act as second messenger ligands in signal transduction. Steroid hormones, like testosterone, bind to proteins in the nucleus to alter transcription patterns. Neurotransmitters bind to receptors on dendrites to cause action potential propagation. Inhibitors can bind to receptors to block other ligands from interacting.

Example Question #2 : Transport And Signaling

Which of the following is NOT true regarding receptors and ligands?

Possible Answers:

Binding of a ligand always turns on the protein to which it is bound.

It is possible for a receptor to bind more than one ligand.

The receptor for a ligand may either be on the cell's surface or inside the cytoplasm.

Ligands usually make covalent bonds with their receptors.

Ligands are usually proteins.

Correct answer:

Ligands usually make covalent bonds with their receptors.

Explanation:

Ligands and receptors are both usually proteins. Since proteins can fold into a wide variety of shapes, the receptor-ligand interaction is very specific. In some cases, certain receptors will bind two ligands that are similar in structure. For example, hemoglobin binds to both  and , but binds  with much higher affinity. Ligands bind receptors using only weak bonds (hydrogen bonds and Van der Waals forces). Depending on the nature of the ligand (whether it can cross the lipid bilayer or not), its receptor may be either on the cell's surface, floating in the cytoplasm, or on the nuclear membrane.

Example Question #4 : Transport And Signaling

Which of the following includes the four most common groups of ligands in biology?

Possible Answers:

Substrates, inhibitors, activators, and tracers

Substrates, inhibitors, neurotransmitters, and tracers

Substrates, activators, neurotransmitters, and tracers

Substrates, inhibitors, activators, and neurotransmitters

Inhibitors, activators, neurotransmitters, and tracers

Correct answer:

Substrates, inhibitors, activators, and neurotransmitters

Explanation:

In biochemistry, ligands are any substance that forms a complex with a biomolecule to serve a biological purpose. The four primary types of ligands have their functional state determined by their three-dimensional chemical conformation. Tracers in the body often take the form of radioligands, but are not ligands themselves.

Example Question #10 : Transport And Signaling

Chemotaxis refers to movement of an organism in response to which of the following stimuli?

Possible Answers:

Gravity

Vibrations

Chemicals

Light

Sound

Correct answer:

Chemicals

Explanation:

Chemotaxis refers to the movement of an organism in response to a chemical stimulus. Single or multicellular organisms may direct their movements according to certain chemicals in their environment. This is important because these organisms need to find food, flee from harmful substances, and chemotaxis also aids in development. Positive chemotaxis is movement towards a higher concentration of the chemical, whereas negative chemotaxis is movement away from the chemical.  

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