Base excision repair (BER) systems directly remove the damaged base and replace it in DNA.

TLS Online TPP Program

#Id: 9034

#Unit 4. Cell Communication and Cell Signaling

Ligand binding depends on: 

Multiple weak, noncovalent forces

Molecular complementarity

TLS Online TPP Program

#Id: 9035

#Unit 4. Cell Communication and Cell Signaling

Binding of the ligand to the receptor causes the receptor to change from an inactive conformation (R) to an active conformation (R*). Only the active R* conformation of the receptor can trigger the signal transduction pathway.

TLS Online TPP Program

#Id: 9036

#Unit 4. Cell Communication and Cell Signaling

The affinity of a signal molecule’s binding to its receptor is quantified by the dissociation constant for binding (Kd).

TLS Online TPP Program

#Id: 9037

#Unit 4. Cell Communication and Cell Signaling

A plot of the amount of ligand bound to the receptor

[RL] versus the amount of free ligand [L] called a

ligand-binding or saturation curve

TLS Online TPP Program

#Id: 9038

#Unit 4. Cell Communication and Cell Signaling

The levels of insulin present in the body and the Kd for binding of insulin to its receptor on liver cells,

1.4 × 10−10 M (0.14 nM). The normal concentration of insulin in the blood is  5 × 10−12 M. 

The fraction of insulin receptors with bound insulin, [RL]/[RT], at equilibrium as 0.0344

TLS Online TPP Program

#Id: 9039

#Unit 4. Cell Communication and Cell Signaling

The tighter the binding of a ligand to its receptor,the lower the concentration of ligand needed to achieve binding to 50 percent of the receptors.