1. Cell Signaling

2. Cellular responses due to cell signaling
Changes in the activity or function of specific enzymes and other proteins present in the cells
Changes in the amount of protein produced by a cell e.g. modification of transcription factors that stimulate or repress gene expression
Transcription: Transcription is the first step of gene expression, in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase. 
Transcription factor: is a protein that binds to specific DNA sequences, thereby controlling the flow (or transcription) of genetic information from DNA to mRNA

3. Ligand binding to cell-surface receptors triggers activation of transcription factors that determine the precise pattern of gene expression.
Long term signaling responses: division, differentiation, communication with other cells
Alterations in the signaling pathways cause human diseases e.g. cancer, diabetes, and immune defects.
Signals are essential in enabling differentiated cells to respond to their environment by changing their shape, metabolism or movement

4. 1. NF-kB impacts expression of more than 150 genes involved in the immune response to infection.
Activated by many protein hormones that act on immune system cells
2. Cytokines maintains appropriate levels of blood cells

5. 8 classes of cell surface receptor that activate transcription factors
Ligand binding causes activation by inducing 2 or more receptors to form a complex
Most signaling pathways involve 1 or more protein kinases
Kinase can be:
1.Intrinsic part of receptor
2. Tightly bound to the receptor