Main intracellular functions controlling growth

Growth factors are a large group of different extracellular
molecules that bind with high specificity
to cell surface receptors (1). Their binding
to the receptor (2) activates intracellular signal
transduction proteins (3). This initiates a cascade
of events resulting in activation of other
proteins (often by phosphorylation) that act as
second messengers (4). Hormones of different
types are a heterogeneous class of signaling
molecules (5). They enter the cell either by diffusion
through the plasma membrane or by
binding to a cell surface receptor (6). Some hormones
require an intranuclear receptor (7).
Eventually the signal cascade results in activation
or inactivation of transcription factors (8).
Before transcription and translation ensue, an
elaborate system of DNA damage recognition
and repair systems (9) make sure that cell proliferation
is safe (cell cycle control, 10). In the
event that faults in DNA structure have not been
repaired prior to replication, an important
pathway sacrifices the cell by apoptosis