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Biology Chapter 7
Cell signaling and Communication

7.1 What are Signals, and how do cells respond to them?
- Signal transduction is a process of a cell reacting to the influx of a signal from extracellular sources by its receptors

- a Signal transduction pathway is the process of signal transduction

- Chemical signals that reach cells by diffusion/circulation includes: a) Autocrine – diffuse cells that make them
b) Paracrine – diffuse & affect nearby cells
c) Hormones(circulating signals) – signals to distant cells, travel through circulatory organs

- cells do not react unless there IS a receptor that is SPECIFIC to the signal

- Signal Transduction pathway involves 3 actors:
a) signal
b) receptor
c) response

- Signals:
a) are necessary in order for a cell to maintain homeostasis b) binds to a receptor and activated and causes changes within the cell

- Receptors(e.g.EnvZ):
a) form a complex within the membrane
b) react to signals such as:
i) temperature
ii) concentration difference
c) change their conformation/dimentional structure when stimulated

- Domains:
a) are sequences of amino acids folded into a particular shape b) acts as an enzyme, opening the active site of the receptor, forming a Protein Kinase that: i) is an enzyme that catalyzes the transfer of a phosphate group from ATP to another molecule ii) leads the receptor proteins to go through phosphorylation, leading to function & shape change

EnvZ + ATP EnvZ-P + ADP (by Protein Kinase)

- Responders(e.g.OmpR)
a) are proteins that the phosphorylated protein binds to
b) are important in three functions:
i) ‘extracellular’ signals lead to ‘internal’ change of the cell through transduction ii) the altered responder has function (e.g. OmpR has relation to gene expression – on OmpC) the OmpC(Protein) discretes out, clogging the pore and re-balancing the concentration rate iii) The signal is amplified in the process – from a single enzyme to many molecules...
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