Cells are continuously receiving information from their
surroundings and inturn, responding in a way that is determined by their genes
and the chemical or physical agents that after the manner in which genes are
expressed. Those chemicals or physical agents are termed as epigenetic factors.
E.g. a sugar that activates or reprocess the expression of a gene could be
considered an epigenetic factor. Cells are able to respond to a variety of
different chemical and physical agents in their environment. These agents are referred
to as signals. Those signals can be of two types:
Physical Signals- They are generally restricted to energetic
blows, heat and electromagnetic radiation(light)
Chemical Signal- They may be simple as an ion or as complex
as a peptide or a steroid hormone. Signals may induce transitory or permanent
change in cells e.g. an amino acid in the environment can turn off genes
involved in its synthesis. The change however are transitory since withdrawal
of the amino acid reverses the expression of the genes involved. In the
development of a multicellular organism from a single fertilized egg the
signals are capable of permanently altering a number of cells. This allows the
development of different tissues and organs. The condition of cancer is also an
outcome of such alterations where the genes of differentiated cells are altered
by mutation resulting in the going out of control and ultimately killing the
host.
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CHEMICAL SIGNALS
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I. Proteins and Peptide
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EGF- Epidermal Growth Factor
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FGF- Fibroblast Growth Factor
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TNF- Tumor Necrosis Factor
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PDGF- Platelet Derived Growth Factor
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TGF- Transforming Growth Factor
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IFN- Interferon
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IL- Interleukin
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ERYP- Erythroprotein
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INS- Insulin
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II. Nonpeptide Neurotransmitters
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SER- Serotonin
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MEL- Melatonin
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DOP- Dopamine
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EPI- Epinephrine
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ACH- Acetylcholine
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GLU- Glutamic Acid
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GABA- Gama Aminobutyric Acid
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III. Steroids and other membrane soluble molecules
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EST- Estrogen
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TES- Testosterone
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TYX- Thyroxine
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RA- Retonic Acid
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General Principles
How do chemical signals interact with cell?
The signal molecules first interact with the signal
transduction, pathways by specifically binding to protein receptors in the
cytoplasm that are referred to as cytoplasmic receptors. The receptors for the
signal molecules are found on the outer surface of the cells.
How do light signals interact with cells?
Rhodopsin is the receptor that respond to light. It is found
embedded in the membranes of rod and cone cells in the retinas of animals with
color vision. Phytochromes are the light receptor in many plant cells consisting
of a linear tetrapyrole that function as the chromopore and a protein portion
to anchor the chromopore to the inside surface of the plasma membrane and
communicate a signal to one or more signal pathways.
What role the G Protein play in signaling?
It is the G Protein that determine that whether the signal
will be stimulatory or inhibitory signals that stimulate are called agonists
and that inhibit are known as antagonist.
What role do Phosphates play in signal pathways?
The control of a cell physiology is effected by the phosphorylated
state of its proteins. Protein phosphates are such enzymes that remove
phosphate groups from proteins.
How does the proteins
Kinase function in signal pathway?
Protein Kinases Phosphorylate other proteins rather than
Non-Protein molecules such sugar and
lipids. Some protein kinases are stimulated at the beginning of signal
transduction pathway by specific growth factor whereas others are stimulated
along the signal pathway. Although some proteins kinases are membrane bound,
the vast majority are found free in the cytoplasm. The protein kinases are categorized
on the basis of which amino acid they phosphorylate as well as on the basis of
the factors required for their activity.
The cellular communication seems to play a vital role in growth proliferation,
differentiation, movement and even the programmed cell death in case of all
biological identity.
-Amar Jyoti
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