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Signal Transduction – Hormones
Signal Transduction & Signaling
- Cells have specific response – How?
- What is the sequence of events?
To answer these questions we must go through some basics first, which are explained in the coming lessons.
Signal Transduction
Signal molecules are of different types and the process of transferring the signal into the cell is called Signal transduction.
Signal molecules can be:
- Hormones
- Drugs
- Toxins
- Chemicals
- Bacteria
- Neurotransmitters.
There are two types of cells in signal transduction:
- The sender cell where the signal originates and,
- The target cell that receives the signal.
The signal alters or modulates the activity/function of the cell
Types of Signal Transduction
- Autocrine
- Paracrine
- Juxtacrine
- Endocrine
1. Autocrine
Autocrine signaling occurs when same cell acts as sender & recipient e.g.
- Growth
- Differentiation
- Immune & inflammatory response
2. Paracrine
Paracrine signaling is affected by local mediators which have their effect near the site of secretion without entering the circulation.
The effect is rapid and transient.
Examples are:
- Prostaglandins &
- Neurotransmitters
3. Juxtacrine
Juxtacrine signaling occurs when the two types of cells are adjacent to each other so, that the contact is established through gap junctions or through protein molecules on the surface of the two cells.
4. Endocrine
Endocrine signaling is between cells which are located at a distance from each other & the signal may be:
Hormones or chemical messengers secreted into circulation.
Once they reach the target cell, they bind to specific target cell receptors with high affinity.
Signal transduction
Plasma carrier proteins exist for all classes of endocrine hormones.
Carrier proteins for peptide hormones prevent hormone destruction by plasma proteases.
Carriers for steroid & thyroid hormones allow these hydrophobic hormones to be present in the plasma.
Carriers for small, hydrophilic amino acid-derived hormones prevent their filtration through the renal glomerulus, greatly prolonging their circulating half-life.
Definition-Hormones
“Any compound produced by a specialized secretory cell which, by binding to its specific receptor, alters the metabolism of the cell that has its receptor”.
Hormones
Hormones can be:
- Water Soluble
- Lipid Soluble
1. Lipid Soluble Hormones
Lipid soluble hormones can get into the cell through the plasma membrane and do not need any receptor on the cell surface e.g. Steroids.
Hormone receptor complex binds Hormone Response Elements (HRE), of enhancer regions in the spacer DNA.
By this they control of Gene expression (this process requires hours).
Examples are:
- Steroids
- Calcitriol
- Thyroxine
- Retinoic acid.
2. Water Soluble Hormones
Water soluble hormones cannot get into the cell because of the lipid bilayer of cell membrane.
The Receptors for the water soluble hormones are on the surface of the cell membrane.
Second messenger is usually involved for the transduction of the signal which in turn activates a Protein kinase.
The Protein kinase phosphorylates proteins to modify enzyme activity (requires minutes).
These hormones control gene expression through cAMP Response Element Binding proteins (CREB proteins).
This process also requires hours.
Examples are:
- Insulin
- Glucagon
- Catecholamines
Water soluble hormones – act through Cell surface receptors.
Lipid soluble hormones – act through Intracellular receptors.
Sir signalling pathways or in k diffrences k tables b upload kr den kindly.
sir protein ki slides bhi upload kar dein please.
Protein lectures are on my youtube channel named house of biochemistry