Signal conduction Flashcards by mohamed nascer

what is the definition of signal transduction?

refers to the overall process of converting extracellular signals into intracellular responses and explains how cells communicates with each others

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who are the role players in signal transduction?

signaling molecules ( Hormones )

receptors

signal transduction proteins and second messenger ( G protein, CAMP )

effector protein –> either inhibited or activated

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why is signal transduction required?

because signal is important for multiple processes including :

Growth , survival , differentiation , migration , proliferation and apoptosis

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how do cells communicate in multicellular organism?

Signalling molecules —> hormones
- Signals could act over long distances or immediate neighbour cells

RECEPTORS

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which cells are emitters and which are receivers?

most cells are both emitters and receivers of signals

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what are the 2 types of modes of cell communication?

Direct

Indirect

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whats an example of direct communications?

cell – cell directly

by adhesion molecules

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what are the types of indirect communications?

paracrine ( cytokines )

synpatic —> Neurotransimitter

Endocrine –> hormones

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what is paracrine communications?

cell will secrete the hormone –> it will affect cells in the same organ or neighboring hormones

example : prostaglandins , cytokines

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what is synaptic signalling?

performed by neuros that transmit signal electricity along their aoxns –> RELEASE OF NEUROTRANSMITTERS at synapses which are often located far away from cell body

ACTION POTENTIAL RELEASES THEM

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what is endocrine signalling?

depends on endocrine cells which secrete hormones into the bloodstream that are then distributed widely throughout the body

hormone travels far distance for effect

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what are the classifications of hormones?

steroid hormones ( from cholesterol ) –> aldosterone, cortisol, androgens, estrogen, progesterone

Amino acid hormones ( From tyrosine ) –> thyroid, catecheloamines

Protein/ peptide hormones –> Everything else

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describe the characterstitics of protein / peptide hormones?

Synthesized as prohormones, prehormones –> require activation by cleavage and removal of extra parts

water soluble , polar

Stored in membrane and released by exocytosis

travel in the blood directly without the need of a binding protein

Easily degraded in the blood and by GIT

example : Insulin

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describe steroid hormone?

synthesized by cholesterol

lipid soluble

cannot be stored in the membrane , synthesized and secreted

cannot travel freely in the blood , must be bound to a protein

Not degraded by GIT or blood

Longer half life because its usually bound

Example : adrenal gland hormones

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describe the characteristics of amine hormones?

thyroid –> similar to lipid soluble but can be stored

catecholamines –> similar to water soluble

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where are the receptors of lipid soluble hormones?

intracellular

usually the effect is promotion of gene expression

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where are the receptors for water soluble hormones?

extra cellular because they cannot pass through the membrane

what do you call the process of synthesizing hormones?

translation

what are the types of receptors ?

extracellular receptors

Intracellular receptors

what are the characteristics of signal transduction?

specific and very sensitive

specificity is achieved by PRECISE MOLECULAR
COMPLEMENTARY BETWEEN SIGNAL AND RECEPTOR MOLECULE

what are the types of extracellular receptors?

Transduction by CELL SURFACE RECEPTORS

Water soluble —>

1- Receptors enzyme ( catalytic receptors )

2- Receptors involving second messenger molecules

3- ligand gated ion channels ( Neurotransimittter receptors linked to ion channels ) ionotropic

what are the types intracellular receptors ?

Lipid soluble ligands –>

1- cytosolic –> cortisol

2- nuclear —> Thyroid, Steroids

describe the process cellular signal by INTRACELLULAR RECEPTORS ?

Hormone enter the cell —> bind to the receptor —> Receptor ligand complex —–> Enter the nucleus and BIND to specific regions of the DNA enhancer region —-> CAUSE INCREASING EXPRESSION OF THE SPECIFIED GENE —->Increase synthesis of MRNA –> increased protein synthesis

what are examples that work by transduction of intracellular receptors?

Vitamind D

steroid

thyroid

retinoic acid

All are lipid soluble

describe the effect of intracellular receptors and transduction?

the effects are not immediate because time is required for gene transcription and then mRNA translation ---> but the duration of action will be longer increased protein synthesis

describe ligand gate ion channels mechanism of action?

receptor is found on muscle/effector organ --> hormone/neuro transmitter will bind to it --> Opening of cation channels ( NA ,CA ) --> NA + FLOWS IN AND THUS DEPOLARIZATION OF RECIEVING CELL --> INITIATES ANOTHER ACTION POTEINTAL IF NEURON CONTRACTION OF MUSCLE IF MYOCYTE

what is an example of hormone working via ligand gated iron channels?

ACH neutrotransmitter

describe receptor enzyme process

these transmembrane catalytic receptors have INHERENT TYROSINE KINASE ACTIVITY as part of their structure once hormone binds to it the kinase is activated --> TYROSINE KINASE ACTIVITY WILL INCREASE AND PHSOPHRYLATE THE TARGET PROTEIN OR PHOPSHRYLATE ITSELF example : Insulin

what are example receptors that work by receptor enzyme?

insulin

what is the general composition of receptor enzyme?

2 alpha units --> alpha where the enzyme binds 2 beta units --> beta half of it intracellular and half is extracellular --> has tyrosine kinase enzyme

describe the G protein couple receptor mechanism?

hormone binds to the receptor --> receptor GPD will be activated by GTP ---> GTP will bind to the the second messenger which is adenylate cyclase ---> Adenylate cyclase will increase CAMP by inhibiting PPi --> CAMP will activate PROTEIN KINASE A --> pka will activate or inhibit the target protein Example epinephrine, glucagon

what are examples of g coupled receptors?

epinephrine glucagon

which subunit of GPD will get activated?

S subunit

which part of GPD is movable? and moves to adenyl cyclase?

Alpha subunit

what is the reason behind this second messenger mechansim?

signal amplification --> one signal could lead to many effectss

what is the other example of a second messenger?

phosphatidylinistol system

whats the function of phosphatidyinositol system?

it activates phospholipase C ( PLC) Which will divide phoshatidyinositol into INOSITOL TRIPHOSPHATE and 1,2 Diacylglycerol

what is the function of IP3?

increases calcium level --> myosin light chain kinase vasoconstriction

what is the function of 1,2 diacylglycerol ?

activate protein kinase C

how is the signal terminated ?

phosphatases ( removal of phosphate added by kinase ) GTP hydrolysis ( Inhibition of GPD ) protein degradation ( Degradation of hormone ) receptor endocytosis inhibition of gene transcription ( in case of intracellular )

what are the commonest methods in measuring hormones?

elisa chromatographic assay mass spectroscopy

how is elisa performed?

enzyme linked immunosorbent assay 1- antigen is colored and given to the body 2- body forms antibodies 3- antibody and antigen bind --> color