WEEK 2 (2)Dr.zein cell receptors 2014,1.ppt

8/10/2019 WEEK 2 (2)Dr.zein cell receptors 2014,1.ppt

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1)Cytokines peptides secreted by cells into the ECF act as

autocrines, paracrines, or endocrine hormones as leptin produced

by adipocytes are

sometimes called adipokines


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Endocrine system

The endocrinesystem

broadcasts its hormonalmessages to essentially

all cells by secretion into

blood and extracellular

fluid.

Like a radio broadcast,

it requires a receiverto

get the message

In the case of endocrine

messages, cells must

bear a receptorfor the

hormone being broadcast

in order to respond.

Nervous system

The nervous

systemexerts point-to-

point control

through nerves,

similar tosending

messages by

conventional

telephone.

Nervous control

is electricalin

nature and fast.


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Endocrineglands or specialized

cells release hormones

into the circulating

blood that influencethe function of cells at

another location in the

body.

Paracrine

in which cells secret substances

that diffuse into the extracellular

fluid and affect neighboring

cells.


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Three Stages of Signal Transduction

1. Reception of extracellular signal by cell

2. Transductionof signal from outside of cell to inside of cell

often multi-stepped

Note not necessarily transduction of ligand

3. Cellular Response

Response is inititiated and/or occurs entirely within receiving

cell


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2a. Transduction

2b. Transduction

2c. Transduction

2d. Transduction

1. Reception

3. ResponseResponses usually involve increasing or decreasing some

Proteins unction


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1.Proteins and Polypeptides, including hormones secreted by the anterio

and posterior pituitary gland, the pancreas (insulin and glucagon), the

parathyroid gland (parathyroid hormone), and many others.

2.Derivatives of the amino acid

Tyrosine, secreted by the thyroid (thyroxine and triiodothyronine)

and the adrenal medullae (epinephrine and norepinephrine)

Tryptophane-derived hormones as Serotonin and Melatonin

Glutamic acid-derived hormone as Histamine

3. Steroids hormones:-are derived mainly from cholesterol secreted

by the adrenal cortex (cortisol and aldosterone), the ovaries

(estrogen and progesterone), the testes (testosterone), and the

placenta (estrogen and progesterone)

Eicosanoids: small molecules synthesized from fatty acid substrates

(e.g. arachidonic acid) its receptors located within cell

membranes

ass cat on o ormones


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Lipid-soluble Hormones Steroids

Lipids derived from cholesterol in

SER

Different functional groups attachedto core of structure provideuniqueness

Interact with specific intracellularreceptors (within the cell) to turnspecific genes on or off effective forhours or days

Thyroid hormones

Tyrosine ring plus attached iodinesare lipid-soluble

Activate enzymes involved in thecatabolism of fats and glucose

Help set our basal metabolic rate


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Six steps of cell-cell communication:

1. Synthesis of signal.

2. Release of the signaling molecule by the signalingcell: exocytosis, diffusion, cell-cell contact.

3. Transport of the signal to the target cell.

4. Detection of the signal by a specific receptorprotein

5. A change in cellular metabolism, function ordevelopment triggered by the receptor-signalcomplex

6. Removal of the signal

R t


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Receptors

Cell membrane

ReceptorsCytoplasmic

Receptors

Nuclear

ReceptorsFor protein, some a.aderivatives

As GH, insul in and

catecholamines

Estrogen,

testosterone

and cortisole

Thyroid

hormones

Classif ied according to the subcellular second

messenger that mediate the information from the cell

membrane receptors to inside the cell

1. G-Protein Coupled Receptors (GRCR)2. I on channel receptors3. Receptors-linked-Kinase

4. Receptor- kinase


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Cell Surface Receptor-mediated

Signaling

1.G-Protein Coupled Receptors (GRCR)

2.Ion channel receptors

3. Receptors-linked-Kinase

4. Receptor- kinase

a. Voltage gated ion channel

b. L igand gated ion channel


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GPCRs are involved in a range of signaling pathways

including light detection odorant detection and detection

of certain hormones and neurotransmitters

Many different mammalian cell-surface receptors

including GPCRs are coupled to a trimeric signal-

transducing

G protein

Ligand binding activates the receptor which activates the

G protein which activates an effector enzymeto generate

an

intracellular second messenger

e.g.

adenylyl cyclase

converts ATP to

c MP

depending on regulation at the effector protein

this

pathway can be either activated or inhibited

Gsproteins result in stimulation of the effector enzyme

Gi proteins result in inhibition of the effector enzyme

1-G-Protein-Linked Receptors


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G-Protein-Linked Receptors

Fig. 11.7

I I h l t


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I-Ion-channel receptors

ligand binding changes the confirmation of the receptor so that

specific ions flow through it

-the resultant ion movement alters the electric potential across the

plasma membrane

found in high numbers on neuronal plasma membranes

e.g. ligand-gated channels for sodium and potassium

also found on the plasma membrane of muscle cells

binding of acetylcholine results in ion movement and eventual

contraction of muscle

They are of two types;-


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2A-Voltage-gated ion channel


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2B-Ligand-gated ion channel


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3 Tyrosine kinase l inked receptors


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Lack intrinsic catalytic activity

Binding of the ligand results in the formation of a receptor

dimer (2 receptors)

This dimer then activates a class of protein called tyrosinekinases

This activation results in the phosphorylation of downstream

targets by these tyrosine kinases

E.g Receptors for cytokines such as erythropoietin receptor

3-Tyrosine kinase-l inked receptors

4 Tyros ne K nase Receptors


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-Also called receptor tyrosine kinases OR ligand-tr iggeredprotein kinases -Similar to tyrosine-linked receptors -

ligand binding results in formation of a dimer

-BUT: they differ from tyrosine-linked receptorsintrinsic

catalytic activity

4-Tyros ne-K nase Receptors


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WEEK 2 (2)Dr.zein cell receptors 2014,1.ppt