B ioc he mi st ry Chemical Communication: Neurotransmitters and Hormones

1. BiochemistryChemical Communication:Neurotransmitters and Hormones Chapter 24

2. Chem Communication • Chemical Communication: molecules that send a message in living systems • Communications parts: • Chemical Messengers - small molecules released to carry message • Receptors - protein molecules on surface of cell membranes • Secondary messengers – molecule that carries the molecule from the receptor and amplifies it.

3. Signal Transmission • Neurons: specialized nerve cells • Signals travel along nerve axons usually as an electrical impulse • Signal “jumps” gaps with chemicals called neurotransmitters

4. Parts of a Neurotransmitters • Cell body • neurons • Axon • covered by myelin sheath • Dendrites • hair like structuresprotruding from cell

5. Hormones and NeurotransmittersWhat is the Difference??? • Neurotransmitters act over a short distance (across a synaps .000002 cm) • Hormones are created in one location and have an effect at a greater distance – head to toe From Yahoo images

6. Neurotransmitters Five Classes of Chemical Messengers: • Cholinergic -e.g. Acetylcholine • Amino Acid • Adrenergic -e.g. Epinephrine • Steroid • Peptidergic -e.g. Enkephalins All five can be neurotransmitters The last three can be hormones

7. Cholinergic Neurotransmitter 1st type of chemical message: • Acetylcholine neurotransmitter • Electric impulses cause release of acetylcholine • Acetylcholine travels to next nerve cell • Electric impulsecarried thru eachneuron

8. PATHWAY: • electric impulse releases acetylcholine frompresynaptic endings • acetylcholine travels across synapse • receptors on postsynaptic endings cause chem changes in cell and an electricalimpulse is released • after the impulse, acetylcholine at the postsynaptic ends is hydrolyzed with acetylcholinesterase • the receptor is ready withinmilliseconds to fire again

9. Cholinergic Neurotransmitter 2nd type of chemical message: Acetylcholine is hydrolyzed with acetylcholinesterase Which closes the channel

10. Neurotransmitters • Acetylcholine • hydrolyzed by acetylcholinesterase

11. Acetylcholinesterase • The inhibition of Acetylcholinesterase is one way to control neurotransmission • Look at nerve gas page 615 • Nicotine – low doses prolongs the effect of acetylcholine – it’s a stimulant – in high doses it can cause convulsions • Snake venom and poison dart frogs – see handout

12. Amino Acid - Messengers • Amino Acids are distributed thorught the neurons • They exist individually or as peptides • Some are Excitatory Neurotransmitters (glutamic acid, aspartic acid, cysteine) • Some are Inhibitory neurotransmitters (glycine, b-alanine, taurine, aminobutyric acid)

13. Amino Acid - Messengers • Amino acid messengers have receptors. • They behave in a similar fashion to Cholinergic messengers • The removal is not accomplished by a enzime, but by a process called reuptake. • Reuptake is when a transporter molecule brings the amino acid back through the presynaptic membrane

14. Adrenergic - Messengers • Monoamines and Amino Acids • Epinephrine • Serotonin • Dopamine • Histomine • These messengers work in a similar fashion to acetylcholine by being absorbed on a receptor, but this reception causes a big change on the inside of the cell

15. Adrenergic - Messengers • Once the receptor on the outside of the cell absorbs the messenger then there is an Activation of cyclic AMP (cAMP)within the cell • Rx at outer surface • Amplification of signal (thousands of times on the inside!)

16. cAMP

17. Norepinephrine • cAMP is formed when a monoamine neurotransmitter (like epinephrine) is adsorbed on the surface

18. Norepinephrine • cAMP separates regulatory unit (R) from catalytic unit (C) • Catalytic unit will next phosphorylate the ion-translocating protein

19. Norepinephrine • Ion-translocating protein opens the channel for ion flow

20. MAO s • The signal is amplified thousands of times • Because the cAMP is a secondary messenger, this process is SLOW: • from 0.1 seconds to several minutes • To inactivate the adrenergic neurotransmitters, the body oxidizes them to aldehydes • These enzymes are called MAO’s • monoamine oxidases • antidepressant drugs inhibit MAO’s

21. Cholera • Cholera – is severe dehydration as a result of diarrhea • Occurs when over activated G proteins produce excess cAMP • This excess opens the ion channels • This leads to the outflow of ions and water from epithelial cells to the intestine. • See Handout

22. Adrenergic Neurotransmitters • Histamine is a neurotransmitter • synthesized in the brain from histidine • Absorbed by H1 and H2 receptors in body • Receptors can be blocked by Benadryl, Zantac, Tagamet (allergy medication) • By blocking the receptor – symptoms of hayfever and asthma are reduced

23. Peptidergic Neurotransmitters • Includes homones such as: • Insulin • Glucagons • Pancreatic hormones • Vasopressin • Oxytocin • And many others • All peptidergic hormones act through secondary messengers

24. Peptidergic Neurotransmitters • Enkephalins (brain peptides) were the first isolated • present in certain neurons • bind to pain receptors, inhibit sensation of pain • synthetic antagonists: • morphine • heroin • Demerol • These are problematic due to side effects of addiction, respritory depression, and constipation

25. Hormones • Secreted by specific tissues • Released into blood stream • Adsorbed onto specific receptor sites • Pituitary glad is responsible for release of many hormones • luteinizing hormone, interstitial cell-stimulating hormone, prolactin, mammotropin, vasopressin, oxytocin • Other glands include: • thyroid, pancreatic islets, adrenal, kidney, ovaries, testes

26. Hormones • Location of major endocrine organs:

27. Hormones • Target organs for hormones secreted by the pituitary gland: