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Chapter 17

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Chemistry 1027A/B
Kay Calvin

Chemistry 1027B Chapter 17: Chemistry and Medicine Medicines, Prescription Drugs, and Diseases: The Top Tens  Over-the-counter drugs: those that can be bought in any supermarket or drugstore  Prescription drugs: cannot be purchased without instructions from a physician o A substance is available only by prescription if:  It has potentially dangerous side effects  It should bused only by people with specific medical problems  It treats a condition so serious that a person with that condition should be under a doctor’s care o The most prescribed drug in 2008 was Lipitor, which lowers blood cholesterol and stabilizes plaque while acting as an anti-inflammatory  A drug is classified as one or the other by the Food and Drug Administration (FDA)  All drugs have a trade name and a generic name o Trade name: the brand name, or the name used by the drug manufacturer o Generic name: a drug’s generally accepted common chemical name  Once the patent protection on a drug has expired, it can be manufactured and marketed competitively by many companies and prescribed by its generic name  Often, prescriptions written by the generic name are cheaper to fill  The dramatic decrease in infectious diseases since 1900 can be attributed in large measure to the development of antibiotics  Also AIDS continues to be a very serious health issue, AIDS deaths in the U.S. have dropped dramatically due to intensive educational programs regarding AIDS prevention and the development of drugs that, although unable to cure AIDS, can prolong life expectancy dramatically o The cost of these drugs has, at least in part, prevented their use on a worldwide basis Drugs for Infectious Diseases  Infectious disease: a disease caused by microorganisms  Antibiotic: a substance produced by a microorganism that inhibits the growth of other microorganisms o A person falls victim to an infectious disease when invading microorganisms multiply faster than the body’s immune system can destroy them o Help the immune system by either destroying invaders or preventing their multiplication Penicillins  Pathogenic: capable of causing disease  Amoxicillin, the most-prescribed antibiotic, is a penicillin  All penicillins kill growing bacteria by preventing normal development of their cell walls  Unlike our cells and those of other animals, bacteria rely in a rigid cell wall  The rigidity is maintained by cross-linking bonds between peptide chains  Penicillins inhibit the enzyme that forms these cross links and prevent the reaction from occurring, causing the cell to burst Other Classes of Antibiotics  The cephalospirins are similar in structure to the penicillins and also act by disrupting cell wall synthesis o They are widely used in hospitals because of their low toxicity and broad range of antibacterial activity o All cephalosporins have the same general structure in which 1 is often a hydrogen, and2R and 3 are substituents with several functional groups  Other kinds of antibiotics attack bacteria in different ways from the penicillins and cephalosporins o Many interfere with the synthesis or functioning of bacteria DNA  Tetracyclines and erythromycin inhibit bacterial protein synthesis  Rifampin inhibits RNA synthesis from DNA  After more than a half-century of use, many antibiotics are not nearly as effective as they once were AIDS: A Viral Disease  Other than vaccination, there are very few knows ways to combat viral diseases o This is because they are essentially chemical parasites – they take over the DNA of human cells and put it to work for their own reproduction o It is difficult to attack the cells reproducing the virus without also attacking the host’s own cells  HIV is a retrovirus: the virus enzyme carries out RNA-directed synthesis of DNA rather than the usual DNA- directed synthesis of RNA o It consists of an outer double lipid layer surrounding a matrix containing proteins, an enzyme called reverse transcriptase, and RNA  Attack of HIV on a T cell of the immune system: o The virus enters the lymphocyte and produced its own DNA o The DNA enters the lymphocyte nucleus, where it combines with the lymphocyte’s DNA o Through the cell’s normal processing, DNA is transcribed to messenger RNA and, back outside the nucleus, the viral RNA provides the template for the production of proteins that assemble into new virus particles  Protease inhibitors taking in combination with older AIDS drugs dramatically lowers the concentration of the virus in the patients’ blood, often to below detectable levels o A combination of drugs overcomes the major problem with single-drug therapy – if a few virus particles are left alive by a drug treatment, the virus can very quickly adapt by converting to a drug-resistant from  Protease inhibitors act by inhibiting a protease enzyme o By fitting into the active site of the enzyme, the inhibitors prevent the enzyme from functioning o Because this enzyme cuts a long protein chain into smaller proteins essential to survival of the HIV virus, halting its action kills the virus  The new drug combination is not yet a cure – it is extremely expensive, it is unavailable in many developing countries, and it can have unpleasant side effects Steroid Hormones  Hormones are produced by glands and secreted directly into the blood  They serve as chemical messengers, regulating biological processes by interacting with receptors that are sometimes distant from where they are secreted  Hormones are chemically diverge but are mostly proteins or steroids Neurotransmitters  Hormones and neurotransmitter have in common their roles as chemical messengers within the body  Neurotransmitters carry nerve impulses from one nerve to the next or to the location where a response to the message will occur  The body has a number of neurotransmitters, each it with its own distinctive molecular receptors and functions Norepinepherine, Serotonin, and Antidepressive Drugs  Norepinepherine and serotonin are neurotransmitters with receptors throughout the brain o Norepinepherine helps to control the fine coordination of body movement and balance, alertness, and emotion; it also affects mood, dreaming, and the sense of satisfaction o Serotonin is involved in temperature and blood pressure regulation, pain perception, and mood o Serotonin and norepinepherine appear to work together to control the sleeping and waking cycle  The normal cycle of neurotransmitter action at nerve synapses, the gaps between nerve endings, is as follows: o The neurotransmitter is released from the neuron o The neurotransmitter crosses the synapse to interact with the receptor o The neurotransmitter is inactivated, either by re-uptake by the neuron it came from or by conversion to an inactive form by an enzyme  The biochemistry of mental depression is not fully understood, but a deficiency of norepinepherine and serotonin (and possibly dopamine as well) almost certainly plays a role o Evidence is provided by the manner in which three classes of influence the action of these neurotransmitters  The tricyclic antidepressants prevent inactivation of neurotransmitters by preventing their e-uptake by neurons, which increases the concentration of the neurotransmitter in the synapse  The monoamine oxidase inhibitors diminish the action of monoamine oxidase, which is the enzyme that inactivated norepinepherine and serotonin  Selective serotonin inhibitors prevents the recapture of serotonin by neurons that release it (and has become the choice for treating serious clinical depression) o For each of these three classes of drugs the major mechanism of action is to increase the concentration of neurotransmitters at synapse Dopamine  Produced in several areas of the brain, where it helps to integrate finer muscular movement as well as o control memory and emotion  Dopamine does not cross the blood-brain barrier and thus cannot be administered as a drug o L-Dopa is able to cross the barrier and can then be converted to dopamine in the brain  Used to alleviate Parkinson’s symptoms  Dopamine has also been identified as the neurotransmitter that produces the feelings of well-being and reward associated with drug addiction  Drugs that block dopamine receptors have been used to treat schizophrenia (a complex condition not solely attributed to dopamine activity) Epinephrine and the Fight-or-Flight Response  Epinephrine, also known as adrenaline, is both a neurotransmitter in the brain and a hormone released from the adrenal gland  Its sudden discharge when we are frightened produces the fight-or-flight response, which includes increased blood pressure, dilation of blood vessels, widening of the pupils, and erection of the hair  Because of its widespread and rapid effects, epinephrine has a number of medical uses, notably in crisis situations such as cardiac arrest, dangerously low blood pressure, acute asthma, and anaphylactic shock The Dose Makes the Poison  The amount of chemical substance that enters the body is known as a dose  Whether a dose of a given substance is poisonous or not depends on the size of the dose  For a given individual, age, gender, eight, and general state of health also play a role in the effect of a given dose  Doses of medications and poisons are customarily expressed as milligrams per kilogram of body weight (mg/kg)  A quantitative measure of toxicity is obtained by administering various doses of substances to be tested to laboratory animals o The dose found to be lethal in 50% of a large number of test animals under controlled conditions is called the LD 50ethal dose – 50%) and is usually reported in milligrams of the substance per kilogram of body weight o Since species differences can produce different L50values for a given poison, defining risk to human beings based on animal data is difficult, but it is generally safe to assume that a chemical with a low LD value for 50 severalspecies will also be quite toxic to humans Painkillers of all Kinds  Analgesics: drugs that relieve pain; some are illegal drugs, some are prescription drugs, and some are OTC drugs Opium and its Relatives  Chemically, opium is an alkaloid – an organic compound that contains nitrogen, is a base, and is produced by plants  About 10% of crude opium is morphine, which is medically valuable as a strong painkiller able to produce sedation and loss of consciousness, is primarily responsible for the effects of opium  The term opioid is now applied to all compounds with morphine-like activity  Heroin, the diacetate ester of morphine, does not occur in nature but can be synthesized from morphine o Their structures differ in only one kind of functional group, but is much more addictive than morphine and for that reason has no legal use in the U.S.  Codeine, a methyl ether of morphine, is one of the alkaloids in opium and is used in cough syrup and for relief of moderate pain o Less addictive than morphine, but its analgesic activity is only about 1/5 of morphine  One of the most effective substitutes for morphine is meperidine, which is less addictive than morphine and is now sold as Demerol. Mild Analgesics  When milder general analgesics are required, few compounds work as well for many people as aspirin  Aspirin is also an antipyretic (fever reducer) and an anti-inflammatory agent (reduces inflammation)  Aspirin inhibits cyclooxygenase, the enzyme that catalyzes the reaction of oxygen with polyunsaturated fatty acids to produce prostaglandins. Excessive prostaglandin production causes fever, pain, and inflammation – just the symptoms aspirin relieves  Aspirin
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