Lecture 20

1. Lecture 20 Nutrition: Food for Thought (cont.) May 23, 2005

2. Carbohydrates • Composition: Carbon, Hydrogen, Oxygen • Used as a fuel (4 Cal/g; while fat is 9 Cal/g) and as an energy storage also, namely glycogen, a carbohydrate chain mainly in liver and muscle • Produced by all plants and animals to store chemical energy. • Also form a supporting skeleton for plant cells. • Polymers: doesn’t just refer to plastic! (macromolecules – repeating units of small molecules bonded together)

3. Carbohydrates: Polymers • Polymers can get so large that they can acquire distinct physical properties – cellulose and starch, for example. (sweet/not sweet, soluble/insoluble) • Monosaccharides: glucose, fructose • Disaccharides: sucrose, lactose • Oligosaccharides: corn syrup, raffinose (found in seeds) • Raffinose is not digested in the small intestine, passed into the colon where bacteria digest them, producing large quantities of CO2 and other gases. • Polysaccharides: starch, cellulose, gums, agar • Starch is used as sugar storage in plants. • Cellulose is structural support in plants – indigestible fiber for us. • Hemicelluloses are partially soluble in water, contribute to softening of cooked vegetables and fruit. • Gums, agar – used for thickening, stabilizing, producing smooth textures.

4. Carbohydrates

5. Starch vs. Cellulose Starch Cellulose

6. Alcohol • Composition: Carbon, Hydrogen, Oxygen • Not a carbohydrate; metabolized differently; does provide energy (7 Cal/g). • CH3 group resembles fats (hydrocarbon chain), OH group resembles water • alcohol mixes easily with water and also fatty substances; can penetrate cell membranes • Methanol: CH3OH • Ethanol: C2H5OH • Isopropanol: C3H7OH • Longer chains…

7. Alcohol • Food: Mouth  stomach  small intestines (food absorbed)  large intestines (water absorbed) • Alcohol: Mouth  stomach (~20% alcohol absorbed/metabolized)  small intestines (most alcohol absorbed) • About 10% of alcohol is not absorbed, excreted from the body in sweat, urine and breath (breathalizer tests). The rest has to be metabolized (eliminated). • After alcohol is absorbed into the blood – sent to the liver where it is metabolized. • Rapidly mixes through the aqueous blood stream, since it is water soluble. • Easily crosses membranes, including the blood-brain barrier, to affect large number of organs. • Alcohol dehydrogenase (ADH; a protein) in stomach breaks down some alcohol. • About 30% metabolized in men, only 10% in women. • Men experience slower rise in blood alcohol, can drink more before feeling effects. • Empty stomach – alcohol is rapidly absorbed. Food present – alcohol has to wait its turn to come in contact with digestive tract walls. • Remainder absorbed in the small intestine, transferred to blood, and carried to the liver for detoxification by ADH. • Rate of absorption depends on rate of gastric emptying into the small intestine – if food is present, gastric emptying is slowed, absorption is delayed.

8. Alcohol: Alcohol Dehydrogenase • Ethanol  acetaldehyde  acetic acid  CO2 + H2O • Acetaldehyde is highly toxic. • ADH also acts on various other alcohols and fatty acids. • Don’t drink methanol! ADH converts this to formaldehyde (CH2O) – which can enbalm tissues. Low concentrations affects sensitive tissues like the retina  blindness. High concentrations  death. • Ability to metabolize (break down) ethanol dependent on genetics: • Some ADH genes are protective against alcoholism, common in Asian populations, convert alcohol to acetaldehyde more quickly than normal. Acetaldehyde builds up, making carriers who drink too much uncomfortable, so they are discouraged from drinking a lot. • Acetaldehyde is broken down by acetaldehyde dehydrogenase (ALDH) to non-toxic acetic acid. • Certain people have defective ALDH gene (common in Asians), that doesn’t metabolize acetaldehyde as rapidly as normal • Drinking too much causes acetaldehyde build-up, facial flush, general sick feeling. • Some drugs given to deter drinking inhibit ALDH, so that the patient feels very ill after drinking.

9. Alcohol: Alcohol Dehydrogenase • Limited amount of ADH limits rate of alcohol digestion – 5-6 hours to clear the alcohol in 4 ounces of whiskey. If drink more than 16 oz/day, blood will never be cleared of alcohol. • Fixed rate of ADH digestion – exercise, food will not help sober up faster. • When liver is working to detoxify alcohol, it can’t do anything else – normal liver functions suppressed. • Women vs. men: women have smaller blood volume, less ADH in stomach.  higher BAC/drink then men because they absorb more alcohol.

10. Alcohol: Drunkenness Ethanol: • is not a stimulant, but a depressant – decreases activity of the nervous system. • doesn’t ‘warm you up’ – increased blood flow in capillaries just below the skin causes flushed feeling. Deep body heat transferred from blood to the skin, and is then transferred to the air, so body as a whole is cooled. • interferes with antidiuretic hormones, kidneys send water to bladder instead of absorbing it back into the body. • Effects on the liver: • Liver is required for many functions – food digestion and absorption, removal of toxins, making blood proteins required for clotting and immunity, etc. • Alcohol metabolism results in the formation of toxic acetaldehyde and free radicals, which can damage liver cells and cause inflammation.

11. Alcohol: Hangovers • Hangovers: mild withdrawal from alcohol. • Cure: another drink? Prolonging the inevitable. • Hypersensitivity to light, sound – leftover compensation for depression of nervous system • Dry mouth, headache – water loss • Headache from enlarged cranial blood vessels – caffeine may constrict them • Fatigue • depressed blood sugar because glycogen in the liver has been broken down to glucose and secreted in the urine. • Lactic acid buildup since liver is too preoccupied to process it. • Upset stomach – alcohol stimulates gastric acid production • Some drinks cause worse hangovers, presumably because of the presence of congeners – byproducts of fermentation • Highest levels of congeners in red wine and dark liquors • White wine, clear liquors have fewer congeners – less severe hangovers. • Different drinks have different congeners – combining them can make things worse.

12. Alcohol: Fermentation • Alcohol molecules made as a byproduct of sugar breakdown to produce energy; reverse of ADH reaction. • Most organisms then break down the alcohol further, but yeast is an exception. • Yeast excretes the alcohol into the surroundings as a defensive chemical weapon – protects against competition from other microbes. • Yeast used in alcohol making – Saccharomyces • Can survive on very little oxygen, but only partially breaks down sugar • C6H12O6 2CH3CH2OH + 2CO2 + energy • Also introduces other flavorful compounds into the mix: • amino acids transformed into higher alcohols • reactions between alcohols and acids to form fruity-smelling esters • after death, cell machinery digests cell and release contents into the liquid, where they continue to generate flavor. • Since alcohol is toxic to cells, yeast can tolerate about 20% alcohol before dying.