Week 6 notes from textbook PDF

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ethyl alcoholWeek 6: Carbohydrates Lesson 1– What Are the Carbohydrates? *Section 4. 4 The Chemist’s View of Carbohydrates -dietary carbohydrate family includes:  Monosaccharides: single sugars (aka simple carbohydrates)  Disaccharides: sugars composed of pairs of monosaccharides  Polysaccharides...

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Week 6: Carbohydrates Lesson 1– What Are the Carbohydrates? *Section 4.1 4.1 The Chemist’s View of Carbohydrates -dietary carbohydrate family includes:   

Monosaccharides: single sugars (aka simple carbohydrates) Disaccharides: sugars composed of pairs of monosaccharides Polysaccharides: (starches and fibres) large molecules composed of chains of monosaccharides

-carbohydrate: compounds composed of carbon, oxygen and hydrogen, arranged as monosaccharides or multiple monosaccharides. Most, but not all carbs have a ratio of one carbon molecule to one water molecule (CH2O) -monosaccharides most important in nutrition are hexoses; sugars with six atoms of carbon and formula C6H12O6 -each atom can form a certain number of chemical bonds with other atoms:    

Carbon atoms= 4 Nitrogen atoms= 3 Oxygen atoms= 2 Hydrogen atoms= 1 ethyl alcohol

-sugars: monosaccharides and disaccharides -monosaccharides: carbohydrates of the general CnH2nOn that typically form a single ring 

formula

Ones important for digestion all have same numbers and kinds of atoms but different arrangements (account for differing sweetness of each) -galactose is barely sweet, while fructose is VERY sweet

Glucose -glucose: a monosaccharides; sometimes known as blood sugar or dextrose; can be represented in many ways:

-glucose serves as essential energy source for all body’s activities

-it is one of the two sugars in disaccharides, and unit from which polysaccharides are made -starch (one polysaccharide) is chief food source of energy, another glycogen, is an important storage form of energy -disaccharides:

Fructose -fructose: a monosaccharide; sometimes known fruit sugar or levulose, fructose found abundantly fruits, honey, and saps

as in

-is the sweetest of sugars; arrangement stimulates taste buds to produce the sweet sensation -occurs naturally in fruits and honey, other sources are ones that are sweetened with highfructose corn syrup (cereals, soft drinks) Galactose -galactose: a monosaccharide; part of the disaccharide lactose -occurs naturally as a single sugar in few foods

-similar but position of OH group differs slightly

Disaccharides -disaccharides: pairs of monosaccharides linked together -pairs of the 3 monosaccharides; glucose occurs in all 3; second member of the pair is fructose, galactose, and another glucose -these carbs, and all other energy nutrients are put together and taken apart by similar chemical reactions; condensation and hydrolysis

Condensation -condensation: a chemical reaction in which water is released as two reactants combine to form one larger product  

Links 2 monosaccharides together A hydroxyl group (OH) and a hydrogen atom (H) to create a water molecule -the two originally separate

monosaccharides link together with a single oxygen

Hydrolysis -to break disaccharide into two -molecule of water splits to provide H and OH needed to complete the resulting monosaccharides -commonly occur during digestion

Maltose -maltose: a disaccharide composed of two glucose units; sometimes known as malt sugar -produces whenever starch breaks down (which happens during carb digestion), also during fermentation process that yields alcohol -present in barley Sucrose -sucrose: a disaccharide composed of glucose and fructose; commonly known as table sugar, beet sugar, or cane sugar, occurs in many fruits and some vegetables and grains -tastes sweet accounting for some natural sweetness of fruits, vegetables, and grains -fructose is accessible to the taste receptors -table sugar sucrose refined from juices of sugarcane and sugar beets, then granulated -raw sugar= less refined; very similar to table sugar Lactose -lactose: a disaccharide composed of glucose and galactose; commonly known as milk sugar -principle carbohydrate of milk -contributes half the energy (kcalories) provided by skim milk Polysaccharides -polysaccharide: compounds composed of many monosaccharides linked together, an intermediate string of 3-10 monosaccharides is a oligosaccharide -contains many glucose units -3 types glycogen, starches, fibres -glycogen= storage form of energy in body (built of glucose units) -starch= storage form of energy in plants (built of glucose units) -fibre=provide structure provide structure in stems, trunks, roots, leaves, and skins of plants (composed of a variety of monosaccharides and other carbohydrate derivatives) Glycogen

-glycogen: an animal polysaccharide composed of glucose; manufactured and stored in the liver and muscles as storage form of glucose, glycogen is not a significant food source of carbohydrate and is not counted as a dietary carbohydrate in foods -found in limited meats and not at all in plants (glycogen in animal muscles rapidly hydrolyzes after slaughter); therefore, food is not a significant source of carbohydrate -glycogen stores glucose for future use -when hormonal message “release energy” arrives at glycogen storage sites (liver or muscle cell), enzymes respond by attacking the branches of glycogen, making a surge of glucose available -liver cells produce glucose to be sent directly to the blood -muscles use glucose for themselves Starches -starches: plant polysaccharides composed of glucose -plant cells store glucose as starches -starch molecules are packed side by side in grains (like wheat or rice, root crops, tubers, such as yams and potatoes, legumes such as peas and beans -after eating, body hydrolyzes starch and uses glucose for energy -ALL starchy foods come from plants   

Grain is richest food source of starch Some starch digests more slowly and release glucose later in digestion (liked cooked beans) Resistant starch: starch that, for the most part, escapes digestion and absorption in the small intestines of healthy people -technically a kind of fibre -starch of raw potatoes, resists digestion -most remains intact until bacteria of colon eventually break it down -may support healthy colon

Fibres -dietary fibres: in plant foods, the non-starch polysaccharides that are not digested by human digestive enzymes, although some are digested by GI tract bacteria. Dietary fibres include cellulose, hemicelluloses, pectins, gums, and mucilages, as well as the nonpolysaccharides lignins, cutins, and tannins

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Are the structural parts of plants -vegetables, fruits, whole grains, legumes Most are polysaccharides Bonds between their monosaccharides cannot be broken down by digestive enzymes -contribute no monosaccharides, therefore, no energy

-dietary fibres usually grouped into 2 categories: soluble fibres and insoluble fibres -soluble fibres: nonstarch polysaccharides that dissolve in water to form a gel (e.g. pectin from fruit used to thicken jellies)   

Easily digested by bacteria in the colon (fermentable) Found in oats, barley, legumes, and citrus fruit Most often associated with protecting against heart disease and diabetes by lowering blood cholesterol and glucose level, respectively

-insoluble fibres: nonstarch polysaccharides that do not dissolve in water (e.g. tough, fibrous structures, found in the strings of celery and the skin of corn kernels) 

Promote bowel movements, alleviate constipation and prevent diverticular disease

-functional fibres fibres that have been extracted from plants, manufactured and added to foods -total fibre= dietary fibres+ functional fibres -phytic acid: a non-nutrient component of plant seeds; also called phytate, occurs in the husks of grains, legumes, and seeds, and is capable of binding minerals such as zinc, iron, calcium, magnesium, and copper in insoluble complexes in the intestine, which the body excretes unused 

NOT a dietary fibre, but often found in same foods -close association makes it difficult to determine if either or both bind minerals, preventing their absorption -binding present risk of mineral deficiencies (but risk is minimal when total fibre intake is reasonable- less than 40 grams per day) and mineral intake adequate

Summary

Lesson 2– Digestion & Absorption *Section 4.2 4.2 Digestion and Absorption of Carbohydrates Carbohydrate Digestion

-long chains of starchenzymes break it down to shorter chainsdisaccharidesmonosaccharides

-process begins in mouth In the Mouth -thoroughly chewing stimulates flow of saliva -amylase: and enzyme that hydrolyzes amylose (a form of starch); amylase is a carbohydrase (enzyme that breaks down carbohydrates) 

Hydrolyzes starch to shorter polysaccharides and to the disaccharide maltose

-very little carb digestion in mouth due to little time spent there In the Stomach -bolus mixes with stomach’s acid and protein-digesting enzymes (which INACTIVATE salivary amylase) -stomach’s acid continues breaking down starch (to small extent); but juices contain no enzymes to digest it -fibres linger in stomach and delay gastric emptying (giving feeling of satiety) -satiety: the feeling of fullness and satisfaction that occurs after a meal and inhibits eating until the next meal; determines how much time passes between meals In the Small Intestines -performs most of work of carbohydrate digestion -pancreatic amylase (carb digesting enzyme) enters the small intestine via pancreatic duct and continues breaking down polysaccharides into shorter glucose chains and maltose -final step takes place on outer membranes of the intestinal cells -enzymes that break down disaccharides:   

Maltase breaks maltose into 2 glucose molecules Sucrase breaks sucrose into 1 glucose and 1 fructose molecule Lactase breaks lactose into 1 glucose and 1 galactose molecule

-now, all polysaccharides are broken down to monosaccharides In the Large Intestine -within 1-4 hours after mealall sugars and most of starches have been digested only fibres remain in digestive tract -fibres ATTRACT water in large intestines (softens stool for comfortable passage) -bacteria in GI tract ferment some fibres generates water, gas, and short chain fatty acids -cells of colon use small fat molecules for energy

-metabolism of short chain fatty acids also occurs in the liver fibres can contribute some energy (1.5-2.5 kcals per gram) Carbohydrate Absorption -glucose can be absorbed in lining of mouth, but for the most part, nutrient absorption takes place in the small intestines  

Glucose and galactoseenter by active transport Fructoseabsorbed by facilitated diffusion (slows entry and produces a smaller rise in blood glucose)

-unbranched chains of starch are digested slowlyproduce smaller rise in blood glucose -branched chainsmore places for enzymes to attack, and release glucose rapidly -blood from small intestines circulates livercells take up fructose and galactose and convert them to other compounds *most often glucose -thus, all disaccharides provide AT LEAST ONE glucose molecule directly (through conversion of fructose and galactose to glucose in the liver Lactose Intolerance -lactase activity highest after birth, declines during childhood and adolescence (to about 5-10% of the activity at birth) -only about 30% of people retain enough lactase to digest and absorb lactose efficiently throughout adult life Symptoms -when lactose molecules remain in the intestine undigested, they attract water causing:   

Bloating Abdominal discomfort Diarrhea

-undigested lactose become food for intestinal bacteria (multiple and produce irritating acid and gas) -lactose intolerance: a condition that results from inability to digest the milk sugar lactose; characterized by bloating, gas, abdominal discomfort, diarrhea. Differs from a milk allergy, which is caused by an immune reaction to the protein in milk Causes -lactase deficiency: a lack of the enzyme required to digest the disaccharide lactose into its component monosaccharides (glucose and galactose)

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May also develop when intestinal villi are damaged by disease, certain medicines, prolonged diarrhea and malnutrition May be temporary or permanent Rare, but infants can be born with this

Prevalence -varies widely among ethnic groups -trait is genetically determined -lowest among Scandinavians and other northern Europeans -highest among Aboriginal peoples and South East Asians Dietary Changes -total elimination of milk products is not usually necessary -many people with lactose intolerance can consume up to 6 grams of lactose without any symptoms -successful strategiesincrease intake of milk products gradually, take them with other meals, spread intake throughout day -yogurt containing live bacteria seems to improve lactose intolerance a change in GI bacteria accounts for ability to adapt to milk products -manage dietary consumption rather than restrict -most can handle fermented milk products such as kefir -kefir: a fermented milk created by adding lactobacillus acidophilus and other bacteria that break down lactose to glucose and galactose, producing a sweet, lactose-free product -lactose diminishes as cheese ages, so older cheeses are better tolerated -people who consume few or no milk products must take care to meet riboflavin, vitamin D, and calcium needs Lesson 3– Foods & Use in the Body *Section 4.3 (NOT “The Glycemic Response”), 4.4, 4.6 4.3 Glucose in the Body -primary role of carbs= supply cells with glucose for energy starch contains most of body’s glucose supply -when sugar molecules adhere to body’s protein and fat molecules; sugars attached to protein change its shape and function; when they bind to lipids in a cell’s membrane, they alter the way cells recognize one another

-glycobiology: the study of sugars A Preview of Carbohydrate Metabolism -glucoseplays central role in carb metabolism Storing Glucose as Glycogen -liverstores 1/3 of body’s total glycogen, and releases glucose into bloodstream as needed -after meal, blood glucose rises, liver links excess glucose (by condensation reactions into long, branching chains of glycogen) -when blood glucose fallsliver cells break glycogen (by hydrolysis reaction) into single molecules of glucose and release them into bloodstream 

Limited amount of glucose becomes available to supply energy to brain and other tissues regardless of whether the person has eaten recently

-muscle cells also store glucose as glycogen (hoard most of supply for energy during exercise) -brain maintains small amount of glycogen (thought to provide emergency energy reserve during sever glucose deprivation) -glycogen holds water which makes it bulky body can only store enough for energy for short periods of time (less than a day during rest and a few hours of exercise) for long term energy reserves, body uses water-free fuel; fat Using Glucose for Energy -enzymes break glucose in half (halves can be put back together to make glucose) or broken down into even smaller segments that cannot be re-formed -small segments yield energy when they are broken down completely to CO2 and water -because liver’s glycogen stores last only for hours, person needs to eat dietary carb frequently people who don’t attend to these needs frequently; draw energy from nutrients, fats, and proteins (but not as easily) Making Glucose from Protein -glucose= preferred energy source for brain cells, other nerve cells, and RBCs -amino acids of protein can be converted into glucose to some extent, BUT AA and proteins have other jobs that no nutrient can perform -fat CANNOT be converted into glucose to any extent

-when carbs are not eaten, body proteins (primarily from liver and skeletal muscle) are broken down to make glucose to fuel brain and other special cells -gluconeogenesis: the making of glucose from a noncarbohydrate source -protein-sparing action: the action of carbohydrate (and fat) in providing energy that allows protein to be used for other purposes Making Ketone Bodies from Fat Fragments -when there is inadequate carb supply, fat takes an alternative metabolic pathway  

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Instead of entering main pathway; fat fragments combine and form ketone bodies Ketone bodies: the metabolic products of the incomplete breakdown of fat when glucose is not available in the cells -provide alternate fuel source during starvation -when production exceeds use; they accumulate in blood and cause ketosis Ketosis: an undesirably high concentration of ketone bodies in the blood and urine -most ketone bodies are acidic; ketosis disturbs body’s normal acid-base balance -acid-base balance: the equilibrium in the body between acid and base concentrations To spare ketosis, body needs 50-100 grams of carbs a day

Using Glucose to Make Fat -body must find extra way to handle glucose -when glucose is abundant; energy metabolism shifts to use more glucose instead of fat if this is not enough to restore the balance, the liver breaks glucose into smaller molecules and puts them together to make fat (more permanent energy storage compound) -when carb is abundantfat is either conserved (by using more carb in the fuel mix) or created (by using excess carb by to make body fat) fat travels to fatty tissues for storage; fat cells can store seemingly unlimited quantities of fat The Constancy of Blood Glucose -every body cell depends on glucose for its fuel use to some extent -cells of brain and rest of nervous system depend almost exclusively on glucose for their energy they have limited ability to store glucose they draw on supply of glucose in fluid surrounding them, blood brings glucose from small intestine (food) or liver (via glycogen breakdown or gluconeogenesis) Maintaining Glucose Homeostasis -normal blood glucose 4-6mmol/L -body must maintain levels to function normally

-if blood glucose falls below normalperson may become dizzy or weak -if blood glucose rises above normal person may become fatigued  fluctuations left untreated can be fatal

The Regulating Hormones -blood glucose homeostasis regulated by 2 hormones: insulin and glucagon 

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Insulin: hormone secreted by special cells in the pancreas in response to (among other things) increased blood glucose concentration, primary role it to control transport of glucose from the bloodstream into the muscle and fat cells Glucagon: a hormone that is secreted by special cells in the pancreas in response to low blood glucose concentration and elicits release of glucose from liver glycogen stores Homeostasis: the maintenance of constant internal conditions by the body’s control systems

-after meal, blood glucose levels rise, special cells of pancreas (beta cells) respond by secreting insulin into the blood (amount of insulin corresponds with amount of rise in glucose) -insulin contacts receptors and reactions occur that result in ushering glucose from blood into cells most cells take glucose and use it right away, but liver and muscle cells store it

-elevated blood glucose returns to normal levels as excess glucose is stored as glycogen and fat -in between meals, blood glucose levels fall, other special cells of pancreas (alpha cells) respond by secreting glucagon into blood, which raises blood glucose by signalling liver to break down its glycogen stores and release glucose into blood -epinephrine also signals liver to release glucose -epinephrine: a hormone of the adrenal gland that modulates the stress response; formerly called adrenaline 

Ensures all body cells have energy fuel in emergencies

Balancing within the Normal Range -maintenance of normal blood glucose depends on 2 processes: 1. blood glucose below normal food can replenish it, or in absence of food, glucagon signals liver to break down glycogen stores 2. blood glucose levels rises above normalinsulin can signal cells to take glucose for energy -to maintain eat balanced meals at regular intervals; abundant carbs, including fibres, and little fat (helps slow...