Biomolecules - Carbohydrates PDF

 \ **BIOMOLECULES** **Monomers & Polymers** - Macromolecules are actually ma - de up of even smaller subunits. Each subunit of a macromolecule is called a **monomer**. - The macromolecules themselves are called **polymers**, because they are made up of many of these subunits. I....

 \ **BIOMOLECULES** **Monomers & Polymers** - Macromolecules are actually ma - de up of even smaller subunits. Each subunit of a macromolecule is called a **monomer**. - The macromolecules themselves are called **polymers**, because they are made up of many of these subunits. I. **CARBOHYDRATES** Sources of Carbohydrates a. Simple Sugars b. Complex Carbohydrates c. Dietary Fiber Digestion and Absorption Functions Blood glucose regulation Dietary sweeteners Dietary Recommendations - are an important source of energy. - Has a monomer **monosaccharide** - provide structural support for cells and help with communication between cells. - Made up of CHO Types of Carbohydrates [Simple Carbohydrates] - monosaccharides - disaccharides [Complex Carbohydrates] - oligosaccharides - polysaccharides - glycogen - starches - fibers 1. Monosaccharides: Single Sugars Glucose - carbohydrate form used by the body, referred to as "blood sugar" - basic sub-unit of other larger carbohydrate molecules - found in fruits, vegetables, honey Fructose - sweetest of the sugars - occurs naturally in fruits & honey, "fruit sugar" - combines with glucose to form sucrose Galactose - combines with glucose to form lactose, "milk sugar" 2. Disaccharides Sucrose ("table sugar") - glucose + fructose Lactose ("milk sugar") - glucose + galactose Maltose ("malt sugar") - glucose + glucose Joining and Cleaving Sugar Molecules  3. Complex Carbohydrates a. Oligosaccharides - short carbohydrate chains of 3 - 10 monosaccharides - found in legumes and human milk - Examples: - raffinose - stachyose b. Polysaccharides - long carbohydrate chains of monosaccharides linked by glycosidic bonds - alpha (a) bonds (starch) - beta (b) bonds (found in fiber) b.1 Starch - plant storage form of carbohydrate - long branched or unbranched chains of glucose - amylose - amylopectin b.2 Glycogen - highly branched chains of glucose units - animal storage form of carbohydrate - found in LIVER and MUSCLE - Humans store \~ 100g in liver; \~ 400g in muscle - negligible source of carbohydrate in the diet (meat) b.3 Fiber **Dietary Fiber** - non-digestible carbohydrates (chains of monosaccharides) and lignin that are intact and intrinsic in plants (includes oligosaccharides) **Functional Fiber** - isolated, non-digestible carbohydrates that have beneficial physiological effects in humans - dietary fiber found in all types of plant foods - refining removes fiber from whole grains and other foods - types of non-starch polysaccharides include: cellulose hemicelluloses pectins gums & mucilages b-glucans chitin & chitosan lignans Digestion & Absorption **1. Mouth** - chewing - *salivary amylase* **2. Stomach** - fibers remain in the stomach longer, delays gastric emptying 3. **Small Intestine** - pancreas secretes enzyme *pancreatic amylase* - enzymes located on the cell membranes of the intestinal epithelial cells complete digestion - only monosaccharides can be absorbed - glucose & galactose absorbed by ACTIVE TRANSPORT - fructose absorbed by FACILITATED DIFFUSION - all three monosaccharides travel in the portal vein to the liver - three fates of glucose at the liver - Energy, storage as glycogen, released to blood 4. **Large Intestine** - resistant starches and fibers may be digested by bacteria - produces ***short chain fatty acids*** - absorbed by the intestine and used for energy (dietary fiber yields about 2 kcal/g) - other health benefits (more later in semester) **Lactose Intolerance** - occurs as a result of insufficient lactase & low lactase activity - lactose molecules from milk remain in the intestine undigested - **lactose intolerance** ≠ **milk allergy** - undigested lactose digested by bacteria producing irritating acid and gas - symptoms include bloating, abdominal discomfort, diarrhea - individuals who consume little or no milk products may be at risk of developing nutrient deficiencies - dairy options: yogurt, aged cheddar, small quantities of milk (\~ ½ cup), acidophilus milk, cottage cheese - best to consume with other foods and spread intake throughout day - gradual increases in milk intake may cause intestinal bacteria to adapt Alternatives to Milk **1. Calcium** - canned fish with bones, bone soup stock, broccoli, cauliflower, calcium fortified beverages, blackstrap molasses **2. Vitamin D** - 15 minutes exposure to SUNLIGHT several times per week - fortified margarine, fortified cereals, fatty fish (herring, tuna, salmon, sardines), fortified soy or rice milk **3. Riboflavin** - beef, chicken, liver, clams, mushrooms, broccoli, breads, fortified cereals **Functions of Carbohydrates** **1) Energy** - glucose fuels the work of most of the body's cells - preferred fuel of NERVOUS TISSUE (the brain, nerves) and RED BLOOD CELLS (RBC) - excess glucose is stored as GLYCOGEN in liver and muscle tissue **2) Sparing Body Protein** - if diet does not provide enough glucose, then other sources of glucose must be found - if carbohydrate intake **\< 50 - 100 g**, body protein will be used to make glucose - an adequate supply of carbohydrate spares body proteins from being broken down to synthesize glucose **3) Preventing Ketosis (Anti-ketogenic)** - carbohydrates required for the complete metabolism of fat - incomplete fat metabolism produces KETONES - an adequate supply of carbohydrate (\> 50 -- 100 g per day) prevents KETOSIS **Ketosis** - A metabolic state or process in order to keep our body working. When it doesn't have enough carbohydrates from food for your cells to burn for energy, it burns fat instead. As part of this process, it makes ketones. **Fiber** - beneficial for weight control by contributing to satiety & delay gastric emptying - soluble fibers lower blood cholesterol to help reduce risk of cardiovascular disease - minimizes risk of and helps control Type II Diabetes - insoluble fibers help promote intestinal health by enlarging stool size and easing passage of stool **Soluble Fiber** - examples include gums, pectins, mucilages, some hemicelluloses - functions: - delay gastric emptying - slow transit through the digestive system - delay glucose absorption - bind to bile, help decrease cholesterol - food sources: fruits **Insoluble Fiber** - examples include cellulose, hemicellulose - functions: - speed transit through the digestive tract - delay glucose absorption - increase fecal weight and soften stool to ease passage - reduces risk of hemorrhoids, diverticulitis and appendicitis - food sources: cereal grains, legumes, vegetables, nuts Excessive amounts of fiber may lead to: - displacement of other foods in the diet - intestinal discomfort - interference with the absorption of other nutrients **Regulation of Blood Glucose** Optimal functioning of the body is dependant on keeping levels of glucose within certain parameters. Elevated blood glucose = Hyperglycemia Low blood glucose = Hypoglycemia The ENDOCRINE SYSTEM is primarily responsible for regulating blood glucose. The two main hormones are INSULIN and GLUCAGON. **Diabetes Mellitus** - a disorder of energy metabolism due to failure of insulin to regulate blood glucose - results in hyperglycemia - acute symptoms include thirst, increased urine production, hunger - long term consequences include increased risk of heart disease, kidney disease, blindness, neural damage - two forms: Type I and Type II **Type I** - accounts for about 10% of cases - occurs when **b cells** of the pancreas are destroyed - insulin cannot be synthesized - without insulin, blood glucose levels rise because the tissues are unable to access the glucose - death occurs shortly after onset unless given injections of insulin **Type II** - occurs when cells of body are unable to respond to insulin - called "insulin insensitivity" or "insulin resistance" - blood glucose levels rise - insulin secretion increases in an attempt to compensate - leads to **hyperinsulinemia** **Hypoglycemia** - dramatic drop in blood glucose - symptoms similar to an anxiety attack: rapid weak heart beat, sweating, anxiety, hunger, trembling, weakness - RARE in healthy people - may occur as a result of poorly managed Diabetes or other causes: - reactive hypoglycemia - fasting hypoglycemia **The Glycemic Index** - a measure of the extent to which a food raises blood glucose concentration & elicits an insulin response compared to pure glucose **Sugar** Intrinsic sugars - from intact fruits & vegetables Added sugars - saccharides added to foods & beverages by manufacturer, cook, or consumer Free sugars - added sugars + concentrated sugars (i.e. from honey, syrups, and juices) Why is sugar added to foods? - flavour enhancement - provide texture and colour - permits fermentation - adds bulk - acts as a preservative - balance acidity **Dental Caries** Sugars, whether consumed from the diet or from complex carbohydrates partially digested in the mouth, contribute to tooth decay. **Reducing risk of caries formation** - eat sugary foods with meals - limit between meal snacks containing sugars and starches - brush and floss teeth regularly - if brush and flossing not possible, rinse teeth with water or chew sugar-free gum **Nutritive & Artificial Sweeteners** Nutritive Sweeteners - imparts sweetness and provides energy - includes natural sweeteners, refined sweeteners, and sugar alcohols Refined Sweeteners - composed of simple sugars extracted from other foods Non-Nutritive (Artificial) Sweeteners - impart sweetness but provide a negligible amount of energy **Sugar Alcohols** - examples: sorbitol, mannitol, xylitol - considered sugar replacers: use similar amount as sugar and provide about 2 kcal per gram - only found in commercial foods (common in chewing gum) - bacteria that produce cavity causing acid don't metabolize sugar alcohols **Artificial Sweeteners** **Aspartame** - 200x sweeter than sugar, yields 4 kcal per gram - made of two amino acids: - individuals with PKU (genetic disorder) cannot convert **phenylalanine** to **tyrosine** effectively, increase's in blood phenylalanine concentration can be toxic **Saccharin** - one study found that excess may cause bladder cancer in rats, but longitudinal human studies show no support for saccharin causing bladder cancer **Acesulfame K** - cannot be digested by the body thus provides no energy - not affected by heat so can be used in cooking - 200x sweeter than table sugar **Sucralose** - made from sugar but does not contribute to energy because it is not digested - approved by the FDA in U.S. in 1998, used in Canada since 1992 - sold under trade name Splenda - 600x times sweeter than table sugar How much carbohydrate do I need? AMDR (Adults) - **45 - 65%** of total average energy intake RDA for Carbohydrates (Adults) = **130 g per day** Daily Value (2000 kcal diet) = **300 g per day** AI for Fiber (Adults)\* - Men: **38 g per day** - Women: **25 g per day** Sugar = **max 10% of energy intake** *\*Note: after age 50, recommendations decrease to 30 and 21 g per day for men and women respectively.*