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LIFESCI 2N03 (107)
Lecture

Oct 24 - Updated Carbohydrates Lecture Notes - LIFESCI 2N03

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Department
Life Sciences
Course Code
LIFESCI 2N03
Professor
Danny M.Pincivero

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LECTURE 5 LIFESCI 2N03 Lecture 5: Carbohydrates October 21, 23, 24, 2013  Carbohydrate – “hydrate of carbon”; manufactured by plants o Making a glucose molecule o Eg/ making a glucose molecule  6 CO2+ 6 H 2 + Energy  C H6O12 66O 2  Storage form of glucose o Animals – glycogen  Glycogen – branches at points; compact manner; liver higher in glucose; 8-10 glucose units then branch o Plants – starch (amylopectin and amylose) and fiber  Amylopectin – more bioavailable; ¾ starch; branched linear chains 25-30 glucose units, then branch  Amylose – ¼ of all starch available in plant based sources; less bioavailable than amylopectin (more compact)  Fiber – non-digestible carbohydrates (in plants); our bodies do not have the enzymes to breakdown certain fibers o Soluble Fibre  Dissolves in hot water  Forms a gel in GI system – does not move fast  Slows gastric/intestinal motility – advantage; absorbs fatty acids consumed with this fiber  “Fuller” feeling, absorbs FA’s  Decreases cardiovascular disease, because less cholesterol is absorbed into body  Eg/ Oat, bran, dried beans, nuts o Insoluble Fibre  Does not dissolve in hot water  Absorbs water into GI system  Speeds intestinal motility  Decreases Type II DM – because increased motility decreases glucose absorption time  Can lead to nutrient deficiencies  Eg/ Vegetable, fruit skins, whole grains  Function of Carbohydrates 1. Burned for energy 2. Ribose and deoxyribose sugars – serve as part of DNA and RNA 3. Structure and strength of plants 4. Linked to proteins and lipids  Glycoprotein – covalent link between protein and a carbohydrate monomer; found on cell surfaces – help to strengthen outer membrane of cells and for cell-cell adhesion  Glycolipid – forms myelin around neuron axons (insulation barrier for increase in speed of transmission along neuron)  Forms of Carbohydrates o Monosaccharide’s – simple form of CHO  Contains 3-9 carbon atoms  Eg/ Glucose, fructose, galactose,6C12 O6  Sugar alcohols  Derived from monosaccharide  Used as a sweetener (sorbitol made from glucose); sweetness in sugarless gum  Chemical modification of glucose molecule – changes the way our body perceives and senses monosaccharide o Glucose does not provide sweet flavor; fructose provides sweetness o Sorbitol can add the sweet flavor (carries calories, and larger sweet effect – negligible amount needed to be included, negligible about of calories)  Figure:  Monosaccharides enter into cardiovascular system from intestinal villi  Note: lipids and cholesterol do not go directly into cardiovascular system 1 LECTURE 5 LIFESCI 2N03 o Disaccharides – sucrose, lactose, maltose o Oligosaccharides – 3-9 CHO monomers  Considered to be a complex carbohydrate o Polysaccharides (≥ 10 monosaccharides)  Dietary from – starch  Vegetables and fruits  Grains – wheat, corn, oats, barley, rice  Legumes – peas, beans, lentils, soy  Tubers – potatoes, yams, cassava (toxic in raw form) Fiber  Soluble fiber – fermentable (bacteria can break it down anaerobically) becomes short chain fatty acids and can be absorbed to the body (very small amount) Starch  Begins in mouth, salivary glands begins to break down larger chain glucose molecules  Small intestine, pancreatic amylases accelerates breakdown of polysaccharides  Maltase, sucrose, lactase – intestinal cells use these enzymes to breakdown disaccharide in small intestines 2 LECTURE 5 LIFESCI 2N03  Purpose of consuming carbohydrates 1. Energy needs  Fuel source for neurons (only uses glucose except during starvation; can uptake protein); most amino acids are considered to be glucogenic  RBCs only use glucose; anaerobic, lacking mitochondria and nuclei; no ability to regenerate  Need CHO to metabolize other fuels; “fat burns in a flame of carbohydrates”  Ketone Bodies  Major source of production is the liver (in mitochondria)  Accumulation from protein and fat metabolism  Heart and renal cortex cells; ketone bodies are used as fuel  Starvation and Other Diseases o Brain neurons use ketone bodies (water soluble) – converted to Acetyl CoA o High levels of ketone bodies in blood reduces adipocyte lipolysis (regulates fat breakdown; feedback mechanism); increases reliance on CHO for energy  Type I Diabetes Mellitus – characterized by high level of ketones produced, and high lipolysis; no insulin (insulin has the effect of reducing lipolysis; no regulatory mechanism for fat breakdown) 2. Pregnancy  Fetus and placenta “feed” on glucose  Gestational diabetes – elevated blood glucose (inability to regulate glucose) during pregnancy; greater risk of developing Type I diabetes; usually ceases after birth but can persist 3. Spares muscle protein degradation for energy  Glucose must be synthesized from muscle protein when insufficient carbs from diet  proper diet will prevent muscle protein degradation  Amino acids converted to 1) ketone bodies 2) fatty acids 3) glucose o Ketone bodies – when harnessed from muscle tissues; recycle and use tissue o Fatty acids – can only occur when there is a high energy diet – there is a metabolic pathway to convert amino acids to fatty acids if energy needs are met o Glucose – amino acids are glucogenic  Gatorade will spare muscle breakdown o Exercise  glycolysis is elevated; storage of carbs in liver cells are begin metabolized and have to be restocked o Illness  infection  increased WBC (glucose); continues intake of carbohydrates to feed elevated metabolic state Carbohydrates and Energy  Glucose carried in the body o Always supply of glycogen in cardiovascular system o Liver stores glycogen more densely than muscle o Plasma glucose fluctuates with amount eaten, what was eaten, type of carbohydrate o Muscle tissue contains more energy than liver tissue – more muscle cells in the body than liver cells; muscle distributed throughout body  Overall glucose content o Blood glucose – 30 g o Liver glycogen – 90 g o Muscle glycogen – 350 g  ATP yield for CHO and fats 3 LECTURE 5 LIFESCI 2N03 o 5.1 kcal/L of2O (carbohydrates) – better fuel source when metabolized aerobically than fat o 4.8 kcal/L of2O (fats) o Due to substrate level phosphorylation – refers only to glucose; direct making of ATP from transformation of macronutrient; 4 extra ATP from glycolysis in cytoplasm  Minimum intake of CHO: 130 g/day for nervous system function  Figure: Body reactions to ingesting carbohydrates o 2. Glucose in blood binds to B-cells in pancreas which stimulates insulin production  Type I DM – B-cells are destroyed by body; insulin is not produced (#2 inhibition; pancreas)  high blood glucose o 3. Insulin binds muscle and liver cells to promote glucose uptake in cells – remove glucose from blood as glycogen  Type II DM – 9/10 of Canadians with DM; muscle cells not responding to insulin (insulin resistant) (#3 inhibition; muscle tissue)  high blood glucose o 4. Homeostatic level; blood glucose declines but does not deplete (not too high, not too low) o 5. Glucagon from a-cells in pancreas to maintain homeostasis of blood glucose – promotes glycogen breakdown (glycogenolysis) from liver and blood glucose increases  External cellular signal, stimulant of glycogenolysis  Glycemic Index (GI) – a measure (no units) of the potential food to raise blood glucose levels o High GI – blood glucose response is quicker in cardiovascular system  Increase [glucose] fast  increase blood [insulin] fast  7TM (7 transmembrane) receptor binds insulin – deactivates lipase  Diet chronically high in high GI foods – insulin continues to be secreted, muscle cells begin to be resistant to insulin  Exercise causes muscle cell contraction – same effect as insulin, stimulates proteins that pull glucose into cell o Fructose content; have to convert to glucose  lower GI o 2 different standards – one slide of white bread or pure glucose (both taken as 100%) o High GI ≥80 o Mid GI 56-59 o Low GI <56 4 LECTURE 5 LIFESCI 2N03 o Factors affecting the GI of foods 1. Proportion of CHO content of the ingested food  Increased % CHO, increase GI  Examples (compare to pure glucose ingestion) o Ice Cream 61  Fat molecules slow rate of glucose absorption o Baked Potato 85 o Instant Rice 91 o CHO easily broken down and absorbed o If GI is the factor – french fries are healthier than baked potatoes because lower GI 2. Type of carbohydrates  Simple vs. Complex  Role in Fat Storage – insulin action 3. Cooking  Heat helps to disrupt chemical bonds – faster digestion  Eg/ o Pasta GI (5 min boiled) 34 o Pasta GI (10 min boiled) 40  Blood glucose response to feeding o Glycemic Load – amount of carbs, blood glucose will increase (as opposed to rate of blood glucose increase)  GI multiplied by the amount of available carbohydrates in a food source/100  Predictor of developing Type II diabetes mellitus and cardiovascular disease  Eg/  Corn Muffin GI = 102 (compared to glucose), 29 g carbs/serving, GL = 20  Bran Muffin GI = 60 (compared to glucose), 24 g carbs/serving, GL = 15 o High fibre – indigestible  Fruits – high GI, low glycemic load  Watermelon – blood glucose increases quickly, but not by a lot  Blood Glucose Response to Feeding  Eat  blood glucose begins to rise  eventually goes down, undershoots then stabilizes  Baked potatoes  magnitude of increase in blood glucose is much larger and enters system more quickly (dotted line)  Ice cream (red line) o Fat molecules compete with intestinal absorption of glucose  Glycemic Index – slope of curve; how fast blood glucose concentration increases  Glycemic Load – magnitude of blood glucose concentration 5 LECTURE 5 LIFESCI 2N03 Pancreatic Hormones  Insulin o Produced by beta cells of the pancreas o Helps cells take in glucose from the blood o Stimulates the liver to take up glucose and convert it to glycogen o Overall effect of lowering blood glucose o 51 amino acid sequence, with 2 chains (A and B) o Disulfide bridges between cysteine residues  Glucagon o Produced by alpha cells of the pancreas o 29 amino acid polypeptide o Signals a physiologically starved state o Stimulates the breakdown of glycogen to glucose o More glucose is available to cells of the body o Stimulates gluconeogen
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