Lectures 5, 6, & 7 - Carbohydrates

Lectures 5, 6, & 7 - Carbohydrates - CARBOHYDRATES 1...

Info icon This preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: CARBOHYDRATES 1 Next couple of classes… • Classification & Structure • Digestion & Function • Metabolic Pathways • Impact on Health …of carbohydrates2 Carbohydrate Classification SIMPLE • Monosaccharides - Cannot be hydrolyzed into a small - Are reducing • Most common = glucose • Occurs naturally • Cannot be hydrolyzed into a small unit • Disaccharides common = sucrose monosac charides joined by an acetyl (glycosidi • Most common = sucrose • Two monosaccharides joined by an acetyl bond (glycosidic bond) COMPLEX • Oligosaccharides • Polysaccharides - Homo - & ALL CHO polysacchari have a H:O ration of 2:1 - Glycogen • Homo- & hetero-polysaccharides • Glycogen (animal) • Starch & Cellulose (plant) • All CHO have a H:C ratio of 2:1 3 Monosaccharides TRIOSE METABOLITES OF GLUCOSE PENTOSE COMPONENTS OF DNA AND RNA HEXOSE NUTRITIONALLY THE MOST IMPORTANT 4 *Anomeric carbon (location of carbonyl group) Stereoisomerism • Why is this important? - Biological systems are stereospeific – Biological systems are stereospecific • Same molecular formula and sequence, but differ in 3D space • Different types: (mirror image) – Enantiomers (mirror image) (not a mirror) – Diastereomers (not a mirror) Chiral carbon - A carbon with • Chiral carbon – A carbon with four different atoms or groups 5 Stereoisomerism • Chiral carbon • Fischer Projection • Exist in two forms: D vs. L – Depends on highest chiral carbon OH on the right = D OH on the left = L - Depend on highest chiral carbon OH on the right = D OH on the left = L The number of stereoisomers for a molecule = 2n (where n = # chiral carbons) D - monosaccharides are nutritionally more important because digestive enzymes are stereospecific for D sugars. D-monosaccharides are nutritionally more important because digestive 6 enzymes are stereospecific for D sugars Carbohydrate Nomenclature, cont. New chiral centre 2 possible conformations (alpha or beta) 2 possible Beta more common conformations (α or β) GLUCOSE FRUCTOSE Fischer Model Haworth Model Hemiacetal --> monosaccharide containing an aldehyde Hemiketal --> monosaccharide containing a ketone Hemiacetal monosaccharide containing an aldehyde Hemiketal monosaccharide containing a ketone 7 Haworth Model • From Fischer projection to Haworth Model HEMIACETAL • Rules for what’s up and what’s down? 1) None-acetyl/ketal CH2OH always pointed up 1) CH 2OH always pointed up 2)Hydroxyl groups - Right in Fischer model, down in Haworth 2) Hydroxyl groups - Left in Fischer model, up in Haworth right in Fischer model, down in Haworth 3) Hemiacetal (alpha or beta ) leftOHingroup Fischer up in Haworth - Alpha has the pointingmodel, down - Beta has the OH group pointing up 3) Hemiacetal (alpha or beta) alpha has the OH group pointing down beta has the OH group pointing up 8 Haworth Model • From Fischer projection to Haworth Model HEMIKETAL • Rules for what’s up and what’s down? Same rules apply for hemiacetal and hemiketal Same rules apply for hemiacetal and hemiketal sugars 9 Recap for CHO Nomenclature • Anomeric vs. chiral carbon - Anomeric carbon = carbonyl group - Chiral carbon = 4 different atoms/ groups • D vs. L configuration - D configuration is nutritionally more important • Alpha or beta configuration of hemiacetal or hemiketal group - 2X more beta vs. alpha configuration - Beta has -OH group on anomeric carbon pointing ip • Fischer Projection Haworth Model - Linear Vs cyclic 10 Let’s practice…. H C O H C OH H C OH H C OH CH2OH How many carbons? So this called a what? Triose? Pentose? Hexose? 5 carbons Is this an aldose or ketose? Aldosepentose 11 H 1 H H H 2 3 4 5 C O C OH C OH C OH CH2OH Which carbon is the ANOMERIC carbon? Carbon one What is the highest numbed chiral carbon? carbon 4 How many sterioisomers exist? 8 because 2^n = 2^3 = 8 12 H C O H C OH H C OH H C OH CH2OH Is this sugar in the D or L conformation? D on the right of the structure 13 H OH C O H H C OH H H C OH H H C OH H 1 2 3 4 5 CH2OH C C OH C OH C O CH2OH 5 CH2OH How do we place hydroxyl groups on Haworth model? 4 β-D ribose 1 3 REMEMBER …..right in Fischer model means down in Haworth projection OH O 2 OH α-D ribose 14 Disaccharides • Most common oligosaccharide • 2 monosaccharides attached by a glycosidic bond (formed between 2 hydroxyl groups) – The anomeric carbon hydroxyl group of one monosaccharide + the hydroxyl group at Carbon 4/6 in the other monosaccharide • Glycosidic bond can also be alpha or beta… • Configuration of the anomeric OH group determines whether the disaccharide is alpha or possible outcomes [alpha(1,4), apha(1,6), Beta(1,4), Beta(1,6)] beta possible outcomes [α(1,4), α(1,6), β(1,4), β(1,6)] 15 Common Disaccharides •Found in sugar - Found in sugar cabe, fruits cane, fruits - glucose + fructose + fructose -•glucose Non-reducing •Non-reducing! - Found in milk - galactose •Found +inglucose milk - Reducing •galactose + glucose •Reducing! - Found in beer & liquor •Found in beer & - glucose + glucose liquor - Reducing •glucose + glucose •Reducing! 16 Polysaccharides • Long strings or branches of monosaccharides (min. of 6) attached by glycosidic bonds • Homopolysaccharides • Heteropolysaccharides – Both exist in nature, but homopolysaccharides more abundant in food 17 Polysaccharides • Starch (Amylose, Amylopectin) plants – Both forms are polymers of D-glucose • Glycogen animal tissue • Is there an advantage for branching? - Yes, provides a larger number of ends from which to cleave glucose when energy is required – Yes…provides a larger number of ends from which to cleave glucose when energy is required. 18 Dietary Fibre • Non-digestible complex CHO • Structural part of plants Insoluble Soluble Lignin Pectins Gums Mucilages Cellulose Hemicellulose Remains intact through intestinal tract (does not dissolve in water) Forms gel (does dissolve in water) 19 Characteristics of Dietary Fibre? • Characteristics of solubility? – Water-holding ability • Ability of a fibre to hold water, become a viscous solution - Ability of a fibre to hold water, become a viscous solution – Adsorptive ability • Ability of a fibre to bind enzymes and nutrients - Ability of a fibre to bind enzymes and nutrients • Insoluble (cellulose, lignin, some hemicelluloses) • Remains intact throughout the digestive system • Decrease transit time • Increases fecal bulk - Remains intact throughout the digestive system - Decrease transit time - Increase fecal bulk • Soluble (pectins, gums, B-glucans, some hemicelluloses) • Forms a gel • Delays gastric emptying • Decreases nutrient absorption - Forms a gel - Delays gastric emptying - Decrease nutrient absorption 20 Nutrition News 21 • Cellulose – – – – – – Both a dietary fibre and functional fibre Homopolysaccharide of glucose Linear polymer of β1,4 glucose units Poorly fermented by gut bacteria Found in bran, legumes, nuts, peas, etc… Lack of cellulose-fermenting microbes (metanogens) 22 • Hemicellulose – Heteropolysaccharide that varies between plants – Both α and β conformation – Both pentoses and hexoses • Xylose is the most common sugar – Can appear branched or linear – The solubility and fermentability of hemicellulose depends on the sugar composition. – Found in bran, whole grains, nuts, and some vegetables/fruits 23 • Pectin – – – – – Both a dietary and functional fibre Part of the primary cell wall of plants Backbone of unbranched α1,4-linked-D galacturonic acid Stable at low pH Highly fermented by gut bacteria • Therefore a good bulking agent – Rich in fruits, such as apples, oranges, lemons, grapefruit, etc • Resistant Starch – – – – – – Not digested by humans Four main types, termed RS1 – 4 Typically found in plant cells walls Resistant to amylase activity Conveys some of the advantages of soluble and insoluble fibres Americans consume ~10g of RS/ day 24 Health Benefits of Fibre • Maintains function & health of the gut • ↓ constipation (insoluble fibre) • Stimulates muscle contraction to break down waste - Stimulates muscle contraction to break down waste - Decreases risk of bacterial infections • Decreases risk of bacterial infections • ↑ satiety (soluble fibre) - Delays gastric emptying - Benefits for long term weight control? • Delays gastric emptying • Benefits for long term weight control? 25 Health Benefits of Fibre, cont. Decrease cardiovascular disease risk by lowering blood cholesterol Psyllium seed husks Psyllium seed husks 26 • Classification & Structure • Digestion & Function • Metabolic Pathways • Impact on Health …of carbohydrates27 Carbohydrate Digestion • Mouth - Saliva down alpha 1,4-glycosidic bonds) – (alpha-amylase...breaks Saliva (α-amylase…breaks - Cellulose and lactose are resistant down α1,4-glycosidic bonds) - Produces few monosaccharides – Cellulose and lactose are resistant – Produces few monosaccharides – Stomach – α-amylase digestion continues - Alpha-amylase digestion continues until pH drops, untildeactivate pH drops, then enzyme then enzyme - CHO --> dextrins and maltose deactivated – CHO dextrins and maltose – Intestine – Pancreatic α-amylase - Panreactic alpha-amylase - pH a problem – notpH not a problem - alpha-1,6 bonds lead to isomaltose production – α -1,6 bonds lead to isomaltose production 28 Brush Border enzyme activity •Also -called sucrase Also called sucrase - sucrose releases --> glucose + fructose •sucrose glucose + fructose •Also called - Also called isomaltase isomaltase - Breaks alpha-1,6 glycosidic bonds releases 2 glucose •Breaks α-1,6 glycosidic bonds 2 glucose lactose releases--> glucose + galactose glucose + lactose Maltose 2-->glucose Maltose 2 glucose galactose See Diagrams 29 Lactose Intolerance •AGE •ETHNICITY •95% Asians •5% Northern Europeans •GENETICS Lactose intolerant vs. lactase persistent 30 Monosaccharide absorption • Very efficient • Nearly all absorbed by the end of the jejunum – Fates for glucose? • 15% leaks back out into lumen - 15% leaks back out into lumen - 25% diffuses intodiffuses circulation into via basolateral membrane • 25% circulation via - 60% transported into circulation by GLUT2 basolateral membrane • 60% transported into circulation by GLUT2 • Active transport system for glucose and galactose • Facilitated transport for fructose – GLUT5 on apical surface – GLUT2 on basolateral surface 31 Functions? • Glucose = primary source of energy for cells • Carbohydrates spare protein – Prevents breakdown of protein for energy – Allows protein to concentrate on building, repairing, and maintaining body tissue • Prevents ketosis – When carbohydrates limited, fat can be broken down for energy, which creates ketone bodies and makes the body acidic • Only source of energy for the brain • Ensure the growth of healthy bacteria in the gut 32 • Classification & Structure • Digestion & Function • Metabolic Pathways • Impact on Health …of carbohydrates33 GLYCOGENOLYSIS GLUCONEOGENESIS production of glucose from non glucose sources to produce the energy that is produced when breaking down glucose GLYCOGENESIS CARBOHYDRATE METABOLISM GLYCOLYSIS KREB’S CYCLE HEXOSE MONOPHOSPHATE SHUNT generates bionsynthetic 34 Key Points: Know the ‘purpose’ of each pathway, ‘key’ steps and enzymes will be highlighted ….but don’t worry…. Details about each step, enzymes and structures are important but you have been tested on those in biochemistry. The enzymes you need to know will be specifically indicated in diagrams… Think ‘big picture’ and ‘integration’ 35 2 1 3 Glucose has three fates in a cell: 1) Enters glycogenesis for energy storage 2) Enters glycolysis for energy production 3) Enters hexose monophosphate shunt to generate precursors for biogenesis This “decision” depends on requirements of the cell (i.e. ENERGY VS BIOSYNTHESIS) 36 Glycogenesis - energy homeostasis - primary site in liver (lesser extend in muscle-secondary site) 2 main hormones that regulate -insulin -glycagon negative (-) regulation in muscle glycogen synthase insulin (+) enzyme hexokinase (muscle) enzyme glucokinase (liver) (+) insulin glycogenin (scaffold protein) - can have several glycogenin branches 37 Glycogenolysis breakdown of glycogen hormone glucagon (+) glycogen phosphorylase break only alpha1-4 glycosidic bons alpha1,6 -bond -->debranching 38 Glycogenesis / Glycogenolysis similar to a figure 8 Beta-cell (insulin) (+) Alpha-cell (glucagon) 39 Where is energy produced? 1. Substrate-level Phosphorylation In - cytoplasm (glycolysis) -mitochondria mitochondria (Kreb’s (krebs) cycle) Eg. red blood cells and cytoplasm (glycolysis) 2. Oxidative Phosphorylation - mitochondria (ETC) In mitochondria (electron transport chain) 40 Glycolysis cytoplasm glucose galactose • Glycolytic enzymes in cytoplasm • All life on earth performs glycolysis insulin (+) glucokinase/he fructose phosphofructokinase (+) (-) insulin ATP • Endpoints depends on available O2 Glucagon ETC – Aerobic – Anaerobic pyruvate vs pyruvic acid (structural difference ) NET: 4ATP + 2NADH (-2ATP) triose (O2) anaerobic and aerobis Metabolic fate of pyruvate? 41 lacking oxygen Anaerobic metabolism of glucose glycolysis we have 2 pyruvic acid molecules • Lactic acid – Output? process used in yeast and making wine&beer this process(left side) takes place in prolonged muscle contraction • Ethanol – Output? cori cycle glucose can only take place in the liver not the muscles heart 42 Cori Cycle The Cori Cycle occurs in times where oxygen is unavailable (anaerobic state) in the muscle, leading to the production of lactate. Lactate is transported back to the liver, where gluconeogenesis allows for the conversion of pyruvate back to glucose. For 2 molecules of lactate to form glucose the cell consumes 6 ATP molecules. Can not be sustained forever….because more energy is consumed than produced 43 Hexose Monophosphate shunt -pentose phosphate pathway -Bionsynthesis • Important for NADPH production and ribose glucose-6 phosphate dehydrogenase synthesis (-) irreversible pathway crucial for the biosynthesis of fatty acid Eg. muscle biosynthesis needs of the cell reversible biosynthesis of DNA/RNA (pentose sugars) 44 Pyruvate Dehydrogenation complex ATP (-) uni-directioned (-) 3 key enzymes in this complex (gate keeper to kreps cycle) - pyruvate dehydrogenase - dihydrolipoyl transocetylase - dihydrolipoyl dehydrogenase located in the mitochondria Thiamine Niacin Riboflavin Pantothenic acid ETC co-factors (vitamins) 2x 45 Krebs Cycle • Over 90% of the energy in food released here • A common and final catabolic pathway for products of protein, lipid and carbohydrates • Mitochondrial matrix not all substrates entering the kreps completely used 46 C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy CHO, protein, fat DO NOT NEED TO MEMORIZE 1 glucose glycolysis --> 2 ATP + 2NADH (=6ATP) P.D.H --> 2NADH (=6ATP) Krebes (X2)-->3NADH (=9ATP) + 1FADH2 + 1GTP Kreb’s Cycle TOTAL: 36 ATP protein -> pyruvate (alanine, serine, threonine, cysteine) amino acid equivalent to 3 ATP equivalent to 2 ATP 47 Source: Nature Education 3(9):11 glucokinase Gluconeogenesis phosphofructokinase liver all cytoplasm also kidney (e.g. starvation) muscle, adipose tissue lack enzymes for gluconeogenesis muscle lactate? Cori Cycle pyruvate kinase 48 cori cycle anaerobic sate liver-->gluconegeonesis Gluconeogenesis pyruvate carboxylase Moving oxalacetate out leave the of the mitochondria and cant mitochondria into the cytoplasm malate dehydrogenase Key step to initiate gluconeogenesis recoup energy here malate dehydrogenase gluconeogenesis converted to phphoenolpyruvate 49 PEPCK Monday February 11 In class (5:30 am – 6:50 pm) Rozanski Hall 101 Multiple choice only Bring a PENCIL! Bring a CALCULATOR! 50 Integrated Metabolism Think beyond carbohydrates… ‘Big picture’ of metabolic pathways: inter-conversion and oxidation of fats, proteins, carbohydrates Body’s energy needs and metabolic homeostasis See diagram (next) 51 Integrated Metabolism 52...
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern