Lecture 3 Carbohydrates PDF

Carbohydrates Introduction to Human Biology 1 Semester 1 CARBOHYDRATES Learning outcomes Be able to define a carbohydrate. Be able to classify carbohydrates and know the basis for the classification. Be able to list members of the four groups of carbohydrates. Be able to explain the significance of...

Carbohydrates Introduction to Human Biology 1 Semester 1 CARBOHYDRATES Learning outcomes Be able to define a carbohydrate. Be able to classify carbohydrates and know the basis for the classification. Be able to list members of the four groups of carbohydrates. Be able to explain the significance of the geometry of the bonds in carbohydrates. Be able to explain the significance of the types of bonds that connect glucose units in carbohydrates. Be able to describe the different types of storage and structural polysaccharides and describe what makes them different from each other. Be able to list the main functions of carbohydrates in biological systems.  Carbon: The Backbone of Life Living organisms consist mostly of carbon-based compounds Carbon has ability to form large, complex, and varied molecules Proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds Organic chemistry is the study of compounds that contain carbon, regardless of origin Organic compounds range from simple molecules to colossal ones  Hydrocarbons Hydrocarbons are organic molecules made of only carbon and hydrogen Many organic molecules, such as fats, have hydrocarbon components Hydrocarbons can undergo reactions that release a large amount of energy The BIG Molecules of Life Four classes of large biological molecules: Carbohydrates Lipids Proteins Nucleic acids Macromolecules are large molecules and are complex Large biological molecules have unique properties that arise from the orderly arrangement of their atoms  Monomers come together to form polymers A polymer is a long molecule consisting of many similar building blocks The repeating units that serve as building blocks are called monomers Most macromolecules are polymers Carbohydrates Proteins Nucleic acids Lipids are not polymers Animation: Polymers  The Synthesis and Breakdown of Polymers Enzymes are specialized macromolecules that speed up chemical reactions (catalyst) such as those that make or break down polymers A dehydration reaction occurs when two monomers bond together through the loss of a water molecule Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction Carbohydrates serve as fuel and building material Carbohydrates include sugars and the polymers of sugars The simplest carbohydrates are monosaccharides, or simple sugars Eg: glucose Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks Break down to monomers (simple sugars) Sugars Monosaccharides have molecular formulas that are usually multiples of CH2O Glucose (C6H12O6) is the most common monosaccharide Monosaccharides are classified by The location of the carbonyl group (as aldose or ketose) The number of carbons in the carbon skeleton  Animation: Disaccharides © 2017 Pearson Education, Inc. Polysaccharides Polysaccharides, the polymers of sugars, have storage and structural roles The structure and function of a polysaccharide are determined by sugar monomers positions of glycosidic linkages What Are Carbohydrates?  Produced by plants during photosynthesis.  After eating plant foods, humans convert the carbohydrates into glucose.  Glucose Most abundant carbohydrate. Preferred source of energy for the blood, brain, and nervous system  Carbohydrate - rich plant foods make up the foundation of diets all over the world Classification of Carbohydrates Carbohydrates can be classified as; Simple (monosaccharides and disaccharides) Complex (oligosaccharides and polysaccharides). Classification of Carbohydrate The simplest carbohydrates are monosaccharides / simple sugars (e.g. glucose, fructose, galactose, and mannose). Disaccharides, double sugars, consist of two monosaccharides joined by a condensation reaction. Examples: Glucose + galactose = Lactose Glucose + glucose = Maltose More than 2 sugar units that can be broken down by hydrolysis to their simple sugar constituents.  Classification of Carbohydrates  2-10 simple sugars are called oligosaccharides. Polysaccharides are polymers of >10 monosaccharides. Examples: Starch, glycogen, chitin, cellulose Carbohydrates Definition and some properties. All contain carbon, hydrogen, and oxygen atoms They contain hydrogen and oxygen in the same ratio as water (2:1) and typically can be broken down to release energy in the animal body Carbohydrates are Very hydrophilic – very soluble in water. Due to the large numbers of polar hydroxyl groups (OH). Most soluble molecules in the cell. Functions of Carbohydrates 1. Carbohydrates are a source of energy (sugar + oxygen = c a r b o n dioxide + water + energy (ATP) (1 mole of glucose = 686 kcal of energy released) and a source of building materials for the cell. 2. Some carbohydrates are important as short term energy storage molecules (simple sugars such as glucose (dextrose) and fructose). 3. Long term energy storage molecules (starch in plants and glycogen in animals). 4. Structural molecules - Cellulose (all plant cell walls). 5. Source of carbon atoms for the synthesis of many other compounds within the cell. 6. Some carbohydrates are important components of DNA and RNA 7. Carbohydrates play major roles in the working process of the immune system Carbohydrate Structure Isomerisation (same atoms present, different arrangement). It is possible for the atoms in a 6-Carbon sugar to take up different positions on the carbon chain. This gives rise to structural isomers. Structural isomerism is defined as isomers having identical molecular formulas but differing in the order in which the individual atoms are connected. Stereoisomerism - the isomers have the same molecular formula and the same structural formula but differ in the spatial arrangement of the atoms in the molecule The word chirality, or right - and left - handedness, comes from the Greek for "hand". It is used for structures which can not be superimposed on their mirror image (such as human hands), and instead, exist in two distinct left and right configurations. Be able to draw a simple sugar → Monosaccharides:. Isomerisation Because the position of individual atoms within a sugar molecule varies, many monosaccharides are isomers of one another. Example, glucose and fructose share the molecular formula C6H12O6, but are structurally different. Enantiomers – isomers that are mirror images of one another Be able to draw a simple sugar →. CARBOHYDRATES Monosaccharides General characteristics i). Water soluble. ii). White. (iii) Crystalline solids (iv) Sweet taste. Monosaccharides can an be classified based on; (i). Location of the carbonyl group (C=O). ALDOSE SUGARS Terminal group is an aldehyde (Ex: glucose). KETOSE SUGARS Carbonyl group is located on a carbon that is not at Carbohydrates Monosaccharides (ii). Number of carbons in the skeleton 1. 3 C Triose (C3H6O3) 2. 4 C Tetrose (erythrose in rhubarb) 3. 5 C Pentose (Ribose in nucleic acid) 4. 6 C Hexose (6 carbons) 5. 7 C Heptoses Mannoheptulose, found in avocados. Diagram for illustration purposes. MONOSACCHARIDES Glucose, fructose, galactose, and mannose. When studying the structure of monosaccharides we observe two arrangements of the atoms; In crystalline form, the majority of monosaccharides are present in a “long chain” structure. Sugars dissolved in a solution convert into a “ring” structure to form the two arrangements in the diagram; (i) Alpha glucose (OH group on C1 projects downwards below C1) or, (ii) Beta glucose (OH group on C1 projects upwards above C1). Be able to recognise the ring structure of Glucose Diagram for illustration. Understand and know the difference Between an alpha and a beta arrangement. The ring forms of sugars are the structures that react to form carbohydrate dimers and polymers. The key point in carbohydrate numbering is to look for the carbon which is an aldehyde or a ketone (the carbonyl carbon). This will be the end of the monosaccharide which is numbered lowest. 2. Disaccharides Monosaccharides connected by a condensation/dehydration reaction. The chemical bonds between the molecules are called glycosidic bonds. This covalent bonding reaction occurs between OH groups. G a l a c t o s e → https://www.youtube.com/watch?v=5H8SKas4 5Rk Examples Sucrose = α glucose + fructose Lactose = β galactose + glucose Trehalose Maltose = α glucose+ α glucose glucose + glucose. Cellobiose A repeating (Starch broken disaccharide down by amylase enzyme →in cellulose glucose Maltose) (β glucose- Diagrams for illustration→ Disaccharides Geometry of the Glycosidic bonds 1. Glycosidic bond determines the properties and behaviour of carbohydrates. 2. Enzyme (protein catalysts) in cells can break one type of glycosidic bond but not another. E.g. An enzyme that may recognise and break down sucrose (α 1-2 linkage/bond) may not react with maltose (α 1-4 linkage). Why?? Enzyme activity is very specific. https://www.youtube.com/watch?v=eMuyKN_VW3k Enzyme hydrolysis https://www.youtube.com/watch?v=aRSfPLp_I10 Enzyme reactions in general Understand the structures but you will not be asked to draw 3. Oligosaccharides Polymer of sugars containing typically three to approximately ten sugars. Functions: Found on the plasma membrane of animal cells attached to proteins and lipids. Have many functions including cell–cell recognition. 4. Polysaccharides Illustrations → Many monosacchardes. Connected together by dehydration/condensation synthesis. Polysaccharides differ from each other in; 1. The amount of branching in the molecules. 2. The way in which the molecules are connected to each other. Functions: (1). Energy storage (starch in plants and as Glycogen in animals) Stored in various locations in the cell. Broken down at various times (2). Structural. Cellulose in plant cell Polysaccharides 1. Energy Storage: In plants Starch (i)Amylose: unbranched. α 1 → 4 glycosidic bonds. (ii)Amylopectin: α 1 → 4 glycosidic bonds and α 1 → 6 glycosodic bonds. Amylopectin differs from amylose in being highly branched. (~ 30 units) Plants can store surplus glucose as starch molecules and withdraw it when needed for energy or carbon. Plants store starch within plastids (amyloplasts). Illustration diagram Polysaccharides 1. Energy Storage in ANIMALS Glycogen is the storage polysaccharide in animals. (α 1 → 4 linkages). (α 1 → 6 ) linkages ~8-12 residues. Glycogen is highly branched, like amylopectin. Humans and other vertebrates store glycogen in the liver and muscles but only have about a one day supply. Storage and release under hormonal control. Diagrams illustration Insert Fig. 5.6b - glycogen Polysaccharides 2. STRUCTURAL POLYSACCHARIDES CHITIN: Building materials for the cell or whole organism. Long‐chain unbranched polysaccharide made of N‐acetylglucosamine residues (instead of glucose) linked through β ‐ 1 → 4 covalent bonds. Chitin is not digestible by humans. Chitin forms the exoskeleton of crabs, lobsters and insects. Chitin also forms the structural support for the cell walls of many fungi. Illustration diagrams Structural polysaccharides Cellulose :Component of the wall of plant cells. Most animals cannot digest cellulose. Cellulose is a polymer of (β1-4) glucose monomers. Structure below for illustration purposes only Cell walls of bacteria composed of the structural polysaccharide called Peptidoglycan The chemical formula for glucose is C6H12O6. What is the formula for an oligosaccharide containing 10 glucose units/monomers? A). C60H120O60 B). C60H100O50 C). C60H102O51 D). C60H111O51.