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Biological molecules  LEARNING OUTCOMES By the end of this lecture you should be able to: describe how large biological molecules are made from smaller molecules. describe the structure and function of carbohydrates. Classify the carbohydrates to monosaccharide, disaccharide, oligosaccha...

Biological molecules  LEARNING OUTCOMES By the end of this lecture you should be able to: describe how large biological molecules are made from smaller molecules. describe the structure and function of carbohydrates. Classify the carbohydrates to monosaccharide, disaccharide, oligosaccharide and polysaccharide.  The four most common elements in living organisms are, in order of abundance, hydrogen, carbon, oxygen and nitrogen. They account for more than 99% of the atoms found in all living things. Carbon is particularly important because carbon atoms can join together to form long chains or ring structures. They can be thought of as the basic skeletons of organic molecules to which groups of other atoms are attached. Organic molecules always contain carbon and hydrogen.  The functional groups, as they play different functions in molecules, generally determine the nature and functions of organic compounds, Seven such functional groups are, Hydroxyl groups, Carboxyl groups, Amino groups, Carbonyl groups, aldehydes, ketones, Phosphate groups, sulfhydryl group, disulfide bridges (-S-S ) and Methyl groups. Before you can understand the topics there are some key vocabulary terms you need to know. Molecule Macromolecule Monomer Polymer Molecule A group of two or more atoms held together by covalent bonds. A macromolecule is a large biological molecule such as a protein, polysaccharide or nucleic acid. A monomer is a relatively simple molecule which is used as a basic building block for the synthesis of a polymer; many monomers are joined together to make the polymer, usually by condensation reactions; common examples of molecules used as monomers are monosaccharides, amino acids and nucleotides. A polymer is a giant molecule made from many similar repeating subunits joined together in a chain; the subunits are much smaller and simpler molecules known as monomers; examples of biological polymers are polysaccharides, proteins and nucleic acids. A monomer A polymer Forming Monomers Hydrolysis reaction – Hydro = water – lysis = break – Water is added and the lysis of the polymer occurs. Forming Macromolecules Formed from Condensation reactions called dehydration synthesis (removal of water). Monomer/ molecule ----- Atoms joined by covalent bonds. Polymer/ macromolecule ---- Long unit made of monomer units. Polymers are formed from — Condensation / dehydration. Monomers are formed form --- Hydrolysis or rehydration. What are the 4 major macromolecules that make up all cells?  Carbohydrates Lipids Proteins Nucleic acids  CARBOHYDRATES Carbohydrates are the most abundant organic molecules in nature. Carbohydrates are present in humans, animal tissues, plants and in micro-organisms. Carbohydrates are also present in tissue fluids, blood, milk, secretions and excretions of animals. A carbohydrate is a biological molecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen– oxygen atom ratio of 2:1 (as in water); in other words, with the empirical formula (CH2O)n or Cn(H2O)n.  Carbohydrates are polyhydroxy aldehydes or ketones, or substances that yield such compounds on hydrolysis. Some carbohydrates also contain nitrogen, phosphorus, or sulfur. The suffix-ose indicates that a molecule is a carbohydrate, and the prefixes tri-, tetr-, pent-, and so forth indicate the number of carbon atoms in the chain. Classification of carbohydrates it is: Simple sugars (Monosaccharides and Disaccharides). Complex sugars (Polysaccharides).  Another type of classification scheme is based on the hydrolysis of certain carbohydrates to simpler carbohydrates i.e. classifications based on number of sugar units in total chain. Monosaccharides: single sugar unit. Disaccharides: two sugar units. Oligosaccharides: 3 to 10 sugar units. Polysaccharides: more than 10 units. The most common monosaccharides have three to eight carbon atoms. Monosaccharide containing an aldehyde group are classified as aldoses; those containing a ketone group are classified as ketoses. 1. Monosaccharides Monosaccharides are simple sugars, or the compounds which possess a free aldehyde (CHO) or ketone (C=O) group and two or more hydroxyl (OH) groups. They are the simplest sugars and cannot be hydrolysed further into smaller units. Monosaccharides are colorless, crystalline solids that are freely soluble in water but insoluble in nonpolar solvents. Most have a sweet taste. Examples of monosaccharides include glucose (dextrose), fructose and galactose.  The backbones of common monosaccharides are unbranched carbon chains in which all the carbon atoms are linked by single bonds. In the open-chain form, one of the carbon atoms is double-bonded to an oxygen atom to form a carbonyl group; each of the other carbon atoms has a hydroxyl group. If the carbonyl group is at an end of the carbon chain (that is, in an aldehyde group) the monosaccharide is an aldose. If the carbonyl group is at any other position (in a ketone group) the monosaccharide is a ketose. The simplest monosaccharides are the two three-carbon trioses: glyceraldehyde, an aldotriose, and dihydrorryacetone, a ketotriose. Ring structures One important aspect of the structure of pentoses and hexoses is that the chain of carbon atoms is long enough to close up on itself and form a more stable ring structure. This can be illustrated using glucose as an example. When glucose forms a ring, carbon atom number 1 joins to the oxygen on carbon atom number 5. The ring therefore contains oxygen, and carbon atom number 6 is not part of the ring. the hydroxyl group, –OH, on carbon atom 1 may be above or below the plane of the ring. The form of glucose where it is below the ring is known as α- glucose and the form where it is above the ring is β-glucose. The same molecule can switch between the two forms. Two forms of the same chemical are known as isomers. D and L monosaccharides One form in which H atom at carbon 2 is projected to the left side and OH group to the right is designated as D-form and the other form where H atom is projected to the right side and OH group to the left is called as L-form (note the use of small capital letters D and L) For example, the glyceraldehyde has only one asymmetric carbon atom (numbered as 2) and it can, therefore, exist in 2 isomeric forms. Common monosaccharides 1. Glucose The essential energy source for all body functions. Other names: Dextrose and Blood Sugar. A component of each disaccharide. 2. Galactose Seldom occurs freely in nature. Binds with glucose to form sugar in milk: lactose. Once absorbed by the body, galactose is converted to glucose. 3. Fructose The sweetest of all sugars Occurs naturally in fruits and honey. 2- Disaccharides A disaccharide consists of 2 monosaccharide units (similar or dissimilar)held together by a glycosidic bond( links a sugar to another group). Its general formula is Cn(H2O)n-1 (C12H22O11). The disaccharides of physiological importance are as follows 1)Maltose 2)Isomaltose 3)Sucrose 4)Lactose 5)Lactulose. The joining of two monosaccharides takes place by a process known as condensation. The two molecules of α-glucose combine to make the disaccharide maltose. α-glucose and β-fructose combine to make the disaccharide sucrose. Notice that fructose has a different ring structure to glucose. Glucose + Fructose = sucrose Table sugar. Found naturally in plants: sugar cane, sugar beets, honey. Sucrose may be purified from plant sources into Brown, White and Powdered Sugars. Glucose + Galactose = lactose The primary sugar in milk and milk products. Many people have problems digesting large amounts of lactose (lactose intolerance). Glucose + Glucose = Maltose Produced when starch breaks down.  Maltose can be converted from icodextrin which is used in dialysis solutions. Sucrose : It is often used in medications to impart a more pleasant taste to often unpalatable chemicals. Iron Sucrose : is a medicine which is used in iron deficiency. 3- Oligosaccharides Oligosaccharide, any carbohydrate of from three to six units of simple sugars (monosaccharides). A large number of oligosaccharides have been prepared by partially breaking down more complex carbohydrates (polysaccharides). Oligosaccharides can have many functions including cell recognition and cell binding. Most of the few naturally occurring oligosaccharides are found in plants. Trisaccharide: Raffinose (glucose + galactose + fructose). Tetrasaccharide: Stachyose (2 galactose + glucose + fructose) 4- Polysaccharides Most carbohydrates found in nature occur as polysaccharides, polymers of medium to high molecular weight and containing 10 or more monosaccharide units. Polysaccharides, also called glycans, differ from each other in the identity of their recurring monosaccharide units, in the length of their chains, in the types of bonds Linking the units, and in the degree of branching. Further classified into homopolysaccharides and heteropolysaccharides. Unlike sugars they are not sweet.  I. HOMOPOLYSACCHARIDES Homopolysaccharides contain only a single monomeric species. Some homopolysaccharides serve as storage forms of monosaccharides that are used as fuels; starch and glycogen are homopolysaccharides of this type. Other homopolysaccharides (cellulose and chitin, for example) serve as structural elements in plant. II. Heteropolysaccharides Heteropolysaccharides contain two or more different kinds of monomeric species. Heteropolysaccharides provide extracellular support for organisms of all kingdoms. For example, the rigid layer of the bacterial cell envelope (the peptidoglycan) is composed in part of a heteropolysaccharides built from two alternating monosaccharide units. In animal tissues, the extracellular space is occupied by several types of heteropolysaccharides, which form a matrix that holds individual cells together and provides protection, shape, and support to cells, tissues, and organs. Types of Polysaccharides 1- Starch Starchis a polymer of glucose and The major digestible polysaccharide in our diet. The storage form of carbohydrate in plants. Sources: Wheat, rice, corn, rye, barley, potatoes, etc. Two types of plant starch: 1. Amylose 2. Amylopectin. Amylose: is in the form of straight chain linked together with α- 1-4, linkages indicating 300 – 5,500 glucose units per molecules, molecular wt range from 105 to 106. Generally it is water soluble and gives blue colour with iodine. Amylopectins: It contain beside straight chain several branched chains, which are arranged in α—1-4 and β-1-6 linkage units, one molecule of amylopectin contains 50,000 to 5,00,000 glucose molecules, molecular wt. range from 107 to 108, it is insoluble in water and gives purple colour 2- Cellulose form cell walls in plant cells. also called fiber or ruffage. indigestible by humans. 3- Glycogen The storage form of glucose in the body. Stored in the liver and muscles. Found in tiny amounts in meat sources. Not found in plants. Not a significant food source of carbohydrate. 4- Dextrin: It is the intermediate product In the hydrolysis of strach by acids or enzymes. Dextrin consist of a complex mixture of molecule on the different size and structure. Dextrin occur in the leaves of all starch producing plants. They generally have sweet taste. 5- Heparin It is also called as alpha heparin. It is an anti coagulant present in liver and is secreted by Mast cell of liver in Addition it is also found in lungs splein walls of large arteries and in small quantity in lungs. It is a polymer of repeating Disaccharides units of D-glucoseamine and two uronic acid molecule. Heparin also contains sulfate groups that are negatively charged. Role of Carbohydrates in Living Organisms Carbohydrates perform numerous roles in living organisms. Polysaccharides serve for the storage of energy (e.g. starch and glycogen) and as structural components (e.g. cellulose in plants and chitin in arthropods). The 5-carbon monosaccharide ribose is an important component of coenzymes (e.g. ATP, FAD and NAD) and the backbone of the genetic molecule known as RNA. The related deoxyribose is a component of DNA. Saccharides and their derivatives include many other important biomolecules that play key roles in the immune system, fertilization, preventing pathogenesis, blood clotting, and development.