M 3.2 Carbohydrates PDF

M 3.2 (i) Biological molecules - carbohydrates  Learning Outcomes: Introduce the four main elements of biological importance. Describe the main classes of organic compounds. Discuss the structure of monosaccharides and the glycosidic bond. Explain polysaccharide structure an...

M 3.2 (i) Biological molecules - carbohydrates  Learning Outcomes: Introduce the four main elements of biological importance. Describe the main classes of organic compounds. Discuss the structure of monosaccharides and the glycosidic bond. Explain polysaccharide structure and describe cellulose, starch and chitin. Organism Organisation of Living Matter Organ systems work together in a Population functional organism. A population Organism consists of Organ system organisms of the (e.g., skeletal system) same species. Tissues and organs Population make up organ systems. Organ system Organ Community (e. g., bone) Tissues The populations of form organs. different species that Organ populate the same area make up a community. Tissue Loading… (e.g., bone tissue) Cells associate to form tissues. Community Tissue Bone cells Cellular level Atoms and molecules Nucleus make up the cytoplasm Cell and form organelles, Ecosystem A community together such as the nucleus and with the nonliving mitochondria (the site environment forms of many energy Organelle an ecosystem. transformations). Ecosystem Organelles perform various functions of the cell. Macromolecule Biosphere Chemical level Biosphere Earth and all of its Atoms join to form communities constitute molecules. Oxygen atom the biosphere. Macromolecules are Molecule Hydrogen large molecules such as atoms proteins and DNA. Water Figure 1-6  p7 Biomolecules consist of compounds Carbohydrates [sugars] Proteins Lipids [Fats] Nucleic acids Inorganic compounds: Organic compounds: Oxygen [O2] Compounds of C, H, O, N Carbon dioxide [CO2] Water [H2O] Inorganic acids, bases & salts  Why are these compounds so important? Constitute the structures of cells and tissues Participate & regulate metabolic reactions Loading… Transmit Information Provide energy for life  Carbohydrates Carbohydrates are composed of Carbon, Hydrogen and Oxygen in a 1:2:1 ratio Carbohydrate means hydrate (water of) carbon –Reflects 2:1 ratio of hydrogen to oxygen (H2O) Carbohydrates include –Sugars –Starches and glycogen –Cellulose –Chitin Sugars and starches are energy sources for cells Cellulose and chitin are structural components Carbohydrates are composed of sugar units – saccharides Monosaccharides, Disaccharides and Polysaccharides  Types of Carbohydrates sugars starches cellulose/chitin Energy source Structural For cells  Carbohydrates – Sugars/starches One sugar unit - Monosaccharides eg: Glucose [a metabolic fuel] Two sugar units - Disaccharides eg: Sucrose (glucose + fructose) [table sugar] Many sugar units - Polysaccharides eg: Glycogen, Starch [fuel stores]  Glucose –Glucose most abundant monosaccharide –It is a hexose sugar C6H12O6 –It is used as an energy source in most organisms –It is oxidised by the cell in cellular respiration –It is used as a component in the synthesis of other compounds such as amino acids and fatty acids –Mechanisms have evolved to keep it at a relatively constant level in the blood –Diabetes is a breakdown in that mechanism  Glycosidic Bonds Join sugars together Monosaccharides (simple sugars) can be joined together via glycosidic bonds to create polymers of Disaccharides, and polysaccharides Enzym e Sucrose Glucos Fructose C12H22O e C6H12O 11 C6H12O 6 6  Common Disaccharides Common Disaccharides Sucrose Glucose- a (1-2)-fructose Lactose Galactose- b(1-4)-glucose Maltose Loading… Glucose- a(1-4)-glucose  Sucrose Sucrose Common table sugar Extracted from cane or beet Hydrolysed by the enzyme Invertase to an equimolar mixture of glucose and fructose  Maltos e Maltos e A homodimer of glucose units Occurs as a by-product of starch hydrolysis Degraded to glucose by Maltase  Lactose Lactose Lactose Occurs in milk , Hydrolysed by Lactase (human) or b- Galactosidase (bacteria) In some populations “Lactose Intolerance” is observed: – nausea pain – cramps diarrhoea Due to lactose accumulation in the ileum – osmotic effects  Polysaccharides Polysaccharides Means “Many sugars” Thousands of monosaccharide rings joined by glycosidic linkages usually Glucoses They are the most abundant carbohydrates in nature Include Starches, Glycogen and Cellulose, chitin It may be a long single chain or a branched chain Enzymatic or acid hydrolysis will release monosaccharides Homopolysaccharides Glucans Mannans Heteropolysaccharides  a - Amylose a - Amylose A long unbranched chain of glucose units linked by a(1-4) bonds Mr ~ 2,000 - 500,000 Daltons Not truly water-soluble but forms hydrated micelles (Micelles - *) In the micelles, the polymer forms a helical coil a (1-4)  Amylopecti n Amylopecti n A highly-branched polymer Branch-length ~ 24 - 30 glucose residues (depending on the species) Backbone linkages = a(1-4) Branch-points = a(1-6) a (1-6) a (1-4)  Amyloplasts – starch granules (a)  Hydrolysis of Starch (i) Hydrolysis of Starch (i) The a-Amylase enzyme: – Found in saliva & pancreatic juices – Important in digestion of starch – Cleaves a(1-4) bonds randomly to produce a mixture of glucose and maltose  Hydrolysis of Starch (ii) Hydrolysis of Starch (ii) The b-Amylase enzyme: Found in malt Cleaves single maltose units successively from the non-reducing end of the polymer Specific for a(1-4) bonds  Hydrolysis of Starch (iii) Both a- and b-amylases degrade a- amylose to completion They will also degrade amylopectin But cannot break down a(1-6) bonds Products include Dextrins (short chains) Ultimate product is a “Limit Dextrin” A debranching enzyme, a(1-6) glucosidase, Is needed for complete degradation Glycoge n  Polysaccharide – Cellulose Cellulose is the most abundant carbohydrate on the planet It makes up over 50% of carbon compounds in plants It is a structural carbohydrate –Wood is about 50% cellulose –Cotton is about 90% cellulose –The cell walls of plants are cellulose The bonds between the glucose units are (Beta) b 1-4 glycosidic linkages Humans and most animals do not have the enzymes necessary to break these bonds Cellulose only provides roughage in the diet. Cellulose fibers in the plant cell wall.  Polysaccharide – Chitin Chitin is a structural carbohydrate found in animals It is the main component in the cell wall of fungi It also forms the external skeleton of insects, crayfish and other arthropods  Glycoprotein s e.g. Integral membrane proteins  Glycoprotein s Secreted proteins (e.g. antibodies) Contain oligosaccharides in glycosidic linkage to Serine, Threonine or Asparagine  Phosphorylated Sugars Phosphorylated sugars occur as intermediates in energy- yielding metabolism – e.g. Glucose-6-phosphate (glycolysis) Loading… Phosphorylation also makes sugars anionic and allows some of them to participate in in glycosidic bonding as reactive intermediates  Reading Chapter 3 ‘The Chemistry of Life’ Organic Compounds Solomon 10th Ed. p44 -54 Solomon 11th Ed. p50 -55 Chapter 1 ‘A view of Life’ Solomon 11th Ed. p6 -7