Fundamentals of Human Biology - Carbohydrates PDF

Fundamentals of Human Biology FUNBIO.1 Biological molecules: Carbohydrates P r o f Wa r r e n T h o m a s DAT E: 2 2 S ep t 2 0 2 4 Learning outcomes Introduce the four main elements of biological importance. Describe the main classes of organic compounds. Discuss the structure of monos...

Fundamentals of Human Biology FUNBIO.1 Biological molecules: Carbohydrates P r o f Wa r r e n T h o m a s DAT E: 2 2 S ep t 2 0 2 4 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. Discuss the role of carbohydrates in glycosylated compounds 2 Biological Molecules FUNBIO. 1 Carbohydrates FUNBIO. 2 Proteins FUNBIO. 3 Lipids and Nucleic Acids  Organism Organisation of Living Matter Organ systems work together in a functional organism. Population A population consists of Organ system organisms of the same (e.g., skeletal system) Tissues and species. organs make up organ systems. Organism Population Organ Organ (e. g., bone) Tissues form organs. system Community The populations of different species that populate the same area make up Tissue Organ a community. (e.g., bone tissue) Cells associate to form tissues. Bone cells Community Tissue Cellular level Nucleus Atoms and molecules make up the cytoplasm Cell Ecosystem and form organelles, A community together with the such as the nucleus and mitochondria (the site nonliving environment forms of many energy transformations). Organelles an ecosystem. perform various functions of the cell. Organelle Ecosystem Macromolecule Biosphere Biosphere Earth and all of its communities Chemical level constitute the biosphere. Molecule Atoms join to form molecules. Hydrogen atoms Macromolecules are large molecules such as proteins and DNA. Oxygen atom Water Biomolecules consist of compounds Carbohydrates [Sugar] 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 structure of cells and tissues Participate & regulate metabolic reactions 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 is the most abundant monosaccharide It is a hexose sugar C6H12O6 It is used as an energy source in most organisms It is oxidized 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 Enzyme Sucrose Glucose Fructose C12H22O11 C6H12O6 C6H12O6 Glycosidic Bonds Join sugars together Monosaccharides (simple sugars) can be joined together via glycosidic bonds to create polymers of Disaccharides, and polysaccharides Enzyme Sucrose Glucose Fructose C12H22O11 C6H12O6 C6H12O6 Common Disaccharides Sucrose Glucose- α(1-2)-fructose Lactose Galactose- β(1-4)-glucose Maltose Glucose- α(1-4)-glucose  𝛂-Glucose Linear intermediate form β -Glucose (ring form) (ring form) a b 𝛂-Glucose β -Glucose Sucrose Common table sugar Extracted from cane or beet Hydrolyzed by the enzyme Invertase to an equimolar mixture of glucose and fructose Maltose A homodimer of glucose units Occurs as a by-product of starch hydrolysis Degraded to glucose by Maltase  Lactose Lactose Lactose Occurs in milk, it is hydrolyzed by Lactase (human) or b-Galactosidase (bacteria) In some populations “Lactose Intolerance” is observed: – nausea pain – cramps diarrhea 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  Storage Polysaccharides Storage Polysaccharides Plants - Starch Animals - Glycogen Deposited as granules in the cytoplasm Starch A homopolymer of 𝛂-Glucose units joined by glycosidic bonds Two forms (i) a-Amylose (ii) Amylopectin Parenchyma cells of the potato, showing the central cell with obvious nucleus and purple- stained starch. LM X83.   - Amylose α- 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 * Micelle – hollow spherical structure formed by aggregates of amphipathic molecules such as polysaccharides, glycolipids and detergents, with hydrophilic groups on the outside and polar groups inside.  Amylopectin Amylopectin A highly-branched polymer Branch-length ~ 24 - 30 glucose residues (depending on the species) Backbone linkages = α(1-4)  (1-6) Branch-points = α(1-6)  (1-4)  Amyloplasts – starch granules (a)  Hydrolysis of Starch (i) Hydrolysis of Starch (i) The α-Amylase enzyme: – Found in saliva & pancreatic juices – Important in the digestion of starch - Cleaves α(1-4) bonds randomly to produce a mixture of glucose and maltose  Hydrolysis of Starch (ii) Hydrolysis of Starch (ii) The β-Amylase enzyme: Found in malt Cleaves single maltose units successively from the non-reducing end of the polymer Specific for α(1-4) bonds Hydrolysis of Starch (iii) Both α- and β-amylases degrade α-amylose to completion They will also degrade amylopectin, But cannot break down α(1-6) bonds Products include Dextrins (short chains) The ultimate product is a “Limit Dextrin” A debranching enzyme, α(1-6) glucosidase, is needed for complete degradation Glycogen  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 β (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  Glycoproteins (eg Integral membrane proteins) Cell-Cell Recognition and Communication Regulate Cellular Adhesion Regulation of cell signalling Glycoproteins (secreted proteins eg antibodies) Protein Stability and Folding Phosphorylated Sugars Phosphorylated sugars occur as intermediates in energy-yielding metabolism – e.g. Glucose-6-phosphate (glycolysis) 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 Compound Solomon 10th Ed. p44-54 Solomon 11th Ed. p50-55 Chapter 1 ‘A view of Life’ Solomon 11th Ed. p6 -7 Thank you F O R M O R E I N F O R M AT I O N P L E A S E C O N TA N T P r o f Wa r r e n T h o m a s E MA IL: w ath omas@ rcs i-mub. com