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Large Molecules

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Douglas Davidson

Large Molecules  Monomer (-OH) + Monomer (-H) → Polymer + H2O(l) o Condensation: monomers (e.g. amino acids) join to form polymers (e.g. proteins) o Glycosidic bond forms when two carbohydrate monomers join together o Hydrolysis: break down of a polymer; reverse reaction  Polymers are also called macromolecules (e.g. starch, proteins, triglyceride) Carbohydrates  Organic molecules in which C, H and O bind together in the ratio Cx(H2O)y  Serve as an energy source important for the brain and cellular respiration  Plants produce carbohydrates by using energy from sunlight o 6CO2 + 6H2O + energy (from sunlight) → C6H12O6(carbohydrate) + 6O2  Animals eat plant materials to obtain the produced carbohydrates  They can then be used in animal metabolism to release energy o C6H12O6 + 6O2 → 6CO2 + 6H2O + energy Monosaccharides Triose (3 carbons) Product of respiration and photosynthesis Pentose (5 carbons) Found in RNA and DNA - Ribose nucleic acids - Deoxyribose Hexose (6 carbons) Source of energy in respiration - Glucose Main energy source in brain - Fructose Found in sweet-tasting fruits - Galactose Disaccharides (two sugar residues) Sucrose (glucose + fructose) Transport carbohydrates in plants Maltose (glucose + glucose) Formed from digestion of starch Lactose (glucose + galactose) Carbohydrates found in milk Polysaccharides (many sugar residues) Starch (alpha-glucose) Main storage of carbohydrates - in plants Glycogen (alpha-glucose) - in humans and animals Cellulose (beta-glucose) Important component of the plant cell wall Starch  Consists of amylopectin and amylose (both are made of α-glucose) o Amylopectin is branched via 1,6-glycosidic bonds o Amylose forms a stiff helical structure via 1,4-glycosidic bonds o Both are compact molecules → starch can be stored in small space  The ends are easily broken down to glucose for respiration  Does not affect water potential as it is insoluble  Readily hydrolysed by the enzyme amylase found in the gut and saliva  Major carbohydrate used in plants o Found as granules (chloroplast) o Each granule contains amylopectin combined by a larger amount of amylose  Commonly used sources are corn (maize), wheat, potato, rice Glycogen  Branched, storage, polymer of glucose linked via glycosidic bonds  Found in skeletal muscle and in the liver  Chains are linked by alpha-1,4-linkage, branches are linked by alpha-1,6-linkages  Glycogen is broken down to glucose by glycogenolysis (glycogen phosphorylase)  Major site of daily glucose consumption (75%) is the brain via aerobic pathways  Most of the remainder is utilized by erythrocytes, skeletal muscle, and heart muscle  Glucose is obtained from diets or from amino acids and lactate via gluconeogenesis  Storage of glycogen in liver are considered to be main buffer of blood glucose levels Cellulose  Polysaccharide consisting of long beta-glucose chains  Linked together by hydrogen bonds to form microfibrils  Structural function is a important component of plant cell walls  Its tensile strength helps plant cells in osmosis //cell does not burst in dilute solutions Proteins Structure  Proteins are polymers of amino acids  Proteins are made up by different combinations of 20 amino acids o They have a general structure: o The difference between different amino acids is found in the R-grou
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