Large Molecules Monomer (-OH) + Monomer (-H) → Polymer + H2O(l) Condensation: monomers (e.g. amino acids) join to form polymers (e.g. proteins) Glycosidic bond forms when two carbohydrate monomers join together 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 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 C6H12O6 + 6O2 → 6CO2 + 6H2O + energy Monosaccharides Monosaccharides Triose (3 carbons) Product of respiration and photosynthesis Pentose (5 carbons)- Ribose- Deoxyribose Found in RNA and DNAnucleic acids Hexose (6 carbons)- Glucose- Fructose- Galactose Source of energy in respirationMain energy source in brainFound in sweet-tasting fruits Disaccharides (two sugar residues) Disaccharides 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) Polysaccharides Starch (alpha-glucose) Main storage of carbohydrates in plants Glycogen (alpha-glucose) Main storage of carbohydrates 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) Amylopectin is branched via 1,6-glycosidic bonds Amylose forms a stiff helical structure via 1,4-glycosidic bonds 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 Found as granules (chloroplast) 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 They have a general structure: The difference between different amino acids is found in the R-group When two amino acids join together, they release -H and -OH groups highlighted in red below Peptide bond is formed between alpha-carbon and nitrogen Condensation reaction Primary structure of a protein Sequence of amino acids Joined together by covalent peptide bonds Secondary structure Hydrogen bonds between amino acids Made of a combination of alpha-helices and beta-pleated sheets Proportion of α-helix and β-sheet depends on sequence (primary structure) Tertiary structure Complex globular shape Folding and twisting of polypeptides (H-bond) Polypeptides contain many peptide bonds Quaternary structure Several polypeptide chains //several tertiary structures combined Haemoglobin has 4 polypeptide chains Collagen has 3 polypeptide chains, twisted around each other Globular proteins are soluble and has folded chains Fibrous proteins are insoluble and long, thin, twisted chains Same amino acid sequence → same shape always Bonds Found in Proteins Hydrogen bonds Between R-groups are easily broken, but are numerous The more bonds, the stronger the structure Disulphide bonds Between sulphur-containing amino acid cystine Strong bonds found in skin and hair Denaturation Destruction of tertiary structure, can be done by heat Protein structure is lost and cannot reform → dysfunctional Absorption and Function Absorption of proteins in the digestive tract Proteins are taken in as food They are broken down in the digestive tract into their individual amino acids Amino acids are recombined in the body to form different proteins Good food sources include beans, milk, cheese, fish, meat Several substances are composed of proteins with distinct functions Keratin, collagen are main components in hair, muscles, tendons, skin Enzyme amylase digests starch Haemoglobin transports O2 in the blood stream Insulin regulates glucose storage Lipids Easily dissolved in organic solvents but not in water Triglycerides (fats and oils) Serves as an energy reserve in plant and animal cells Consists of 3 fatty acids linked by ester bonds to glycerol Excess energy available from food/photosynthesis is stored as triglycerides Can be broken down later to yield energy when needed Fats and oils contain twice as many energy stored per unit of weight as carbohydrates Triglycerides (TG) are also called triacylglycerides (TAG) Saturated fatty acids -COOH group without double bonds in the carbohydrate chain May cause blockage of arteries which can lead to strokes and heart attacks High melting point / solid at room temperature (fats) / typical animal fats Unsaturated fatty acids -COOH group with double bonds in the carbohydrate chain Low melting point / liquid at room temperature (oils) Found in plants Phospholipids Formed by replacing one fatty acids in a triglyceride with a phosphate group Phosphate is polar / hydrophilic / does mix with H2O Fatty acid tails remain non-polar / hydrophobic / insoluble, does not mix with H2O Form a ball called a micelle when placed in a polar solution (e.g. water)