The Structure and Function of Large Biological Molecules Chapter 5

Macromolecules Macromolecules (or polymers) are long, chain-like molecules Consists of many similar or identical building blocks (monomers) linked by covalent bonds Includes carbohydrates, nucleic acids, and proteins Lipids are not a true macromolecule Built via condensation or dehydration reaction (or dehydration synthesis) Take away water molecule Helped by enzymes to speed reaction Breakdown via hydrolysis Add water molecule Occurs in digestion

Carbohydrates Monomers: monosaccharides or simple sugars Simplified formula is CH2O Structure is used to classify sugars General structure includes a carbonyl group and multiple hydroxyl groups Location of carbonyl will determine if it is aldose or ketose (aldehyde or ketone sugars) Sugars are made up of 3-7 carbons in skeleton which may be linear or ringed Spatial arrangement around asymmetric carbons is important Examples: glucose, fructose, galactose Important in cellular respiration and synthesis of materials

Carbohydrates Disaccharides: 2 sugars joined by a covalent bond The covalent bond is known as a glycosidic linkage when it is between 2 monosaccharides The bond is formed by dehydration reaction Examples: Maltose, sucrose, lactose

Carbohydrates Polymers: polysaccharides; these are macromolecules also formed via glycosidic linkages Storage polysaccharides Starch – polymer of glucose monomers found in plants; starch allows plants to stockpile glucose α configuration of glucose Humans consume these in potatoes and grains Glycogen – a branched polymer of glucose found in most vertebrates; largely stored in liver and muscle cells and is released when the body needs sugar

Carbohydrates Structural Polysaccharides Cellulose – major component in cell walls β configuration of glucose (every other glucose monomer in upside down) Important in digestion – humans do not have the appropriate enzymes to digest β linkages, but promotes healthy digestion Most abundant organic compound on Earth Chitin – used by arthropods in exoskeletons Similar structure to cellulose, but contains nitrogen

Lipids Lipids do not include true polymers and are not generally considered macromolecules They are grouped together because they are hydrophobic Largely composed of hydrocarbons Includes: fats, phospholipids, steroids, waxes and pigments

Lipids Fats (triacylglycerol or triglyceride) – composed of glycerol attached to 3 fatty acids bonded via an ester linkage Ester linkage occurs between hydroxyl and carboxyl groups Glycerol – alcohol with 3 carbons each with its own hydroxyl group Fatty acid – long carbon skeleton (16-18 common) with one carbon end associated with a carboxyl group. The rest is a long hydrocarbon chain. Important in energy storage and protection

Lipids Fats Saturated fat or fatty acid Unsaturated fat or fatty acid No double bonds which allows the greatest number of hydrogens to be attached to the carbon skeleton Includes most animal fats Solid at room temp Unsaturated fat or fatty acid Has 1 or more double bonds and thus fewer hydrogen atoms A kink in the chain will occur whenever a cis double bond occurs (as opposed to trans double bonds – ie trans fats found in hydrogenated veg. oil) Includes plant and fish oils Liquid at room temp

Lipids Phospholipids – essential for cell membrane composition Similar to fat molecule, but only have 2 fatty acids attached to glycerol The 3rd hydroxyl group is attached to a phosphate group (these can in turn bond to other molecules) Hydrocarbon tail is hydrophobic (inside the bilayer), phosphate group is hydrophilic (face outward)

Lipids Steroids – carbon skeleton composed of 4 fused rings with different chemical groups attached Includes many hormones and cholesterol Fat can affect cholesterol levels

Proteins Proteins account for ~50% of cell’s dry mass and extremely important in functions

Proteins Monomers are amino acids Polymers are polypeptides 20 different amino acids that are composed of an asymmetric carbon surrounded by an amino group, carboxyl group, hydrogen and an R group or side chain which varies Polymers are polypeptides Different combinations of A.A. allows for the variety of proteins A.A. are attached with a covalent bond between the carboxyl group of one to the amino group of another called a peptide bond

Proteins Protein structure and function are intimately linked The specific folds of a protein are determined by the ordering of A.A. in the polypeptide chain. This folding in turn determines shape. Shape will then determine function.

Proteins Primary Structure – the unique sequence of amino acids Secondary Structure – coils and folds in the polypeptide chain caused by hydrogen bonds between repeating constituents α helix – a coil held together by hydrogen bonds at every 4th A.A. β pleated sheet – folding creating pleats at particular intervals

Proteins Tertiary Structure – Overall shape of a polypeptide due to interactions of R groups Shape may be reinforced by disulfide bridges Covalent bond between sulfhydryl groups Quaternary Structure – overall protein structure (potentially several polypeptide chains interacting)

Proteins Changes in primary structure lead to changes in further structures, potentially leads to a misfunctioning or nonfunctioning protein Example: Sickle Cell Protein shape and function can also be changed via denaturation pH, temperature, salt concentration, etc.

Proteins Chaperonins or chaperone structure are specialized proteins that assist in the proper folding of proteins Are not specific, but keep the protein away from potentially bad influences Folding is spontaneous

Nucleic Acids Main function is to store and transmit genetic information 2 kinds: RNA and DNA These are both polymers/macromolecules The monomers are nucleotides Composed of a nitrogenous base, a 5-carbon sugar, and a phosphate group Nucleosides are this unit minus the phosphate group

Nucleic Acids Two groups of nitrogenous bases Two kinds of sugars Pyrimidines: single 6-C ring Cytosine, thymine, uracil Purines: double fused rings (1 5-C, 1 6-C) Adenine, guanine Two kinds of sugars RNA – ribose DNA – deoxyribose

Nucleic Acids Nucleotides are linked together by phosphodiester linkages Covalent bond between a phosphate group and a sugar This creates the sugar-phosphate backbone One end will have a phosphate attached to a 5’ carbon; the other will have a hydroxyl group on a 3’ carbon (these are the ends of DNA and this plays a role in replication) The opposing sides of DNA are linked via hydrogen bonds and twist about an imaginary axis creating the double helix