The Structure and Function of Macromolecules

The Structure and Function of Macromolecules

Macromolecules are polymers Polymer long molecule consisting of many similar building blocks. Monomer the small building block molecules. Carbohydrates, proteins and nucleic acids are polymers. There are 1000 s of different kinds of macromolecules, and an enormous variety of polymers can be built from a small set of monomers.

Fig. 5-2 HO 1 2 3 H HO H Short polymer Dehydration removes a water molecule, forming a new bond Unlinked monomer H 2 O HO 1 2 3 4 Longer polymer H (a) Dehydration reaction in the synthesis of a polymer HO 1 2 3 4 H Hydrolysis adds a water molecule, breaking a bond H 2 O HO 1 2 3 H HO H (b) Hydrolysis of a polymer

Carbohydrates Function fuel and building material. Simplest carbohydrate monosaccharides (single sugars) are the monomers of polysaccharides. Monosaccharides usually have molecular formulas (CH 2 O) n the most common monosaccharide, glucose is C 6 H 12 O 6

Monosaccharides Can be drawn as linear skeletons, but many sugars form rings in aqueous solutions. Note the abbreviated form, and numbering.

Disaccharides Disaccharides are formed when dehydration reaction joins two monosaccharides. Glycosidic linkage the covalent bond that forms between the monosaccharides. Note the linkage between two glucose molecules to form maltose, and the linkage to form sucrose from glucose and fructose is specified by which carbons of the ring are joined.

Fig. 5-5 1 4 glycosidic linkage Glucose Glucose (a) Dehydration reaction in the synthesis of maltose Maltose 1 2 glycosidic linkage Glucose Fructose Sucrose (b) Dehydration reaction in the synthesis of sucrose

Polysaccharides Polymers of sugar have storage and structural roles. Starch storage polysaccharide of plants Monomer: glucose Amylose unbranched form, Amylopectin branched form

Glycogen Storage polysaccharide in animals in humans glycogen is mainly found in liver and muscle cells. Note the more extensive branching, means more ends of chains where single glucose molecules can be broken off for energy available rapidly.

Cellulose Structural polysaccharide component of the cell wall of plants. Polymer of glucose, but the glycosidic linkages differ. Two ring forms of glucose alpha ( ) and beta (β) are responsible for the difference. Glucose β Glucose

Fig. 5-7bc (b) Starch: 1 4 linkage of glucose monomers (c) Cellulose: 1 4 linkage of β glucose monomers

Cellulose Polymers with glucose are helical Polymers with β glucose are straight In the straight chains, H atoms on one strand can bond with OH groups on other strands. The cellulose molecules grouped together form strong building materials for plants. As well, the enzymes that carry out hydrolysis of glycosidic linkages can t hydrolyze β glycosidic linkages.

Cellulose Cellulose in the human diet passes through the digestive tract. Even though no energy is extracted, insoluble fibre is still important to healthy functioning of the digestive tract. The only organisms capable of breaking down cellulose are microbes, and those organisms like cows, and termites that have those microbes living in their digestive tracts.

Lipids Do not form polymers, instead have a unifying characteristic: Little or no affinity for water (non-polar). Hydrophobic because they consist mainly of hydrocarbons.

Fats Fats are made from two smaller molecules: glycerol and fatty acids. Fatty acid Glycerol Dehydration reaction in the synthesis of a fat

Fig. 5-11b Ester linkage (b) Fat molecule (triacylglycerol)

Fats Fats separate from water because water molecules form hydrogen bonds with each other, and exclude the fats. In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a tryacylglycerol, or triglyceride.

Fatty acids Fatty acids vary in length (# of C s) and number and location of double bonds. Saturated fatty acids maximum number of hydrogen atoms possible, no double bonds Unsaturated fatty acids one or more double bonds, fewer hydrogens Monousaturated one double bonds Polyunsaturated two or more double bonds

Fats Fats made from saturated fatty acids are solid at room temp. Most animal fats are saturated. Fats made from unsaturated fatty acids are liquid at room temp. - oils. Plants fats are usually unsaturated.

Fats and diet A diet rich in saturated fats may contribute to atherosclerosis plaque deposits lining the arteries leading to cardiovascular disease. Trans fats formed by hydrogenation which adds hydrogen to unsaturated fats. These fats may contribute more that saturated fats to cardiovascular disease.

Function Major function of fats energy storage. In humans fat is stored in adipose cells very compact, very little water. Fats also have 2X the energy per gram of carbohydrate Fats also function in insulating the body, and cushioning vital organs

Phospholipid In a phospholipid, two fatty acids attach to glycerol, along with a phosphate group. The two fatty acid tails are hydrophobic, but the phosphate group forms a hydrophilic head. When phospholipids are added to water, they self assemble with the hydrophobic tails pointing to the interior.

Fig. 5-13 Hydrophobic tails Hydrophilic head Choline Phosphate Glycerol Fatty acids Hydrophilic head Hydrophobic tails (a) Structural formula (b) Space-filling model (c) Phospholipid symbol

Phospholipids are assembled into a bilayer with tails away from water, that is the major component of cell membranes.

Steroids Steroids all have a carbon skeleton consisting of four fused rings. Cholesterol component of animal cell membranes, also precursor to forming steroid hormones such as estrogen and testosterone.

Proteins Proteins have diverse structure meaning they have a wide range of functions. As catalysts called enzymes speeding up the rate of reaction in organisms, can be used repeatedly as they are not used up in the reaction Structural support, cellular communications, movement, defense against foreign substances

Amino acids Amino acids have a central carbon that has a carboxyl group, an amino group, a hydrogen and an R group attached. Amino acids differ in their properties based on different R groups or side chains.

Fig. 5-UN1 carbon Amino group Carboxyl group

Fig. 5-17a Nonpolar Glycine (Gly or G) Alanine (Ala or A) Valine (Val or V) Leucine (Leu or L) Isoleucine (Ile or I) Methionine (Met or M) Phenylalanine (Phe or F) Tryptophan (Trp or W) Proline (Pro or P)

Fig. 5-17b Polar Serine (Ser or S) Threonine (Thr or T) Cysteine (Cys or C) Tyrosine (Tyr or Y) Asparagine (Asn or N) Glutamine (Gln or Q)

Fig. 5-17c Electrically charged Acidic Basic Aspartic acid (Asp or D) Glutamic acid (Glu or E) Lysine (Lys or K) Arginine (Arg or R) Histidine (His or H)

Polypeptides Polypeptides are polymers built from their monomer, amino acids. Peptide bond covalent bond between the carboxyl group of one amino acid and the amino group of the next amino acid. Polypeptides range in length up to thousands of monomers. Each polypeptide has a unique sequence of amino acids. A protein is made of one or more polypeptides in a unique three dimensional shape.

Fig. 5-18 Peptide bond (a) Peptide bond Side chains Backbone (b) Amino end (N-terminus) Carboxyl end (C-terminus)

Fig. 5-19 A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape Groove Groove (a) A ribbon model of lysozyme (b) A space-filling model of lysozyme

STRUCTURE dictates FUNCTION The sequence of amino acids determines a protein s 3D structure A protein s structure determines its function

Levels of Structure Primary structure unique sequence of amino acids Secondary structure coils and folds in the polypeptide chain Tertiary structure determined by interactions between side chains. Quaternary structure a protein that consists of multiple polypeptide chains.

Fig. 5-21a The sequence of amino acids is like the order of letters in a long word. 15 + H 3 N Amino end Primary Structure 1 10 Amino acid subunits 5 Primary structure is determined by inherited genetic information. 20 25

Primary structure A slight change in primary structure can affect a protein s ability to function if it affects its shape. Example: Sickle-cell inherited blood disorder caused by a single amino acid change in the protein hemoglobin

Fig. 5-22 Primary structure Normal hemoglobin Val His Leu Thr Pro Glu Glu 1 2 3 4 5 6 7 Primary structure Sickle-cell hemoglobin Val His Leu Thr Pro Val Glu 1 2 3 4 5 6 7 Secondary and tertiary structures subunit Secondary and tertiary structures Exposed hydrophobic region subunit Quaternary structure Normal hemoglobin (top view) Quaternary structure Sickle-cell hemoglobin Function Molecules do not associate with one another; each carries oxygen. Function Molecules interact with one another and crystallize into a fiber; capacity to carry oxygen is greatly reduced. 10 µm 10 µm Red blood cell shape Normal red blood cells are full of individual hemoglobin moledules, each carrying oxygen. Red blood cell shape Fibers of abnormal hemoglobin deform red blood cell into sickle shape.

Fig. 5-22c 10 µm 10 µm Normal red blood cells are full of individual hemoglobin molecules, each carrying oxygen. Fibers of abnormal hemoglobin deform red blood cell into sickle shape.

Secondary structure helix coiled regions β pleated sheet - folded sections The coils and folds of secondary structure result from hydrogen bonds between repeating parts of the polypeptide backbone.

Fig. 5-21c Secondary Structure pleated sheet Examples of amino acid subunits helix

Tertiary Structure Interactions among side chains including: Hydrogen bonds, Hydrophobic interactions Strong covalent bonds called disulfide bridges

Quaternary Structure When two or more polypeptide chains form one macromolecule Examples: Collagen consists of three polypeptides Hemoglobin consists of four polypeptides (2 alpha and 2 beta chains)

Fig. 5-21g Polypeptide chain Chains Iron Heme Collagen Chains Hemoglobin

Determining Protein Structure Physical and chemical conditions can affect the structure of proteins. Alterations in ph, salt concentration, and temperature can cause a protein to unravel. Denaturation the loss of a protein s proper 3D structure. A denatured protein is unable to function.

Folding assistance Chaperonins proteins that assist in the proper folding of other polypeptides