BISC 101: Biological Macromolecules STUDENT COPY PDF

Dr. Onkar S. Bains BISC 101 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: The molecules of life All living things are made up of four classes of large biological molecul...

Dr. Onkar S. Bains BISC 101 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: The molecules of life All living things are made up of four classes of large biological molecules: 1. Carbohydrates 2. Lipids 3. Proteins 4. Nucleic acids Macromolecules are large molecules composed of thousands of covalently connected atoms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept A: Macromolecules are polymers, built from monomers A polymer is a long molecule consisting of many similar building blocks These similar building-block molecules are called monomers Three of the four classes of life’s organic molecules are polymers Polymer is like a chain while the links within the chain are the monomers – Carbohydrates, Proteins, Nucleic acids – Exception = Lipids are not polymers! Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Synthesis and breakdown of polymers Monomers form polymers by condensation reactions (also called dehydration synthesis) 4 4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Polymers can disassemble by hydrolysis reactions, a reaction that is essentially the reverse of the dehydration reaction 4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept B: Carbohydrates serve as fuel and building material Carbohydrates includes both sugars and their polymers The simplest carbohydrates are monosaccharides (monomers) Disaccharides consist of two monosaccharides joined by a glycosidic linkage Polysaccharides are polymers of carbohydrates (more than two monosaccharides) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Storage polysaccharides GLYCOGEN STARCH Consists of glucose monomers Consists of glucose monomers Major form of energy storage Major form of energy storage in humans, animals, fungi and in plants bacteria Giycogen Chloroplast Starch Mitochondria granules Amylose is a linear polysaccharide with many glucose monosaccharide units 0.5 m while amylopectin and glycogen are branched 1 m Amylose Amylopectin Glycogen (10-20%) (80-90%) (b) Glycogen: Copyright © 2005 Pearsonan animal Education, Inc. polysaccharide publishing as Benjamin Cummings (a) Starch: a plant polysaccharide  Structural polysaccharides Cellulose is a major component of the tough wall that enclose plant cells – The cell wall gives the plant its actual shape – The cell wall also acts as a gatekeeper, because it determines what can come in and out of the cell in order to keep the cell protected Cellulose is a linear polysaccharide with many glucose monosaccharide units Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Chitin is another structural polysaccharide that… – is made up of a polymer of N-acetylglucosamines (derivatives of glucose) – is found in the exoskeleton of crustaceans (i.e., crab, lobster, shrimp) and insects, as well as the beaks of cephalopods (i.e., squid, octopus) – provides structural support for the cell walls of many fungi glucose N-acetylglucosamine Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept C: Lipids are a diverse group of hydrophobic molecules Lipids are the one class of large biological molecules that do not form polymers The unifying feature of lipids is having little or no affinity for water Lipids are hydrophobic because they consist mostly of hydrocarbons The most biologically important lipids are fats, phospholipids, and steroids Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Fats Fats are constructed from two types of smaller molecules: glycerol and fatty acids (both are monomers) Glycerol is a three-carbon alcohol with a hydroxyl group (OH) attached to each carbon A fatty acid consists of a carboxyl group (COOH) attached to a long carbon skeleton Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Fatty acids vary in the length and number and locations of double bonds they contain SATURATED UNSATURATED No double bonds Have one or more double between carbons in fatty bonds between carbons in acid chain fatty acid chain More solid at room More liquid at room temperature temperature Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Phospholipids Have only two fatty acids and one phosphate group attached to glycerol (which is different from a triglyceride) Consists of a hydrophilic “head” and hydrophobic “tails” – Hydrophobic fatty acid chains + hydrophilic head that is charged Form a bilayer arrangement found in cell membranes We will talk more about cell membranes later on in the term Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Steroids Steroids are lipids characterized by a carbon skeleton consisting of four fused rings One steroid, cholesterol, is found in animal cell membranes and is a precursor for some hormones Cholesterol and phospholipids are amphipathic molecules (contains both hydrophilic and hydrophobic elements) … soaps and detergents are other examples Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept D: Proteins include a diversity of structures, resulting in a wide range of functions Proteins account for more than 50% of the dry mass of most cells Monomers are called amino acids – Amino acids are organic molecules possessing both carboxyl (COOH) and amino (NH2) groups – They differ in their properties due to differing side chains, called R groups Polypeptides comprise of amino acids held together by peptide bonds Peptide bond indicated by green arrow: Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Proteins perform many functions in a cell: Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  20 different amino acids make up proteins – You do not need to memorize chemical structures of amino acids but you should be able to look at the R-group of each amino acid and identify it as polar or non-polar CH3 CH3 CH3 CH3 CH3 CH CH2 H CH3 CH3 CH2 H3C CH O O O O O H3N+ C C H3N+ C C H3N+ C C H3N+ C C H3N+ C C O– O– O– O– O– H H H H H Glycine (Gly) Alanine (Ala) Valine (Val) Leucine (Leu) Isoleucine (Ile) Nonpolar CH3 CH2 S H2C CH2 NH O CH2 H2N C C CH2 O CH2 CH2 O– O O H H3N+ C C H3N+ C C H3N+ C C O– O– O– H H H Methionine (Met) Phenylalanine (Phe) Tryptophan (Trp) Proline (Pro) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  OH NH2 O NH2 O C OH SH C CH2 Polar OH CH3 CH2 CH CH2 CH2 CH2 O CH2 O O O O O H3N+ C C H3N+ C C H3N+ C C H3N+ C C H3N+ C C H3N+ C C O– O– O– O– O– O– H H H H H H Cysteine Tyrosine Asparagine Glutamine Serine (Ser) Threonine (Thr) (Gln) (Cys) (Tyr) (Asn) Acidic Basic NH3+ NH2 NH+ –O O O– O C C CH2 C NH2+ NH Electrically CH2 CH2 O CH2 CH2 CH2 charged O H3N+ C C CH2 CH2 CH2 H3N+ C C (also polar) O O– CH2 O– H3N+ C C O CH2 H H O– H H3N+ C C CH2 O O– H H3N+ C C O– H Aspartic acid Glutamic acid Lysine (Lys) Arginine (Arg) Histidine (His) (Asp) (Glu) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Protein shape and function A functional protein is not just a polypeptide chain, but one or more polypeptides precisely twisted, folded, and coiled into a molecule of unique shape A protein’s specific shape determines how it functions Primary structure – simplest level of protein structure – consists of a linear sequence of amino acids held together by peptide bonds Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Secondary structure – Folding or coiling of the polypeptide into a repeating configuration (with assistance of hydrogen bonds) – Includes the  helix and the  pleated sheet –  helix protein example = keratin (abundant in skin, hair, nails) –  sheet protein example = fibroin (major Note that the R-groups of each amino acid component of silk) faces towards the outside of  helix Note that the R- groups protrude out from  sheet in opposite directions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Tertiary structure – Overall three-dimensional shape of a polypeptide – Results from interactions (bonds) that form between R groups of different amino acids Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Quaternary structure – Overall protein structure that results from the aggregation of two or more tertiary subunits – Example – collagen is comprised of three polypeptide chains – Example – hemoglobin in red blood cells is comprised of four subunits in total (two alpha and two beta subunits) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Protein folding Most proteins probably go through several intermediate states on their way to a stable conformation Chaperonins… – are protein molecules that assist in the proper folding of other proteins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Denaturation occurs when a protein unravels and loses its native shape – Intermolecular bonds formed in the quaternary, tertiary and secondary structures of protein are broken – Peptide bonds between amino acids are not broken Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept E: Nucleic acids store, transmit, and help express hereditary information If the primary structure of a polypeptide determines a protein’s shape, what determines the primary structure? Genes… – are the units of inheritance – program the amino acid sequence of polypeptides – are polymers made of nucleic acids Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Structure of nucleic acids Nucleic acids exist as polymers called polynucleotides, made up of nucleotide monomers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Nucleotide monomers are held together by phosphodiester bonds Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Types of nucleic acids There are two types of DNA is double stranded while RNA is nucleic acids: single stranded – Deoxyribonucleic acid (DNA) – Ribonucleic acid (RNA) DNA contains the instructions to create proteins, but it does not make proteins itself DNA sends out a message, in the form of RNA, describing how to make the protein Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings  Quick summary table of biological molecules Polymers Lipids No polymers * * = glycerol + 3 fatty acids (i.e., triglycerides) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings