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The Chemical Building Blocks of Life Chapter 3 1 Biological Molecules • The framework of biological molecules consists of carbon bonded to other carbon molecules, or other types of atoms. – Hydrocarbons consist of carbon and hydrogen. Covalent bonds store considerable energy. Make good fuels 2 Biological Molecules • • Functional groups – specific groups of atoms attached to carbon backbones retain definite chemical properties Macromolecules. – proteins – nucleic acids – lipids – carbohydrates 3 Functional Group Structural Formula Hydroxyl OH Carbonyl C O O Carboxyl C OH H Amino N H Sulfhydryl S H O– Phosphate Methyl Example H H H C C OH H H Ethanol H O H C C H H Acetaldehyde H O H C C OH H Acetic acid O H H HO C C N CH3 H Alanine H H HO C C S H H H b-mercaptoethanol OH OH H O O P O– H C C C O P O– H H H O– O Glycerol phosphate H O O H O– C C C H C H H H Pyruvate 4 Macromolecules • Macromolecules are often polymers. – long molecule built by linking together small, similar subunits Dehydration synthesis removes OH and H during synthesis of a new molecule. Hydrolysis breaks a covalent bond by adding OH and H. 5 6 Proteins - C, H, O, N, S A. B. C. Amino acids Peptide bonds Polypeptide chains H R O H-N- C-C H H Amine Group - OH Acid Group 7 Protein Function 8 Amino Acids • contain an amino group (-NH2), a carboxyl group (-COOH) and a hydrogen atom, all bonded to a central carbon atom – twenty common amino acids grouped into five classes based on side groups nonpolar amino acids polar uncharged amino acids charged amino acids aromatic amino acids special-function amino acids 9 Amino Acids • Peptide bond links two amino acids. – A protein is composed of one or more long chains of amino acids linked by peptide bonds (polypeptides). 10 NONAROMATIC AROMATIC Nonpolar CH3 CH3 CH3 CH CH2 CH3 CH3 CH3 CH2 CH H C C O– H3N+ C C O– H3N+ C H3N+ C H O H Alanine (Ala) O H H3 CH3 CH2 H C C H O O– H3N+ Glycine (Gly) C C H O H O– H3 C N+ OH C C NH2 O H3 C C H O H3 N+ C H O O– O CH2 C CH2 CH2 C C H O H3 N+ C C O– H O Tyrosine (Tyr) NH2 C H3 O– Threonine Asparagine Glutamine (Thr) (Asn) (Gln) O– O– OH CH2 C C N+ H O CH2 O– Charged O H O CH2 CH2 N+ H O Serine (Ser) O– H3N+ C C O– H3N+ C C O– C C O– CH2 NH2 O O N+ CH2 Leucine Isoleucine Phenylalanine Tryptophan (Leu) (Ile) (Phe) (Trp) Polar uncharged OH CH3 C O– H3N+ C C H O Valine (Val) NH C H3 N+ C HC C C H O NH+ N H CH CH2 O– H3 N+ C C CH2 NH3+ NH CH2 CH2 CH2 CH2 CH2 CH2 O– H O Glutamic Aspartic Histidine acid (Glu) acid (Asp (His) H3 N+ NH2+ C C O– H O Lysine (Lys) H3 N+ C C O– H O Arginine (Arg) 11 Protein Structure The shape of proteins is extremely important and can determine the function Water’s tendency to hydrophobically exclude nonpolar molecules literally shoves the nonpolar portions of the protein to the interior Many shapes Primary – the specific amino acid sequences Secondary – formed by hydrogen bonding Alpha helix – coils Beta pleated sheet - foldbacks motifs - folds or creases supersecondary structure 12 1 Primary structure R H H O R H H O R H H C C N C C N C C N C C N C C N C H O H H O H H O R R R 2 Secondary structure b pleated sheet b a b motif a helix 3 Motifs a turn a motif 13 Protein Structure Tertiary - final folded shape of globular protein (3-dimensional shape) based on bonding of side groups Domains – independent functional units of the protein 100–200 amino acids long encoded by a specific DNA sequence (exon) Quaternary - forms when two or more polypeptide chains associate to form a functional protein 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4 Tertiary structure 5 Domains Domain 1 6 Quaternary structure Domain 2 Domain 3 15 Chaperone Proteins • Chaperone proteins are special proteins which help new proteins fold correctly. – Chaperone deficiencies may play a role in facilitating certain diseases. 16 • Unfolding Proteins Denaturation refers to the process of changing a protein’s shape. – usually rendered biologically inactive pH temperature Ionic concentration salt-curing and pickling used to preserve food 17 Nucleic Acids - C, H, O, N, P • • Deoxyribonucleic Acid (DNA) – Encodes information used to assemble proteins. Ribonucleic Acid (RNA) – Reads DNA-encoded information to direct protein synthesis. 18 Nucleic Acid Structure • Nucleic acids are composed of long polymers of repeating subunits, nucleotides. – five-carbon sugar – Phosphate group – nitrogenous base Purines double ringed adenine and guanine Pyrimidines – single ringed cytosine, thymine, and uracil 19 59 Phosphate group P P O P O P Cytosine (both DNA C C N and RNA) C C O N H Thymine O (DNA only) C N H C CN C O NH2 H P P H NC CH N U Y H Phosphodiester R R O Guanine I bonds I N M NCC N H E H C I H3C C C NH2 D H S N N I H H N 5-carbon O E sugar S C Nitrogenous base H C N H CN C O H H C O NH2 Adenine NCC N Uracil (RNA only) H O OH 39 20 Nucleic Acid Structure • • DNA exists as double-stranded molecules. – double helix – complementary base pairing Chargaff’s rule hydrogen bonding RNA exists as a single stand. – contains ribose instead of deoxyribose – contains uracil in place of thymine 21 Structure of DNA 22 • • Lipids Lipids are loosely defined as groups of molecules that are insoluble in water. – fats and oils Phospholipids form the core of all biological membranes. – composed of three subunits Glycerol - backbone fatty acid – long tail phosphate group – head Polar head - hydrophilic Nonpolar tail - hydrophobic 23 Phospholipids form membranes micelle 24 Fats and Other Lipids • Fats consist a of glycerol molecule with three attached fatty acids (triglyceride / triglycerol). – Saturated fats - all internal carbon atoms are bonded to at least two hydrogen atoms – maximum # of H – Unsaturated fats - at least one double bond between successive carbon atoms Polyunsaturated contains more than one double bond usually liquid at room temperature 25 Fats as Energy Storage Molecules • Fats, on average, yield about 9 kcal per gram versus 4 kcal per gram for carbohydrates. – Animal fats are saturated while most plant fats are unsaturated. Consumption of excess carbohydrates leads to conversion into starch, glycogen, or fats for future use. 26 Carbohydrates • Carbohydrates are loosely defined as molecules that contain carbon, hydrogen, and oxygen in a 1:2:1 ratio. – monosaccharides - simple sugars 27 – disaccharides - two monosaccharides joined by a covalent bond H H O H H C O H H C O C M o n o s a c c h a r i d e H HH C C 2 X G l u c o s eO H HO H HO O C H H C O H O HO H H C C C C H O H H O H H O H2 O 2 H O H H C D i s a c c h a r i d e M a l t o s e C H O H H C O C H H C H O C HH H C O HO H H C H C H HO O H CO C C C H O H H O H 28 – polysaccharides - macromolecules made of monosaccharide subunits isomers - alternative forms of the same substance – Many C6H1206 29 Carbohydrate Transport and Storage • • Transport disaccharides – Humans transport glucose as a simple monosaccharide. – Plants transform glucose into a disaccharide transport form. Storage polysaccharides – plant polysaccharides formed from glucose – starches most is amylopectin – Animal starch is glycogen 30 Structural Carbohydrates • Cellulose - plants – alpha form or beta form of ring Chitin - arthropods and fungi modified form of cellulose 31