Chapter 5: The Molecules of Life The Structure and Function of Macromolecules

Macromolecules Giant molecules Built from monomers –Condensation reaction (dehydration reaction): One monomer provides a hydroxyl group while the other provides a hydrogen to form a water molecule –Hydrolysis: bonds between monomers are broken by adding water (digestion)

Four Major Classes of Organic Compounds found in Living Cells Carbohydrates Lipids Proteins Nucleic Acids

Carbohydrates Serve as fuel and building materials Includes both sugars and the polymers of sugars Types: –Monosaccharide –Disaccharide –Polysaccharide

Monosaccharides Also know as simple sugars CH 2 O formula Composed of a carbonyl group (C=O) with multiple hydroxyl group (-OH) Classified by: –Location of carbonyl group aldehydes (aldoses, aldehyde sugar) ketones (ketone sugar) –Size of the carbon skeleton 3 C-trioses 5 C-pentoses 6 C- hexoses Major nutrient for cells through cellular respiration Monomer of disaccharides

Disaccharides Consist of two monosaccharides joined by a glycosidic linkage through a condensation or dehydration reaction Types: –Sucrose =glucose + fructose –Lactose = glucose + galactose –Maltose = glucose + glucose Sometimes called “double sugars” or “reducing sugars”

Polysaccharides Macromolecules Polymers of monosaccharides joined by glycosidic linkages Sugar monomers and position of glycosidic linkage determine the function of the polysaccharide Alpha and Beta glucose is determined by the position of the hydroxyl group on the #1 Carbon

Storage Polysaccharides Starch –Made of glucose monomers –Storage polysaccharide of plants –Has 1-4 glycosidic linkages making it unbranched and helical in shape –Amylopectin is a branched for of starch Glycogen –Made of glucose monomers –Storage polysaccharide of animals –Has 1-6 glycosidic linkages having alternating glucose molecules

Structural Polysaccharide Cellulose –Major component of plant cell walls –Polymer of glucose with beta glycosidic linkages therefore, the glucose alternate position –Parallel cellulose molecules are grouped as microfibrils making them strong building material –Beta linkages cannot be hydrolyzed by enzymes. That is why it is referred to by humans as “insoluble fiber” –Grazing animals have cellulose-digesting bacteria in their rumen, the first compartment of their stomach

Structural Polysaccharide Chitin –structural polysaccharide used to build exoskeletons of insects, spiders, and crustaceans –Used to make dissolvable surgical thread –Used by fungus to build cell walls instead of cellulose Similar in structure to cellulose but has an added nitrogen functional group

Lipids Does not consist of polymers Hydrophobic Types: –Fats –Phospholipids –Steroids Function –A gram of fat stores more than twice as much energy as a gram of a polysaccharide –Fat stored in adipose tissue cushions major organs –Layer of fat below skin insulates the body

Fats Large molecules assembled together by dehydration reactions Three fatty acids attach to glycerol by forming ester linkages – bond between a hydroxyl group and a carboxyl group

Saturated vs. Unsaturated Fatty acids vary in length and in the number and locations of double bonds –Saturated fats No double bonds between carbon atoms composing the chains Solid at room temperature –Unsaturated fats One or more double bonds formed by the removal of hydrogen atoms from the carbon skeleton Liquid at room temperature due to kinks in the fatty acid tails caused by cis double bond –“Hydrogenated” means they have been synthetically converted from an unsaturated fat to a saturated fat by the addition of hydrogen atoms –Polyunsaturated fats have more than one double bond

Phospholipids Contains only 2 fatty acids attached to glycerol Phosphate group attached to third hydroxyl group of glycerol Hydrocarbon ‘Tails’ are hydrophobic Phosphate ‘head’ is hydrophilic Form cell membrane –Hydrophobic tails point toward interior –Hydrophilic head on exterior forming a boundary between the cell and its environment

Steroids Lipids with a C skeleton consisting of 4 fused carbon rings Functional group attached cause variation in steroid Ex: Cholesterol:found in cell membranes ;precursor for other steroids (sex hormones); causes atherosclerosis

Proteins Importance: –Instrumental in nearly everything organisms do Speed up chemical reactions (Enzymes acting as catalysts) Structural support Storage Transport Cellular communications Movement Defense against foreign substances –Make up 50% dry weight of cells –The most structurally sophisticated molecules known

Polypeptide of Amino Acids Polymer of Amino Acids –Organic molecule possessing both carboxyl and amino groups –Asymmetric carbon atom at center of the amino acid is called the alpha carbon –R group or side chain differs with each of the 20 different amino acids

Protein Structure Primary Secondary Tertiary Quaternary

Primary Structure Unique sequence of Amino Acids Can spontaneously arrange itself into a three-dimensional shape determined and maintained by the interactions responsible for secondary and tertiary structure Conformation dependent on: –Linear structure –Physical and chemical environment of protein Each type of protein has a unique primary structure of amino acid

Secondary Structure Coils & folds as a result of hydrogen bonds between repeating constituents of the primary structure Alpha Helix –coiling caused by bonding between every fourth amino acid – keratin in hair; Beta Pleated Sheet –Bonds between two parallel sections –Make up the core of many globular proteins –Spider silk

Tertiary Structure Overall shape due to interactions of the primary structure and the side chain amino acids R groups –Hydrophobic –Disulfide bridges –Hydrogen bonds –Ionic bonds All types of interactions can occur in one protein

Quaternary Structure Two or more polypeptide chains aggregated into one macromolecule –collagen (connective tissue) –hemoglobin

Denaturation/Renaturation Protein unravels and loses its native conformation Causes protein to loose its ability to function Caused by: –pH –Salt concentration –Temperature Some proteins can renature when environmental conditions restore to normal

Chaperonins Protein molecules that act as a shelter for other proteins that are in the process of folding Keep folding protein separated from “bad influences” in the cytoplasmic environment

Nucleic Acids Types –Deoxyribonucleic acid (DNA) –Ribonucleic acid (RNA) Both are important for protein synthesis –DNA->RNA->protein Polymers of nucleotides called polynucleotide Each nucleotide is comprised of: –nitrogenous base –pentose sugar –phosphate group The portion of the nucleotide without the phosphate group is called the nucleoside

Nucleotide Monomers Pyrimidines –Six-carbon ring and nitrogen atoms Cystosine Thymine-only found in DNA Uracil-only found in RNA Purines –Six-carbon ring attached to a five- carbon ring Adenine Guanine Pentose in RNA is Ribose while Pentose in DNA is Deoxyribose

Nucleotide Polymers Adjacent nucleotides are linked together by covalent bonds called phosphodiester linkages between the –OH group on the 3’ carbon on one nucleotide and the phosphate on the 5’ carbon on the next nucleotide

DNA Double Helix Inheritance based on DNA replication Double helix (Watson & Crick ) –H bonds~ between paired bases –Van der Waals~ between stacked bases Complementary base pairing –A to T –C to G

Genetic Transmission The unique sequence of the bases on a DNA polymer is in the 5’ to 3’ end sequence determines amino acid sequence of genes passed to next generation and evolutionary links DNA Strands are antiparallel Each strand used as a template in DNA replication process