The Structure and Function of Large Biological Molecules Chapter 5
The Molecules of Life Living things made up of 4 classes of large biological molecules (macromolecules) : 1. Carbohydrates 2. Lipids 3. Proteins 4. Nucleic acids Molecular structure and function are linked Unique, emergent properties
Macromolecules are polymers, built from monomers polymer -long molecule of many building blocks monomers - single unit Sucrose
The Diversity of Polymers Each cell has thousands of different macromolecules built from monomers Macromolecules vary among cells, among species, and between species
Carbohydrates serve as fuel and building material Carbohydrates = sugars and sugar polymers Monosaccharides = single sugars Ex. glucose (C 6 H 12 O 6 ) major fuel for cells raw material for building molecules
Sugars often form rings (in aqueous solution) (a) Linear and ring forms (b) Abbreviated ring structure
Disaccharide = two sugars Ex. lactose, sucrose, maltose
Polysaccharides Polysaccharides - polymers of sugars = starch storage and structural roles The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages
Storage Polysaccharides Starch plants store starch Glucose polymer Glycogen Animals store glycogen (glucose polymer) Humans in liver and muscle cells
Chloroplast Starch Mitochondria Glycogen granules 0.5 µm 1 µm Amylose Glycogen Amylopectin (a) Starch: a plant polysaccharide (b) Glycogen: an animal polysaccharide Amylose - unbranched Amylopectin - branched Glycogen is more branched than starch
Structural Polysaccharides Cellulose =component of tough wall of plant cells polymer of glucose (glycosidic linkages differ from starch) The difference is based on two ring forms for glucose:
Enzymes digest cellulose in some animals Cows, termites, have symbiotic relationships with microbes that digest cellulose In humans, cellulose is indigestible fiber Mastigophoran, anaerobic, methane
Chitin in the exoskeleton of arthropods and in fungi (a) The structure (b) Chitin forms the (c) of the chitin exoskeleton of monomer. arthropods. Chitin is used to make a strong and flexible surgical thread. Cicada exoskeleton
Lipids are hydrophobic Lipids - fats, phospholipids, steroids Triglyceride = 3 fatty acids joined glycerol
Saturated fats maximum number of H possible (no double bonds) Solid at room T (animal fats) Unsaturated fats one or more double bonds Liquid at room T (plant, fish oils) (a)
Coronary artery disease associated with diet rich in saturated fats
Hydrogenation process of converting unsaturated fats to saturated fats by adding hydrogen Extends shelf life, prevents oil separation Ex. margarine, peanut butter
The good news: Fats store energy (adipose cells) Cell membranes need lipid Lipid cushions and insulates
Steroids Steroids Ex. estrogen, testosterone Cholesterol Steroid in animal cell membranes Synthesized in the liver
Proteins Proteins = more than 50% of dry mass of cells Protein functions structural support collagen pigment - melanin transport - hemoglobin cellular communications movement defense against foreign substances-antibodies
Enzymes All are proteins catalyst speeds up chemical reactions reusable specific to each reaction essential to life Heat or chemicals may denature animation
Polypeptides Polypeptides polymers built from set of 20 amino acid building blocks may be a few or thousands long protein one or more polypeptides has a function
Peptide Protein
Protein Structure and Function proteins consists of one or more polypeptides twisted, folded, and coiled into unique shape Groove Groove (a) A ribbon model of lysozyme (b) A space-filling model of lysozyme
sequence of aa determines a 3D structure structure determines function Antibody protein Protein from flu virus
Four Levels of Protein Structure Primary structure =unique sequence of amino acids 1 5 10 15 20 25
Secondary structure = coils and folds helix and pleated sheet H-bonds Example: spider silk β pleated sheet Strong as steel Stretchy α helix
Tertiary structure determined by interactions between amino acids hydrogen bonds ionic bonds hydrophobic interactions disulfide bridges (covalent bonds)
Tertiary structure
Quaternary structure two or more polypeptide chains may form one macromolecule ex. hemoglobin activity α Chains β Chains Hemoglobin
A patient with sickle cell disease
Denaturation of proteins Denaturation Loss of protein structure biologically inactive ph, heat, chemicals
The Roles of Nucleic Acids Deoxyribonucleic acid (DNA) replicates prior to cell division contains codes for proteins (genes)
Nucleic acids hold a code Gene unit of inheritance code for protein primary structure composed of DNA
The Structure of Nucleic Acids Nucleotides Nitrogenous bases Pyrimidines G,A,T,C building blocks (monomers) Pyrimidines (cytosine, thymine, and uracil) Cytosine (C) Thymine (T, in DNA) Purines Uracil (U, in RNA) Purines (adenine and guanine) Adenine (A) Guanine (G) (c) Nucleoside components: nitrogenous bases
Nucleotides contain sugar DNA deoxyribose RNA ribose (ribonucleic acid) Sugars Deoxyribose (in DNA) Ribose (in RNA) (c) Nucleoside components: sugars
Sugar phosphate backbone DNA Polymers
The DNA Double Helix A DNA molecule has 2 strands that form double helix hydrogen bonds between: adenine (A) thymine (T) guanine (G) cytosine (C) DNA replication Before a cell divides
DNA, Proteins and Evolution DNA is inherited Cell to cell Parent to offspring Closely related species more similar in DNA sequence than more distantly related species Human/human 99.1 % Human/chimp 98.5% Molecular biology used to assess evolutionary relatedness