Transcript ppt
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 (C6H12O6) • 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 Mitochondria Glycogen granules Starch 0.5 µm 1 µm Glycogen Amylose Amylopectin (a) Starch: a plant polysaccharide Amylose - unbranched Amylopectin - branched (b) Glycogen: an animal polysaccharide 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 of the chitin monomer. Cicada exoskeleton (b) Chitin forms the exoskeleton of arthropods. (c) Chitin is used to make a strong and flexible surgical thread. 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 (a) Liquid at room T (plant, fish oils) • 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 β pleated sheet Example: spider silk 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 α Chains • activity 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 G,A,T,C building blocks (monomers) – Pyrimidines (cytosine, thymine, and uracil) – Purines (adenine and guanine) Nitrogenous bases Pyrimidines Cytosine (C) Uracil (U, in RNA) Thymine (T, in DNA) Purines Adenine (A) Guanine (G) (c) Nucleoside components: nitrogenous bases •Nucleotides contain sugar •DNA deoxyribose •RNA ribose (ribonucleic acid) Sugars Deoxyribose (in DNA) (c) Nucleoside components: sugars Ribose (in RNA) DNA Polymers Sugar phosphate backbone 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