Chapter 5: Structure and Function of Macromolecules AP Biology 2011

Transcription

1 Chapter 5: Structure and Function of Macromolecules AP Biology Macromolecules Fig. 5.1 Carbohydrates Lipids Proteins Nucleic Acids Polymer - large molecule consisting of many similar building blocks Monomers - repeating units that serve as building blocks of polymers 2 Synthesis of Polymers Often formed by condensation reactions Fig

2 Breakdown of Polymers Many polymers are broken down by the process of hydrolysis Fig Formation of Polymers Each class of polymers is formed by a specific set of monomers All organisms share the same monomer types but are unique based on the arrangement of those monomers Huge variety of polymers can be built from a small set of monomers 5 Carbohydrates Mainly function as fuel and building material Includes both sugars and the polymers of sugars Monosaccharides Multiples of CH2O simplest sugars used for fuel can be converted into other organic molecules can be combined to form polymers 6

3 Classification of Monosaccharides Aldoses (Aldehyde Sugars) Ketoses (Ketone Sugars) Trioses: 3-carbon sugars (C 3 H 6 O 3 ) Glyceraldehyde Dihydroxyacetone Pentoses: 5-carbon sugars (C 5 H 10 O 5 ) Classified by the location of the carbonyl group (aldose or keytose) and the number of carbons in the carbon skeleton Ribose Ribulose Hexoses: 6-carbon sugars (C 6 H 12 O 6 ) Glucose Galactose Fructose 7 Forms of Monosaccharides Can be linear or form rings Rings formed readily in aqueous solutions 8 Disaccharides Consist of two monosaccharides Joined by a glycosidic linkage through a dehydration reaction Fig

4 Polysaccharides Polymers of sugars Have huge roles in organisms for storage and structure ex. Starch ex. Glycogen 10 Energy Storage: Starch and Glycogen Both are polymers consisting entirely of glucose monomers (αglucose) Starch - major storage form of glucose in plants Glycogen - major storage form of glucose in animals Chloroplast Starch granules (a) Starch: 1 µm a plant polysaccharide Mitochondria Glycogen granules (b) Glycogen: 0.5 µm an animal polysaccharide Amylose Amylopectin Glycogen Fig Structural Polymers: Cellulose Polymer of glucose that has different glycosidic linkages than starch because it is formed from β-glucose Major component of cell walls in plants Difficult to digest (a) α and β glucose ring structures Fig. 5.7 α Glucose β Glucose (b) Starch: 1 4 linkage of α glucose monomers (c) Cellulose: 1 4 linkage of β glucose monomers 12

5 Chitin The structure of the chitin monomer Important structural polysaccharide Chitin forms the exoskeleton of arthropods. Found in exoskeleton of arthropods Chitin is used to make a strong and flexible surgical thread that decomposes after the wound or incision heals. Fig Lipids Only class of large biological molecules that do not consist of polymers Unifying feature is lack of an affinity for water Hydrophobic ex. Fats ex. Phospholipids ex. Steroids 14 Fats Constructed from two types of smaller molecules, a single glycerol and three fatty acids Fig

6 Saturated fatty acids Have the maximum number of hydrogen atoms possible Have no double bonds Unsaturated fatty acids Have one or more double bonds (a) Saturated fat Structural formula of a saturated fat molecule Space-filling model of stearic acid, a saturated fatty acid Fatty Acids Fatty acids vary in length and number and locations of double bonds they contain Fig (b) Unsaturated fat Structural formula of an unsaturated fat molecule Space-filling model of oleic acid, an unsaturated fatty acid Cis double bond causes bending. 16 Phospholipids Have only two fatty acids Have a phosphate group instead of the third fatty acid Consist of a hydrophilic head and hydrophobic tails Hydrophilic head Choline Phosphate Glycerol Hydrophobic tails Fatty acids Hydrophilic head (a) Structural formula (b) Space-filling model Hydrophobic tails (c) Phospholipid symbol Fig Cell Membranes Made up of phospholipids arranged as a result of their hydrophilic and hydrophobic regions Self-assemble in the presence of water Hydrophilic head WATER Hydrophobic tail WATER Fig

7 Steroids Lipids characterized by a carbon skeleton consisting of four fused rings Ex. cholesterol found in cell membranes precursor for some hormones H 3 C CH 3 CH 3 CH 3 CH 3 Figure 5.15 HO 19 Proteins Account for more than 50% of the dry mass of most cells Have many structures and functions inside of the cell structure, storage, transport, cellular communications, movement, and defense against foreign substances Fig Enzymes Type of protein that acts as a catalyst speeding up chemical reactions 1 Active site is available for a molecule of substrate, the reactant on which the enzyme acts. Substrate (sucrose) 2 Substrate binds to enzyme. Glucose OH Fructose H O Enzyme (sucrase) H 2 O Figure Products are released. 3 Substrate is converted to products. 21

8 Polypeptides Amino Acids - monomers of a protein with carboxyl and amino groups Differ in properties based on different side chains (called R groups) Polypeptides - polymers of amino acids linked by peptide bonds Protein - consists of one or more polypeptides 22 Amino Acid Types Nonpolar Polar Electrically charged (acidic and basic) Nonpolar side chains; hydrophobic Side chain (R group) Glycine Alanine Valine Leucine Isoleucine (Gly or G) (Ala or A) (Val or V) (Leu or L) (Ile or I) Methionine Phenylalanine Tryptophan Proline (Met or M) (Phe or F) (Trp or W) (Pro or P) Polar side chains; hydrophilic Serine Threonine Cysteine Tyrosine Asparagine Glutamine (Ser or S) (Thr or T) (Cys or C) (Tyr or Y) (Asn or N) (Gln or Q) Electrically charged side chains; hydrophilic Basic (positively charged) Acidic (negatively charged) Fig Aspartic acid (Asp or D) Glutamic acid (Glu or E) Lysine (Lys or K) Arginine (Arg or R) Histidine (His or H) 23 Amino Acid Linkages Linked by peptide bonds Fig

9 Protein Structure and Function Functional protein has one or more polypeptides precisely twisted, folded, and coiled into a unique shape Groove Groove (a) A ribbon model (b) A space-filling model Antibody protein The sequence of amino acids determines the protein s threedimensional structure and the structure determines the function Protein from flu virus Figs Primary structure Protein Structure Amino acids Amino end Levels Primary structure of transthyretin Primary unique sequence of amino acids (determined by genetic info) Fig Carboxyl end Secondary structure α helix Secondary coils and folds of the polypeptide chain Hydrogen bond β pleated sheet β strand, shown as a flat arrow pointing toward the carboxyl end Hydrogen bond 26 Primary Structure Fig Tertiary structure Tertiary determined by interactions of side chains (R groups) Quaternary many polypeptide chains Quaternary structure Transthyretin polypeptide Transthyretin protein (four identical polypeptides) Hydrogen bond Hydrophobic interactions and van der Waals interactions Disulfide bridge Ionic bond Polypeptide backbone 27

10 Case Study: Sickle Cell Disease Results from a single amino acid substitution in the protein hemoglobin substitution of valine for glutamic acid the abnormal hemoglobin molecule crystalizes deforming the cell into a sickle shape causes blood flow to be impeded Sickle-cell hemoglobin Normal hemoglobin Primary Structure Secondary and Tertiary Structures β subunit Exposed hydrophobic region β subunit α α β Quaternary Structure Normal hemoglobin β β α Sickle-cell hemoglobin β α Function Molecules do not associate with one another; each carries oxygen. Molecules crystallize into a fiber; capacity to carry oxygen is reduced. Red Blood Cell Shape 10 µm 10 µm Fig Protein Conformation Depends on the physical and chemical conditions of the protein s environment If ph, salt concentration, temperature, or other aspects are altered the protein may denature Denaturation - the protein unravels and loses its native conformation Den a tur a i t on Normal protein Re n a u a i t r t on Denatured protein Fig Protein Folding Proteins must go through several intermediate states on their way to a stable conformation Chaperonins - protein molecules that assist in the proper folding of other proteins Cap Polypeptide Correctly folded protein Hollow cylinder Chaperonin (fully assembled) Steps of Chaperonin 2 The cap attaches, causing 3 Action: the cylinder to change 1 An unfolded poly- shape in such a way that peptide enters the it creates a hydrophilic cylinder from environment for the one end. folding of the polypeptide. The cap comes off, and the properly folded protein is released. Fig

11 Structure Determination EXPERIMENT Diffracted X-rays Difficult to determine the 3D structure of a protein X-ray source X-ray beam RESULTS Crystal Digital detector X-ray diffraction pattern X-ray crystallography NMR spectroscopy RNA DNA Fig RNA polymerase II 31 Store and transmit hereditary information Genes unit of inheritance determine the amino acid sequence of polypeptides Two types: Deoxyribonucleic acid (DNA) - double stranded Ribonucleic acid (RNA) - single stranded Nucleic Acids Synthesis of mrna NUCLEUS Movement of mrna into cytoplasm Synthesis of protein Polypeptide DNA mrna mrna CYTOPLASM Ribosome Amino acids Fig Nucleic Acids Monomer - nucleotide Polymer - polynucleotide 5! end 5!C 3!C Sugar-phosphate backbone 5!C Nucleoside Nitrogenous base 5!C 3!C Phosphate group (b) Nucleotide 3!C Sugar (pentose) 1!C Fig ! end (a) Polynucleotide, or nucleic acid 33

12 Nucleotide Monomers Made up of nucleosides (nitrogenous base and sugar) and phosphate groups Cytosine (C) Nitrogenous bases Pyrimidines Thymine (T, in DNA) Purines Uracil (U, in RNA) Sugars Nucleotide - nucleoside and phosphate group Adenine (A) (c) Nucleoside components Guanine (G) Deoxyribose (in DNA) Ribose (in RNA) Fig Nucleotide Polymers Made up of nucleotides linked by the -OH group on the 3 carbon of one nucleotide and the phosphate on the 5 carbon on the next 5! 3! Sugar-phosphate backbones Hydrogen bonds DNA organized in a double helix of two antiparallel nucleotide strands Base pair joined by hydrogen bonding forms hydrogen bonds with the complementary strand (A pairs with T and C with G) 3! (a) DNA 5! Base pair joined by hydrogen bonding (b) Transfer RNA Fig