* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Nerve activates contraction
Survey
Document related concepts
Signal transduction wikipedia , lookup
Magnesium transporter wikipedia , lookup
Phosphorylation wikipedia , lookup
Protein moonlighting wikipedia , lookup
Protein phosphorylation wikipedia , lookup
Protein (nutrient) wikipedia , lookup
Protein folding wikipedia , lookup
Circular dichroism wikipedia , lookup
Intrinsically disordered proteins wikipedia , lookup
Nuclear magnetic resonance spectroscopy of proteins wikipedia , lookup
List of types of proteins wikipedia , lookup
Biosynthesis wikipedia , lookup
Transcript
Polymer Principles Most macromolecules are polymers Polymer = (Poly = many; mer = part); large molecule consisting of many identical or similar subunits connected together. Monomer = Subunit or building block molecule of a polymer Macromolecule = (Macro = large); large organic polymer Formation of macromolecules from smaller building block molecules represents another level in the hierarchy of biological organization. There are four classes of macromolecules in living organisms: Carbohydrates Lipids Proteins Nucleic acids Polymerization reactions = Chemical reactions that link two or more small molecules to form larger molecules with repeating structural units. Condensation reactions = Polymerization reactions during which monomers are covalently linked, producing net removal of a water molecule for each covalent linkage. Figure 5.2 The synthesis and breakdown of polymers Polymerization Reaction Condensation or Dehydration Reaction Requires energy, biological catalysts (enzymes) Digestive enzymes catalyze hydrolytic reactions Unity in life--only about 40-50 common monomers Diversity too---new properties emerge from complex arrangements of monomers into polymers Figure 5.3 The structure and classification of some monosaccharides 3 5 Carbohydrates--sugars and their polymers Sugars--smallest carbohydrates 6 Simple sugars--monomers of carbohydrates called monosaccharides (CH2O) Major nutrients for cells e.g. glucose Glucose can be produced by photosynthesis from CO2, H2O, and sunlight Store energy--cellular respiration Raw material for other organic molecules Used as monomers for disaccharides and polysaccharides--condensation reactions Asymmetrical carbon--enantiomers Figure 5.4 Linear and ring forms of glucose Figure 5.5 Examples of disaccharide synthesis Polysaccharides = Macromolecules th at are p olym ers o f a f ew hu ndred or tho usand m ono saccharides. Are f orme d by linking mono me rs in e nzyme- mediat ed cond ensat ion react ions Have two import ant b iological f unct ions: 1 ) Energy stor age ( st arch and g ly cogen) 2 ) Stru ctur al suppo rt (c ellulose and chit in) Figure 5.6 Storage polysaccharides Cells hydrolyze storage polysaccharidesas needed for for energy Starch--glucose polymer in plants Amylose--unbranched polymer Amylopectin--branched polymer Most animals can digest starch potato, wheat, corn, rice Glycogen--glucose storage polysaccharide in animals Very highly branched Stored in muscle and liver Figure 5.7 Starch and cellulose structures Figure 5.7 Starch and cellulose structures Figure 5.7x Starch and cellulose molecular models Glucose Glucose Cellulose Starch Figure 5.8 The arrangement of cellulose in plant cell walls Cellulose reinforces plant walls Hydrogen bonds Cellulose cannot be digested by most organisms--no enzyme to break beta 1-4 linkage Insoluble fiber, digestion Figure 5.x1 Cellulose digestion: termite and Trichonympha Figure 5.x2 Cellulose digestion: cow Figure 5.10 Chitin, a structural polysaccharide: exoskeleton and surgical thread Lipids: Diverse Hydrophobic Molecules Lipids = Diverse group o f organic compoun ds th at are insolub le in w at er, but wi ll dissolv e i n nonp olar s olvents ( e.g., eth er chlorof orm, benz ene) . Importa nt gro ups are fat s, phospholipids, and st eroids. Fat s st ore large amount s of energ y Fat s = Macromolecules are c onst ruct ed f rom: Glycerol, a th ree-carbon alcoho l Fat t y acid ( carboxylic acid) = Compos ed of a carboxyl gro up at one e nd a nd an a t ta ched hyd rocarbon ch ain (“ t ail” ) Figure 5.11 The synthesis and structure of a fat, or triacylglycerol Carboxyl group has acid properties Hydrocarbon chain, 16-18 carbons Nonpolar C-H bonds, hydrophobic (Condensation Reaction) (bond between hydroxyl group and a carboxyl group) Fats: hydrophobic, not water soluble variation due to fatty acid composition fatty acids can be the same or different fatty acids can vary in length fatty acids can vary in the number and location of double bonds (saturation) A triglyceride Figure 5.12 Examples of saturated and unsaturated fats and fatty acids Saturated fats no double bonds between carbons in the tail saturated with hydrogen solid at room temp most animal fats, bacon grease, lard, butter Unsaturated fats one or more double bonds in tail kinks the tail so cannot pack closely enough to solidify at room temp most plant fats Artificial hydrogenation, peanut butter, margarine Fats have many useful functions Energy storage 9 vs 4 Kcal/gram more compact fuel than carbohydrates Cushions organs e.g. kidney Insulates against heat loss Phospholipids Phospholipids = Compounds with molecular building blocks of glycerol, two fatty acids, a phosphate group, and usually, an additional small chemical group attached to the phosphate. Differs from fat in that the third carbon of glycerol is joined to a negatively charged phosphate group Can have small variable molecules (usually charged or polar) attached to phosphate Are diverse depending upon differences in fatty acids and in phosphate attachments Show ambivalent behavior toward water. Hydrocarbon tails are hydrophobic and the polar head (phosphate group with attachments) is hydrophilic. Cluster in water as their hydrophobic portions turn away from water. One such cluster, a micelle, assembles so the hydrophobic tails turn toward the water-free interior and the hydrophilic phosphate heads arrange facing outward in contact with water. Are major constituents of cell membranes. At the cell surface, phospholipids form a bilayer held together by hydrophobic interactions among the hydrocarbon tails. Phospholipids in water will spontaneously form such a bilayer. Figure 5.13 The structure of a phospholipid Phospholipids = Compounds with molecular building blocks of glycerol, two fatty acids, a phosphate group, and usually, an additional small chemical group attached to the phosphate. Differs from fat in that the third carbon of glycerol is joined to a negatively charged phosphate group Can have small variable molecules (usually charged or polar) attached to phosphate Are diverse depending upon differences in fatty acids and in phosphate attachments Show ambivalent behavior toward water. Hydrocarbon tails are hydrophobic and the polar head (phosphate group with attachments) is hydrophilic. Are major constituents of cell membranes. Phospholipid Bilayers of Cell Membranes Steroids Steroids = Lipids which have four fused carbon rings with various functional groups attached. Cholesterol is an important steroid and is the precursor to many other steroids including vertebrate sex hormones and bile acids. Is a common component of animal cell membranes. Can contribute to atherosclerosis. Figure 5.15 Cholesterol, a steroid Memebranes Bile salts--absorption of fats HDL and LDL---triglycerides, phospholipids, cholesterol, protein LDL receptor deficiency--more deposition of cholesterol in arterial walls HDL--aid in removal of cholesterol from tissues Polypeptide chains = Polymers of amino acids that are arranged in a specific linear sequence, linked by peptide bonds Protein = A macromolecule consisting of one or more polypeptide chains folded and coiled into specific conformations Proteins make up 50% of the dry weight of cells Proteins vary extensively in structure, each with a unique 3-dimensional shape (conformation) Although they vary in structure and function, they are commonly made from only 20 amino acid monomers Figure 5.17 The 20 amino acids of proteins: nonpolar Amino acid = building blocks of proteins Asymmetric carbon (alpha carbon) bonded to H, Carboxyl group, Amino group, variable R-group (side chain) Physical and chemical properties of the side chain determine the uniqueness of each amino acid At normal cellular pH both the amino and carboxyl group are ionized---pH determines which ionic state predominates Alpha carbon, asymmetric Amino Side chain (R group) Hydrophobic side chain Carboxyl Figure 5.17 The 20 amino acids of proteins: polar and electrically charged Hydrophillic side chain Figure 5.18 Making a polypeptide chain Amino Peptide bond = covalent bond formed by condensation reaction Carboxyl Backbone has a repeating sequence N-CC-N-CC-… Figure 5.19 Conformation of a protein, the enzyme lysozyme Protein’s function depends on its specific conformation Protein conformation = 3-dimensional shape Native conformation = functional conformation found under normal biological conditions The conformation of a protein enables it to bind specifically to another molecular e.g. hormone/receptor, enzyme/substrate, antibody/antigen Conformation is a consequence of a specific linear sequence of amino acids polypeptide chain coils and folds spontaneously, mostly due to hydrophobic interactions stabilized by chemical bonds and weak interactions between neighboring regions of the folded protein The primary structure of a protein 4 levels of protein structure Primary Secondary Tertiary Quaternary Primary structure sequence of amino acids determined by genes slight change can have large effect on function e.g. sickle-cell hemoglobin sequence can be determined in the lab A single amino acid substitution in a protein causes sickle-cell disease Sickled cells The secondary structure of a protein Secondary structure = regular, repeated coiling and folding of a protein’s polypeptide backbone Contributes to final conformation Stabilized by H-bonds Two major types of secondary structures Alpha helix helical coil stabilized by H-bonds found in fibrous proteins e.g. keratin and collagen and some gobular proteins e.g. lysozyme Beta pleated sheet a sheet of antiparallel chains folded into accordion pleats held together by H-bonds found in gobular proteins e.g. lysozyme also in fibrous proteins e.g. fibroin (silk) Spider silk: a structural protein Examples of interactions contributing to the tertiary structure of a protein (Weak interaction) Tertiary structure = 3-dimensional shape due to bonding between and among side chains and to interactions between side chains and the aqueous environment (Weak interaction) Strong interaction (covalent bond) (Weak interaction) The quaternary structure of proteins Quaternary structure = structure that results from the interactions between several polypeptide chains Supercoiled structure gives it strength Review: the four levels of protein structure Figure 5.22 Denaturation and renaturation of a protein Proteins can be denatured by: transfer to an organic solvent, alters hydrophobic interactions chemical agents that disrupt hydrogen bonds, ionic bonds, disulfide bridges excessive heat--disrupts weak interactions Figure 5.23 A chaperonin in action Figure 5.24 X-ray crystallography Figure 5.25 DNA RNA protein: a diagrammatic overview of information flow in a cell Nucleic Acids store and transmit hereditary information Protein conformation is determined by primary structure Primary structure is determined by genes Genes are hereditary units that consist of DNA, a type of nucleic acid Two types of nucleic acids DNA (Deoxyribonucleic Acid) contains coded information that programs all cell activity contains directions for its own replication copied and passed from one generation to the next found primarily in the nucleus of eukaryotic cells makes up genes that contain instructions for protein synthesis via mRNA RNA (Ribonucleic Acid) functions in the actual synthesis of proteins coded for by DNA Sites of protein synthesis are on ribosomes mRNA carries encoded genetic messages from nucleus to the cytoplams The flow of genetic info is from DNA to RNA to protein Figure 5.26 The components of nucleic acids Nucleic Acid = polymer of nucleotides linked together by condensation reactions Nucleotide = building block of nucleic acid made of: a 5 carbon sugar, phosphate group, nitrogenous base Nucleic acid polymers (polynucleotides) are nucleotides linked together by phosphodiester linkages Each gene contains a unique sequence of nitrogenous bases which codes for a unique sequence of amino acids in a protein Figure 5.27 The DNA double helix and its replication Table 5.2 Polypeptide Sequence as Evidence for Evolutionary Relationships