BISC160 chapter 3.docx

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University of Mississippi
Biological Science
BISC 160
Dr.Beckie Symula

Chapter 3 8/23/2013 3:53:00 PM 3.1 What kinds of molecules characterize living things?  Proteins: formed from different combinations of 20 amino acids  Carbohydrates: can form giant molecules by linking together chemically similar sugar monomers(monosaccharides) to form polysaccharides  Nucleic acids: four kinds of nucleotide monomers linked together in long chains  Lipids: form large structures from a limited set of smaller molecules, but noncovalent forces maintain the interactions between the lipid monomers  Polymers with molecular weights exceeding 1000 grams per mole are considered macromolecules  Functional groups give specific properties to biological molecules o Functional groups are certain small groups of atoms found together in very different biological molecules.  Attaches to a larger molecule and confers its specific chemical properties on the larger molecule  Polarity  Acidic/basic  Energy release  Isomers have different arrangement of the same atoms o Isomers are molecules that have the same chemical formula but the atoms are arranged differently  Structural: differ in how their atoms are joined together  Optimal: occur when a carbon atom has four different atoms attached to it, which allows two different ways of making attachments, each the mirror image of each other  The structures of macromolecules reflect their functions o When eating things, the molecules you take in can be broken down and rebuilt into the varieties of those molecules needed by humans o Functions of macromolecules  Energy storage  Structural support  Protection  Catalysis  Transport  Defense  Regulation  Movement  Information storage Only nucleic acid Directly related to their 3D shape and to the sequences and chemical properties of their monomers  Most macromolecules are formed by condensation and broken down by hydrolysis o Condensation reactions: polymers are constructed from monomers, dehydration reactions, result in covalent bonds between monomers(a water is removed) o Hydrolysis reactions break down polymers into their monomers; water is broken down 3.1 Summary: The four kinds of large molecules that distinguish living tissues are proteins, lipids, carbohydrates, and nucleic acids. These biological molecules carry out a wide range of life-sustaining functions. Most of them are polymers, made up of linked monomeric subunits. Very large polymers are called macromolecules. 3.2 What are the chemical structures and functions of proteins?  Enzymes are catalytic proteins that speed up biochemical reactions  Defensive proteins such as antibodies recognize and respond to non-self substances that invade the organism from the environment  Hormonal and regulatory proteins such as insulin control physiological processes  Receptor proteins receive and respond to molecular signals from inside and outside the organism  Storage proteins store chemical building blocks—amino acids—for later use  Structural proteins such as collagen provide physical stability and movement  Transport proteins such as hemoglobin carry substances within the organism  Genetic regulatory proteins regulate when, how, and to what extent a gene is expressed  Energy storage and information storage are not usually performed by proteins  Polypeptide chains—unbranched polymer of covalently linked amino acids.  Amino acids are the building blocks of proteins o Have both a carboxyl functional group and an amino functional group attached to the same carbon atom, called the alpha carbon.  Also attached are the side chain called R-group and a hydrogen atom  Two isomeric forms, D-amino acids and L-amino acids  Only L-amino acids are commonly found in proteins in most organisms o Both the carboxyl and amino groups of amino acids are ionized  Carboxyl has lost a hydrogen ion  Amino group has gained a hydrogen ion  Thus, amino acids are simultaneously acids and bases o See Table 3.1  5 amino acids have electrically charged hydrophilic side chains  Five amino acids have polar side chains that are uncharged, hydrophilic  Seven amino acids with nonpolar hydrophobic side chains  Three special cases  Cysteine: can react with another cysteine chain in an oxidation reaction to form a disulfide bond, which determine how a polypeptide chain unfolds  Glycine consists of a single hydrogen atom and is small enough to fit into tight corners in the interior of a protein molecule  Proline lacks hydrogen and forms a covalent bond with the hydrocarbon side chain, making a ring structure  Peptide linkages form the backbone of a protein o When amino acids polymerize, the carboxyl and amino groups are the reactive groups  Condensation reaction between carboxyl and amino group o Two characteristics important in 3D structure of proteins:  C-N linkage, the adjacent alpha carbons are not free to fully rotate, which limits folding of the chain  Oxygen-Carbon in the carboxyl group carries a slight negative charge, whereas the hydrogen bound to the nitrogen in the amino group is slightly positive. Favors hydrogen bonds  The primary structure of a protein is its amino acid sequence  The secondary structure of a protein requires hydrogen bonding o Regular, repeated spatial patterns in different regions of a polypeptide chain; determined by carboxyl/amino hydrogen bonding o The α helix  Right-handed coil resulting from hydrogen bonds that form between the slightly positive hydrogen of the N-H of one amino acid and the slightly negative oxygen of the C=O of another  The β pleated sheet  Formed from two or more polypeptide chains that are almost completely extended and aligned  The tertiary structure of a protein is formed by bending and folding o The interactions between R groups determine tertiary structure o These interactions:  Disulfide bridges between specific cysteine side chains  Hydrogen bonds between side chains  Hydrophobic side chains  Van der Waals forces stabilize interactions between hydrophobic side chains  Ionic bonds form salt bridges between amino acids o Three models to depict structures  Space-filling model: used to study how other molecules interact with specific sites and R groups on a protein’s surface  Stick model: emphasizes the sites where bends occur in order to make the folds of the polypeptide chain  Ribbon model: shows different types of secondary structure and how they fold into the tertiary structure  The quaternary structure of a protein consists of subunits o Results from the way subunits bind together and interact  Shape and surface chemistry contribute to protein function o Shape: A molecule will not bind to a protein unless there is a general ―fit‖ between their 3D shapes o Chemistry: exposed R groups permit chemical interactions via ionic, hydrophobic, and hydrogen bonding  Environmental conditions affect protein structure o Increases in temperature cause rapid molecular movement and thus can break hydrogen bonds and hydrophobic interactions o Alterations in pH can change the pattern of ionization of carboxyl/amino groups
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