General Biology 121- Chapter 5: The Structure and Function of Large Biological Molecules
General Biology 121- Chapter 5: The Structure and Function of Large Biological Molecules Bio 121
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This 10 page Class Notes was uploaded by Audrey Notetaker on Friday October 2, 2015. The Class Notes belongs to Bio 121 at Syracuse University taught by Wiles in Fall 2015. Since its upload, it has received 20 views. For similar materials see Intro to biological sciences in Biological Sciences at Syracuse University.
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Date Created: 10/02/15
Chapter 5 The Structure and Function of Large Biological Molecules The Molecules of Life The most important large molecules found in all living things can be sorted into 4 main classes carbohydrates lipids proteins and nucleic acids But on the molecular scale members of 3 of these classes carbohydrates proteins and nucleic acids are big and therefore called The architecture of a big biological molecule plays an essential role in its function Big molecules exhibit unique emergent properties from the orderly arrangement of their atoms Macromolecules are polymers built from monomers The 3 macromolecules are chainliked molecules called A polymer is a long molecule consisting of many similar or identical building blocks linked by covalent bonds like how a train consists of a chain of cars The repeating units that serve as the building blocks of a polymer are smaller molecules called Some monomers have functions of their own The Synthesis and Breakdown of Polymers The chemical mechanisms by which cells make and break down polymers are basically the same in all cases In cells these processes are facilitated by specialized macromolecules that speed up chemical reactions Monomers are connected by a reaction in which 2 molecules are covalently bonded to each other with the loss of a water molecule This is known as When a bond forms between 2 monomers each monomer contributed part of the water molecule that s released during the reaction one monomer provides a hydroxyl group while the other provides a hydrogen This reaction is repeated as monomers are added to the chain one by one making a polymer Polymers are dissembled to monomers by a process that s essentially the reverse of the dehydration reaction It means water breakage The bond between monomers is broken by the addition of a water molecule with a hydrogen from water attaching to one monomer and the hydroxyl group attaching to the other Digestion is a good example of hydrolysis Carbohydrates serve as fuel and building material include sugars and polymers of sugars The simplest carbohydrates are the or simple sugars these are the monomers from which more complex carbohydrates are built are double sugars consisting of 2 monosaccharides joined by a a covalent bond formed between 2 monosaccharides by a dehydration reaction Carbohydrate macromolecules are polymers called composed of many sugar building blocks Sugars Glucose fructose and ribose are types of monosaccharides Monosaccharides particularly glucose are major nutrients for cells During cellular respiration cells extract energy from glucose molecules by breaking them down in a series of reactions Simple sugar molecules serve as raw material for the synthesis of other types of small organic molecules like amino acids and fatty acids are double sugars consisting of 2 monosaccharides joined by a a covalent bond formed between 2 monosaccharides by a dehydration reaction For example maltose also known as malt sugar is a disaccharide formed by the linking of 2 molecules of glucose Sucrose a table sugar is also a disaccharide lts 2 monomers are glucose and fructose Lactose a sugar present in milk is another disaccharide Polysaccha rides are macromolecules polymers with a few hundred to a few thousand monosaccharides joined by glycosidic linkages Some polysaccharides serve as storage material hydrolyzed as needed to provide sugar for cells Other polysaccharides serve as building material for structures that protect the cell or whole organism The architecture and function of a polysaccharide are determined by its sugar monomers and by the positions of its glycosidic linkages Storage Polysaccharides Plants and animals store sugars for later use in the form of storage polysaccharides Plants store a polymer of glucose monomers as granules within cellular structures known as which include chloroplasts Synthesizing starch enables the plant to stockpile surplus glucose Because glucose is a major cellular fuel starch represents stored energy The sugar can later be withdrawn from this carbohydrate quotbankquot by hydrolysis Animals store a polysaccharide called a polymer of glucose that s like amylopectin but more branched Hydrolysis of glycogen in these cells releases glucose when the demand for sugar increases This stored fuel can t sustain an animal for long Structural Polysaccharides Organisms build strong materials from structural polysaccharides For example a polysaccharide is a major component of the tough walls that enclose plant cells Cellulose is a polymer of glucose but the glycosidic linkages in these 2 polymers differ ln plant cell walls parallel cellulose molecules held together in this way are grouped into units called These cablelike micro brils are strong building material for plants and an important substance for humans because cellulose is the major constituent of paper and the only component of cotton Cellulose is an important part of a healthy diet is a carbohydrate used by arthropods to build their exoskeletons lt s found in fungi which use this polysaccharide instead of cellulose as the building material for their cell walls Lipids are a diverse group of hydrophobic molecules are the one class of large biological molecules that doesn t include true polymers and they re not big enough to be considered macromolecules They also mix poorly with water because of their molecular structure Fats phospholipids and steroids are all types of lipids Fats are large molecules assembled from smaller molecules by dehydration reactions They re constructed form 2 kinds of smaller molecules glycerol and fatty acids is an alcohol each of its 3 carbons bears a hydroxyl group A has a long carbon skeleton The carbon at one end of the skeleton is part of a carboxyl group while the rest of the skeleton consists of a hydrocarbon chain The C H bonds in the hydrocarbon chains of fatty acids are the reason fats are hydrophobic 3 fatty acid molecules are each joined to glycerol by an ester linkage a bond formed by a dehydration reaction between a hydroxyl group and a carboxyl group This resulting fat a thus consists of 3 fatty acids linked to one glycerol molecule A is a fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds thus maximizing the number of hydrogen atoms that are attached to the carbon skeleton An that has one or more double bonds with one fewer hydrogen atom on each doublebonded carbon Most double bonds in naturally occurring fatty acids are cis double bonds which cause a link in the hydrocarbon chain wherever they occun A fat made from saturated fatty acids is called a Most animal fats are saturated the hydrocarbon chains of their fatty acids the quottailsquot of the fat molecules lack double bonds and their exibility allows the fat molecules to pack together tightly Saturated animal fats are solid at room temperature like lard and butter Fats of plants and sh are Usually liquid at room temperature plant and sh fats are referred to as oils like olive and cod liver oil The kinks where the cis double bonds are located prevent the molecules from packing together closely enough to solidify at room temperature on food labels means that unsaturated fats have been converted to saturated fats by adding hydrogen Peanut butter and margarine are hydrogenated to prevent lipids from separating out into liquid form A diet rich in saturated fats is one of several factors that may contribute to atherosclerosis are unsaturated fats that formed arti cially during hydrogenation of oils containing one or more trans double bonds o The major function of fats is energy storage 0 A gram of fat stores more than twice as much energy as a gram of polysaccharide like starch Since plants are immobile they can function with bulky energy storage in the form of starch But animals must carry their energy stores with them Phospholipids Cells couldn t exist without phospholipids They re essential for cells because they re major constituents of cell membranes A is made up of glycerol rather than three The 3rel hydroxyl group of glycerol is joined to a phosphate group which has a negative electrical charge in the cell 0 The 2 ends of phospholipids show different behavior toward water The hydrocarbon tails are hydrophobic and are excluded from water But the phosphate group and its attachments form a hydrophilic head that has an affinity for water When phospholipids are added to water they selfassemble into doublelayered structures called shielding their hydrophobic portions from water 0 At the surface of a cell phospholipids are arranged in a similar bilayer The hydrophilic heads of the molecules are on the outside of the bilayer in contact with the aqueous solutions inside and outside of the cell The hydrophobic tails point toward the interior of the bilayer forms a boundary between the cell and its external environment Steroids are lipids characterized by a carbon skeleton consisting of 4 fused rings Different steroids are distinguished by the particular chemical groups attached to this ensemble of rings 0 a type of steroid is an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other biologically important steroids like hormones However a high level of cholesterol in the blood may contribute to atherosclerosis 54 Proteins include a diversity of structures resulting in a wide range of functions 0 Most functions within a living being depend on proteins 0 are biologically functional molecules made up of one or more polypeptides each folded and coiled into a speci c 3D structure Some proteins speed up chemical reactions while others play a role in defense storage transport cellular communication movement or structural support Life wouldn t be possible without most of which are proteins They re biological molecules that act as catalysts and help complex reactions occur everywhere in life Enzymatic proteins regulate metabolism by acting as chemical agents that selectively speed up chemical reactions without being consumed by the reaction Enzymes can perform its function over and over again They keep cells running by carrying out the processes of life Proteins are constructed from the same set of 20 amino acids linked in unbranched polymers The bond between amino acids is called a so a polymer of amino acids is called a An Overview of Protein Functions P gt P Pquot39gtS l l 39 Enzymatic proteins selective acceleration of chemical reactions Defensive proteins protection against disease Storage proteins storage of amino acids Transport proteins transport of substances Hormonal proteins coordination of an organism s activities Receptor proteins response of cell to chemical stimuli Contractile and motor proteins movement Structural proteins support Amino Acid Monomers An amino acid is an organic molecule with both an amino group and a carboxyl group The center of the amino acid is a carbon atom called the alpha carbon lts four different partners are an amino group a carboxyl group a hydrogen atom and a variable group symbolized by R The R group also called the side chain differs with each amino acid The physical and chemical properties of the side chain determine the unique characteristics of a particular amino acid thus affecting its functional role in a polypeptide Polypeptides Amino Acid Polymers A is the covalent bond between the carboxyl group on one amino acid and the amino group on another formed by a dehydration reaction A is a polymer of many amino acids linked by peptide bonds Protein Structure and Function The speci c activities of proteins result from their intricate 3D architecture the simplest level of which is the sequence of their amino acids A functional protein is one or more polypeptides twisted folded and coiled into a molecule of unique shape The amino acid sequence of each polypeptide that determines what 3D structure the protein will have under normal cellular conditions A protein s speci c structure determines how it works The function of a protein depends on its ability to recognize and bind to some other molecule 4 Levels of Protein Structure All proteins share 3 superimposed levels of structure known as primary secondary and tertiary structure The quaternary structure arises when a protein consists of 2 or more polypeptide chains Primary Structure The of a protein is its sequence of amino acids in a polypeptide chain The primary structure is like the order of letters in a very long word The primary structure is determined by inherited genetic information It also dictates secondary and tertiary structure Secondary Structure Most proteins have segments of their polypeptide chains repeatedly coiled or folded in patterns that contribute to the protein s overall shape These coils and folds are referred to as They re the result of hydrogen bonds between the repeating constituents of the polypeptide backbone One secondary structure is the which is a coil held together by hydrogen bonding between every fourth amino acid The other main type of secondary structure is the Within this secondary structure the polypeptide chain folds back and forth 2 regions of the chain lie parallel to each other and are held together by hydrogen bonds between atoms of the polypeptide backbone Tertiary Structure 0 The is the overall shape of a polypeptide resulting from interactions between the side chains R groups of the various amino acids 0 A is a type of chemical interaction caused when molecules that don t mix with water coalesce to exclude water Hydrogen bonds between polar side chains and ionic bonds between positively and negatively charged side chains also help tertiary structure Covalent bonds caed may further reinforce the shape of a protein They re a covalent bond formed when the sulfur of one cysteine monomer bonds to the sulfur of another cysteine monomer Quaternary Structure 0 A is the overall protein structure that results from the aggregation of these polypeptide subunits They re de ned by the characteristic 3D arrangement of its constituent subunits each a polypeptide Hemoglobin the oxygenbinding protein of red blood cells It s another example of a globular protein with a quaternary structure It consists of 4 polypeptide subunits two of one kind a and two of another kind B Both a and B subunits consist primarily of a dhelical secondary structure Each subunit has a nonpolypeptide component caed heme with an iron atom that binds oxygen 55 Nucleic acids store transmit and help express hereditary information o A is a discrete unit of hereditary information consisting of a speci c nucleotide sequence in DNA or RNA in some viruses are polymers made of monomers caed Nucleic acids serve as a blueprint for proteins and through the actions of proteins for all ceuar activities The 2 types are DNA and RNA The Roles of Nucleic Acids The 2 types of nucleic acids and enable living organisms to reproduce their complex components from one generation to the next is a nucleic acid molecule usually a doublestranded helix in which each polynucleotide strand consists of nucleotide monomers with a deoxyribose sugar and the nitrogenous bases adenine A cytosine C guanine G and thymine T lt s capable of being replicated and determining the inherited structure of a cell s proteins is a nucleic acid consisting of a polynucleotide made up of nucleotide monomers with a ribose sugar and the nitrogenous bases adenine A cytosine C guanine G and uracil U It s usually singlestranded and it functions in protein synthesis in gene regulation and as the genome of some viruses The process by which information encoded in DNA directs the synthesis of proteins or in some cases RNAs that aren t translated into proteins and instead function as RNAs This entire process is called DNA is the genetic material that organisms inherit from their parents Each chromosome contains one long DNA molecule usually carrying several hundred or more genes When a cell reproduces itself by dividing its DNA molecules are copied and passed along from one generation of cells to the next Encoded in the structure of DNA is the information that programs all the cell s activities Each gene along a DNA molecule directs synthesis of a type of RNA called mRNA interacts with the cell s protein synthesizing machinery to direct production of a polypeptide The ow of genetic information DNA l RNA l protein The sites of protein synthesis are cellular structures are called DNA resides in the nucleus Messenger RNA conveys genetic instructions for building proteins from the nucleus to the cytoplasm The Components of Nucleic Acids Nucleic acids are macromolecules that exist as polymers called A is composed of 3 parts a 5carbon sugar a nitrogenous base and one or more phosphate groups In a polynucleotide each monomer has only one phosphate group There are 2 families of nitrogenous bases pyrimidines and purines A has one sixmembered ring of carbon and nitrogen atoms The members of the pyrimidine family are cytosine C thymine T and uracil U o are bigger with a 6membered ring fused to a 5membered ring The purines are adenine A and guanine G o The speci c pyrimidines and purines differ in the chemical groups attached to the rings Adenine guanine and cytosine are found in both DNA and RNA thymine is found only in DNA and uracil only in RNA 0 In DNA the sugar is deoxyribose in RNA its ribose The deoxyribose lacks in oxygen The Structures of DNA and RNA Molecules Adenine in one strand of the double helix always pairs with thymine in the other and guanine always pairs with cytosine Transfer RNA brings amino acids to the ribosome during the synthesis of a polypeptide
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