Biological Sciences
Monomers
Monomers are small molecules that can bond to form larger molecules known as polymers. In biological systems, monomers are the building blocks for macromolecules such as proteins, carbohydrates, and nucleic acids. These molecules play a crucial role in various biological processes and are essential for the structure and function of living organisms.
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eBook - PDFElements of Polymer Science & Engineering
An Introductory Text and Reference for Engineers and Chemists
- Alfred Rudin(Author)
- 1998(Publication Date)
- Academic Press(Publisher)
2 1 Introductory Concepts and Definitions reader may have learned in other branches of science. This should not be cause for alarm, since all the more important definitions that follow are clear in the contexts in which they are normally used. Ll.l Polymer Polymer means many parts and designates a large molecule made up of smaller repeating units. Thus the structure of polystyrene can be written H H H H t i l l '^ CH2-C-CH2-C- CH2-C-CH2-C--(o) (S) (o) (^ M Polymers generally have molecular weights greater than about 5000 but no firm lower limit need be defined since the meaning of the word is nearly always clear from its use. The word macromolecule is a synonym for polymer. 1.1.2 Monomer A monomer is a molecule that combines with other molecules of the same or different type to form a polymer. Acrylonitrile, CH2=CHCN, is the monomer for polyacrylonitrile: H H t I ^ C H ^ -C -C H o -C -C H o -I I CN CN 1-2 which is the basic constituent of acrylic fibers. 1.1.3 Oligomer An oligomer is a low-molecular-weight polymer. It contains at least two monomer units. Hexatriacontane (n-CH3—(CH2)29—CH3) is an oligomer of polyethylene A^^ CH2CH2CH2CH2CH2CH2CH2CH2CH2 '^l 1-3 H 1 1 c-1 CN CH2-H 1 1 -C -1 CN 1.1 Some Definitions 3 Generally speaking, a species will be called polymeric if articles made from it have significant mechanical strength and oligomeric if such articles are not strong enough to be practically useful. The distinction between the sizes of oligomers and the corresponding polymers is left vague, however, because there is no sharp transition in most properties of interest. The terms used above stem from Greek roots: mews (part), poly (many), oligo (few), and mono (one). 1 . 1.4 Repeating Unit The repeating unit of a linear polymer (which is defined below) is a portion of the macromolecule such that the complete polymer (except for the ends) might be produced by linking a sufficiently large number of these units through bonds between specified atoms.
eBook - PDF- Johan R C van der Maarel(Author)
- 2007(Publication Date)
- WSPC(Publisher)
The structure of any biopolymer is determined by the nature of the building blocks ( i.e . the monomeric units) in combination with environmental conditions such as the temperature, the solvent (water) and the presence of salts and/or other molecular components. The monomeric units of nucleic acids, proteins and polysaccharides are largely different and will be discussed in the next section. A unique feature of biopolymers is that most of them are essentially heteropolymers, because they may contain a variety in monomeric units. The biological relevance of a biopolymer is ultimately based on the sequence of the Monomers, i.e . the primary structure. In the case of DNA, the primary structure is the sequence of bases attached to the sugar rings, which determines the genetic code. For proteins, it is the amino acid sequence, which eventually determines, together with environmental conditions, their 3– dimensional shapes and biological functions. The properties of polysaccharides are also largely determined by the nature of the monomeric Chapter 1: Biopolymers 3 units, more specifically in the way they are connected. A fundamental characteristic of biopolymers is the formation of hierarchical structures at successive length scales. Starting from the primary structure, the monomeric units are organized in a certain local molecular conformation. This local conformation is commonly referred to as the secondary structure. Examples of secondary structures are the famous double-helical arrangement of the two opposing strands in the DNA molecule (the duplex) and α − helixes and β − sheets formed by the polypeptide chains in proteins. At a larger distance scale, a biopolymer can adopt a defined 3– dimensional conformation: the so-called tertiary structure. This is particularly relevant for proteins, which largely owe their biological functioning to their 3–dimensional structure, but also nucleic acids and polysaccharides have tertiary structures.
eBook - PDFIntroduction to Polymer Science and Chemistry
A Problem-Solving Approach, Second Edition
- Manas Chanda(Author)
- 2013(Publication Date)
- CRC Press(Publisher)
Chapter 1 Introductory Concepts 1.1 Basic De fi nitions Many of the terms, de fi nitions, and concepts used in polymer science are not encountered in other branches of science and must be understood in order to fully discuss the synthesis, characterization, structure, and properties of polymers. While most of these are discussed in detail in subsequent chapters, some are of such fundamental importance that they must be introduced at the beginning. 1.1.1 Polymer The term polymer stems from the Greek roots poly (many) and meros (part). The word thus means “many parts” and designates a molecule made up by the repetition of some simpler unit called a mer . Polymers contain thousands to millions of atoms in a molecule that is large; they are also called macromolecules . Polymers are prepared by joining a large number of small molecules called Monomers . The structure of polystyrene, for example, can be written as (I) or, more conveniently, as (II) , which depicts the mer or repeating unit of the molecule within parentheses with a subscript, such as n , to represent the number of repeating units in the polymer molecule. (II) The value of n usually ranges from a few hundred to several thousand, depending on the molecular weight of the polymer. The polymer molecular weight may extend, on the higher side, 1 2 Chapter 1 to several millions. Often the term high polymer is also used to emphasize that the polymer under consideration is of very high molecular weight. 1.1.2 Monomer Monomers are generally simple organic molecules from which the polymer molecule is made. The structure of the repeating unit of a polymer is essentially that or closely related to that of the monomer molecule(s). The formula of the polystyrene repeating unit (II) is thus seen to be essentially the same as that of the monomer styrene CH 2 CH-C 6 H 5 .
eBook - PDF- Julianne Zedalis, John Eggebrecht(Authors)
- 2018(Publication Date)
- Openstax(Publisher)
These large molecules are composed mainly of six elements—sulfur, phosphorus, oxygen, nitrogen, carbon, and hydrogen (SPONCH)—in different quantities and arrangements. Complex polymers are built from combinations of smaller Monomers by dehydration synthesis, a chemical reaction in which a molecule of water is removed between two linking Monomers. (Think of a train: each boxcar, including the caboose, represents a monomer, and the entire train is a polymer.) During digestion, polymers can be broken down by hydrolysis, or the addition of water. Both dehydration and hydrolysis reactions in cells are catalyzed by specific enzymes. Dehydration reactions typically require an investment of energy for new bond formation, whereas hydrolysis reactions typically release energy that can be used to power cellular processes. The four categories of macromolecules are carbohydrates, lipids, proteins, and nucleic acids. Evidence supports scientists’ claim that the organic precursors of these biological molecules were present on primitive Earth. Information presented and the examples highlighted in the section support concepts and Learning Objectives outlined in Big Idea 1 of the AP ® Biology Curriculum Framework. The Learning Objectives listed in the Curriculum Framework provide a transparent foundation for the AP ® Biology course, an inquiry-based laboratory experience, instructional activities, and AP ® Exam questions. A learning objective merges required content with one or more of the seven Science Practices. Big Idea 1 The process of evolution drives the diversity and unity of life. Enduring Understanding 1.D The origin of living systems is explained by natural processes. Essential Knowledge 1.D.1 There are several hypotheses about the natural origin of life on Earth, each with supporting scientific evidence. Science Practice 1.2 The student can make claims and predictions about natural phenomena based on scientific theories and models.
- Manas Chanda, Salil K. Roy(Authors)
- 2008(Publication Date)
- CRC Press(Publisher)
1 Characteristics of Polymers 1.1 What Is a Polymer? A molecule has a group of atoms which have strong bonds among themselves but relatively weak bonds to adjacent molecules. Examples of small molecules are water (H 2 O), methanol (CH 3 OH), car bon dioxide, and so on. Poly mers contain thousands to millions of atoms in a molecule which is large; they are also called macromolecules. Poly mers are prepared by joining a large number of small molecules called Monomers. Poly mers can be thoug ht of as big buildings, and Monomers as the bricks that go into them. Monomers are generally simple organic molecules containing a double bond or a minimum of two active functional groups. The presence of the double bond or active functional groups act as the driv ing force to add one monomer molecule upon the other repeatedly to make a poly mer molecule. This process of transformation of monomer molecules to a poly mer molecule is know n as polym erization. For example, ethylene, the prototy pe monomer molecule, is ver y reactive because it has a double bond. Under the influence of heat, lig ht, or chemical agents this bond becomes so activated that a chain reaction of self-addition of ethylene molecules is generated, resulting in the production of a hig h-molecular-weight material, almost identical in chemical composition to ethylene, known as polyethylene, the poly mer of ethylene (Figure 1.1). The difference in behavior between ordinary organic compounds and polymeric materials is due mainly to the large size and shape of polymer molecules. Common organic materials such as alcohol, ether, chloroform, sugar, and so on, consist of small molecules having molecular weights usually less than 1,000. The molecular weights of polymers, on the other hand, vary from 20,000 to hundreds of thousands. The name polymer is derived from the Greek poly for many and meros for parts. A polymer molecule consists of a repetition of the unit called a mer .
- Himadri B. Bohidar(Author)
- 2015(Publication Date)
- Cambridge University Press(Publisher)
Structure of Biopolymers Living matter is composed mainly of carbon, nitrogen, hydrogen, oxygen, sulphur and phosphorous. Carbon is the most abundant element of life and is found in the majority of compounds present in living organisms. Organic compounds such as nucleotides, amino acids and monosaccharides act as monomer units for the complex biomolecules—nucleic acids (DNA and RNA), proteins and polysaccharides, respectively. These eventually form large biopolymers which further organize and assemble as cell organelles, cells, tissues, organs and finally the whole organism. 13.1 Nucleic acids Primarily, nucleic acids serve as repositories and transmitters of genetic information. They are polymers of nucleotides held by 3 and 5 ′ ′ phosphate bridges. There are mainly two types of nucleic acids, namely deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is organized into genes which are the fundamental units of genetic information. These genes control protein synthesis. Components of nucleic acids include sugar, base and phosphate diester molecules. Sugars: RNA contains D-Ribose while DNA contains D-Deoxyribose. They differ in structure at C 2 where deoxyribose has one oxygen less than the ribose. This is shown in Fig. 13.1. 13 Structure of Biopolymers | 207 Figure 13.1 Representation of sugar molecule found in DNA and RNA. Bases: The nitrogenous bases of purine and pyrimidine derivatives are found in nucleotides. These are aromatic heterocyclic compounds. Purines are numbered in anti-clockwise direction and pyrimidines in the clockwise direction. DNA and RNA contain the same purines, i.e., adenine (A) and guanine (G). The pyrimidine cytosine (C) is found in both. However, with respect to the second pyrimidine base, DNA contains thymine (T) while RNA contains uracil (U). The molecular structure of these nitrogenous bases is illustrated in Fig.
eBook - PDFPhysical Chemistry of Macromolecules
Macro to Nanoscales
- Chin Han Chan, Chin Hua Chia, Sabu Thomas, Chin Han Chan, Chin Hua Chia, Sabu Thomas(Authors)
- 2014(Publication Date)
- Apple Academic Press(Publisher)
Part 1: Physical Chemistry of Macromolecules This page intentionally left blank This page intentionally left blank CHAPTER 1 INTRODUCTION HANS-WERNER KAMMER CONTENTS 1.1 Global Structure of Macromolecules ........................................................... 4 1.2 Chemical Structure of Macromolecules ...................................................... 5 Keywords .............................................................................................................. 8 References ............................................................................................................. 8 4 Physical Chemistry of Macromolecules: Macro to Nanoscales The high molecular mass compounds or polymers consist of large molecules hav-ing molecular masses in the order of 10 4 to 10 6 g/mol. The molecules of these compounds are formed by low-molecular units of identical chemical structure, called Monomers. Monomers are covalently linked to build up a polymer mol-ecule or a macromolecule, frequently like a chain. Therefore, macromolecules are also termed chain molecules. The combination of a large number of Monomers to a polymer molecule generates completely new properties, such as elasticity or the ability to form fibers or films. The large molecules also display flexibility. In the beginning of 20th Century, it was believed that molecular masses of many thousand dalton are impossible and macromolecules were seen as physi-cally bounded associates or colloids. Indeed for a stable macromolecule the bond-ing energy RT must exceed approximately 2.48 kJ/mol at room temperature. The measurements of vapor or osmotic pressure provide strong arguments for exis-tence of chemically bounded large molecules. If macromolecules would exist just as colloids or associates one could find conditions in increasingly diluted solutions where they decay into their constituents, that is one would find lower molecular masses.
eBook - PDF- Colin J Sanderson(Author)
- 2007(Publication Date)
- WSPC(Publisher)
Even simple organisms require a very large number of different molecules to make them work. They need to move, ingest, excrete, and respond to the environment and to other organisms. As organisms became more complex the diversity of molecules required for normal 3. How Biological Molecules Are Put Together 49 function increases, so that a lot of biology is about understanding how this enormous diversity of structure is built up from the basic elements: C arbon, O xygen, N itrogen, H ydrogen, P hosphorous and S ulphur. In each case the first letter is the chemical symbol. Note that the first four elements, which make up the bulk of biological tissue, are all present in the atmosphere. Now for some simple chemistry: carbon has the property of forming four bonds which allows the formation of carbon chains and each of the carbons in the chain is able to form two side reactions, normally taken up by hydrogen, but offering the possibility to add side chains to the mole-cule. Carbon chains are relatively stable and form the backbone of bio-logical molecules, which the early chemists referred to as organic mole-cules to distinguish them from the “non-living” inorganic molecules. Sometimes these carbon chains are interrupted by oxygen or a nitrogen molecule to provide different properties, and sometimes they form rings as in the sugar molecules. That’s enough chemistry: from now on we are mostly interested in the “groups” which add on to the carbon backbone and can leave aside the chemical bonding. Biological molecules are polymers or chains of basic units. Whereas DNA is made up of double stranded polymers of four bases , proteins are linear polymers of amino acids . Carbohydrates are polymers of sugar units, and lipids are made up of aggregates of fatty acids . In the diagrams the carbon backbone is not shown in detail as it is the groups at the ends and the side chains which are most interesting for understanding function.
eBook - PDFMethods in Molecular Biophysics
Structure, Dynamics, Function
- Igor N. Serdyuk, Nathan R. Zaccai, Joseph Zaccai(Authors)
- 2007(Publication Date)
- Cambridge University Press(Publisher)
Biological macromolecules, although they are made up of a concatenation of subunits, have evolved to fulfil specific functions and have specific properties that are very dif- ferent from those of classical polymers. All the molecules in a living organism either are proteins or can be considered as products of protein action. Proteins are made up of properly folded polypeptides of amino acid residues, and may include prosthetic groups with specific properties (such as the haem group, which binds oxygen). 62 A Biological macromolecules and physical tools Colour in proteins (e.g. the red in haemoglobin, or green in chlorophyll binding proteins) is always due to a prosthetic group, because amino acids absorb in the UV region. There are 20 main amino acids in natural proteins, with a variety of chemical characteristics: acid and base, polar and non-polar, aliphatic and aromatic. Primary structure is the subunit sequence in the macromolecule; secondary structures are favoured local chain conformations arising from chemical and steric constraints; tertiary structure is the three-dimensional conformation of the macromolecular chain (given by the coordinates of the constituent atoms); quaternary structure is the organi- sation of different or similar chains in a macromolecular complex. The secondary structures of proteins can be expressed on a Ramachandran plot in terms of angles of rotation of the peptide planes in the chain around the so-called alpha-carbons, to which the amino acid side-chains are bound. α-helices and β -sheets are the main secondary structures found in proteins. The tertiary structure results from weak (non-covalent, except for the disulphide bond between two cysteines) interactions between the amino acids in the polypeptide chain. Protein domains with distinct features have been identified in the solved tertiary struc- tures.
eBook - PDFLife's Origin
The Beginnings of Biological Evolution
- J. William Schopf(Author)
- 2002(Publication Date)
- University of California Press(Publisher)
chapter 4 From Building Blocks to the Polymers of Life james p. ferris the biopolymers in the first life Nucleic acids and proteins play a central role in life on Earth today. These polymeric biochemicals, composed, respectively, of nucleotides (figure 4.1 a) and amino acids (figure 4.2 a), provide the catalysis, the genetics, and some of the structure of all living systems. The genetic in-formation in the nucleic acid DNA (deoxyribonucleic acid) is transcribed to the nucleic acid RNA (ribonucleic acid; figure 4.1 b), and this infor-mation is then translated from RNA to protein. Most contemporary liv-ing systems need other polymers as well. Today, for example, the up-to-date organism uses polymers of sugar— carbohydrates —to store energy and build (plant) cell walls. It is unlikely that the first forms of life needed such polymers. But it is fairly certain that polymeric nu-cleotides and polymers of amino acids—or biochemicals similar to them—have been present in living systems since life’s emergence. How many different kinds of biopolymers were assembled in the first forms of life? It would be easier to agree on these necessary components if scientists could agree on what properties the first life forms had, or even on what “life” is (Luisi 1998 ). Three definitions illustrate the vary-ing views. Version 1 is a minimalist definition, according to which life is a self-sufficient system maintained by replication and subject to change by mutation. Thus, the simplest form of life is an assemblage of nucleic acids sustained by an external source of nutrients (to provide energy), its integrity preserved by the binding of biopolymers to a mineral surface. Version 2 , a more complex definition, posits a semipermeable barrier (a 113 114 James P. Ferris Figure 4.1. The structure of RNA .
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