Macromolecule
A macromolecule is a very large
Definition
The term macromolecule (
Usage of the term to describe large molecules varies among the disciplines. For example, while biology refers to macromolecules as the four large molecules comprising living things, in chemistry, the term may refer to aggregates of two or more molecules held together by intermolecular forces rather than covalent bonds but which do not readily dissociate.[6]
According to the standard
Because of their size, macromolecules are not conveniently described in terms of
Properties
This section needs additional citations for verification. (May 2013) |
Macromolecules often have unusual physical properties that do not occur for smaller molecules.[how?]
Another common macromolecular property that does not characterize smaller molecules is their relative insolubility in water and similar
High concentrations of macromolecules in a solution can alter the
Linear biopolymers
All
DNA, RNA, and proteins all consist of a repeating structure of related building blocks (
In most cases, the monomers within the chain have a strong propensity to interact with other amino acids or nucleotides. In DNA and RNA, this can take the form of Watson–Crick base pairs (G–C and A–T or A–U), although many more complicated interactions can and do occur.
Structural features
DNA | RNA | Proteins | |
---|---|---|---|
Encodes genetic information | Yes | Yes | No |
Catalyzes biological reactions | No | Yes | Yes |
Building blocks (type) | Nucleotides | Nucleotides | Amino acids |
Building blocks (number) | 4 | 4 | 20 |
Strandedness | Double | Single | Single |
Structure | Double helix | Complex | Complex |
Stability to degradation | High | Variable | Variable |
Repair systems | Yes | No | No |
Because of the double-stranded nature of DNA, essentially all of the nucleotides take the form of Watson–Crick base pairs between nucleotides on the two complementary strands of the double helix.
In contrast, both RNA and proteins are normally single-stranded. Therefore, they are not constrained by the regular geometry of the DNA double helix, and so fold into complex three-dimensional shapes dependent on their sequence. These different shapes are responsible for many of the common properties of RNA and proteins, including the formation of specific binding pockets, and the ability to catalyse biochemical reactions.
DNA is optimised for encoding information
DNA is an information storage macromolecule that encodes the complete set of instructions (the genome) that are required to assemble, maintain, and reproduce every living organism.[11]
DNA and RNA are both capable of encoding genetic information, because there are biochemical mechanisms which read the information coded within a DNA or RNA sequence and use it to generate a specified protein. On the other hand, the sequence information of a protein molecule is not used by cells to functionally encode genetic information.[1]: 5
DNA has three primary attributes that allow it to be far better than RNA at encoding genetic information. First, it is normally double-stranded, so that there are a minimum of two copies of the information encoding each gene in every cell. Second, DNA has a much greater stability against breakdown than does RNA, an attribute primarily associated with the absence of the 2'-hydroxyl group within every nucleotide of DNA. Third, highly sophisticated DNA surveillance and repair systems are present which monitor damage to the DNA and repair the sequence when necessary. Analogous systems have not evolved for repairing damaged RNA molecules. Consequently, chromosomes can contain many billions of atoms, arranged in a specific chemical structure.
Proteins are optimised for catalysis
Proteins are functional macromolecules responsible for catalysing the biochemical reactions that sustain life.[1]: 3 Proteins carry out all functions of an organism, for example photosynthesis, neural function, vision, and movement.[12]
The single-stranded nature of protein molecules, together with their composition of 20 or more different amino acid building blocks, allows them to fold in to a vast number of different three-dimensional shapes, while providing binding pockets through which they can specifically interact with all manner of molecules. In addition, the chemical diversity of the different amino acids, together with different chemical environments afforded by local 3D structure, enables many proteins to act as
RNA is multifunctional
RNA encodes genetic information that can be translated into the amino acid sequence of proteins, as evidenced by the messenger RNA molecules present within every cell, and the RNA genomes of a large number of viruses. The single-stranded nature of RNA, together with tendency for rapid breakdown and a lack of repair systems means that RNA is not so well suited for the long-term storage of genetic information as is DNA.
In addition, RNA is a single-stranded polymer that can, like proteins, fold into a very large number of three-dimensional structures. Some of these structures provide binding sites for other molecules and chemically active centers that can catalyze specific chemical reactions on those bound molecules. The limited number of different building blocks of RNA (4 nucleotides vs >20 amino acids in proteins), together with their lack of chemical diversity, results in catalytic RNA (
The Major Macromolecules:
Macromolecule
(Polymer) |
Building Block
(Monomer) |
Bonds that Join them |
---|---|---|
Proteins | Amino acids | Peptide |
Nucleic acids | Phosphodiester | |
DNA | Nucleotides (a phosphate, ribose, and a base- adenine, guanine, thymine, or cytosine) | |
RNA | Nucleotides (a phosphate, ribose, and a base- adenine, guanine, uracil, or cytosine) | |
Polysaccharides | Monosaccharides | Glycosidic |
Lipids | unlike the other macromolecules, lipids are not defined by chemical Structure. Lipids are any organic nonpolar molecule. | Some lipids are held together by ester bonds; some are huge aggregates of small molecules held together by hydrophobic interactions. |
Carbohydrates | carbon, hydrogen, and oxygen | |
Major protein Complexes? |
Branched biopolymers
Synthetic macromolecules
See also
References
- ^ ISBN 978-0-7167-4955-4.
- ^ Life cycle of a plastic product Archived 2010-03-17 at the Wayback Machine. Americanchemistry.com. Retrieved on 2011-07-01.
- ^ Gullapalli, S.; Wong, M.S. (2011). "Nanotechnology: A Guide to Nano-Objects" (PDF). Chemical Engineering Progress. 107 (5): 28–32. Archived from the original (PDF) on 2012-08-13. Retrieved 2015-06-28.
- .
- .
- ISBN 0-13-720459-0
- S2CID 98774337. Archived from the original(PDF) on 2007-02-23.
- PMID 16825427.
- ISBN 978-1-4292-2936-4. Fifth edition available online through the NCBI Bookshelf: link
- ISBN 978-0-8153-4111-6.. Fourth edition is available online through the NCBI Bookshelf: link
- ISBN 978-0-06-273099-2.
- ISBN 978-1-59327-202-9.
- PMID 12203280.
External links
- Synopsis of Chapter 5, Campbell & Reece, 2002
- Lecture notes on the structure and function of macromolecules
- Several (free) introductory macromolecule related internet-based courses Archived 2011-07-18 at the Wayback Machine
- Giant Molecules! by Ulysses Magee, ISSA Review Winter 2002–2003, ISSN 1540-9864. Cached HTML version of a missing PDF file. Retrieved March 10, 2010. The article is based on the book, Inventing Polymer Science: Staudinger, Carothers, and the Emergence of Macromolecular Chemistry by Yasu Furukawa.