R might symbolize just a single hydrogen atom or it may represent a group of many atoms. Notice that some functional groups are relatively simple, consisting of just one or two atoms, while some comprise two of these simpler functional groups. It is present in several classes of organic compounds as part of larger functional groups such as ketones, aldehydes, carboxylic acids, and amides.
In ketones, the carbonyl is present as an internal group, whereas in aldehydes it is a terminal group. Hydrogen bonds between functional groups within the same molecule or between different molecules are important to the function of many macromolecules and help them to fold properly into and maintain the appropriate shape for functioning. Most macromolecules are made from single subunits, or building blocks, called monomers. The monomers combine with each other using covalent bonds to form larger molecules known as polymers.
In doing so, monomers release water molecules as byproducts. At the same time, the monomers share electrons and form covalent bonds. As additional monomers join, this chain of repeating monomers forms a polymer. Different types of monomers can combine in many configurations, giving rise to a diverse group of macromolecules. Even one kind of monomer can combine in a variety of ways to form several different polymers: for example, glucose monomers are the constituents of starch, glycogen, and cellulose.
These reactions are similar for most macromolecules, but each monomer and polymer reaction is specific for its class. For example, in our bodies, food is hydrolyzed, or broken down, into smaller molecules by catalytic enzymes in the digestive system.
This allows for easy absorption of nutrients by cells in the intestine. Each macromolecule is broken down by a specific enzyme. For instance, carbohydrates are broken down by amylase, sucrase, lactase, or maltase. Proteins are broken down by the enzymes pepsin and peptidase, and by hydrochloric acid. Lipids are broken down by lipases. Breakdown of these macromolecules provides energy for cellular activities. Visit this site to see visual representations of dehydration synthesis and hydrolysis.
Learning Objectives Explain why carbon is important for life Identify common elements and structures found in organic molecules Explain the concept of isomerism Understand the synthesis of macromolecules Explain the importance and use of functional groups Explain dehydration or condensation and hydrolysis reactions.
Hydrocarbons Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen, such as methane CH 4 described above. Hydrocarbon Chains Hydrocarbon chains are formed by successive bonds between carbon atoms and may be branched or unbranched. When two carbon atoms form a double bond, the shape is planar, or flat. Single bonds, like those found in ethane, are able to rotate. Double bonds, like those found in ethene cannot rotate, so the atoms on either side are locked in place.
Hydrocarbon Rings So far, the hydrocarbons we have discussed have been aliphatic hydrocarbons , which consist of linear chains of carbon atoms. Single or double bonds may connect the carbons in the ring, and nitrogen may be substituted for carbon. Describe the most abundant elements in nature.
What are the differences between organic and inorganic molecules? Organic Molecules Organic molecules in organisms are generally larger and more complex than inorganic molecules. The simplest organic molecule is methane CH 4 , depicted here. Why are Carbon atoms the most versatile molecular building blocks used by living organisms? Chemistry Matter Elements. Oct 10, Explanation: It is quite that remarkable that carbon should offer such a rich and diverse chemistry, and you are right to ask why.
Related questions What periodic table elements are radioactive? We often use hydrocarbons in our daily lives as fuels—like the propane in a gas grill or the butane in a lighter. The many covalent bonds between the atoms in hydrocarbons store a great amount of energy, which releases when these molecules burn oxidize.
Methane, an excellent fuel, is the simplest hydrocarbon molecule, with a central carbon atom bonded to four different hydrogen atoms, as Figure illustrates. The carbons and the four hydrogen atoms form a tetrahedron, with four triangular faces. For this reason, we describe methane as having tetrahedral geometry.
As the backbone of the large molecules of living things, hydrocarbons may exist as linear carbon chains, carbon rings, or combinations of both. This three-dimensional shape or conformation of the large molecules of life macromolecules is critical to how they function.
Successive bonds between carbon atoms form hydrocarbon chains. These may be branched or unbranched. Thus, propane, propene, and propyne follow the same pattern with three carbon molecules, butane, butene, and butyne for four carbon molecules, and so on. These geometries have a significant impact on the shape a particular molecule can assume. So far, the hydrocarbons we have discussed have been aliphatic hydrocarbons , which consist of linear chains of carbon atoms.
Another type of hydrocarbon, aromatic hydrocarbons , consists of closed rings of carbon atoms. Examples of biological molecules that incorporate the benzene ring include some amino acids and cholesterol and its derivatives, including the hormones estrogen and testosterone. We also find the benzene ring in the herbicide 2,4-D. Benzene is a natural component of crude oil and has been classified as a carcinogen. Some hydrocarbons have both aliphatic and aromatic portions.
Beta-carotene is an example of such a hydrocarbon. The three-dimensional placement of atoms and chemical bonds within organic molecules is central to understanding their chemistry. Structural isomers like butane and isobutene in Figure a differ in the placement of their covalent bonds: both molecules have four carbons and ten hydrogens C 4 H 10 , but the different atom arrangement within the molecules leads to differences in their chemical properties.
For example, butane is suited for use as a fuel for cigarette lighters and torches; whereas, isobutene is suited for use as a refrigerant and a propellant in spray cans. Geometric isomers , alternatively have similar placements of their covalent bonds but differ in how these bonds are made to the surrounding atoms, especially in carbon-to-carbon double bonds.
In the simple molecule butene C 4 H 8 , the two methyl groups CH 3 can be on either side of the double covalent bond central to the molecule, as Figure b illustrates. When the carbons are bound on the same side of the double bond, this is the cis configuration.
If they are on opposite sides of the double bond, it is a trans configuration. In the trans configuration, the carbons form a more or less linear structure; whereas, the carbons in the cis configuration make a bend change in direction of the carbon backbone. Molecules consisting of large strings of atoms of carbon and other elements are the result. These strings can grow linearly, or they can close in and form rings or hexagonal structures that can also combine with other structures to form even larger molecules.
The possibilities are almost limitless. To date, chemists have catalogued almost 10 million different carbon compounds. The most important for life include carbohydrates, which are formed entirely with carbon, hydrogen, lipids, proteins and nucleic acids, of which the best-known example is DNA.
Silicon is the element just under carbon in the periodic table, and it's about times more abundant on Earth. Like carbon, it has only four electrons in its outer shell, so why aren't the macromolecules that form living organisms silicon-based?
The main reason is that carbon forms stronger bonds than silicon at temperatures conducive to life, especially with itself. The four non-paired electrons in silicon's outer shell are in its third orbital, which can potentially accommodate 18 electrons. Carbon's four unpaired electrons, on the other hand, are in its second orbital, which can accommodate only 8, and when the orbital is filled, the molecular combination becomes very stable.
Because the carbon-carbon bond is stronger than the silicon-silicon bond, carbon compounds stay together in water while silicon compounds break apart.
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