Learning Objectives

By the finish of this section, you will be able to do the following:

Explain why carbon is important for lifeDescribe the function of functional teams in biological molecules

Many complicated molecules dubbed macromolecules, such together proteins, main point acids (RNA and also DNA), carbohydrates, and lipids consist of cells. The macromolecules room a subset of organic molecules (any carbon-containing liquid, solid, or gas) the are particularly important because that life. The an essential component for all of these macromolecules is carbon. The carbon atom has distinctive properties that enable it to type covalent bonds come as numerous as four various atoms, make this versatile facet ideal to serve as the basic structural component, or “backbone,” that the macromolecules.

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Individual carbon atoms have an incomplete outermost electron shell. With an atomic variety of 6 (six electrons and six protons), the an initial two electrons to fill the inner shell, leaving 4 in the second shell. Therefore, carbon atom can form up to 4 covalent bond with various other atoms to fulfill the octet rule. The methane molecule offers an example: it has actually the chemical formula CH4. Each of its four hydrogen atoms develops a solitary covalent bond through the carbon atom by sharing a pair of electrons. This outcomes in a filled outermost shell.


Hydrocarbons

Hydrocarbons room organic molecule consisting entirely of carbon and hydrogen, such together methane (CH4) defined above. We frequently use hydrocarbons in our day-to-day lives as fuels—like the propane in a gas grill or the butane in a lighter. The numerous covalent bonds in between the atoms in hydrocarbons save a good amount of energy, which releases as soon as these molecule burn (oxidize). Methane, great fuel, is the simplest hydrocarbon molecule, through a main carbon atom external inspection to four different hydrogen atoms, together (Figure) illustrates. The shape of that is electron orbitals identify the form of the methane molecule’s geometry, where the atom reside in 3 dimensions. The carbons and also the four hydrogen atoms kind a tetrahedron, with four triangular faces. Because that this reason, we define methane as having actually tetrahedral geometry.


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Hydrocarbon Rings

So far, the hydrocarbons we have debated have to be aliphatic hydrocarbons, i beg your pardon consist of linear chains of carbon atoms. Another type of hydrocarbon, aromatic hydrocarbons, is composed of closed ring of carbon atoms. We discover ring frameworks in hydrocarbons, periodically with the visibility of dual bonds, i m sorry we can see by to compare cyclohexane’s structure to benzene in (Figure). Examples of biological molecules that incorporate the benzene ring incorporate some amino acids and also cholesterol and its derivatives, consisting of the hormones estrogen and also testosterone. We additionally find the benzene ring in the herbicide 2,4-D. Benzene is a organic component of crude oil and has been classified as a carcinogen. Some hydrocarbons have both aliphatic and also aromatic portions. Beta-carotene is an instance of such a hydrocarbon.


Carbon can type five- and also six-membered rings. Single or twin bonds may affix the carbons in the ring, and nitrogen may be substituted because that carbon.

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Which the the following statements is false?

Molecules through the formulas CH3CH2COOH and also C3H6O2 might be structure isomers.Molecules must have actually a twin bond to it is in cistrans isomers.To it is in enantiomers, a molecule must have at least three various atoms or groups associated to a main carbon.To it is in enantiomers, a molecule must have at least four different atoms or groups linked to a main carbon.

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In triglythrade (fats and also oils), long carbon chains well-known as fat acids might contain dual bonds, which can be in one of two people the cis or trans configuration, together (Figure) illustrates. Fats with at the very least one double bond in between carbon atoms room unsaturated fats. When some of this bonds room in the cis configuration, the resulting bend in the chain’s carbon backbone means that triglyceride molecules cannot fill tightly, so they continue to be liquid (oil) in ~ room temperature. Alternatively, triglycerides v trans double bonds (popularly dubbed trans fats), have relatively linear fatty acids that space able to load tightly together at room temperature and form solid fats. In the human diet, trans fats are linked to an enhanced risk that cardiovascular disease, so many food manufacturers have diminished or got rid of their use in recent years. In comparison to unsaturated fats, we call triglycerides without double bonds in between carbon atom saturated fats, meaning that castle contain every the hydrogen atom available. Saturated fats room a solid at room temperature and also usually of animal origin.


These space-filling models display a cis (oleic acid) and a trans (eliadic acid) fatty acid. An alert the bending in the molecule caused by the cis configuration.

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Enantiomers

Enantiomers are molecules the share the same chemical structure and chemical bonds however differ in the three-dimensional placement of atoms so that they room non-superimposable winter images. (Figure) reflects an amino mountain alanine example, wherein the 2 structures room nonsuperimposable. In nature, just the L-forms the amino acids do proteins. Part D creates of amino acids are seen in the cell wall surfaces of bacteria, but never in your proteins. Similarly, the D-form of glucose is the key product the photosynthesis and we rarely see the molecule’s L-form in nature.


D-alanine and also L-alanine are instances of enantiomers or mirror images. Only the L-forms the amino acids are used to do proteins.

Functional Groups

Functional groups are teams of atoms that take place within molecules and confer details chemical nature to those molecules. We uncover them along the “carbon backbone” the macromolecules. Chains and/or rings of carbon atoms with the occasional substitution of an aspect such together nitrogen or oxygen form this carbon backbone. Molecules v other aspects in their carbon backbone room substituted hydrocarbons.

The functional teams in a macromolecule room usually attached to the carbon backbone in ~ one or several different places along its chain and/or ring structure. Each of the four varieties of macromolecules—proteins, lipids, carbohydrates, and nucleic acids—has its own characteristic collection of functional teams that contributes significantly to that is differing chemistry properties and also its role in living organisms.

A functional group can get involved in specific chemical reactions. (Figure) mirrors some of the essential functional groups in organic molecules. They include: hydroxyl, methyl, carbonyl, carboxyl, amino, phosphate, and also sulfhydryl. These teams play an essential role in developing molecules choose DNA, proteins, carbohydrates, and lipids. We normally classify functional groups as hydrophobic or hydrophilic depending upon their fee or polarity characteristics. An example of a hydrophobic team is the nonpolar methyl molecule. Among the hydrophilic functional groups is the carboxyl group in amino acids, some amino mountain side chains, and also the fat acids that kind triglycerides and phospholipids. This carboxyl team ionizes to relax hydrogen ions (H+) indigenous the COOH group resulting in the negatively fee COO– group. This contributes to the hydrophilic nature of everything molecule top top which it is found. Various other functional groups, such together the carbonyl group, have a partly negatively fee oxygen atom the may type hydrogen bonds through water molecules, again make the molecule much more hydrophilic.


These functional groups are in plenty of different organic molecules. R, also known as R-group, is an abbreviation for any group in i m sorry a carbon or hydrogen atom is attached come the remainder of the molecule.

Hydrogen bonds in between functional teams (within the same molecule or in between different molecules) are essential to the role of many macromolecules and aid them come fold appropriately into and maintain the ideal shape because that functioning. Hydrogen binding are also involved in assorted recognition processes, such as DNA complementary base pairing and also the binding of one enzyme to its substrate, as (Figure) illustrates.


Section Summary

The unique properties the carbon do it a central part of organic molecules. Carbon binds to oxygen, hydrogen, and nitrogen covalently to kind the plenty of molecules crucial for cellular function. Carbon has four electrons in its outermost shell and also can kind four bonds. Carbon and hydrogen can kind hydrocarbon chain or rings. Functional teams are groups of atoms that confer particular properties come hydrocarbon (or substituted hydrocarbon) chain or rings that specify their as whole chemical characteristics and also function.

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(Figure) i beg your pardon of the complying with statements is false?

Molecules with the recipe CH3CH2COOH and also C3H6O2 might be structure isomers.Molecules must have a dual bond to it is in cistrans isomers.To it is in enantiomers, a molecule must have actually at least three different atoms or groups connected to a central carbon.To be enantiomers, a molecule must have at the very least four various atoms or groups linked to a main carbon.