Biochemical Concepts - AP Biology

Glycerol is composed of an alcohol attached to three carbons each bearing a hydroxyl group.

A glycosidic linkage is defined as a covalent bond created by a dehydration reaction between two monosaccharides. The resulting product is called a disaccharide.

A saturated fat contains no double bonds in its fatty acid chain. Just remember that saturated means the fat is saturated with hydrogens. Double bonds eliminate two hydrogen atoms per occurrence, and are present in unsaturated fats.

Energy is stored in the form of glucose. Cells, in turn, tap into glucose reserves to fuel cellular respiration. The carbon in glucose also serves as raw materials for the synthesis of other molecules such as amino acids.

When two monosaccharides connected together by a glycosidic linkage into a single unit, the product is called a disaccharide. Strings of monosaccharides linked together are called polysaccharides.

Starch is a storage polysaccharide in plants. It is a polymer consisting solely of glucose. Glucose is a source of fuel for cells; therefore, starch is stored for energy.

Starch is a storage polysaccharide in plants. It is a polymer consisting solely of glucose. Glucose is a source of fuel for cells; therefore, starch is stored for energy.

Glycogen is a polysaccharide used as energy storage in animals. Glycogen is a polymer made up of glucose units and undergoes hydrolysis to release glucose when demand for sugar increases.

The polysaccharide cellulose is a major component of plant cell walls. Similar to starch, cellulose is made up of glucose though the linkages in the polymers are different.

Carbon is phenomenally important to life as we understand it. The ability to form bonds with up to four different atoms gives carbon an incredible chemical diversity, and allows for carbon to make long chains and aromatic compounds. The ability to make long chains and aromatic compounds accounts for the formation of nucleic acids, proteins, and lipids (macromolecules that are absolutely essential to life). Binding properties of carbon also relate to the structure and orientation of biological compounds, which are important aspects of organic chemistry.

In its ground state carbon has four valence electrons, two its full s subshell and two in a partially filled p subshell. Normally, this would indicate that carbon forms two bonds, since only two of the electrons are in orbitals that are not already paired. Carbon, however, is able to form hybrid orbitals by combining the three p orbitals and one s orbital to form four identical sp3 orbitals, each containing one electron. This means that carbon can form four bonds, allowing it to achieve a stable octet.

For biology, the important note is that carbon can make four bonds. Organic chemistry is the study of carbon and how these bonds function to create organic and biological materials.

The chemical properties of an element are, in a large part, determined by the number of bonds that element can form with other elements. Silicon, like carbon, can form four bonds with other elements, and thus is the most similar. This can easily be seen on a periodic table as elements with similar properties are grouped together in the same column. Note that these similarities arise from having the same number of valence electrons.

Carbon has four valance electrons, allowing it to form a wide range of bonds with other atoms.

When carbon bonds to four separate substituents, it forms a tetrahedral structure. Because of its ability to hybridize orbitals, carbon can also bond to three substituents by forming a double bond, or to two substituents via two double bonds or the combination of a single bond and a triple bond. This variability in molecular bonding and shape allows carbon to exist in numerous compounds, exhibiting a number of different properties and functions.

Carbon is incapable of forming a quadruple bond, and it is not magnetic. Though carbon has a relatively low atomic mass, one would expect hydrogen to be the most relevant element if low mass was the most pertinent property of carbon. Carbon can form ionic bonds (generally with metals), but is most commonly found in organic molecules where it forms covalent bonds.

Hydrogen bonds are the intermolecular forces that allow it to engage in cohesion. Ionic bonds are strong bonds within a molecule between a cation and anion. Polar covalent bonds are bonds within a molecule in which there is a slight charge on the elements. Nonpolar covalent bonds are bonds within a molecule in which there is no charge on the elements.

Life is "carbon-based" or predominantly carbon because it can form stable bonds with itself, but also with a variety of other types of elements. Electronegativity increases from left to right on the periodic table, but also from bottom to top. While carbon is relatively high and right on the periodic chart, there are still elements like oxygen or fluorine (the most electronegative) that have a great pull for electrons. While carbon makes up a lot of the universe, it pales in comparison to hydrogen which is the most common element (three fourths of the mass of our universe). Therefore ratios do not matter. The polar and nonpolar nature of molecules are important for the functions of life (like membranes), but were it not for the bonding of carbon to itself, the nonpolar molecules would not be able to form. Thus, its bonding versatility is the main reason for life being carbon based.

Water is a polar molecule, and thus can adhere to different surfaces; thus, adhesion is the correct answer here. Cohesion is close, as cohesion describes the ability of water to stick to itself due to its polarity. We want the property that allows water to stick to other surfaces, not to itself. Polymerization involves chains of similar molecules, and does not occur in water. Parsimony is the principle that the simplest explanation is usually the reality of a situation (such as when tracing evolutionary histories). Gravity does not play into the properties of water.

The properties of water make it essential to life. Cohesion refers to its ability to form hydrogen bonds, attracting the molecules together and contributing to its high surface tension. Adhesion refers to water's attractive properties to other substances, and helps processes like absorption through the xylem. Solid ice is less dense than liquid water, allowing life to exist below the frozen surfaces of lakes and ponds. The polarity of water is essential for numerous biological processes and makes it a good solvent for most biological molecules. Finally, the high specific heat of water makes it resistant to temperature change, allowing life forms to maintain relatively constant internal temperatures.

The high specific heat and surface tension of water contribute to its high boiling point, helping to keep it in liquid form for most biological processes.

Nonpolar compounds will not be adequately dissolved in aqueous solutions. Lipids are nonpolar compounds that are mainly insoluble in water. This causes lipids to congregate together, rather than be broken apart in aqueous solutions. Lipids will generally come together to form globs or balls called micelles.

Ions, amino acids, and sugars (carbohydrates) are all polar, and will be adequately dissolved and ionized by water.

These properties of water are all a result of hydrogen bonding. Hydrogen bonds result from the electrical attraction between partially positive hydrogen atoms and partially negative oxygen atoms of adjacent water molecules. The differences in electronegativity between hydrogen and oxygen give rise to the hydrogen bonding and associated properties.

Attraction and polarity in water molecules cause them to "stick" to one another. Attraction between water molecules results in cohesion, and attraction between the water molecules and other compounds in the environment results in adhesion. The high surface tension of water is caused by the "sticking" of water molecules to one another, which keep vapor pressure low.

Hydrogen bonding is a temporary intermolecular force, and is different from covalent or ionic bonding. Covalent and ionic bonding result in permanently joined atoms to build molecular structures.