Biochemical Concepts - AP Biology

A fat is a lipid with three fatty chains linked by an ester linkage to glycerol.

A fatty acid consists of a hydrocarbon chain (carbons bound to hydrogen), with even numbers of carbons from 4 to 28, and a carboxyl group at one end. A triglyceride consists of three fatty acids with their carboxyl end bound to glycerol via an ester bond.

A phospholipid has two fatty acid tails, which consist of hydrocarbons with even numbers of carbons ranging from 4 to 28, and a phosphate group attached to a glycerol head, which is hydrophilic. Monoglycerides contain only one fatty acid chain bound to a glycerol head, and triglycerides contain three fatty acid chains.

Monosaccharides such as fructose are carbohydrates not lipids. Waxes, steroid hormones such as testosterone, estrogen and progesterone, and triglycerides (fats) are composed mainly of hydrocarbons and are classified as lipids.

Glycogen is a carbohydrate. It is a polysaccharide that animals use to store glucose when sugars are needed by the body for fuel. All other answer choices are lipids.

Chitin is a carbohydrate. Specifically, it is a polysaccharide used by arthopods to build exoskeletons, and is found in the cell walls of fungi. Waxes are types of lipids, and nucleic acids are DNA and RNA.

The formation of disulfide bridge occurs in the tertiary and/or quaternary level of protein structure. This involves two sulfur atoms sharing a lone pair of electrons to form a covalent bond, which enhances the integrity of the protein's structure. The amino acid that is involved in forming disulfide bridges is cysteine.

Monosaccharides are the smallest unit of carbohydrates. A disaccharide is made up of two monosaccharides joined together. A string of monosaccharides linked together is a polysaccharide.

Chitin is a structural polysaccharide used by arthropods to build their exoskeletons. Chitin is also found in fungi as well. Cellulose is the structural component found in the cell walls of plants.

Arthropods use the polysaccharide chitin to build their exoskeletons. Certain types of fungi also use chitin instead of cellulose for building their cell walls.

Chitin is a type of polysaccharide that is present in the exoskeletons of arthropods, and is the primary substance of the cell wall of fungi. In general, polysaccharides are chains of simple sugars. Another example of a polysaccharide is starch. Waxes are types of lipids. Hemoglobin is a protein, which is made of amino acids. DNA is a nucleic acid, which is a polymer of nucleotides.

The correct answer is covalent bonds because they are the strongest of all bonds present in a water sample. Although hydrogen bonding is present in water it is not the strongest bond in a sample of water. The bonds that make up the water molecule themselves are strongest. Ionic bonds do not exist in water.

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.

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.

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.