Biochemical Concepts - AP Biology

All amino acids have an amino group and a carboxyl group. Amino acids do not have glycerol. The side chain called an R-group is what differentiates amino acids from each other in their chemical properties and functions.

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.

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.

Lipids are a large class of hydrocarbon-based molecules that includes waxes, steroids, phospholipids and fats. Lipids are hydrophobic and have functions in energy storage, providing support to the cell/organism, cell signaling, and make up the majority of the cell membrane.

In osmosis, water diffuses through selectively permeable membranes to regions where the concentration of solute is higher (hypertonic). Osmosis is not the movement of the solute particles.

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.

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.

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.

There are three forms of heat transfer: radiation, convection, and conduction. Radiation is the transfer of heat via electromagnetic waves, such as sunlight of microwaves. Convection is the transfer of heat through a fluid medium, such as water or air currents. Conduction is the direct transfer of heat between environments through physical contact. Since your hand is in physical contact with the glass, heat is transferred by conduction.

Heat is always transferred from a body of higher temperature to a body of lower temperature. Since your hand is warmer than the glass, heat is transferred from the hand to the glass. It can be easier to think of heat transfer in terms of concentration. Like molecules, heat energy will travel from a region of high concentration (hotter) to a region of low concentration (colder) in order to reach equilibrium.