Chapter 2 Lecture

small atoms with 6 or 6 valence electrons tend to be electronegative small atoms with 6 or 7 valence shell electrons, such as oxygen, nitrogen, and chlorine, are electron-hungry. They attract electrons very strongly, a capability called electronegativity.

The reactivity of an atom is based on the number of electrons in its outer valance shell.

False

one potassium atom and one fluorine atom Ionic bonds are commonly formed between atoms with 1 or 2 valence shell electrons (such as potassium) and atoms with 7 valence shell electrons (such as fluorine).

They all have an incomplete valence electron shell.

two double bonds The formation of a double bond (the sharing of two electron pairs) between each oxygen and the carbon would result in each of the three atoms achieving a full valence shell.

four Carbon has four electrons in its valence (outermost) electron shell. Therefore, it will form covalent bonds with four hydrogen atoms. The four electrons contributed by the hydrogen atoms will fill the valence shell of carbon.

Oxygen Oxygen and sulfur both have six electrons in their valence (outermost) electron shells. Therefore, they will form similar types and numbers of bonds with other atoms.

an electirical attraction between opposite charges

Oxygen atoms have a stronger pull on the electrons shared within a covalent bond formed between oxygen and hydrogen.

hydrogen bond The attraction between the slightly negative oxygen atom of one molecule and the slightly positively charged hydrogen atom within a separate water molecule is the basis of hydrogen bond formation. It is a form of dipole-dipole interaction.

No, because the difference in the pull of oxygen on the bonding electrons would be neutralized.

MgO2 → Mg + O2

hyperbolic

The products of exergonic reactions contain more potential energy than the reactants that form them Reactions that release energy are exergonic reactions. These reactions yield products with less energy than the initial reactants, along with energy that can be harvested for other uses.

dehydration synthesis; hydrolysis Dehydration synthesis refers to the joining of molecules by the removal of water. Monosaccharides are joined to form polysaccharides, and amino acids are joined to form proteins by this process. Hydrolysis refers to the breakdown of these larger molecules (polysaccharides and proteins) into smaller molecules (monosaccharides and amino acids) by the addition of water at the bonds that join them. In this process, the larger molecule (or polymer) is degraded to produce smaller molecules (or monomers). Think of monomers as the "building blocks" of polymers.

alkaline solution A pH between 0.0 and 7.0 is acidic. A pH between 7.0 and 14.0 is basic. Therefore, a solution with a pH of 8.3 is an alkaline (or basic) solution. NaOH is an example of a basic compound.

True

is based on the concentration of hydrogen ions in a solution

False Buffers resist abrupt and large swings in the pH of body fluids by releasing hydrogen ions (acting as acids) when the pH begins to rise and by binding hydrogen ions (acting as bases) when the pH drops. Buffers can do this because they consist of a combination of a weak acid and a corresponding weak base. Weak acids and bases dissociate (ionize) partially and reversibly, whereas strong acids and bases dissociate completely and irreversibly.

can form hydrogen bonds Because of its polar nature, water is able to form hydrogen bonds. In fact, many of the special properties of water derive from its extensive hydrogen bonding capacity. In addition, water has a high heat capacity and is considered a universal solvent since it dissolves more substances than any other known solvent.

The swimmer's body contains a higher concentration of electrolytes (salts) compared to the freshwater lake The body of water with the higher concentration of electrolytes, in this case the human body, is the better conductor of electrical currents. In a freshwater lake, there are comparatively few electrolytes (salts) to carry a current away from a swimmer's body.

impaired nerve impulse transmission Salts are ionic compounds that contribute to the ability of nerves to conduct an electrical current.

The polarity of water easily breaks the charges between the oppositely charged ions in the compound.

table sugar, or sucrose (C12H22O11) Sucrose is a molecule that dissolves in water but does not release ions, which are required for a solution to conduct electricity.

a hydrogen atom within a water molecule The negatively charged chloride anion has dissociated from the salt crystal and formed an interaction with the slightly positively charged hydrogen atoms of several water molecules.

a solution Once dissociated, the sodium and chloride ions would be expected to disperse uniformly amongst the surrounding water molecules. This homogenous mixture is called a solution.

The chemical composition of carbohydrates includes two oxygens and one hydrogen for every carbon present. The correct ratio is two hydrogens and one oxygen for every carbon.

Triglycerides are composed of three fatty acids and one glycerol and are stable because they do not dissolve in water. This is true. The long-term stability of triglycerides makes them important energy storage molecules.

water The reaction is called a dehydration synthesis, in which the H from the glycerol's alcohol group and the OH from the fatty acid's acid group are removed as water. The valence electrons are then made up by the forming of an ester bond.

True

energy storage The hydrocarbon groups that dominate the structure of triglycerides are the basis for the efficient and compact energy storage by fat.

proteins Proteins form the major structural materials of the body. Because fibrous proteins are the chief building materials of the body, they are also known as structural proteins. However, not all proteins are construction materials. Many play vital roles in cell function.

The substrate absorbs chemical energy from the enzyme after binding to its active site. Enzymes do not provide energy to their substrates. In fact, enzymes are completely unchanged by their catalytic role and can act again and again.

Secondary protein structures involve hydrogen bonding between amine and carboxyl groups. Hydrogen bonding between certain amine and carboxyl groups creates alpha helices and beta-pleated sheets.

amino acid An amino acid contains an amine group and an organic acid group, but does not contain a peptide bond. Peptides bonds are used to join amino acids (monomers) together, forming larger molecules (polymers) ranging in size from small polypeptides to large proteins.

an amine group and an acid group

an R group The identity of each unique amino acid is determined by the structure of its R group—note differences within the green rectangular area in amino acids (b) through (d).

bonding of amine group to acid group Peptide bonds form from dehydration synthesis reactions between an amine group and an organic acid group.

substrates The substrate is a reactant in an enzyme-catalyzed reaction.

protein Structure B is an enzyme, which is typically primarily composed of protein.

a peptide bond Amino acids are linked by peptide bonds to form peptides.

synthase This figure shows a dehydration synthesis reaction between two monomers forming, resulting in a larger molecule. Such reactions are synthesis reactions.

Less enegy input is required to start the reaction in the presence of enzyme

Both reactions are exergonic Both of the illustrated reactions are exergonic and release the same amount of energy during product formation. The difference is the amount of energy input (activation energy) required to initiate the reactions depending on the presence or absence of enzyme.

the kinetic energy of the reactants Kinetic energy pushes the reactants to an energy level that encourages their interaction and the rearrangement of their chemical bonds. This is why chemical reactions (with or without enzyme) occur faster at higher temperatures.

True DNA provides the basic instructions for building every protein in the body. RNA carries out the orders for protein synthesis issued by DNA.

ATP When broken (hydrolyzed), the high-energy phosphate bonds in the ATP molecule release the energy used to do cellular work.

True ATP is the primary energy-transferring molecule in cells, and it provides a form of energy that is immediately usable by all body cells. Chemically, the triphosphate tail of ATP can be compared to a tightly coiled spring ready to uncoil with tremendous energy when the catch is released. Actually, ATP is a very unstable high-energy molecule because its three negatively charged phosphate groups are closely packed and repel each other.

Energy "lost" during an energy conversion refers to the energy that cannot be used to do work Energy may be converted from one form to another, but some energy is always unusable ("lost" as heat) in such transformations. It is not really "lost" because energy cannot be created or destroyed, but that portion given off as heat is at least partly unusable.