Molecular and Cellular Biology - Exam 1 Test Bank 3

* Figure Q3-28 is an energy diagram for the reaction X-->Y. Which equation below provides the correct calculation for the amount of free-energy change when X is converted to Y

(d) c - a

The energy used by the cell to generate specific biological molecules and highly ordered structures is stored in the form of

(d) chemical bonds

A chemical reaction is defined as spontaneous if there is a net loss of free energy during the reaction process. However, spontaneous reactions do not always occur rapidly. Favorable biological reactions require _____ to selectively speed up reactions and meet the demands of the cell

(d) enzymes

ΔG° indicates the change in the standard free energy as a reactant is converted to product. Given what you know about these values, which reaction below is most favorable

(d) glucose --> CO2 + H2O ΔG° = -686 kcal/mole

ΔG measures the change of free energy in a system as it converts reactant (Y) into product (X). When [Y] = [X], ΔG is equal to

(d) ΔG°

Arrange the following molecules in order with respect to their relative levels of oxidation (assign 5 to the most oxidized and 1 to the most reduced) _____ CH2O Formaldehyde _____ CH4 Methane _____ CHOOH Formic acid _____ CH3OH Methanol _____ CO2 Carbon Dioxide

3 - CH2O Formaldehyde 1 - CH4 Methane 4 - CHOOH Formic acid 2 - CH3OH Methanol 5 - CO2 Carbon Dioxide

Which of the following statements are true or false? If a statement is false, explain why. (A) Enzymes lower the free energy released by the reaction that they facilitate (B) Enzymes lower the activation energy for a specific reaction (C) Enzymes increase the probability that any given reactant molecule will be converted to product (D) Enzymes increase the average energy of reactant molecules

(A) FALSE - Enzymes do not affect the initial energy of the reactants nor the final energy of the products after the reaction is complete, which are the values that determines the change in free energy of a reaction (B) TRUE (C) TRUE (D) FALSE - By lowering the energy of activation, enzymes increase the number of molecules in a population that can overcome the activation barrier

During respiration, energy is retrieved from the high-energy bonds found in certain organic molecules. Which of the following, in addition to energy, are the ultimate products of respiration

(a) CO2, H2O

Oxidation is a favorable process in an aerobic environment, which is the reason cells are able to derive energy from the oxidation of macromolecules. Once carbon has been oxidized to _____, its most stable form, it can only cycle back into the organic portion of the carbon cycle through _____

(a) CO2, photosynthesis

In the first stage of photosynthesis, light energy is converted into what other form of energy?

(a) electrical or (d) kinetic

Oxidation is the process by which oxygen atoms are added to a target molecule. Generally, the atom that is oxidized will experience which of the following with respect to the electrons in its outer shell?

(b) a net loss

Chemical reactions carried out by living systems depend on the ability of some organisms to capture and use atoms from nonliving sources in the environment. The specific subset of these reactions that break down nutrients in food can be described as

(b) catabolic

* Enzymes facilitate reactions in living systems. Figure Q3-29 presents an energy diagram for the reaction X-->Y where the solid line represents changes in energy as the reactant is converted to product under standard conditions, and the dashed line shows changes observed when the same reaction takes place in the presence of a dedicated enzyme. Which equation below indicates how the presence of an enzyme affects the activation energy of the reaction (catalyzed verses uncatalyzed)

(b) d - a VERSES b - a

The second law of thermodynamics states that the disorder in any system is always increasing. In simple terms, you can think about dropping NaCl crystals into a glass of water. The "solvation" and diffusion of ions is favored because there is an increase in

(b) entropy

Catalysts are molecules that lower the activation energy for a given reaction. Cells produce their own catalysts called

(b) enzymes

Seed oils are often dehydrogenated and added back into processed foods as partly unsaturated fatty acids. In comparison with the original oil, the new fatty acids have additional double carbon-carbon bonds, replacing what were once single bonds. This process could also be described as

(b) oxidation

Your body extracts energy from the food you ingest by catalyzing reactions that essentially "burn" the food molecules in a stepwise fashion. What is another way to describe this process?

(b) oxidation

When elemental sodium is added to water, the sodium atoms ionize spontaneously. Uncharged Na becomes Na+ meaning that the Na atoms have been

(b) oxidized

Which of the following is true for a reaction at equilibrium

(b) ΔG° + RT ln [X]/[Y] = 0

At first glance, it may seem that living systems are able to defy the second law of thermodynamics. However, on closer examination it becomes clear that although cells create organization from raw materials in the environment, they also contribute to disorder in the environment by releasing

(c) heat

Chemical reactions that lead to a release of free energy are referred to as "energetically favorable" Another way to describe these reactions is:

(c) spontaneous

Even though cellular macromolecules contain a large number of carbon and hydrogen atoms, they are not all spontaneously converted into CO2 and H2O. This absence of spontaneous combustion is due to the fact that biological molecules are relatively _____ and an input of energy is required to reach lower energy states

(c) stable

Oxidation and reduction states are relatively easy to determine for metal ions because there is a measurable net charge. In the case of carbon compounds, oxidation and reduction depend on the nature of polar covalent bonds. Which of the following is the best way to describe these types of bonds?

(c) unequal sharing of electrons across a covalent bond

Fill in the blanks, selecting from the choices below: Light + _________ + _________-->_________ + heat + sugars CO, CO2, O2, H2, H2O, N2, NO

Light + H20 + CO2 --> O2 + heat + sugars

Indicate whether the following statements are true or false. If a statement is false, explain why. (A) Photosynthetic organisms release only O2 into the atmosphere, while non-photosynthetic organisms release only CO2 (B) The cycling of carbon through the biosphere first requires the incorporation of inorganic CO2 into organic molecules (C) The oxidation of one molecule is always coupled to the reduction of a second molecule (D) During cellular respiration, carbon-containing molecules become successively more oxidized until they reach their most oxidized form, as CO2

(A) FALSE - Plants, as well as photosynthetic algae and bacteria, perform both photosynthesis and respiration; this means that photosynthetic organisms release both O2 and CO2 into the atmosphere (B) TRUE (C) TRUE - This forms the basis for redox pairs (D) TRUE

For the reaction Y-->X at standard conditions with [Y] = 1 M and [X] = 1 M, ΔG is initially a large negative number. As the reaction proceeds, [Y] decreases and [X] increases until the system reaches equilibrium. How do the values of ΔG and ΔG° change as the reaction equilibrates

(a) ΔG becomes less negative and ΔG° stays the same

The equilibrium constant (K) for the reaction Y-->X can be expressed with respect to the concentrations of the reactant and product molecules. Which of the expressions below shows the correct relationship between K, [Y], and [X]

(c) K = [X]/[Y]

When there is an excess of nutrients available in the human body, insulin is released to stimulate the synthesis of glycogen from glucose. This is a specific example of a(n) __________ process, a general process in which larger molecules are made from smaller molecules

(c) anabolic

*

By definition, catalysis allows a reaction to occur more RAPIDLY. Chemical reactions occur only when there is a loss of FREE ENERGY. Enzymes act more SELECTIVELY than other catalysts. A catalyst decreases the ACTIVATION ENERGY of a reaction.

Although the biochemical study of reaction rates and free energies is important for understanding each biological reaction individually, these studies do not provide an accurate picture of what is happening to reactants and products inside the cell

Chemical reactions inside the cell do not reach a state of equilibrium because