Exam 2: Chemical Components of Cells

Choose the answer that best fits the following statement: Cholesterol is an essential component of biological membranes.Although it is much smaller than the typical phospholipids and glycolipids in the membrane, it is a/an __________ molecule, having both hydrophilic and hydrophobic regions.

Most types of molecules in the cell have asymmetric (chiral) carbons.Consequently there is the potential to have two different molecules that look much the same but are mirror images of each other and therefore not equivalent.These special types of isomers are called stereoisomers.Which of the four carbons circled in Figure 2-37 is the asymmetric carbon that determines whether the amino acid (threonine in this case) is a ᴅ or an ʟ stereoisomer? Figure 2-37

The amino acid histidine is often found in enzymes.Depending on the pH of its environment, sometimes histidine is neutral and at other times it acquires a proton and becomes positively charged.Consider an enzyme with a histidine side chain that is known to have an important role in the function of the enzyme.It is not clear whether this histidine is required in its protonated or its unprotonated state.To answer this question, you measure enzyme activity over a range of pH, with the results shown in Figure 2-70.Which form of histidine is necessary for the active enzyme? Figure 2-70

You explain to a friend what you have learned about Avogadro's number.Your friend thinks the number is so large that he doubts there is even a mole of living cells on the Earth.You have recently heard that there are about 50 trillion (5 × 10¹³) human cells in each adult human body and that each human body carries more bacterial cells (the microbiome) than human cells, and the human population is approximately 7.6 billion (7.6 × 10⁹).Armed with this information, you bet your friend $5 that there is more than a mole of cells on Earth.Write out the calculation that proves you are correct.

Avogadro's number was established as the total number of units (atoms or molecules) in a mole, and a mole of any substance is X grams of it, where X is equal to the substance's molecular weight.A standard unit, the mole, allows scientists to calculate concentrations of materials dissolved in solutions. Example: Sulfur has a molecular weight of 32.Therefore, 32 g of sulfur = 1 mole of sulfur = 6 × 10²³ sulfur atoms. How many moles and atoms, respectively, are there in 120 grams of sulfur?

Table 2-14 -Table 2-14 indicates the number and arrangement of electrons in the first four atomic electron shells for selected elements.On the basis of the information in the chart and what you know about atomic structure, which elements are chemically inert?

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase should be used only once. charge length polar covalent molecule salt double bond noncovalent single bond ionic nonpolar weight Whereas ionic bonds form a/an __________, covalent bonds between atoms form a/an __________.These covalent bonds have a characteristic bond __________ and become stronger and more rigid when two electrons are shared in a/an __________.Equal sharing of electrons yields a/an __________ covalent bond.If one atom participating in the bond has a stronger affinity for the electron, this produces a partial negative charge on one atom and a partial positive charge on the other.These __________ covalent bonds should not be confused with the weaker __________ bonds that are critical for the three-dimensional structure of biological molecules and for interactions between these molecules.

Figure 2-5 depicts the structure of carbon.Use the information in the diagram to choose the correct atomic number and atomic weight, respectively, for an atom of carbon. Figure 2-5

Table 2-14 -Table 2-14 indicates the number and arrangement of electrons in the first four atomic electron shells for selected elements.On the basis of the information in the chart and what you know about atomic structure, which elements form stable but reactive diatomic gases?

Which of the following monomer building blocks is necessary to assemble selectively permeable boundaries around and inside cells?

If the isotope ³²S has 16 protons and 16 neutrons, how many protons, neutrons, and electrons will the isotope ³⁵S have, respectively?

DNA and RNA are different types of nucleic acid polymer.Which of the following is true of DNA but NOT true of RNA?

The relative strengths of covalent bonds and van der Waals interactions remain the same when tested in a vacuum or in water.However, this is not true of hydrogen bonds or ionic bonds, whose bond strengths are lowered considerably in the presence of water.Explain these observations.

Substances that release protons when they dissolve in water are acids.Which of the following household substance is acidic?

Which subatomic particles contribute to the atomic mass for any given element?

Which of the following are examples of isomers?

Table 2-14 indicates the number and arrangement of electrons in the first four atomic electron shells for selected elements.Use the information in the table to fill in the blanks for A-E.There may be more than one answer for each. Table 2-14 A.__________ are chemically inert. B.__________ form ions with a net charge of +1 in solution. C.__________ form stable but reactive diatomic gases. D.__________ form ions with a net charge of ?1 in solution. E.__________ form ions with a net charge of +2 in solution.

Aromatic carbon compounds such as benzene are planar and very stable.Double-bond character extends around the entire ring, which is why it is often drawn as a hexagon with a circle inside.This characteristic is caused by electron