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Example Questions
Example Question #21 : Molecular Bonds And Forces
Which intermolecular force would be the result of a polar molecule generating a dipole in a nearby nonpolar molecule?
Dipole-induced dipole
Hydrogen bonding
Ion-dipole
Dipole-dipole
London dispersion force
Dipole-induced dipole
A polar molecule has both positive and negative ends. This dipole can interact in many ways with other molecules, both polar and non-polar. If it interacts with a neighboring nonpolar molecule, there is an induced dipole within that neighbor resulting in a dipole-induced dipole force.
Example Question #22 : Molecular Bonds And Forces
Which statement about biomolecules is false?
They mostly contain ionic bonds
Specific stereoisomers are usually essential
Carbon is a primary element
They mostly contain nonmetal elements
They mostly contain ionic bonds
Biomolecules contain carbon as their key element, and they mostly contain nonmetallic elements. For example, the human body is about 65% oxygen, 20% carbon, 10% hydrogen, and 3% nitrogen - the remaining major elements that make up the human body are calcium, phosphorous, magnesium, sulfur, potassium, sodium, chlorine, and other trace elements like iron and copper. Ionic bonds are rare in biomolecules, as most biomolecules are bound via covalent bonds. Also, to create a specific biomolecule, many of the bonds must be in specific orientations-specific stereoisomers are important, especially with enzymes.
Example Question #1 : Other Intermolecular Forces
Which molecule has polar bonds but is not itself polar?
In , each
bond is polar, as oxygen is much more electronegative than carbon. However, these dipole moments are equal in charge and this molecule is linear with carbon in the middle, so the entire molecule is nonpolar.
In water, oxygen is more electronegative than hydrogen; thus, electrons are pulled toward the oxygen atoms more than towards hydrogen atoms. This gives oxygen a partial negative charge and hydrogen a partial positive charge. The entire molecule is polar since water's molecular geometry is bent.
Methane includes a carbon with a hydrogen attached to each of its four bonds. Electrons are distributed relatively equally across each bond since the electronegativities of hydrogen and carbon are comparable, and the entire molecule is tetrahedral. Thus, neither the individual bonds nor the entire molecule are polar.
In , nitrogen is left with a lone pair of electrons after it bonds with three hydrogen atoms. Because of this lone pair, the molecular geometry is trigonal pyramidal and the entire molecule is polar with the nitrogen atom being slightly negative (high electronegativity) and the hydrogen atoms being slightly positive.
Example Question #4 : Other Intermolecular Forces
Two-tailed amphiphiles in high concentrations form __________.
monolayers
bilayer vesicles
micelles
lysophospholipids
bilayer vesicles
An amphiphile is a molecule that contains both polar and nonpolar groups. Two tailed amphiphiles form bilayer vesicles, whereas one tailed amphiphiles in high concentrations form micelles.
Example Question #21 : Molecular Bonds And Forces
Once inside a potassium channel, a ions sheds the water molecules surrounding it in order to continue through. How is the
ion now stabilized within the channel?
An amino acid stretch with neutral charges
An amino acid stretch capable of forming ionic bonds with the ion
An amino acid stretch with positive charges
An amino acid stretch with negative charges
An amino acid stretch capable of forming hydrogen bonds with the ion
An amino acid stretch with negative charges
Free floating is surrounded by water molecules which stabilize its positive charge. However, once these water molecules are shed due to movement through the potassium channel, something else must stabilize the positively charged
ion. This is accomplished via an amino acid stretch with negatively charged residues. The amino acid stretch responsible for the stabilization is Thr-Val-Gly-Tyr-Gly.
Example Question #21 : Molecular Bonds And Forces
While certain bonds within a polypeptide chain are able to rotate, the actual conformations found in nature are limited. What is a major factor limiting the available conformations?
Steric clashes between side chains in a trans conformation.
Steric clashes between side chains in a cis conformation.
Hydrophobic interactions between side chains in a cis conformation.
Hydrophobic interactions between side chains in a trans conformation.
Steric clashes between backbones in a cis conformation.
Steric clashes between side chains in a cis conformation.
While the peptide bond in a polypeptide chain is locked and unable to rotate, the amino nitrogen-alpha carbon bond can rotate. Additionally, the alpha carbon-carboxyl carbon can rotate as well.
However, like in many other molecules, the cis conformation is energetically unfavorable due to steric hindrance. This steric hindrance occurs when the side chains of two residues are right next to each other within the polypeptide. This is unfavorable, and the trans conformation is therefore preferred.
Example Question #23 : Molecular Bonds And Forces
What is an enantiomer?
Stereoisomers that are not mirror images of each other.
Molecules that have the same chemical bonds but that do not have the same configuration.
Molecules that differ only in the arrangement about a carbon atom.
Molecules with substituent groups on the same side of a double bond.
Stereoisomers that are mirror images of each other.
Stereoisomers that are mirror images of each other.
Enantiomers have the same chemical bonds in different configurations that are non-superimposable mirror images of each other. They differ in their configuration at all chiral centers.
Example Question #421 : Biochemistry
What are van der Waals interactions?
Interactions between hydrophobic molecules
Interactions between compounds containing aromatic rings
Interactions between ions of the same charge
Weak interactions between any two atoms in close proximity
Interactions between ions of different charges
Weak interactions between any two atoms in close proximity
van der Walls interactions are weak attractive interactions that occur between any two atoms in close enough proximity for their electron clouds to interact.
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