Refer to Exercise 21.18 . Figure E21.19 shows the bonding of...

Refer to Exercise 21.18 . Figure E21.19 shows the bonding of cytosine and guanine. The $\mathrm{O}-\mathrm{H}$ and $\mathrm{H}-\mathrm{N}$ distances are each $0.110 \mathrm{nm} .$ In this case, assume that the bonding is due only to the forces along the $\mathrm{O}-\mathrm{H}-\mathrm{O}, \mathrm{N}-\mathrm{H}-\mathrm{N},$ and $\mathrm{O}-\mathrm{H}-\mathrm{N}$ combinations, and assume also that these three combinations are parallel to each other. Calculate the net force that cytosine exerts on guanine due to the preceding three combinations. Is this force attractive or repulsive?

Refer to Exercise 21.18 . Figure E21.19 shows the bonding of cytosine and guanine. The $\mathrm{O}-\mathrm{H}$ and $\mathrm{H}-\mathrm{N}$ distances are each $0.110 \mathrm{nm} .$ In this case, assume that the bonding is due only to the forces along the $\mathrm{O}-\mathrm{H}-\mathrm{O}, \mathrm{N}-\mathrm{H}-\mathrm{N},$ and $\mathrm{O}-\mathrm{H}-\mathrm{N}$
combinations, and assume also that these three combinations are parallel to each other. Calculate the net force that cytosine exerts on guanine due to the preceding three combinations. Is this force attractive or repulsive?

Key Concepts

Hydrogen Bonding

Hydrogen bonding is a type of attractive interaction between a hydrogen atom covalently bound to an electronegative atom (such as oxygen or nitrogen) and another electronegative atom. In molecular biology, hydrogen bonds are crucial for the base pairing that stabilizes the double helix structure of DNA, as seen in the pairing of nucleotides like cytosine and guanine.

Intermolecular Forces

Intermolecular forces are the forces that act between molecules, determining the physical and chemical properties of substances. In the context of molecular interactions such as those between nucleobases, these forces include hydrogen bonds and other noncovalent interactions, which together dictate the overall stability and behavior of molecular assemblies.

Vector Summation of Force Components

When multiple forces act along different directions in a molecule, the net effect is determined by vector summation of these force components. In problems where forces, such as those from hydrogen bonds, act parallel to each other, the individual contributions can be added algebraically to find the overall net force, accounting for both magnitude and direction.

Attractive versus Repulsive Interactions

Attractive interactions occur when the net force between atoms or molecules pulls them together, while repulsive interactions cause them to push apart. In hydrogen bonding, the attractive force stabilizes the structure by lowering the energy of the system, and determining whether a net interaction is attractive or repulsive is essential for understanding molecular conformations and biological functions.

Transcript

00:01 The force between oxygen, oxygen and the hydrogen.

00:11 Our illusion if all which is given by k e squared divided by our pitch square where are which is the 0.11 times 10 to the power minus mind meter we can ride that can he square derided by oh minus r who h square this will be a nine times 10 to the power line times 1.6 times 10 to the power minus 19 divided by, um 0.29 minus 0.11 times tended power minus nine.

01:05 This holes where the excuse us forced to be a positive 7.11 times 10 to the power minus nine.

01:13 New to the force between oxygen and oxygen.

01:17 So oxygen oxygen force is given by f o he's a minus k he squared, divided by our square oxygen oxygen.

01:30 Here we took the left direction to be left is a boss too in the right direction.

01:40 Right direction to be negative.

01:44 So we are using those conventions a year.

01:47 Um, then we get nine times 10 to the dollar.

01:52 Nine dimes.

01:53 Um, minus sign here times 1.6 times 10 to the power minus 19 square divided by our oxygen.

02:04 Oxygen is ah, 0.29 times 10 to the power minus nine square.

02:11 This we get to be minus 2.74 times 10 to the power minus nine newton.

02:20 Um secondly, the force exerted on hydrogen not intrusion by no intrusion.

02:28 So we assume left direction to be positive and the right direction to be inactive.

02:34 The force between hydrogen and nitrogen will be force march.

02:38 Illusion and hydrogen will be k squared, divided by our in minus pitch square.

02:47 This is a cult, okay? a square are nitrogen.

02:51 Nitrogen minus are in my intrusion.

02:56 I rose in distance square...

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