Question

The backbone of a DNA molecule is a polymer of alternating sugar (deoxyribose) and phosphoric acid units held together by a phosphate ester bond. Draw a segment of the polymer consisting of at least two sugar and two phosphate units. Circle the phosphate ester bonds.

Short answer

Draw two deoxyribose sugars linked by a phosphate group and circle the linkage.

Step-by-step solution

Understanding the Structure of DNA

DNA is composed of a sugar-phosphate backbone, where the sugar is deoxyribose, and the phosphate group is phosphoric acid. Each sugar is connected to the next sugar in the chain via a phosphate group, forming a phosphate ester bond.

Drawing the DNA Segment

Begin by drawing two deoxyribose sugar molecules, which have a five-carbon ring structure. Label them as deoxyribose 1 and deoxyribose 2.

Adding Phosphate Groups

Attach a phosphate group to the 5' carbon of the first deoxyribose and another phosphate group to the 3' carbon of the second deoxyribose. Label these phosphate groups as phosphate 1 and phosphate 2, respectively.

Connecting the Sugars with Phosphate Ester Bonds

Connect the 3' carbon of the first sugar with the 5' carbon of the second sugar using phosphate 1 as the bridging link. This forms a phosphate ester bond, completing the backbone section.

Depicting Additional Elements

If desired, you can depict the base pairs connected to the sugar units, but they are not part of the backbone structure being emphasized here.

Circling the Phosphate Ester Bonds

Circle the phosphate ester bond formed between deoxyribose 1 and deoxyribose 2 through phosphate 1. This highlights the structural connection within the backbone.

Key concepts

Phosphate Ester Bond

A phosphate ester bond is a crucial component in the structure of DNA. It forms the connection between the deoxyribose sugars and the phosphate groups. This bond is created when the oxygen atom of the phosphate group bonds to the carbon atom of the sugar. The phosphate ester bond is essential because it extends through the DNA, helping to create a continuous chain.

This type of bond gives DNA its structural stability, allowing it to carry out its role as the repository of genetic information. The bond is covalent, meaning it involves the sharing of electrons between atoms, which adds to its strength and makes it less likely to break under normal conditions.

• Provides structural continuity
• Enhances stability of the DNA molecule
• Involves covalent bonding

In the DNA backbone, the phosphate ester bond connects the 3' carbon atom of one deoxyribose to the 5' carbon atom of the next, creating a reliable chain of connections that allow the genetic information to be stored and transmitted accurately.

Sugar-Phosphate Backbone

The sugar-phosphate backbone is a defining feature of DNA structure. It is made up of alternating units of sugar — specifically deoxyribose — and phosphate groups. This backbone is considered the framework of the DNA molecule, supporting its overall architecture.

This long, repeating structure is why DNA is classified as a polymer. The deoxyribose sugars are linked each to a phosphate group by phosphate ester bonds, forming a continuous backbone. It is this backbone that maintains the integrity of the double-helix structure of DNA by holding together the nucleotide sequence.

• Alternating sugar (deoxyribose) and phosphate units
• Stability through phosphate ester bonds
• Provides DNA structural support

The backbone runs in an anti-parallel direction, meaning the two strands of DNA run in opposite directions, a factor necessary for DNA replication and function.

Deoxyribose

Deoxyribose is the sugar component of the DNA backbone. It is a five-carbon sugar molecularly known as 2-deoxyribose owing to the absence of one oxygen atom compared to ribose, hence the term 'deoxy.' This sugar plays a central role in the formation of the DNA backbone.

The placement of deoxyribose in the backbone involves it alternating with phosphate groups. The 3' and 5' carbon positions in each deoxyribose molecule are critical as they are the sites where the phosphate ester bonds form. This creates a chain that acts as the scaffold for attaching nucleotides, contributing to the integrity of the genetic code.

• Identified as a five-carbon sugar
• Links with phosphate to form backbone
• Central to DNA structure

Each deoxyribose molecule is a building block that helps assemble into the long, stable structure that is capable of storing vast amounts of genetic information.

Polymer Chemistry

Understanding polymer chemistry is key to grasping how DNA functions on a molecular level. DNA itself is a type of polymer, formed from repeating units called monomers. In DNA, these monomers are nucleotides, each consisting of a phosphate group, deoxyribose sugar, and a nitrogenous base.

The polymer nature of DNA provides it with several important properties. It allows for the flexibility needed to pack into the confined space of a cell nucleus, while still maintaining the strength necessary to withstand environmental stressors. Each monomer in the DNA chain is joined by covalent bonds, specifically the phosphate ester bonds that we have discussed.

• DNA as a biological polymer
• Composed of nucleotide monomers
• Provides flexibility and strength

Studying DNA under the lens of polymer chemistry reveals how life encodes genetic information, offering insight into replication, mutation, and evolution. The polymer structure enables DNA to replicate itself accurately, which is vital for heredity and variation.