Each polynucleotide of DNA is made up of small units called _____________.

Question

Prepp Team · Accepted Answer

Understanding DNA Structure and Polynucleotides

Deoxyribonucleic acid (DNA) is a crucial molecule found in almost all living organisms. It carries the genetic instructions needed for an organism to develop, survive, and reproduce. DNA is organized as two polynucleotide strands coiled around each other to form a double helix.

Let's break down the components of DNA.

What is a Polynucleotide?

A polynucleotide is a biopolymer composed of many nucleotide units linked together. In the case of DNA, these nucleotide units are linked by phosphodiester bonds, forming a long chain often referred to as a DNA strand.

The Building Blocks: Nucleotides

The question asks about the small units that make up each polynucleotide of DNA. These fundamental units are called nucleotides.

Each nucleotide in DNA has three main components:

A deoxyribose sugar: A five-carbon sugar molecule.
A phosphate group: A molecule containing phosphorus and oxygen atoms.
A nitrogenous base: One of four types: Adenine (A), Guanine (G), Cytosine (C), or Thymine (T).

These three components are chemically bonded together to form a single nucleotide unit. When many of these nucleotide units are joined end-to-end, they form a polynucleotide chain, which is the backbone of a DNA strand.

Analyzing the Options

Let's look at the other options provided:

Nuclear membrane: This is the double membrane that surrounds the nucleus in eukaryotic cells. It regulates the passage of molecules between the nucleus and the cytoplasm. It is a cellular structure, not a building block of DNA.
Nuclei: This is the plural form of nucleus. The nucleus is an organelle found in eukaryotic cells that contains the cell's genetic material (DNA). It is where DNA is primarily located, but it is not a component unit of the DNA molecule itself.
Nucleus: As explained above, the nucleus is the organelle containing DNA. It is not a small unit that makes up a DNA polynucleotide.

Therefore, the only option that represents the small repeating units making up a DNA polynucleotide is the nucleotide.

In summary, a DNA polynucleotide chain is a polymer, and the monomers (small repeating units) that make up this polymer are nucleotides.

The final answer is $\text{Nucleotide}$.

Term	Definition	Relation to DNA Structure
Nucleotide	A unit consisting of a sugar, phosphate, and nitrogenous base.	The building block of DNA polynucleotides.
Polynucleotide	A chain formed by many nucleotides linked together.	Each strand of the DNA double helix is a polynucleotide.
Nuclear membrane	Membrane surrounding the nucleus.	Encloses the nucleus where DNA is located, but not part of DNA structure.
Nucleus	Organelle containing genetic material.	Cellular compartment where DNA resides, not a component unit of DNA.

Revision Table: DNA Structure Components

Component Level	Description	Example
Smallest Unit (Monomer)	Nucleotide	Deoxyadenosine monophosphate (dAMP)
Chain (Polymer)	Polynucleotide	Single strand of DNA
Full Molecule	Double Helix DNA	Two polynucleotide strands wound together
Location in Eukaryotes	Nucleus	The organelle where DNA is found

Additional Information on Polynucleotides

The nucleotides within a polynucleotide chain are connected by phosphodiester bonds. These bonds form between the 5' phosphate group of one nucleotide and the 3' hydroxyl group of the sugar of the next nucleotide. This creates a sugar-phosphate backbone that is characteristic of nucleic acids like DNA and RNA.

The sequence of the nitrogenous bases (A, T, C, G) along the polynucleotide chain carries the genetic information. The two polynucleotide strands in a DNA double helix are held together by hydrogen bonds between complementary bases (A pairs with T, and C pairs with G).