The Relationship Between DNA and RNA

DNA and RNA are essential building blocks for human life. They have separate and distinct functions but work together in a complex series of molecular interactions.

What is DNA? 

DNA is short for deoxyribonucleic acid. It is the molecule that contains an organism’s genetic code. That code is passed from adults to their offspring during the reproduction process.

Almost all cells in a person's body have the same DNA. Most DNA is located in a cell's nucleus, where it is called nuclear DNA. Some DNA is also in the mitochondria, where it is referred to as mitochondrial DNA or mtDNA.

Nuclear DNA is tightly packed into thread-like structures called chromosomes. Humans have 46 chromosomes. Of these, 22 pairs are autosomes (numbered 1-22 for identification purposes), and one pair are sex chromosomes.

One of each pair of chromosomes comes from the mother’s egg cell and the one from the father’s sperm cell.

Mitochondria are found in cells and convert energy from food into a form that the cells can use. Specifically, mitochondria are located in the cytoplasm, which is the fluid that surrounds the nucleus.

Mitochondrial DNA has 37 genes that are all needed for normal mitochondrial functions. There are 13 genes that provide instructions for making enzymes.

A process called oxidative phosphorylation uses oxygen and simple sugars to create a cell’s main source of energy.

The other 24 genes carry the instructions for making molecules to produce transfer RNA (tRNA) and ribosomal RNA (rRNA). These types of RNA help to assemble amino acids into functioning proteins. Proteins are complex molecules that do a majority of the work in cells.

They’re required for the function and regulation of a person’s tissues and organs.

Proteins are described according to what function they provide in the body. Examples of proteins include antibody, enzyme, messenger, structural component, and transport/storage.

Most DNA does not code protein sequences and is known as non-coding DNA. Some non-coding DNA is transcribed into non-coding RNA molecules.

Coding DNA simply means that DNA is providing instructions for making proteins. 

DNA and health issues

When changes in the structure of mitochondrial DNA takes place, health-related conditions can occur. Some of these include:

The following conditions are associated with changes in the structure of mitochondrial DNA ¹.

• Age-related hearing loss
• Cancers
• Cyclic vomiting syndrome
• Cytochrome c oxidase deficiency
• Kearns-Sayre syndrome
• Lactic acidosis
• Leber hereditary optic neuropathy
• Leigh syndrome
• Maternally inherited diabetes and deafness
• Mitochondrial complex III deficiency
• Mitochondrial encephalomyopathy
• Myoclonic epilepsy with ragged-red fibers
• Neuropathy, ataxia and retinitis pigmentosa
• Pearson marrow-pancreas syndrome
• Progressive external ophthalmoplegia
• Stroke-like episodes

DNA chemical bases

DNA is stored as a code made up of four nitrogen chemical bases. Those chemical bases are ²: 

• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)

How these bases are ordered and sequenced determines what information is available to build and maintain an organism. You can equate this in much the same way that letters of the alphabet are formed to produce words and sentences.

There are two kinds of nitrogenous metabolism bases – purine and pyrimidine. You learn more about them here.

For example, the biological instructions in a DNA sequence of ATCGTT might produce instructions for blue eyes, and a DNA sequence of ATCGCT might provide instructions for brown eyes. In genetic terms, these words are called codons.

These chemical bases pair up with each other to form what are known as base pairs.

Each base also is attached to a five-carbon sugar molecule and a phosphate molecule to form a nucleotide.

Nucleotides join together in two long spiraling strands to form a double helix.

Because DNA can replicate itself, these double helix configurations are duplicated. That is critical when cells divide because each new cell needs an exact copy of the DNA that was found in the old cell ³.

Every DNA sequence that contains protein instructions is known as a gene. Gene sizes vary a lot and can range from about 1,000 bases to 1 million bases ⁴.

Making proteins from DNA instructions occurs in two steps.

Enzymes read the information contained in a DNA molecule. It is transcribed into an intermediary molecule called messenger ribonucleic acid, or mRNA.

Information in the mRNA is translated into a format that amino acids can understand. Amino acids are proteins' building blocks and communicate the exact order amino acids should be linked to create a specific protein.

DNA and reproduction

In sexual reproduction, half of an offspring’s nuclear DNA comes from the male parent. The other half comes from the female parent. 

But offspring inherit all of their mitochondrial DNA from the female parent. That is because only egg cells keep their mitochondria during fertilization. Sperm cells do not. 

Putting DNA into perspective

Just how complicated is the human body?

Consider this. A person’s complete DNA instruction book (also known as a genome) has about 3 billion bases ⁵. However, 99 percent of all of these bases are the same in all people. It’s the other 1 percent that differentiates us.

What is RNA? 

RNA is short for ribonucleic acid.

It is considered one of the three major biological macromolecules essential for all forms of life ⁶.

One of the core theories of molecular biology is that the flow of genetic information starts in DNA, flows to RNA, and then to proteins. Proteins have multiple functions in cells as enzymes, structural components, and in cell signaling.

While DNA is considered a cell's blueprint, RNA is regarded as a copy of the DNA, and when a cell needs to produce and propagate protein, it activates the protein's gene and codes (produces) multiple copies of that piece of DNA to form a messenger, known as mRNA.

The multiple copies of mRNA translate that genetic code into protein through ribosomes. Ribosomes are the catalysts that activate the protein’s gene and also control how much protein is made.

Scientists long believed that RNA only had three primary functions in a cell ⁷.

• As a DNA photocopy (Messenger RNA, mRNA)
• To couple genetic code and protein building blocks (Transfer RNA, tRNA)
• As a structural component of ribosomes (Ribosomal RNA, rRNA)

In recent years, the implications and impacts of RNA have broadened. For example, RNA can act as enzymes that speed up chemical reactions.

RNA has also been shown to play a critical role in regulating cellular processes, including division, differentiation, growth, aging, and death.

Defects in RNAs have also been linked to several significant diseases and health conditions, including some cancers, heart disease, stroke, and others.

RNA and health issues

As genetic science continues to advance rapidly, a lot of valuable connections have been made between RNA and human health issues.

For example, some mRNAs regulate cancer-associated genes that facilitate tumor development. Some tRNA cells have been linked to proteins involved in programmed cell death (apoptosis). When these cells do not die as programmed, it can also lead to cancer.

Researchers studying RNA sequencing have also linked certain RNA transcripts with the proliferation and metastasis of cancer tumor cells. Other RNAs act as cancer suppressors.

When mRNA metabolism is disrupted, it can lead to neurodegenerative diseases such as Alzheimer's disease or amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease) and myotonic dystrophy.

What are the main differences between DNA and RNA?
 

Although they are similar in structure, DNA and RNA have much different roles from each other.

RNA is the central link between DNA and proteins. In molecular biology, this is referred to as the “Central Dogma.”

When genetic information flows from one entity to the next, the process is known as transcription. In simple terms, an RNA copy of a segment of DNA is made. This RNA strand is read by a ribosome and forms a protein.

There are dozens of types of RNA, categorized by their roles. Those roles include:

• Protein synthesis
• Post-transcriptional modification of DNA replication
• Regulatory functions
• Parasitic RNAs

Because RNA is not a paired strand, this allows it to fold into complex, three-dimensional structures. In some cases, it does undergo base pairings with itself to form intrastrand double helixes.

RNAs primarily execute biochemical reactions, but some also have complex regulatory functions as well. Because they are abundant and diverse, RNAs are critical in normal cellular processes and diseases.

Comparing DNA and RNA form and functions 

Function

DNA’s primary purpose is for the long-term storage of genetic information and for the transmission of that information to create new cells and organisms.

RNA transfers DNA genetic codes from a nucleus to ribosomes as part of the creation of proteins.

Structure 

Structurally, the primary difference between DNA and RNA is that DNA is found in a double-helix in cells. RHA is typically a single strand form.

DNA is referred to as a B-form double helix. It is a double-stranded molecule that is made up of a long chain of nucleotides. RNA is referred to as an A-form helix. It is characterized by a single strand helix with shorter chains of nucleotides.

The composition between the two is similar.

DNA is comprised of deoxyribose sugar, a phosphate backbone, and adenine, guanine, cytosine, thymine nitrogenous bases. RNA is composed of ribose sugar, a phosphate backbone, and adenine, guanine, cytosine, uracil bases.

Base Pairing 

DNA is characterized by base pairings of AT (adenine-thymine), and GC (guanine-cytosine)

RNA is characterized by base pairings of AU (adenine-uracil), and GC (guanine-cytosine)

Length 

DNA molecules consist of long chains of nucleotides while RNA molecules generally comprised of shorter chains of nucleotide molecules. 

Location 

Most DNA is located in the nucleus of a cell. A small amount is also found in the mitochondria.

RNA is found primarily in a cell's cytoplasm, but it is usually synthesized in the nucleus. After it is synthesized, it delivers the genetic information to the ribosomes, where it is then translated into proteins.

Stability 

DNA is relatively stable due to C-H bonds. That is augmented by the fact that the body destroys enzymes that might attack DNA. Small grooves in the double helix also protect the strand because this provides minimal space for enzymes to attach. 

By contrast, the O-H bond in the ribose of RNA is more reactive due to the O-H bond in the ribose. It is not stable under alkaline conditions. Also, the large grooves in the molecule make it susceptible to enzyme attack. 

For these reasons, RNA is produced, used, degraded, and recycled constantly.

Unique Features 

DNA replicates itself. RNA is synthesized from DNA and only when it is needed.

Another distinction is that DNA is sensitive to UV light and can be damaged by exposure. That’s not the case with RNA, which tends to be relatively resistant to UV exposure.