Nucleic acids (DNA & RNA) and proteins are very large types of essential biomacromolecules of every living body. Both take part in gene expression which is expressing the information from a gene through proteins.
- There are 2 types of nucleic acids: DNA (Deoxyribonucleic Acid) & RNA (Ribonucleic Acid)
- Genome: The complete set of genes or genetic material present in a cell or organism, composed of DNA & RNA.
- There are 80,000 to 400,000 different varieties of proteins.
- Monomer of Nucleic acids: Nucleotide
- Monomer of Proteins: Amino Acids
Both play an important role in the gene expression mechanism that can be better understood via. the Central Dogma Model of Biology.
Nucleic acids are monomers of nucleotides whereas, Proteins are the monomers of amino acids.
Nucleic acids do contain the same elements as proteins: carbon, hydrogen, oxygen, nitrogen, and phosphorus or sulphur in some.
Nucleic acids are the genetic materials that we get inherited from our parents, and we will be transferring these to our offsprings.
Proteins are the building blocks of life and they bring out the genetic changes in our body phenotypically. Every cell in the human body contains protein.
The genotypic characteristics of organisms depend directly on nucleic acids. And, the phenotypic characteristics of organisms depend directly on proteins.
The gene expression process relates the phenotypic and genotypic characteristics together as nucleic acids take part in protein synthesis.
In simple words, the job of the nucleic acids is to make proteins, and the job of proteins is to express the genetic information that is on the nucleic acid.
Do all nucleic acids code for proteins?
Nucleic Acids do code for proteins but, all types of nucleic acids don’t. In a very simple, word there are both coding DNA & non-coding DNA in the genome.
Coding DNA codes for proteins while non-coding DNA doesn’t. It’s because, coding DNA contains codons to code for specific amino acids while, non-coding DNA doesn’t have any.
The genes of prokaryotes (bacteria) are very simple and tightly packed together, and it is seen that majority of the DNA codes for proteins. Only 20% of a typical prokaryote genome is non-coding in nature.
On the other hand, in case of eukaryotes like humans, other mammals, etc. it is seen that almost 98% of the genomic nucleic acids are non-coding in nature and only 2% codes for proteins in the body.
Experiments done in the 1960s had shown that a large proportion of the eukaryotic DNA is composed of repeated sequences that do not encode proteins.
It was also experimentally studied and proved that the proportion of non-coding DNA goes up as the genome size of the organisms increases. Meaning that the simpler the organisms the less is its genome size and so the less is its non-coding nucleic acids.
This is consistent with the fact that most eukaryotic nuclear DNA is non-coding, while the majority of prokaryotic, viral, and organellar genes are coding.
Why non-coding DNA doesn’t code for proteins?
Non-coding DNAs are as important as the coding DNAs. The job that non-doing DNAs perform can’t be underestimated.
Non-coding DNA doesn’t code for proteins because they don’t have that type of codon arrangement that can encode proteins.
They are functional non-coding DNA molecules that can create functional non-coding RNA molecules like transfer RNA, ribosomal RNA, and regulatory RNAs.
They do not synthesize proteins but they do help the coding DNAs to perform protein synthesis. They only take part in protein synthesis by supporting other coding DNAs.
The functions of non-coding DNA include the transcriptional and translational regulation of protein-coding sequences, origin of DNA replication, DNA folding, etc. Its RNA counterpart is non-coding RNA.
You will find that in a single chromosome there’s a large number of repeating non-coding DNAs between coding DNAs. And, when the DNA segments get transcripted to mRNA then the mRNA strands show introns.
These introns are the RNA version of the non-coding DNA segments that are removed during translation. They help in gene expression regulation and generate many other non-coding RNA molecules.
So the nucleic acid DNA in chromosomes are composed of genes. These genes are segments of coding DNA that encodes proteins.
And the non-coding DNA segments are non-genes or junk DNAs and they help as transcription factors, operators, enhancers, silencers, promoters, insulators, etc.
Why coding DNA only codes for proteins?
Gene consists of those DNA segments that can code for proteins. These are coding DNAs that have specific codons (sequence of three nucleotides) that codes for amino acids of the proteins.
During the gene expression process, both the coding and non-DNA segments get transcripted to the mRNA version. Later on, during translation, the non-coding segments called introns are removed from the mRNA.
During translation (protein synthesis) of mRNA, the tRNA reads the mRNA based on a particular sequence of three nucleotides (codons) and then creates the amino acids respectively.
Each codon consists of three nucleotides, usually corresponding to a single amino acid. For example, the codon CAG represents the amino acid glutamine.
And, we know that amino acids are the monomers of the proteins. Therefore, each protein can have around a hundred to several thousand amino acids.
The central dogma of molecular biology describes the two-step process properly viz. transcription and translation, by which the information in genes flows into proteins: (DNA → RNA → Protein).
Therefore in a quick nutshell, gene expression is the process by which information from a coding DNA segment (genes) is used in the synthesis of a functional gene product which is the protein following the Central Dogma Model.
How are nucleic acids related to proteins?
Both proteins and nucleic acids work in co-ordination to bring on the various changes in a living body. In a living body, the proteins directly bring on the phenotypic changes, and the nucleic acids directly bring on the genotypic changes.
The relationship between Proteins and Nucleic acids is that both find their application in the gene expression process of the living body.
The coding nucleic acids help in making proteins by encoding the amino acids. Whereas, the non-coding nucleic acids help the coding nucleic acids by regulating and controlling the process of gene expression to produce proteins.
Overall, during the gene expression in every living cell of any organism, it is seen that the nucleic acids code for amino acids to create proteins. This can be better explained by the Central Dogma Model of Biology.
The major relationship is that nucleic acids are the main genetic information-carrying molecules of the cell, and, by directing the process of protein synthesis, they determine the inherited characteristics of every living being in their body.
The sequence of the codons in nucleic acids determines the sequence of amino acids in a protein. And the sequence of amino acids determines the structure of a protein, which determines its function.
So, how nucleic acids make proteins?
Nucleic acids DNA & RNA are involved in making proteins. Gene Expression is the process through which nucleic acids conducts various biochemical processes to make proteins as the functional product of genes.
The gene expression process includes DNA replication, DNA transcription to mRNA, mRNA translation to proteins.
To make proteins from nucleic acids the DNA first replicates and then it gets transcribed to form mRNA. Later on, as the process advances, mRNA gets translated into amino acid chains that make proteins.
First, during DNA replication, the DNA divides in a semi-conservation way to produce many copies of the same DNA during cell division.
Secondly, the replicated DNA advances the process of DNA transcription to produce mRNA. It is the process by which the information in a strand of DNA is copied into a new strand of messenger RNA (mRNA).
mRNA will only act as a messenger between DNA and protein formation. This mRNA stores the information on how to code for proteins.
Thirdly, mRNA translation starts to create proteins. The mRNA that was formed from DNA is very short-lived so, it starts to attract ribosomes and with the help of tRNA, it produces a string of amino acids (the basic building blocks of proteins).
A long chain of amino acids emerges as the ribosome decodes the mRNA sequence into a polypeptide or a new protein.
How does DNA control the production of proteins?
We all know that DNA is a very stable molecule. The structure of the DNA is very stable because of the presence of strong covalent bonds between pentose sugar, and hydrogen bonds between nucleotides of the two strands.
Moreover, the presence of Thymine (T) in place of Uracil (U) in DNA protects it from always getting translated into proteins.
It’s all due to the structural stability and the presence of the Thymine nitrogenous base, which helps the DNA to keep the genetic information encrypted from generation after generation until the DNA gets transcribed to mRNA.
Now, the DNA that we got from our parents is something that was only present in a few cells when we were in our embryonic stage of development. Those embryonic cells with the DNA contents replicated numerous times that have resulted in our present-day body structure.
Those DNA contains the information to code for proteins and whenever there’s a need to make proteins, segments of DNA replicates in each cell nucleus using enzymes like DNA-dependent DNA polymerase, DNA ligase, etc. to make new DNA copies.
Then DNA transcription takes place to produce the mRNA version of the DNA. mRNA is single-stranded and contains Uracil in place of Thymine that makes protein synthesis to take place further in the process of gene expression.
The presence of DNA’s coding and non-coding strand is every important to control protein synthesis and only create proteins whenever required to do so
The double helix structure arranges DNA in such a way that it has a template (non-coding) strand and the non-template (coding) strand.
The non-template (coding) strand acts to facilitate proper transcription DNA to make mRNA.
For protein synthesis, messenger RNA must be made from one strand of DNA called the template (non-coding) strand. The other strand, called the coding strand, matches the messenger RNA in sequence except for its use of uracil in place of thymine.
Another way is the presence of non-coding sequences in DNA, that protects the DNA from getting translated into proteins. This happens because the non-coding sequences in DNA is highly responsible to regulate the process of gene expression.
That’s how DNA controls protein synthesis.