Tag: RNA

Introduction

Different metabolic processes are carried out by organisms in order to ensure their existence and to produce progeny. Naturally occurring macromolecules i.e. nucleic acids hold genetic information.RNA and DNA are both types of nucleic acids. These are nucleotide-based macromolecules. DNA is the genetic substance that contains the genetic instructions for unique traits that are expressed as various characters by organisms.

Some viruses have RNA as their genetic material. Almost all cells contain RNA, which plays a specific role in protein synthesis.

DNA

• Deoxyribonucleic acid, usually referred to as DNA, is the genetic substance found in many organisms.
• It is a simple, tightly wound circle in the cytoplasm of prokaryotes.
• In the cell nucleus of eukaryotes DNA is tightly wound into chromosomes.
• Despite being long polymers, nucleic acids are tightly wrapped to fit inside the small cell.
• Even in massive multicellular animals, every cell in the body contains the same copy of DNA.
• During replication, the tightly wound structures are unwrapped to create copies.
• Eukaryotes also have mitochondrial DNA, which codes for proteins exclusive to mitochondria, in addition to the nucleus.

 Composition

• The nucleic acids are long polymeric chains of individual nucleotides.
• The phosphate group, pentose sugar moiety, and a nitrogenous base are all components of nucleotides.
• There are 4 types of nitrogenous bases found in DNA; adenine and guanine are purines while thymine and cytosine are pyrimidines.
• Deoxyribonucleic acid, or DNA, is made up of long chains of individual deoxyribonucleotides connected by phosphodiester linkages.
• The arrangement of nitrogenous bases corresponds to the arrangement of long chains of nucleotides in a  DNA, this sequence encodes the information on DNA and is original to an organism.

Structure

• DNA forms a right-handed double helix with an antiparallel orientation of the two polynucleotide strands. DNA structure resembles a twisted ladder shape.
• The sugar and phosphate groups make the vertical stands of the twisted ladder shape and nitrogenous base pairs resemble the rungs of a ladder. 
• The 3′ carbon of one sugar and the phosphate group linked to the 5′ carbon of the subsequent sugar moiety form a phosphodiester linkage.
• Because of this, the connection is sometimes known as a 3′–5′ phosphodiester linkage.
• A glycosidic bond attaches nitrogenous bases to the first carbon of the sugar.
• Through hydrogen bonding, the nitrogenous bases of opposing strands bind with each other.
• Three hydrogen bonds link cytosine and guanine, while two hydrogen bonds pair adenine and thymine. This is known as complementary base paring.
• The double-helical DNA is twisted with 10 base pairs per turn.
• The deep major grooves and shallow minor grooves are created by these helical turns.

Types of DNA 

 There are two types of DNA depending on where they are located in the cell. The two types of DNA are-Nuclear DNA and Mitochondrial DNA 

• Nuclear DNA- Exists as chromosomes in the nucleus. It is huge and is in response of nearly all the characteristics of an organism.
• Mitochondrial DNA- DNA found in mitochondria is known as mitochondrial DNA. This DNA  primarily codes for proteins needed for the mitochondrial activity. It originates from the female parent and manifests in the mitochondrial matrix as small circular shapes.

RNA

• RNA is also known as Ribonucleic acid.
• Phosphate group, pentose sugar moiety (ribose), and nitrogenous base are all components of ribonucleotides.
• The ribonucleotides include adenine, guanine, cytosine or uracil.
• RNA can be found as single or double-stranded.
• Nearly every cell has RNA, which serves an important role in protein synthesis.
• RNA serves as the genetic material in several viruses.

Types of RNA 

There are three types of RNA found. They are

mRNA or messenger RNA

• mRNA is formed from DNA through transcription. The base pairs of m-RNA are complimentary to base sequences on DNA.
• The nucleotide sequences of mRNA are organized into triplets called codons.
• While several codons can code a single amino acid, each amino acid has a unique codon.
• 64 codons encode twenty amino acids.
• Pre mRNA, a direct byproduct of transcription, undergoes post-transcriptional modifications to become mRNA.
• A guanine group and poly-A tail are added to the pre-mRNA during post-transcriptional modifications to make it more stable.
• The mRNA is the main precursor of protein synthesis.
• It delivers the genetic information from the DNA for protein synthesis. 

rRNA or ribosomal RNA

• They are found in ribosomal subunits along with proteins and enzymes.
• The primary component of ribosomes is ribosomal RNA (rRNA).
• It enables the formation of peptide bonds between two amino acids during protein synthesis. 
• It also ensures that the mRNA and ribosomes are properly aligned during protein synthesis.

tRNA or transfer RNA

• tRNA is important for protein synthesis.
• During translation, amino acids are transferred by the tRNA.
• Each amino acid has a unique tRNA that transports it to the translation site (ribosome).
• It is the smallest of all RNA.
• tRNA has a structure resembling a clover leaf.

Role in protein synthesis  

• Translation is also known as protein synthesis and it  occurs in the ribosomes.
• Proteins are long polypeptide chains that are formed when individual amino acids bind to one another through peptide bonds.
• Each of the three RNA types plays a distinct role in translation-
• Single-stranded mRNA contains the instructions needed to make proteins.
• tRNA interprets the genetic code on the mRNA and the specific amino acids are transported from the amino acid pool to the translation site.
• The ribosomal RNA (rRNA) carries out translation by creating peptide bonds between different amino acids.

Difference between DNA and RNA

DNA	RNA
DNA is Deoxyribonucleic Acid	RNA is ribonucleic acid
It is made up of Adenine, guanine, cytosine, and thymine	It is made up of Adenine, guanine, cytosine, and uracil
Very stable structure	Comparatively less stable structure
Less prone to mutations	More easily prone to mutations
Present in Nucleus and mitochondria.	Present in the Cytoplasm, ribosomes, and nucleus
It is Self-replicating.	Most of the RNA is dependent on DNA for its synthesis.
It is the genetic material of most organisms and helps in the transfer of information from one generation to another.	It is most essential component during protein synthesis.
3 forms of DNA are B-DNA, A-DNA and Z-DNA.	3 types of RNA are found: m-RNA, r-RNA and t-RNA.
Contains a Deoxyribose sugar	Contains a ribose sugar

Summary

The nucleic acids in living things are DNA and RNA. They are organic polymers that are found in nature.  Long chains are created by linking the individual nucleotides together with phosphodiester linkages. In the majority of species, DNA, which is found in the nucleus of the eukaryotes, is the genetic information carrier. In order for the long polymeric chains to fit into the smallest microscopic cells, they must be folded numerous times. RNA primarily functions in protein synthesis. The existence of nucleic acids results in the continuation of life and the performance of particular tasks.

Frequently Asked Questions

1. Difference between 3 forms of DNA.
Ans:

B-DNA	A-DNA	Z-DNA
92% relative humidity	75% relative humidity	High and low salt concentrations
10bp	11bp	12bp
Right-handed	Right-handed	Left-handed
Widest of all	Width 2nm	Narrowest
Most common and stable form	Metastable form	Unstable and has Zig-zag pattern of phosphodiester backbone.

2. What is central dogma?
Ans: The central dogma is a theory of molecular biology that states that genetic information can only move in a single direction i.e  from DNA to RNA to protein. This protein synthesis takes place via three process-

• Replication- This multiplies the DNA stands.
• Transcription–This makes mRNA which encodes information of the DNA.
• Translation- This makes the final proteins that perform various functions in the body.

3.What is a chromosomes?
Ans: The DNA molecule is packed into chromosomes, which are thread-like structures found in the nucleus of every cell. Each chromosome is constructed from DNA that has been tightly wound around proteins called histones which assists in supporting entire chromosome structure.

Introduction

There is no life on Earth without reproduction. For an organism to be classified as a living being, it must be able to reproduce. Reproduction of an individual requires replication of DNA, the molecular basis of life. Nature would not have been as diverse if all organisms reproduced asexually, and there would be no variation among populations. As a result of meiosis, living organisms can undergo variations, which maintain biological diversity and assist in adapting and evolving.

Heredity and Accumulation of Variation During Reproduction

Reproduction passes genetic information from parents to offspring, resulting in the offspring acquiring the same characteristics as their parents. This process is called heredity. Species or groups of organisms of a species may differ in some way due to variation. Variations in sexually reproducing species result from three genetic processes: mutations, independent segregation of chromosomes, and genetic recombination.

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Mutations

Mutations are arbitrary alterations to an organism’s genes that can come from biological, chemical, or physical sources. Alleles which are different versions of the same gene are produced as a result of these modifications in various members of the same species. A mutation is passed down to the next generation in asexually reproducing organisms during mitosis. These changes are integrated into sexually reproducing organisms, nevertheless, where they then undergo further reorganization during sexual reproduction.

Independent Assortment of Chromosomes

Homologous chromosome pairs are found in diploid eukaryotes. Both members of the pair have separate sets of alleles, with one inheriting a set from the mother and the other from the father. These homologous chromosomal pairs divide during meiosis, and the individuals in each pair are then segregated into various daughter nuclei, giving rise to haploid gametes. The number of chromosomal pairs that each gamete acquires is random and unrelated to the other pairings. The resulting diploid individual possesses traits from both parents. This also explains the genetic variances seen in siblings, who all get their personalities from the same parents yet have distinct alleles.

Chromosomal crossing over the homologous chromosomes undergoes an event called “chromosomal crossing over” just before the separation of homologous chromosomes occurs, which causes the recombination of genes on the chromosomes. Recombination involves the exchange of alleles from one chromosome’s homologue with those from the other. The likelihood of variation is increased in sexually reproducing organisms by chromosomal crossing over.

Why is it Important to have Variations?

The expansion of a population’s gene pool requires variation. Increased genetic diversity results from it. In actuality, the foundation of the entire evolutionary history of the planet is inheritance in combination with the variation of the inheritable genes (i.e., “descent with modification”). 

Heredity and variations are the basis for

• Diversified generations of the same lineages
• The evolutionary advantage in adverse conditions
• Adaptations of organisms 
• Evolution of new species 
• For tracing the evolutionary history and classification of an organism’s

Molecular Basis of Inheritance (DNA and RNA)

Mendel’s research with garden peas laid the groundwork for genetics. He was aware that each “factor” had two “variants,” only one of which was passed down from each parent to the offspring, and that each “variant” was responsible for the features observable in organisms. But he didn’t know what this element was. Some ground-breaking studies, such as those conducted by Fredrick Griffith in 1928, Averty, MacLeod, and McCarty in 1944, and Hershey and Chase in 1952, provided unmistakable proof that the DNA, not RNA or proteins, is the molecular foundation of inheritance.

The cornerstone for the continuation of life is the nucleic acids DNA and RNA. The information is stored in the DNA as genes, which are transferred from one generation to the next. The phenotypic characteristics of an individual vary depending on what allele (a variant of a specific gene) is present on the chromosome.

Differences Between the DNA and the RNA:

DNA	RNA
Comprises two polynucleotide strands, coiled around a common axis in a right-handed manner	The RNA molecule is a single polynucleotide strand
Adenine pairs with thymineCytosine pairs with guanine	Adenine pairs with uracilCytosine pairs with guanine
Contains a deoxyribose sugar	Contains a ribose sugar
Carries hereditary information in the form of nucleotide segments known as genes	Translates the gene transcripts (mRNA) from DNA into proteins

Summary 

Reproduction passes genetic information from parents to offspring, resulting in the offspring acquiring the same characteristics as their parents. Mutations are arbitrary alterations to an organism’s genes that can come from biological, chemical, or physical sources. Recombination involves the exchange of alleles from one chromosome’s homologue with those from the other. The phenotypic characteristics of an individual vary depending on what allele (a variant of a specific gene) is present on the chromosome.

 Frequently Asked Questions

1. What are the Factors that Determine the Sex of a Human?
Ans. The sex chromosomes in humans control gender. Males have one X from the mother and one Y from the father, making up the XY sex chromosome combination, whereas females have the XX chromosome pair (one X chromosome from each parent).

2. Do all Characters Always Pass Down from Both Parents?
Ans. No. Some characteristics, and particularly some diseases, can be sex-related and be found on the sex chromosomes. In addition, we are aware that mitochondria contain their DNA. The mother alone is the exclusive source of this mitochondrial DNA. All other nuclear features are passed down through both parents.

3. What is meant by Somatic Variation?
Ans. Genetic material is either inherited or acquired by an offspring from its parents. However, the somatic (non-gametic) cells of the developing zygote may develop mutational alterations that are not integrated into the germline. These characteristics won’t be passed down to the person’s descendants.

4. Is there a chance of Genetic Variation Whenever there is a Crossing-Over?
Ans. On the non-sister chromatids of a homologous pair, the identical allele of a gene may cross over. Crossover may occur in this situation, but unless the alleles on the two chromosomes are distinct, no new variation will result.

5. What are Sex-Linked Traits? Give an Example.
Ans. Traits controlled by a sex chromosome gene or allele are known as sex-linked traits. X-linked recessive conditions are twice as common in females as in males: if 1 in 20 males in a population is red-green colourblind, then 1 in 400 females will be reversed colourblind.