DNA and RNA | CHAPTER 4 | Basic Science

DNA and RNA – Introduction to fundamental concepts of Biological Science including the organization and common characteristics of living matters, cell structures and functions, food production by photosynthesis, harvesting energy, mechanism of cells reproduction, genetics, evolutions, and Human Biology. Introduction to general chemistry including basic concepts about matter, atomic structure, chemical bonds, gases, liquid, and solids, solutions, chemical reactions, acid, bases, and salt;

organic and biochemistry including hydrocarbons and their derivatives, carbohydrates, lipids, proteins, enzymes, vitamins, and minerals, nucleic acids; principles of physics and applications to nursing including gravity and mechanics, pressure, heat and electricity; nuclear chemistry and nuclear physics, effects of radiation on human beings, and protection and disposal. The aim of the course is to acquire knowledge and skills in general biological science, general chemistry and physics.

DNA and RNA

Deoxyribonucleic acid or DNA is a molecule that contains the instructions an organism needs to develop, live and reproduce. These instructions are found inside every cell, and are passed down from parents to their children.

or

Deoxyribonucleic acid or DNA is a biological macromolecule that carries hereditary information in many organisms.

or

DNA is the poly-deoxyribonucleotide that contains many mononucleotides covalently linked by 35′ phosphodiester bond. It is the store house of genetic information.

Location:

• Chromosome of nucleus.
• Mitochondria

Who discovered DNA?

The Swiss biochemist Frederich Miescher first observed DNA in the late 1800s. But nearly a century passed from that discovery until researchers unraveled the structure of the DNA molecule and realized its central importance to biology,

For many years, scientists debated which molecule carried life’s biological instructions. Most thought that DNA was too simple a molecule to play such a critical role. Instead, they argued that proteins were more likely to carry out this vital function because of their greater complexity and wider variety of forms.

The importance of DNA became clear in 1953 thanks to the work of James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin. By studying X-ray diffraction patterns and building models, the scientists figured out the double helix structure of DNA – a structure that enables it to carry biological information from one generation to the next.

The structure of DNA

The DNA is a polymer molecule with four types of basic chemicals. These are called the deoxyribonucleotides. They contain:
1. A sugar (deoxyribose)
2. A negatively charged phosphate group
3. The bases

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

The nucleotides are linked together by covalent phosphodiester bonds.

Figure: Structure of DNA

Double Stranded Helix

When looking at the structure, Watson and Crick found that DNA is a double stranded helix or a ladder that is twisted. Here the bases form the rungs of the ladder and the sugar phosphates are on the outside.

There are hydrogen bonds between a large purine base (A or C) on one strand and a small pyrimidine base (T or C) on the other chain. The base-pair sequence is usually referred to as the primary structure of DNA. This sequence determines the actual structure of the DNA.

Importance of DNA:

• DNA carries the genetic code and this is what is read by the protein synthesis mechanism when it makes new proteins.
• The relationship between DNA and proteins is vital for living organisms. A protein is an abundant and complex molecule found in the body. These may be important for forming the body structure (Structural proteins), messengers, enzymes, hormones etc.

Functions of DNA:

Genetic Information (Genetic Blue Print):

• DNA is the genetic material which carries all the hereditary information
• The genetic information is coded in the arrangement of its nitrogen bases.

Replication:

• DNA has unique property of replication or production of carbon copies (Autocatalytic function).
• This is essential for transfer of genetic information from one cell to its daughters and from one generation to the next.

Chromosomes:

• DNA occurs inside chromosomes. This is essential for equitable distribution of DNA during cell division

Mutations:

• Changes in sequence of nitrogen bases due to addition, deletion or wrong replication give rise to mutations.
• Mutations are the fountain head of all variations and evolution.

Transcription:

• DNA gives rise to RNAs through the process of transcription. It is heterocatalytic activity of DNA

Cellular Metabolism:

• It controls the metabolic reactions of the cells through the help of specific RNAs, synthesis of specific proteins, enzymes and hormones

Differentiation:

• Due to differential functioning of some specific regions of DNA or genes, different parts of the organisms get differentiated in shape, size and functions.

Development:

• DNA controls development of an organism through working of an internal genetic clock with or without the help of extrinsic information

Gene Therapy:

• Defective heredity can be rectified by incorporating correct genes in place of defective ones.

Antisense Therapy:

• Excess availability of anti-mRNA or antisense RNAs will not allow the pathogenic genes to express themselves.
• By this technique failure of angioplasty has been checked. A modification of this technique is RNA interference (RNAi).

Ribo-Nucleic Acid (RNA)

Definition of Ribo-Nucleic Acid (RNA)

RNA molecules are single-stranded nucleic acids composed of nucleotides. RNA plays a major role in protein synthesis as it is involved in the transcription, decoding, and translation of the genetic code to produce proteins.

RNA nucleotides contain three components:

• A Nitrogenous Base
• A Five-Carbon Sugar
• A Phosphate Group

Types of RNA

Structure of RNA

RNA is typically single stranded and is made of ribo-nucleotides that are linked by phosphodiester bonds. A ribonucleotide in the RNA chain contains ribose (the pentose sugar), one of the four nitrogenous bases (A, U, G, and C), and a phosphate group. The subtle structural difference between the sugars gives DNA added stability, making DNA more suitable for storage of genetic information, whereas the relative instability of RNA makes it more suitable for its more short-term functions.

The RNA-specific pyrimidine uracil forms a complementary base pair with adenine and is used instead of the thymine used in DNA. Even though RNA is single stranded, most types of RNA molecules show extensive intra-molecular base pairing between complementary sequences within the RNA strand, creating a predictable three-dimensional structure essential for their function (Figure 1 and Figure 2).

Figure-1

a) Ribonucleotides contain the pentose sugar ribose instead of the deoxyribose found in deoxyribonucleotides.
b) RNA contains the pyrimidine uracil in place of thymine found in DNA

Figure-2

(a) DNA is typically double stranded, whereas RNA is typically single stranded,
(b) Although it is single stranded, RNA can fold upon itself, with the folds stabilized by short areas of complementary base pairing within the molecule, forming a three-dimensional structure.

Differences between DNA and RNA

Well to know

DNA present in:

• Chromosomes and
• Mitochondria

RNA present in:

• Nucleus (chromosome).
• Mitochondria
• Ribosome and
• Endoplasmic reticulum.

Read More…. 

• Definition of Nucleus | CHAPTER 3 | Basic Science