what s gene and their definition

 

GENE

Genes are unit of inheritance. These are located on chromosome in linear form and carried information from parents to offspring by gametes. Gene control the expression of characters. Gene was first visualize by MENDEL and called it factor. The word gene introduce by Johannsen  in 1909. In a simple language gene is a segment of DNA with specific sequence of nucleotide which has coded information for specific character or for specific protein.

TYPES OF GENES

1.   House-keeping genes-

Active in every organisms and all time (example glycolysis)

2.   Luxury genes- Inactive for most of the time and expressed in certain cells or at certain time only when their products are needs.

3.   Structure genes-These  genes code for substances which are needed for the morphological or functional traits of the cell

4.   Control genes-Positive and negative control on functioning of structural genes.     

a)     Regulator genes

b)     Operator genes

c)     Promoter genes

d)     Terminator genes

 

5.   Interrupted gene and discontinuous genes-

                I.          Split genes

             II.          Introns

6.   Alternative genes- These are form different discontinuous genes get connected forming several new combinations.

7.     Overlapping genes- In overlapping sequence code for more than two different proteins. Its means same specific nucleotide sequence is shared in the transcription of two different mRNA for the synthesis of two non-homologous proteins

8.   Transposons genes- jumping genes (from one position to another position in in the genome of a cell)

9.   Smart genes- Artificially constructed genetic molecules composed of one or more genes code for functional protein or enzymes.

 

NUCLEIC ACID {DNA AND RNA}

 History of Nucleic Acid

Nucleic acid was first discovered by Friedrich Miescher in 1869. He gave its first name as nuclein. In the early 1880s Albrecht Kossel further purified the substance and discovered its highly acidic properties. He later also identified the nucleobases.

WHAT IS NUCLEIC ACID

Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nucleic acids are deoxyribonucleic acid and ribonucleic acid.

5-Carbon sugar--    Pentose is a monosaccharide (simple sugar) with five carbon atoms.

Phosphate group--  Phosphate groups are attached to the 5' carbon of a nucleotide and 3'                                            carbon of adjacent nucleotide in a DNA strand.

Nitrogenous base-- 

purines- (Adenine (A) and Guanine (G))

pyrimidine- (Cytosine (C) and Thymine (T)) 

These nitrogenous bases are attached to C1' of deoxyribose through a glycosidic bond. Deoxyribose attached to a nitrogenous base is called a nucleoside.

Types of nucleic acid--

There are two types of nucleic acids: DNA and RNA

1. DNA--deoxyribonucleic acid
2. RNA--Ribonucleic acid 

1.  DNA 

1.  DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA
2. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA)

2.  RNA

1. RNA- A polymer of ribonucleotides, is a single stranded structure. 
2. There are three major types of RNA- m RNA,t RNA and r RNA.

STRUCTURE OF DNA--

1. The structure of DNA is illustrated by a right handed double helix, with about 10 nucleotide pairs per helical turn 
2. Each spiral strand, composed of a sugar phosphate backbone and attached bases, is connected to a complementary strand by hydrogen bonding (noncovalent) between paired bases, adenine (A) with thymine (T) and guanine (G) with cytosine (C).

https://www.nature.com/scitable/content/ne0000/ne0000/ne0000/ne0000/104573282/74---Copy_1_2.jpg

DNA DENATURATION 

• DNA denaturation is the separation of a double strand DNA molecule into two single strands DNA, which occurs when the hydrogen bonds will be breaks present between the double strand of DNA This process occurs when dsDNA expose by heat, change in pH and some chemicals etc.

 DNA REPLICATION

DNA replication is the process where DNA makes same copies of itself . Replication occurs at the rate of between 50 nucleotide per second ( in mammals ) and 500 nucleotides per second ( in bacteria). Watson and crick give this mechanism basis on their double helical structure Each strand of DNA serves as a template on which its complementary strand is synthesised . This method of DNA replication is described as semi - conservative , because each daughter DNA molecule is a hybrid conserving one parental polynucleotide strand and the other one newly synthesised strand.

Important Point of Replication Process-

1. The base pairing during DNA replication, i.e., adenine pairs with thymine and guanine with cytosine.
2. Nucleotide monomers are added one by one to the 3 ' end of the growing strand by the enzyme DNA polymerase. 
3. The sequence of nitrogenous bases in each daughter strand being formed is complementary to the base sequence in the template strand. 
4. C - 3 ' carbon of deoxyribose present on the 3 ' end of the new polynucleotide chain of DNA has OH group and is free to bind to another nucleotide . C - 5 ' carbon of deoxyribose on the 5 ' end of polynucleotide chain has a phosphate . Therefore , the new polynucleotide chain is always synthesized in 5 ' → 3 ' direction.

Requirements for DNA Replication

1. Precursor nucleotide molecules- dNTPs, dATPs, dGTPs, dCTPs, dTTPs.
2. Template DNA 
3. RNA Primer
4. Enzyme-DNA polymerase, Ligase, helicases.
5. Proteins-DNaA, SSB protein