Types of RNA (ribonucleic acid)

Types of RNA

RNA is a polymer of ribonucleotides, formed from DNA by transcription.     And it translates to protein to perform specific functions of cell. Types of RNA are:

Messenger RNA (mRNA):

  • mRNA carries the genetic information from DNA to Ribosome.
  • It acts as a template for protein synthesis.
  • It carries the information for the arrangement of amino acids in a polypeptide chain.
  • They are monocistronic in eukaryotes and polycistronic in prokaryotes (codes for many polypeptide chains).

                         mesenger RNA

Ribosomal RNA (rRNA):

  • Most abundant RNA found in cells.
  • They are the structural components of ribosomes.
  • They are 3 types in prokaryotes 5S, 16S23S.RIBOSOME 70S


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Mutation is a sudden inheritable variation.

  • Term given by Hugo de Vries while working on the plant Oenothera lamarckiana (Evening Primrose).

  • 1st experimental evidence on mutation was given by Morgan while working on eye color in Drosophila. White eye color is due to a recessive mutation having occurred on the X-chromosome.

Mutations are of 2 types: – Chromosomal mutations and Gene mutations.

Chromosomal mutations:

It includes chromosomal aberrations and genomic mutations.

Chromosomal aberrations change in chromosome structure.

They are 4 types: Deficiency, Duplication, Translocation, and Inversion.


It is the loss of certain genes from a haploid genome. It may be terminal or interstitial. E.g.,

  • Notched wing in Drosophila is due to deletion of a segment in X-chromosome.

  • Cri-du-chat syndrome in humans is due to deletion of a part of the short arm of chromosome 5.


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Electron transport chain (ETC)

Electron Transport Chain

Electrons from NADH and FADH2 are passed through a series of electron acceptors present in the inner membrane of mitochondria.

  • 2 NADH produced during glycolysis,
  • 2 NADH, produced during pyruvic acid oxidation, &
  • 6 NADH AND 2 FADH2, produced during Kreb cycle.

Four enzyme complexes of ETC

  1. Complex I – NADH dehydrogenase complex.
  2. Complex II – Succinate-UQ reductase complex.
  3. Complex III – UQH2-cytochrome c reductase complex.
  4. Complex IV – Cytochrome c oxidase complex.


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DNA Structure – Mnemonic

DNA Structure – Mnemonic

PURines (A, G) – PURe As Gold.

A- Adenine
G- Guanine

PYrimidines (C, U, T)-CUT the PY (pie).

C- Cytosine
U- Uracil
T- Thymine

Base Pairing

      A= T(Dna)   =U(Rna)                           G≡C(Dna & Rna)

– Double H Bond                                         – Triple H Bond
– Weaker Bond                                             – Stronger Bond

nucleoSide = base + Sugar.

nucleoTide = base + sugar + phosphaTe.

Simple Nucleotide and Nucleoside


DNA Replication

DNA Replication

  • Occurs in the nucleus during the S phase of the cell cycle.
  • It is an autocatalytic function of DNA.
  • It occurs in a semi-conservative manner.

dna replication


Sequence of base pairs in the genome where DNA replication begins. A Nick is created.


Helps in unwinding the two strands by breaking hydrogen bonds.


Helps in relieving tension caused due to unwinding.

Single stranded binding proteins

Prevents reannealing of the two strands.

Replication fork

Y-shaped fork formed due to the separation of the two strands.


forms the RNA primer at the ORI.

RNA primer

Short strand of RNA formed at ORI as DNA polymerase III requires a free OH group at 3′ end to add nucleotides.


The nucleotides are high energy compounds present in triphosphate form, they act as the substrate for the new strand and also provide energy to form hydrogen bonds between nitrogenous bases.


Addition of nucleotides and it always occurs in 5′→3′ direction.

DNA polymerase III

Needed to form the new strand. Shows polymerization in 5′→3′ direction and exonuclease activity in 3′→5′ direction.

Leading and Lagging strands

3′→5′ strand is the leading strand as the new strand starts forming as the two strands separate. 5′→3′ strand is lagging strands as the new strand starts forming only after a short part of DNA has opened up.

Continuous and Discontinuous

The new strand is formed in a continuous manner in the leading strand and in a discontinuous manner in the lagging strand.

Okazaki fragments

Short fragments formed on the lagging strand.

DNA polymerase I

Shows exonuclease and polymerization activity. Removes RNA primer and adds deoxyribonucleotides in its place.

DNA ligase

Helps in joining of Okazaki fragments.

dna replication