STRUCTURE OF NUCLEIC ACID :

RIBONUCLEIC ACID (RNA )

rRNA,mRNA,tRNA and Micro RNA

BY Dr. Ichha Purak

University ProfessorRanchi Women’s College,Ranchi

http://www.dripurak.com/http://drichhapurak.webnode.com/

Friedrich Miescher  in 1869 discovered substance

nuclein  from the nuclei of pus cells which was

later termed nucleic acid because of having

phosphate group and was of acidic nature.

Nucleic acids are present in all living organisms

(plants,animal,bacteria and even Virus and viriods)

and therefore origin of life is suspected with the

formation of nucleic acids. All living cells contain

both DNA and RNA, while viruses contain either

DNA or RNA, usually not both.

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

2

The nucleic acids are most important

biological macromolecules responsible for transmission and

storage of heredity or genetic information from one

generation to next by means of Replication, Transcription

and Translation.

Nucleic acids are fibre like molecules having much greater

length in comparision to diameter

Nucleic acids are the found in abundance in all living things,

where they function in encoding, transmitting and

expressing genetic information

The nucleic acids are generally associated with proteins to

form nucleoproteins

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

3

There are two types of nucleic acids :

RNA (Ribonucleic acid ) = (Ribonucleotide )n –A U C

G

DNA ( Deoxyribonucleic

acid)=(Deoxyribonucleotide)n– A T C G

These are polymers consisting of long chains of monomers called nucleotides linked in a chain through phosphodiester bond

A nucleotide consists of a nitrogenous base, a

pentose sugar and a phosphate group

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

4

There are two related pentose sugars:

- RNA contains ribose

- DNA contains deoxyribose

The sugars have their carbon atoms numbered with

primes to distinguish them from the nitrogen bases

04

/08

/20

23

5

Stru

cture

of N

ucle

ic Acid

:RN

A

NITROGEN BASES The nitrogen bases in nucleotides consist of two general types: - pyrimidines: cytosine (C), thymine (T) and Uracil (U) - purines: adenine (A) and guanine (G)

04

/08

/20

23

6

Stru

cture

of N

ucle

ic Acid

:RN

A

The primary structure of a nucleic acid

is the nucleotide sequence joined by phosphodiester bonds

The 3’-OH group of the sugar in one nucleotide forms an ester

bond to the phosphate group on the 5’-carbon of the sugar of the

next nucleotide

04

/08

/20

23

7

Stru

cture

of N

ucle

ic Acid

:RN

A

READING PRIMARY STRUCTURE

A nucleic acid polymer has a free 5’-phosphate group at one end and a free 3’-OH group at the other end

The sequence is read from the free 5’-end using the letters of the bases

This example reads

5’—A—C—G—T—3’

04

/08

/20

23

8

Stru

cture

of N

ucle

ic Acid

:RN

A

EXAMPLE OF RNA PRIMARY STRUCTURE

In RNA, A, C, G, and U are linked by 3’-5’ ester bonds between ribose and phosphate

04

/08

/20

23

9

Stru

cture

of N

ucle

ic Acid

:RN

A

RNA is polymer of

Ribonucleotides

RNA is a polymeric

constituent of all living

cells and many viruses. it

is long single stranded

chain of alternating

phosphate and ribose

sugar units with the

nitrogenous bases

Adenine & guanine

(purines) and cytosine and

uracil (pyrimidines)

bonded to ribose sugar.

RIBONUCLEIC ACID (RNA )0

4/0

8/2

02

3Stru

cture

of N

ucle

ic Acid

:RN

A

10

Chemical structure of RNA

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

11

RBONUCLEOTIDES

(AMP )adenosine monophosphate

(GMP) gwanosine monophosphate

PURINES

(CMP) cytidine monophosphate

(UMP) uridine monophosphatePYRIMIDINES

13

STRUCTURE OF RIBO NUCLIC ACIDS

Polymers of four nucleotides Linked by alternating sugar-phosphate

bonds RNA: ribose and A, C, G, U

P sugar

A

P sugar

G

P sugar

C

P sugar

U

AMPCMP

GMP

UMP

RNAs are usually single

stranded, but many RNA

molecules have secondary

structure in which

intramolecular loops are

formed by complementary

base pairing (tRNA and

rRNA ).

Base pairing in RNA follows

exactly the same principles

as with DNA: the two

regions involved in duplex

formation are antiparallel

to one another, and the

base pairs that form are A-

U and C-G

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

14

RNA is much more abundant than DNADFFERENCES BETWEEN RNA AND DNAS N RNA DNA

1 RNA is polymer of Ribonucleotides DNA is polymer of Deoxyribonucleotides

2 RNA has Ribose sugar DNA has Deoxyribose sugar3 Ribose sugar (C5H10O5) has OH-

at C2,C3 &C5Deoxyribose Sugar has OH- only at C3 & C5

4 RNA is generally single stranded Exception tRNA & rRNA at some places are double stranded

DNA is Generally Double Stranded Exception In Bacteriophage Ф- 174 and S-13

5 RNA has Pyrimidines Cytosine and Uracil

DNA has Pyrimidines Cytosine and Thymine

6 RNA generally Non Genetic but in some Viruses it is Genetic Material

DNA is Genetic Material

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

15

7 RNA is not stable DNA is stable in alkaline condition

8 RNA is synthesized by transcription using one strand of DNA as Template

DNA is Synthesized by Replication using both strands of DNA as templates during Interphase

9 In helical regions A-U and C-G are the Base Pairs

A- T and C-G are the Base Pairs

10 The helix geometry of RNA is of A-FormIs destroyed by enzymes and produced again

The helix geometry of DNA is of B-FormProtects itself against enzymes

11 RNA performs the function of a messenger between DNA and the proteins.

DNA performs long term storage and transfer of Genetic Information

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

16

.

RIBOSE

1

OHOCH2

H

H

OH

H

OH

H

OH23

4

5OHOCH2

H

H

OH

H

OH

H

H

1

23

4

5

2-DEOXY-RIBOSE

O N

H N

O

H

CH3

THYMINE

O N

H N

O

H

URACIL

RNA DNA

Molecular Differences between Ribonucleic Acid (RNA)& 2-deoxy-ribonucleic acid (DNA).

Ribose replaces deoxyribose; uracil replaces thymine

RNA0

4/0

8/2

02

3Stru

cture

of N

ucle

ic Acid

:RN

A

17

S N Coding RNA Non-coding RNAs

1 mRNA (Messenger RNA)

2 tRNA ( Transfer RNA)

3 rRNA (Ribosomal RNA

4 snRNA (Small nuclear RNA )

5 snoRNA (Small nucleolar RNA )

6 scRNA (Small cytoplasmic RNA)

7 aRNA (Antisense RNA )

8 miRNA (microRNA )

9 siRNA (small interference RNA )

10 Ribozyme (catalytic RNA )

11 cRNA (Complementary RNA )

12 gRNA ( guide RNA )

TYPES OF RNAs0

4/0

8/2

02

3Stru

cture

of N

ucle

ic Acid

:RN

A

18

MAJOR TYPES OF RNAS0

4/0

8/2

02

3

19

Stru

cture

of N

ucle

ic Acid

:RN

A

04

/08

/20

23

20

Stru

cture

of N

ucle

ic Acid

:RN

A

SYNTHESIS AND MAIN FUNCTIONS OF DIFFERENT RNAs

BRIEF DESCRIPTION OF DIFFERENT RNAS

Messenger RNA(mRNA )-is the only coding RNA as it bears a complementary copy of deoxyribonucleotide sequence present on Gene (DNA segment ) as ribonucleotide sequence. It encodes chemical blueprint for protein synthesis in 5’-3’ direction. It is single stranded

04

/08

/20

23

21

Stru

cture

of N

ucle

ic Acid

:RN

A

Transfer RNA (tRNA) is a

small RNA chain(73-95 nucleotides )

that transfers a specific amino acid

to a growing polypeptide chain at

ribosome during translation.

It acts as a adapter molecule

because it can recognise both a

specific Amino Acid as well as its

codon on mRNA. For loading 20

different protein Amino Acids there

are different tRNAs.(1-20) Each

amino acid is recognized by one or

more specific tRNA

tRNA has a tertiary structure

that is L-shaped one end

attaches to the amino acid

and the other binds to the

mRNA by a 3-base

complimentary sequence

Anticodon

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

22

Ribosomal RNA(rRNA )is the most stable RNA .It is

synthesized by Nucleolar genes

by RNA polymerase I and make

40-60% by weight of total RNA

and is 80% of total RNA of the

cell. It may measure upto 7000

Aᵒ in extended form . It is main

component of ribosomes along

with proteinsRibosomes are the sites of

protein synthesis ,consisting of

ribosomal RNA (65%) and

proteins (35%), have a small

and a large subunit

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

23

Small nuclear RNA

(snRNA) a class of small

eukaryotic RNA molecules

found in the nucleus usually

as ribonucleoproteins which

are involved in processing

heterogenous nuclear

messenger RNA (Splicing of

Exons )U1, U2 U4, U5 and

U6 and also used in RNA

interference

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

24

Small nucleolar RNA (snoRNAs ) are a class of

small RNA molecules that guide chemical modification

(methylation or puedouridylation ) of ribosomal RNAs

Small cytoplasmic RNA (scRNA) small (7S,129

nucleotides) RNA found in cytosol and rough endoplasmic

reticulum associated with proteins ,component of SRP (Signal

Recognition Particle ) that are involved in specific selection and

transport of secretory proteins by recognizing signal sequence at

amino terminus of growing polypeptide chain.

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

25

Signal Sequence directing Protein Targetting

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

26

Antisense RNA (aRNA) is a single stranded RNA

that is complementary to a mRNA strand . Antisence mRNA

(artificially synthesized ) may be introduced into a cell to

inhibit translation of a complementary mRNA by base pairing

to it and physically obstructing (blocking) the translation

machinery. It is thought as promising technique for disease

therapy.

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

27

microRNAs (miRNA )

MicroRNAs were first described in 1993 by Rosalind Lee, Victor

Ambros, and Rhonda Feinbaum in the nematode Caenorhabditis

elegans 

MicroRNAs constitute a recently discovered class of non-coding RNAs

that play key roles in the regulation of gene expression by gene

silencing

Mature microRNAs are short, single-stranded RNA molecules

having about 21- 23 nucleotides in length

The genes encoding miRNAs are much longer than the

processed mature miRNA molecule

MicroRNA genes are transcribed by RNA polymerase II as large

primary transcripts (pri-microRNA)

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

28

Pri-microRNA has a cap and Poly-A tail before undergoing

processing like mRNA Pri-microRNAs are processed by a protein

complex Drosha containing RNase III enzyme to form an

approximately 70 nucleotide precursor microRNA (pre-microRNA).

This molecule has stem-loop structure

This precursor is subsequently transported to the cytoplasm where it

is processed by a second RNase III enzyme, DICER, to form a mature

microRNA of approximately 22 nucleotides

This mature miRNA has some complementary sequences to one or

more mRNAs

The mature microRNA is then incorporated into a ribonuclear particle

to form the RNA-induced silencing complex, RISC, which mediates

gene silencing through RNA interference.

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

29

MicroRNAs usually induce gene silencing by binding to target sites

found within the 3’UTR of the targeted mRNA.

This interaction prevents protein production by suppressing protein

synthesis by initiating mRNA degradation

Since most target sites on the mRNA have only partial base

complementarity with their corresponding microRNA, individual

microRNAs may target as many as 100 different mRNAs.

MicroRNAs play significant role in cell cycle control,apoptosis,stem

cell differentiation etc.MicroRNAs are also involved in tissue-specific

expression

MicroRNAs are a class of post-transcriptional regulators

They are short ~22 nucleotide RNA sequences that bind to

complementary sequences in the 3’ UTR of multiple target mRNAs,

usually resulting in their silencing.

.

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

30

Processing of miRNA

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

31

Function of Micro RNA ( MiRNA) Small but mighty

 a microRNA (miRNA), silences genes0

4/0

8/2

02

3Stru

cture

of N

ucle

ic Acid

:RN

A

32

Small interfering RNA ( siRNA ) is considered

exogenous double-stranded RNA that is taken up by cells, or

enters via vectors like viruses, while miRNA is single stranded

and comes from endogenous (made inside the cell) non-coding

RNA, found within the introns of larger RNA molecules.

siRNA are double stranded RNA fragments,which trigger

catalytically mediated gene silencing by targetting RNA

Induced Silencing Complex ( RISC) to bind and degrade the

mRNA

Both siRNA and miRNA can play a role in epigenetics  through a

process called RNA-induced transcriptional silencing

(RITS). Likewise, both are important targets for therapeutic

use, because of the roles they play in the controlling gene

expression.

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

33

Ribozyme ( Catalytic RNA ) is ribonucleic acid molecules having catalytic activity as protein enzymes

Till 1989 it was believed that all enzymes are proteinaceous in

nature. During observing spilicing mechanism of Group I rRNA

intron from protozoa Tetrahymena thermophila by Thomas Cech

and Sydney Altman, it was realized that no proteins were

involved in this process. It was revealed that RNAs could also

have catalytic function. In this case the rRNA was processed for

removal of intron and spilicing exons without any intervention of

any protein.

This post transcriptional processing of rRNA led to discovery of

RNA enzyme or RIbozyme or Non-protein enzymes.

ExamplesRNase PGroup I and Group II intronsPeptidyl transferase 23S rRNA

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

34

Splicing mechanism of Group I intron .The nucleophile in the first step may be gwanosine,GMP,GDP or GTP

Guide RNA (gRNA) are RNA genes that function in RNA

editing, found in mitochondria by inserting or deleting stretches

of uridylates (Us) . The gRNA forms part of editosome and contain

sequences to hybridize to matching sequences in the mRNA to

guide the mRNA modifications.

Complementary RNA( cRNA ) viral RNA that is transcribed

from negative sense RNA and serves as a template for protein

synthesis

Negative sense RNA viral RNA with a base sequence complementary

to that of mRNA during replication it serves as a template to the

transcription of viral complementary RNA

Positive sense RNA viral RNA with same base sequence as mRNA

during replication function as mRNA ,serving as template for protein

synthesis

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

36

RNA interference Experimental use by introducing

small ds RNAs for functional deactivation of specific genes ,which

induces degradation of complementary single stranded mRNA

encoded by the gene , gene silencing.

RNA interference is a related process in which double stranded

RNA fragnments called small interfering RNAs trigger catalytically

mediated gene silencing most typically by targeting the RNA

induced Silencing Complex (RISC) to bind to and degrade the

mRNA

Attempts to genetically engineer transgenic plants to express

antisense RNA instead activate the RNA pathway, although the

processess result in differing magnitude of gene silencing.

Well known examples include Flavr Savr tomato and two

cultivars of ringspot papaya

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

37

FUNCTIONS OF DIFFERENT RNA

mRNA – It carries genetic formation of DNA ( Gene ) for

protein synthesis from nucleus to ribosome in the form of

genetic code

tRNA – Acts as adapter molecule ,carries Amino Acid and

drops it to particular location by recognising codon on mRNA

by virtue of having anticodon

rRNA – It makes complex with proteins and form ribosomal

subunits which provide space for protein synthesis ,single

ribosomal RNA of smaller subunit helps correct orientation of

mRNA during attachment with respect to P and A sites

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

38

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

39

snRNA – play significat role in eukayotic mRNA processing

By splicing of exons as snRNPs or snurps U1,U2, U4,U5 &U6

scRNA – being component of Signal Recognition Particle (SRP )

helps in targetting of seceretary proteins

snoRNA – Plays role in gene silencing

miRNA – play important role in gene silencing by blocking mRNA

and preventing translation

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

40

Si RNA – Plays important role in gene silencing by interfering

transcription

gRNA- help in RNA editing in mitochondria , forms part of

editosome and hybridize with matching sequence of mRNA

Catalytic RNA –Ribozymes act as protein enzymes in

catalyzing removal of intron, peptide bond formation etc

aRNA- antisense RNA - is artificially used to block translation

of perticular messenger RNAs so as to prevent formation of

some harmful proteins

04

/08

/20

23

Stru

cture

of N

ucle

ic Acid

:RN

A

41

THANK YOU