Not double stranded (except some viruses), deoxyribose  ribose thymine  uracil

(1)

STRUCTURE AND FUNCTION OF RNA

 Not double stranded (except some viruses),

 deoxyribose  ribose

 thymine  uracil

(2)

STRUCTURE AND FUNCTION OF RNA

 messenger RNA (mRNA),

 Transfer RNA (tRNA)

 ribosomal RNA (rRNA)

 mRNA is less stable than

others and can be cleaved by

cellular nuclease.

(3)

RNA Polymerase

It transfers the genetic information from DNA to mRNA.

Catalysts the formation of phosphodiester bonds between ribonucleotides.

The extension of the RNA chain occurs by the addition of nucleotides to the 3 ’OH end of the ribose as in DNA.

RNA polymerase synthesizes in the 5 ‘ 3' direction like DNA polymerase but does not require a primer.

Unlike DNA polymerase, the first base in mRNA synthesized is usually a purine.

RNA polymerase uses a single strand of double-stranded DNA as a template.

Genes are found in both strands of DNA.

(4)

RNA Polymerase

 RNA Polymerases are complex enzymes.

 E. coli contains five subunits β, β ’, α (2 copies), ω (omega) and σ (sigma).

 All of these subunits combine to form the active form of the so-called holoenzyme.

 The sigma factor can be readily separated from this enzyme.

 The role of sigma is to recognize the appropriate site in DNA to initiate RNA synthesis.

(5)

The gene is a DNA region whose final product may be a polypeptide

or an RNA molecule.

(6)

 The genetic code contains the codon for 20 amino acids.

 Amino acids can be modified and incorporated into the protein structure by posttranslational modification.

 21. The amino acid Selenocysteine has the same structure as cysteine, with selenium in the selenocysteine instead of just the sulfur atom.

 The UGA stop codes the codon.

(7)

 Unlike lysine, pyrolysin also has an aromatic ring and

 The UAG is encoded by the stop codon.

 This unique amino acid, found in archaea and

bacteria, was first identified in methanogenic

archaea.

(8)

Reading frame (RF)

The mRNA has codons encoding various amino acids after the

initiating AUG codon, followed by a

stop codon. Such an array is called

a reading frame.

(9)

Open Reading Frame (ORF)

In genome sequence analysis, it is very important to locate the genes encoding protein.

If an RNA can be transcribed, this part of the DNA must contain ORF.

That is, a start codon, codons that encode amino acids, and a stop codon are found in DNA.

The identification of such ORFs in DNA, whether it is a protein or not, is extremely important in genetic

engineering studies.

(10)

Transfer RNA

There are 60 different tRNAs in bacteria and 100-110 different types in mammals.

The tRNA is short (73-93 nucleotides) and single stranded.

Double strands are formed in the tRNA by folding.

The tRNA contains three nucleotides called anticodons that recognize the codon in the mRNA.

The three nucleotides (acceptor ends) at the 3 ’end of all tRNAs do not form pairs, but have a CCA sequence. The amino acid to be transported to the ribose of the most extreme adenine is covalently linked by ester bonds.

(11)

Protein synthesis;

1. Initiation, 2. Elongation,

3. Termination and

4. Folding of the polypeptide Start of protein synthesis:

At the 5 ’end of the mRNA is the

Shine-Dalgarno sequence with 3-9

nucleotides.

(12)

It can synthesize multiple ribosome

proteins on an mRNA. This group of

ribosomes is called polysomes.

(13)

Not double stranded (except some viruses), deoxyribose  ribose thymine  uracil

STRUCTURE AND FUNCTION OF RNA