UNIT I RNA AND TYPES R.KAVITHA,M.PHARM LECTURER DEPARTMENT OF PHARMACEUTICS SRM COLLEGE OF PHARMACY KATTANKULATUR

Transcription

1 UNIT I RNA AND TYPES R.KAVITHA,M.PHARM LECTURER DEPARTMENT OF PHARMACEUTICS SRM COLLEGE OF PHARMACY KATTANKULATUR

2 RNA, as previously mentioned, is an acronym for ribonucleic acid. There are many forms of RNA which are quite similar to DNA. All types of RNA are transcribed from DNA in a process called transcription which is examined in detail in the Transcription and Translation section

3 The 5 Carbon sugar in RNA nucleotides is ribose instead of deoxyribose. (A structural diagram is shown below) RNA nucleotides have Adenine, Guanine, and Cytosine as bases, but Thymine is replaced with Uracil (U), which forms a basepair with Adenine. DNA is double helix, but RNA usually is a single strand which can have complex twisted and folded secondary and tertiary structures. DNA is typically longer than RNA. DNA is generally more stable than RNA. DNA is more resistant to spontaneous and enzymatic breakdown, and damage can be repaired because the opposite strand has complementary information. RNA is more reactive due to a reactive OH side group on the ribose sugar. Direct repairs are not possible if it is a single strand. There are several classes of RNA, each with their own function.

4 TYPES OF RNA: The types of RNA that we are concerned with are: 1.Messenger RNA (mrna) 2.Transfer RNA (trna) 3.Ribosomal RNA (rrna)

5 Messenger RNA: mrna is synthesized on DNA and contains the information needed to build a protein. mrna travels from the nucleus of a cell to ribosome, the place where protein synthesis occurs, and is read by the ribosome. The result is a protein. Hence the name, messenger RNA. The information that mrna carries is written in genetic code a sequence of bases. The code is not complicated it's like a sentence a series of words. Each code word is called a codon, a sequence of three adjacent nucleotides that specifies one of twenty amino acids. There are 64 possible codons (4 x 4 x 4), and each codon codes for an amino acid. The table below shows which codons code for which amino acids.

6 UUU phenylalanine UUC phenylalanine UUA leucine UUG leucine Messenger RNA Codons and Their Corresponding Amino Acids Second Base U C A G UCU serine UCC serine UCA serine UCG serine UAU tyrosine UAC tyrosine UAA stop ** UAG stop ** UGU cysteine UGC cysteine UGA stop ** UGG tryptophan Third Base U C A G CUU leucine CUC leucine CUA leucine CUG leucine CCU proline CCC proline CCA proline CCG proline CAU histidine CAC histidine CAA glutamine CAG glutamine CGU arginine CGC arginine CGA arginine CGG arginine U C A G AUU isoleucine ACU threonine AUC isoleucine ACC threonine AUA isoleucine ACA threonine AUG methionine * ACG threonine AAU asparagine AAC asparagine AAA lysine AAG lysine AGU serine AGC serine AGA arginine AGG arginine U C A G GUU valine GUC valine GUA valine GUG valine GCU alanine GCC alanine GCA alanine GCG alanine GAU aspartate GAC aspartate GAA glutamate GAG glutamate GGU glycine GGC glycine GGA glycine GGG glycine U C A G

7 THE STRUCTURE OF mrna mrna in both prokaryotic and eukaryotic cells is divided into three sections: 1.The 5' Leader (or just Leader) 2.The Coding Region 3.The 3' Trailer (or just Trailer)

8 TRANSFER RNA

9 RIBOSOMAL RNA rrna, or Ribosomal RNA, contributes significantly to the structure of the ribosomes in a cell. mrna, and trna work together the the ribosomes to synthesize proteins. In eukaryotes, rrna is transcribed exclusively within the nucleolus while other types of RNA are synthesized throughout the nucleus. After being produced, long primary rrna strands are processed at once by a special enzyme to yield the specific shorter strands of rrna that are needed for ribosome assembly. In eukaryotes, there are three forms of rrna: 1.18 S S 3.28 S There is also a 5 S form, but it is transcribed from a seperate gene and prepared outside of the nucleolus. In case you are wondering, S is a sedimentation or density unit that is used in describing the results of ultracentrifugation and refelcts the size and shape of a molecule or a particle. The larger the value of S is, the bigger the particle is. rrna forms the skeleton of ribosomes. The remainder of the ribosomes is comprised of proteins made in the cytoplasm. They enter the nucleus and then the nucleolus and then join rrna. The assembly of ribosomes is completed in the cytoplasm. Completed ribosomes have two parts: 1.60 S subunit 2.40 S subunit The 60 S subunit contains the 28 S rrna, the 5.8 S rrna, the 5 S rrna, and around 45 to 50