Gen.Code1

GENETIC CODEANDPROTEIN SYNTHESIS : Here comes your footer ? Page 1 GENETIC CODEANDPROTEIN SYNTHESIS A Presentation by BBIPL

The Central Dogma of Molecular Biology : Here comes your footer ? Page 2 A Presentation by BBIPL The Central Dogma of Molecular Biology Cell

The Genetic Language : Here comes your footer ? Page 3 The Genetic Language The genetic code is a written language not unlike English While English uses 26 letters to spell out words, genetic languages use only 4 nucleotide “letters” The DNA nucleotide language is transcribed into the RNA nucleotide language The nucleotide language must be translated into the amino acid language to make proteins A Presentation by BBIPL

The Nucleotide Language : Here comes your footer ? Page 4 The Nucleotide Language DNA - ATGCATGCATGC RNA - AUGCAUGCAUGC A Presentation by BBIPL

Nucleotide Words : Here comes your footer ? Page 5 Nucleotide Words Words in the nucleotide language are all 3 letters or bases long This means that there can only be 43 = 64 unique words If each codon was only 2 bases long, there would be 42 = 16 possible unique codons This would not provide enough unique meanings to code for the 22 things (20 amino acids plus start and stop) that have to be coded for. A Presentation by BBIPL

A Codon : Here comes your footer ? Page 6 A Presentation by BBIPL A Codon Dr. Aman Biswas

Slide 7 : Here comes your footer ? Page 7 Is Redundancy or Degeneracy of Genetic Code helpful? Q 1 Regarding genetic code A Presentation by BBIPL

The Genetic CodeHelps To Control The Impact Of Point Mutations : Here comes your footer ? Page 8 The Genetic CodeHelps To Control The Impact Of Point Mutations A Presentation by BBIPL

The Genetic Language : Here comes your footer ? Page 9 The Genetic Language The genetic code is a written language not unlike English While English uses 26 letters to spell out words, genetic languages use only 4 nucleotide “letters” The DNA nucleotide language is transcribed into the RNA nucleotide language The nucleotide language must be translated into the amino acid language to make proteins A Presentation by BBIPL

Slide 10 : Here comes your footer ? Page 10 DNA - ATGCATGCATGC RNA - AUGCAUGCAUGC A Presentation by BBIPL

TRANSCRIPTION : Here comes your footer ? Page 11 TRANSCRIPTION A Presentation by BBIPL It takes place by the usual process of complementary base pairing, catalyzed by the enzyme RNA potymerase. The reaction can be divided into four stages. Formation of transcription complex (of DNA and RNA polymerase) 2. Initiation 3. Elongation and 4. Termination.

1. Formation of Transcription Complex : Here comes your footer ? Page 12 1. Formation of Transcription Complex The enzyme RNA polymerase needs to bind with specific sequences on a DNA. These sequences, RNA polymerase is the key enzyme in transcription, it is worthwhile to study the details of its structure and mode of its action. A single type of RNA polymerase is responsible for synthesis of m-RNA, r-RNA and t-RNA in bacteria. A Presentation by BBIPL

Types of RNA Polymerase : Here comes your footer ? Page 13 Types of RNA Polymerase In eukaryotes several different enzymes are required to synthesis the different types of RNA : A Presentation by BBIPL Enzyme types Synthesizes RNA polymerase I … r–RNA RNA polymerase II and … m–RNA RNA polymerase III … t–RNA

Promoter : Here comes your footer ? Page 14 Promoter Recognized by RNA polymerase are called promoter. The size of the promoter region is variable. In prokaryates it varies from 20-200 bases. Core enzyme can not recognize the promoter region, sigma factor is required for recognition and formation of the complex. It occurs in four steps : (i) Sigma factor recognizes the promoter sequences. (ii) RNA polymerase attaches to promoter region. RNA polymernse melts the helical structure and separates two strands of DNA locally. RNA polymerase initiates RNA synthesis. The site at which the first nucleotide is incorporated is called the start site or initiation point. A Presentation by BBIPL

Features of Pribnow : Here comes your footer ? Page 15 Features of Pribnow A Presentation by BBIPL a. The Pribnow box (after the name of its discover, David Pribnow) or-10 box is a sequence contained with the promoter region. It is located 5-10 bases to the left, i.e., upstream the first four bases that will be copied into RNA. It orients RNA polymerase as to the direction and start of synthesis. b. All Pribnow boxes are variants of TATAATG sequences and sometimes referred to as TATA box. Typically it contains nine bases. c.Since the RNA polymerase has a huge size, it comes into contact with Pribnow box. d. Once bound to the Prinbox box, RNA polymerase dissociates from the initial recognition site. e. This complex is active intermediate in RNA chain initiation. The important event is the melting of DNA duplex that takes place about 10 bases pairs upstream of TATA box and extending to the first transcribe base at the start point.

2. Initiation : Here comes your footer ? Page 16 2. Initiation Core enzyme starts transcription at the separated DNA strands of an initiation complex. As the enzyme moves along, the unwound region moves with it. The first base copied is always within six to nine bases of the conserved T of the Pribnow box on the unwound portion of 3'—5' strand of DNA. Formation of hydrogen bonds is always as per the base-pairing rules. A Presentation by BBIPL

3. Elongation : Here comes your footer ? Page 17 3. Elongation a. The core enzyme polymerase moves in 3'—5' direction of the coding strand . b. The incoming NPT forms a phosphodiester bond with 3'–OH end of the preceding ribonucleotide. c. The bases are determined by the sense strand by base-pair roles. d. The DNA helix recluses after RNA polymerase transcribes through it and growing RNA chain dissociates from the DNA. A Presentation by BBIPL

4. Termination : Here comes your footer ? Page 18 4. Termination Specific sequences on the DNA molecule function as the signal for termination of the transcription process. a. The signal could be two inverted GC rich regions separated by intervening region followed by AT rich sequences. b. A sequence of Adenine that codes for 6 to 8 Uracil residues. The Uracil residues are followed by one Adenine. c. There is no unique base for the termination of transcription e.g., for a given promoter, RNA might end with 5 U's or 6 Us' + I A. A Presentation by BBIPL

Slide 19 : Here comes your footer ? Page 19 d. Rho (r) protein and the sequences mentioned, together bring about termination. At specific termination sites the new RNA chain may be released. The rho protein binds very tightly to the RNA (not to polymerase) and in this bound state it behave as ATPase. e. Rho factor then dissociates RNA and RNA polymerase form the DNA. A Presentation by BBIPL

The Operon Model of Gene Expression : Here comes your footer ? Page 20 The Operon Model of Gene Expression On the basis of their studies with the lac system, François Jacob and Jaques Monod proposed the Operon Model of Gene Expression in bacteria. An operon is a cluster of genes that are transcribed as a single mRNA. Genes in an operon code for a diffusible gene product which may be a polypeptide or an RNA molecule. A Presentation by BBIPL

Inducible enzyme : Here comes your footer ? Page 21 Inducible enzyme Sugar(s) in Growth Medium Relative Amount of b- galactosidase Glucose 1 Glucose + lactose 50 Lactose 2500 A Presentation by BBIPL

Genetic Induction : Here comes your footer ? Page 22 Genetic Induction A Presentation by BBIPL

Slide 23 : Here comes your footer ? Page 23 Genetic Induction A Presentation by BBIPL

Slide 24 : Here comes your footer ? Page 24 Genetic Induction A Presentation by BBIPL

Slide 25 : Here comes your footer ? Page 25 Genetic Induction A Presentation by BBIPL

Slide 26 : Here comes your footer ? Page 26 A Presentation by BBIPL Repressible enzymesGenetic Repression

The Genetic Code : Here comes your footer ? Page 27 Stop Codon Names - Ochre - Amber -Umbel †Have amine groups A Presentation by BBIPL The Genetic Code Neutral Non-polar Polar Basic Acidic *Listed as non-polar by some texts S E C O N D B A S E A GGU GGC GGA GGG Gly* AGU AGC AGA AGG Arg G CGU CGC CGA CGG Arg G UGU UGC UGA UGG C GAU GAC GAA GAG AAU AAC AAA AAG Glu CAU CAC CAA CAG A UAU UAC UAA UAG Stop Tyr GUU GUC GUA GUG Val AUU AUC AUA AUG start Ile CUU CUC CUA CUG Leu U UUU UUC UUA UUG Leu Phe Met/ GCU GCC GCA GCG Ala ACU ACC ACA ACG Thr CCU CCC CCA CCG Pro C UCU UCC UCA UCG Ser U C A G U U C A G U C A G U C A G Gln† Trp Cys T H I R D B A S E F I R S T B A S E Asp Lys Asn† Stop Ser His UAA UAG UGA

Wobble base in Codon is Fortuitous : Here comes your footer ? Page 28 Wobble base in Codon is Fortuitous Effect of mutations is minimized in the genetic code. Mutation of the third base in a codon changes the codon meaning only 1/3 of the time. i.e. UUU = Phenylalanine UUC = Phenylalanine A Presentation by BBIPL

Codon AssignmentIs Fortuitous : Here comes your footer ? Page 29 Codon AssignmentIs Fortuitous Because of wobble base pairing, less than 61 tRNAs have to be made 53% of purine to purine or pyrimidine to pyrimidine mutations in the second position result in codons with either the same meaning (i.e. UAA to UGA both = stop) or coding for chemically related amino acids A Presentation by BBIPL

Slide 30 : Here comes your footer ? Page 30 Is Genetic Code always Universal ? Q 2 Redarding genetic code A Presentation by BBIPL