6.0 EXPRESSION OF BIOLOGICAL INFORMATION part 2

1. 6.0 EXPRESSION OF BIOLOGICAL INFORMATION part 2 BY : MDM. NURFAZLINI ISMAIL

2. 6.1 DNA and genetic information 6.2 DNA Replication 6.3 Protein synthesis: transcription and translation 6.4 Gene regulation and expression — Iac operon

3. 6.3 Protein Synthesis: Transcription And Translation At the end of this lesson students should be able to : • Explain briefly transcription and translation. • Introduce codon and its relationship with sequence of amino acid using genetic code table.

4. Overview of Protein Synthesis • The DNA that codes for the proteins is located in the nucleus but proteins are actually made by the ribosomes in the cytoplasm. • DNA is too large to leave the nucleus (double stranded), but RNA can leave the nucleus (single stranded).

5. Overview of Protein Synthesis • Gene expression, the process by which DNA directs protein synthesis, includes two stages: transcription and translation. • Transcription produces single-stranded mRNA • Translation is the synthesis of a polypeptide, using information in the mRNA Nuclearenvelope DNA TRANSCRIPTION Pre-mRNA RNA PROCESSING mRNA TRANSLATION Ribosome Polypeptide

6. Protein Synthesis: Transcription • Occurs in nucleus • mRNA synthesis is catalyzed by RNA polymerase in the 5’ – 3’ direction. • Only one strand will be used as template • Transcription begins at a specific point on the DNA called promoter and terminates at a specific point called terminator site. • RNA synthesis follows the same base-pairing rules as DNA, except that uracil substitutes for thymine

8. Stages in Transcription 1. Initiation RNA polymerase bind to promoter on DNA and unwinds DNA strands 2. Elongation RNA polymerase move along strands of DNA template and adds RNA nucleotides in 5’-3’ directions. 3. Termination RNA polymerase reaches terminator site on DNA and stop transcription

9. Protein Synthesis: Translation • Occurs in ribosome in cytoplasm • A cell translates an mRNA message into protein with the help of transfer RNA (tRNA) • tRNAs transfer amino acids to the growing polypeptide in a ribosome • mRNA carry information in triplet codes known as codon. • Translation begin at specific point of mRNA which is start codon and stop at specific point of mRNA which is stop codon.

10. Stages in Translation - Initiation 3. Proteins called initiation factors bring in the large subunit that completes the translation initiation complex 1. A small ribosomal subunit binds with mRNA and then the small subunit moves along the mRNA until it reaches the start codon (AUG) Largeribosomalsubunit U 3 5 C A P site 2. A tRNAcarrying methionine binds to small subunit of ribosome forming an initiation complex. Met Met 3 5 A G U P i InitiatortRNA  GTP GDP E A mRNA 5 5 3 3 Start codon Smallribosomalsubunit Translation initiation complex mRNA binding site

11. Stages in Translation - Elongation Amino end ofpolypeptide E 3 mRNA Ribosome ready fornext aminoacyl tRNA • Occurs in three steps: codon recognition, peptide bond formation, and translocation • Growing polypeptide chain form at P site and new tRNA with an anticodon complimentary to the codon on mRNA enter the A site. • Translation proceeds along the mRNA in a 5′ to 3′ direction Asite Psite 5 GTP GDP  P i E E P A A P GDP  P i GTP E A P

12. Stages in Translation - Termination P 3. This reaction releases the polypeptide, and the translation assembly then comes apart 1. Termination occurs when a stop codon (UAA, UGA, UAG)in the mRNA reaches the A site of the ribosome Releasefactor Freepolypeptide 5 3 3 3 GTP 2 5 5  2 GDP 2 Stop codon i (UAG, UAA, or UGA) 2. The A site accepts a protein called a release factor, causes the addition of a water molecule instead of an amino acid

13. Codon : Triplets of Nucleotides • The flow of information from gene to protein is based on a codon (triplet bases) on the mRNA. • Each codon will encode for one amino acids as shown in genetic code table. • 3 bases (triplet code) = 1 codon = 1 amino acid • Start codon = AUG = encode for amino acid methionine = Signal for start of translation • Stop codon = UAA , UGA , UAG = no amino acids= Signal for end of the translation

14. DNAtemplatestrand DNA 5 3 molecule A A A A A T C C C C G G T T T T A G G G G C T C Gene 1 3 5 TRANSCRIPTION Gene 2 U G G U U U G G C U C A 5 3 mRNA Codon TRANSLATION Gly Phe Trp Protein Ser Gene 3 Amino acid

15. Genetic Code • The genetic code is a sequence of codon • There are 64 possible combination of triplet bases. • Codons must be read in the correct reading frame in order for the specified polypeptide to be produced • Some of the amino acids are encoded by more than one codon. • However, one codon only encode for one amino acid.

16. 6.4 Gene Regulation and Expression — Iac Operon At the end of this lesson students should be able to: • Explain the concept of operon and gene regulation. • State the components of operon.

17. Operon – The Basic Concept • An operon is cluster of genes that expressed as a group and controlled by single promoter. • Operon system control protein synthesis in prokaryotic cells. • Eukaryotic cells do not have operon system. • The operon can be switched off by a protein repressor An operon is the entire stretch of DNA that includes the operator, the promoter, and structural genes that they control