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Objectives: To outline the flow of genetic information from DNA to protein synthesis.

Expression of genetic information (Part I). Objectives: To outline the flow of genetic information from DNA to protein synthesis. To identify the different types of RNA To compare, the structure of DNA & RNA.

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Objectives: To outline the flow of genetic information from DNA to protein synthesis.

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  1. Expression of genetic information (Part I) Objectives: To outline the flow of genetic information from DNA to protein synthesis. To identify the different types of RNA To compare, the structure of DNA & RNA. To outline the general characteristics of genetic code & transcription process. To explain the importance of tRNA, mRNA & rRNA. To diagram the process of protein synthesis. To compare Eukaryotic & prokaryotic mRNA

  2. Gene DNA d. h. Informational unit is required to carry out one or more cellular function. • Number: 70,000 – 100, 000. • A sequence of bases (A –T – C – G). • Has specific location on DNA d.h. • The 4 bases A, T, C and G, form the 4 letters alphabet of the gene (genetic) language. • The word of the gene is called the genetic code. • The code is formed of 3 letters from the alphabet of gene language. So the genetic code is called triple code DNA strand Letters of alphabet of genetic language Triple code (genetic word) ATCGCCGGATT Gene = Sequence of bases & has specific location

  3. Genetic information flow from nucleus into cytoplasm Triple code 1- Triple code (3 successive bases in DNA) determines the complementary bases of mRNA codon (during transcription). 2- Each codon determines the anticodon of tRNA (during translation). 3- Each tRNA carry specific amino acid, so the codons in mRNA determines the amino acids of polypeptide chain (protein). Transcription mRNA codon Translation by Ribosomes Amino acid of polypeptide chain

  4. Expression of genetic information • Definition: a complex process in which the genetic information in DNA is decoded and used to specify the manufacture of specific protein in the cell. • Includes 2 steps: • 1) Transcription or Copying • mRNA molecules are synthesized as complementary copies of DNA template • 2) Translation • Conversion of genetic language in mRNA molecule (codons) into amino acid language of protein Leads to

  5. RNA - molecules Adenine Guanine Cytosine Uracil • Types : - mRNA (messenger RNA) - tRNA (transfer RNA) - rRNA (ribosome) • Polynucleotides like DNA • It has some differences: 1- Single strand, but folded, form short double stranded segment. 2- Pentose sugar is ribose 3- The base Uracil substitutes for thymine Ph. One Base 5’ 4’ 1’ Sugar 2’ 3’ OH Ph. One Base Sugar OH OH

  6. Overview of transcription and translation

  7. Transcriptionprocess Structure of Gene in DNA strand: 2 strands formDNA d. h. Transcribed region DNA strand Promoter Upstream down stream mRNA region leader sequence trailing region termination signal Protein coding sequence

  8. Promoter: - specific sequence at beginning of the gene - the binding site of RNA –polymerase • Transcribed region: – upstream leader sequence – protein coding sequence (translated region) – down stream trailing sequence • mRNA termination region: - specific sequence at the end of the gene - signal the RNA polymerase to stop the transcription - release mRNA

  9. Transcribed region Steps of Transcription: 1- Binding of RNA –polymerase to the promoter 2- Unwinding of DNA d.h. 3- RNA-polymerase remove 2 phosphates from each complementary nucleoside 4- It covalently links the remaining phosphate to 3’ end of the nucleotides of the growing mRNA chain. 5- addition of nucleotides continues in 5’ 3’ direction. 6- At RNA- termination region, RNA- polymerase receive signal to stop transcription and release mRNA -Non-sense strand - Inactive strand Down str. trailing Upst. leader RNA polymerase 5’ 3’ 3’ Rewinding Unwinding promoter mRNA termination signal -Sense or active strand - DNA template 5’ Transcript mRNA Start codon Stop codon 3’ 5’ -OH P-P-P- Upst. Leader sq. Down str. Trailing sq. Protein coding sequence (translated region) Transcript mRNA

  10. Synthesis of mRNA

  11. Transcription

  12. 1- Proceed in 5’ 3’ direction. 2- Active template DNA –strand called sense strand. 3- Inactive DNA-strand called non-sense strand. 4- The sense strand of 2 different genes is not always the same strand. 5- RNA –polymerase uses nucleoside as a source of energy, in building mRNA. 6- The 1st nucleotide at 5’ –end of mRNA retain its 3 phosphates. 7- Not need to RNA-primer. 8- Transcribed region are: - Upstream leader region. - Protein coding sequence. - Down stream trailing region. 9- Non-transcribedregions: - Promoter. - Termination sequence. 10- Kinds of transcript RNA: - mRNA - tRNA - rRNA • Characters of transcription

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