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

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

Transcription mRNA codon Translation by Ribosomes Amino acid of polypeptide chain 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). Triple code Genetic information flow from nucleus into cytoplasmGenetic information flow from nucleus into cytoplasm

Definition: 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. 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: 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 Expression of genetic information

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

Overview of transcription and translation

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

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

Transcript mRNA -Sense or active strand - DNA template Transcribed region -Non-sense strand - Inactive strand Upst. leader Down str. trailing promoter mRNA termination signal 3’ 5’ Protein coding sequence (translated region) Transcript mRNA Start codon Stop codon Down str. Trailing sq. Upst. Leader sq. RNA polymerase Rewinding Unwinding P-P-P- -OH 5’ 3’ 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 5’ 3’

Synthesis of mRNA

Transcription

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 1 st 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-transcribed regions: - Promoter. - Termination sequence. 10- Kinds of transcript RNA: - mRNA - tRNA - rRNA Characters of transcriptionCharacters of transcription