Objectives:Objectives: To outline the To outline the flow of genetic informationflow of genetic information from from

DNA to protein synthesis.DNA to protein synthesis. To identify the different To identify the different types of RNAtypes of RNA To compare, the To compare, the structure of DNA & RNA.structure of DNA & RNA. To outline the general characteristics of To outline the general characteristics of genetic genetic

codecode & & transcription process.transcription process. To explain the importance of tRNA, mRNA & To explain the importance of tRNA, mRNA &

rRNA.rRNA. To diagram the process of protein synthesis.To diagram the process of protein synthesis. To compare Eukaryotic & prokaryotic mRNATo compare Eukaryotic & prokaryotic mRNA

Expression of genetic Expression of genetic informationinformation

(Part I) (Part I)

Informational unit is required to Informational unit is required to carry out one or more cellular carry out one or more cellular function.function.

Number: 70,000 – 100, 000.Number: 70,000 – 100, 000.

A sequence of bases (A sequence of bases (A –T – C – GA –T – C – G). ). Has specific location on DNA d.h.Has specific location on DNA d.h.

The 4 bases The 4 bases A, T, C and G,A, T, C and G, form the form the 4 letters alphabet of the 4 letters alphabet of the gene gene (genetic) language.(genetic) language.

The word of the gene is called the The word of the gene is called the genetic code.genetic code.

The code is formed of 3 letters from The code is formed of 3 letters from the alphabet of gene language. So the alphabet of gene language. So the genetic code is called the genetic code is called triple triple codecode

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 byRibosomes

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 Genetic information flow from nucleus into from nucleus into cytoplasmcytoplasm

Definition:Definition: a complex process in which the genetic information in DNA is decoded and a complex process in which the genetic information in DNA is decoded and

used to specify the manufacture of specific protein in the cell.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 Expression of genetic informationinformation

TypesTypes : : - mRNA (messenger- mRNA (messenger RNA)RNA) - tRNA (transfer RNA)- tRNA (transfer RNA) - rRNA (ribosome)- rRNA (ribosome)

Polynucleotides like DNAPolynucleotides like DNA

It has some differences:It has some differences: 1- 1- Single strandSingle strand, but folded, , but folded, form short double stranded form short double stranded segment.segment. 2- Pentose sugar is 2- Pentose sugar is riboseribose 3- The base 3- The base UracilUracil substitutes substitutes for for thyminethymine

Ph.One Base

Sugar

Ph.One Base

Sugar

1’

2’3’

4’

5’

OH

Adenine

Guanine

Cytosine

Uracil

OH OH

• RNA - moleculesRNA - molecules

Overview of transcription and translationOverview of transcription and translation

TranscriptionTranscriptionprocessprocess

Structure of Gene in DNA strand: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:Promoter: - specific sequence at beginning of the gene - 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 sequencedown 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 strandUpst.

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- -OH5’

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 mRNASynthesis of mRNA

TranscriptionTranscription

1- Proceed in 5’ 3’ direction.1- Proceed in 5’ 3’ direction.

2- Active template DNA –strand 2- Active template DNA –strand called called sense strandsense strand..

3- Inactive DNA-strand called 3- Inactive DNA-strand called non-non-sense strandsense strand..

4- The sense strand of 2 different 4- The sense strand of 2 different genes is not always the same genes is not always the same strand.strand.

5- RNA –polymerase uses nucleoside 5- RNA –polymerase uses nucleoside as a source of energy, in building as a source of energy, in building mRNA.mRNA.

6- The 16- The 1stst nucleotide at 5’ –end of nucleotide at 5’ –end of mRNA retain its mRNA retain its 3 phosphates.3 phosphates.

7- 7- NotNot need to RNA-primer. need to RNA-primer.

8- 8- Transcribed regionTranscribed region are: are: - Upstream leader region.- Upstream leader region. - Protein coding sequence.- Protein coding sequence. - Down stream trailing region.- Down stream trailing region.

9- 9- Non-transcribedNon-transcribed regions:regions: - Promoter.- Promoter. - Termination sequence.- Termination sequence.

10- Kinds of transcript RNA:10- Kinds of transcript RNA: - mRNA- mRNA - tRNA- tRNA - rRNA- rRNA

• Characters of transcriptionCharacters of transcription