DNA to RNA: Genes, Polymerase And Promoters:

Genes

• Genetic Unit containing Information to make a functional product

  • can code for proteins and RNA

Contents of Genes:

• Structural info : coding info

  • nucleotide bases

• Temporal Information (developmental)

• Positional Info (tissue/cell specific)

  • Gene is switched on: signal passes from 1 cell to the next causing the release of soluble mediators which pass to receptors which signal nucleus

• Inducible signals/ Info (Nutrients, stress, hormones)

  • regulatory info

Prokaryote Gene Organisation:

• Consist of

  • Promoter

  • Leader/ Spacer

  • Cistron/ Coding region

• Where transcription stops and starts isn’t where translation starts and stops

  • spacer/leader in-between

• Can code for multiple polypeptides

PGO - Promoter:

• Defines transcription start and its direction

  • landing pad for RNA polymerase - makes an RNA copy of DNA

  • Contains binding sites for other proteins

PGO - Leader/ Spacer

• Sections of non-translated DNA

• In between transcription and translation stop and start sites

PGO - Cistron/ Coding Regions:

• Sequence of DNA coding for distinct proteins

Eukaryotic Class II Gene Organisation

• Coding sequence to the right of transcription start

• Regulatory sequence more complex - 2 classes

  • Promoter

  • Enhancer

• Also contains:

  • Introns

  • Exons

  • UTR’s

• Sequence only codes for ONE polypeptide

EGO - Promoter

• Contains transcription start site - tells DNA Pol where to start and which direction

  • function dependent on position and orientation in gene

EGO - Enhancer

• Contains more regulatory sequences, bind to proteins

  • if protein is a receptor, signal can be integrated and can decide whether to switch on a gene

• Function independent of position and orientation in a gene

EGO- Introns:

• Non-Coding regions

• In primary transcript

• Absent in mature

EGO - Exons:

• Coding Regions:

• In mature transcript

  • Spliced together with DNA ligase

EGO- Untranslated Region

• Appear before/ after start and stop codon

Size of Eukaryotic and Prokaryotic Genes

• Eukaryote genes: Very large

  • Mostly introns

• Lower E&P genes are smaller

  • Linked to size off the polypeptide they produce

General Transcription Mechanisms

• DNA containing gene consists of

  • coding strand (sense) 5’→3’

    • same sequence as RNA product

  • Template strand (antisense) 3’→5’

    • sequence complimentary to RNA product

• Polymerase reads strand for 5’→3’

  • makes RNA copy

Promoters

• Difference between eukaryotic and prokaryotic’s is the sequence

• Transcription starts at +1 on a gene

• Promoter sequence are -1< and have directionality

  • polymerase looks for prinbow box - only on one strand at -35 and -10 and starts transcribing due to this sequence and its directionality

Transcription Bubble

• RNA polymerase binds to DNA at promoter sequence, opening DNA

  • Uses helicase activity to melt double strand and access the bases

• Polymerises in 5’→3’ direction to make RNA copy of sense strand by base pairing new ribonucleotides with template (antisense) strand

• RNA polymerase makes RNA copy 5’→3’ using base pairing info in 3’→5’

How does RNA polymerase know where and when to bind to DNA and where to stop and start transcription

• due to information found in the gene