Chapter 14: Gene Transcription and RNA Modification

gene

segment of DNA used to make a functional product 

transcription

process of copying DNA into RNA 

translation

produces a polypeptide using the information in mRNA

central dogma of genetics

• DNA replication makes DNA copies that are transmitted from cell to cell and from parent to offspring 

  • DNA stores information in units called genes 

transcription factors

• proteins that bind to promoters or regulatory sequences and control the rate of transcription 

  • Mechanism control when and how much that transcription occurs 

regulatory elements/sequences

• sites where proteins interact with the DNA to control transcription 

RNA produced also has sequences that regulate its function 

• Ribosomal-binding site: provides a location for the ribosome to bind and begin translation  

• Start codons and stop codons 

transcription steps

1. initiation: RNA polymerase binds to DNA

2. elongation: RNA polymerase synthesizes RNA

3. termination: RNA polymerase stops synthesizing RNA

bacteria initiation

promoters in site of RNA polymerase binding and initiation of transcription

• Bases in a promoter sequence are numbered in relation to the transcription start site 

• - 35 sequence and -10 sequence are consensus sequence (AT rich, easy to break)

• +1 is the very first base of messenger RNA (always A)

consensus sequence

most common base found at each location within that group of sequences

• Promoter’s deviation from the consensus sequence determines its transcriptional level 

• The closer the promoter is to the consensus, the higher the transcription rate

transcription rate is determined by RNA polymerase binding

initiation requires RNA polymerase to bind to the promoter

• RNA polymerase holoenzyme binds loosely to the DNA

• scans along the DNA until the promoter is reached

• Sigmas factor recognizes both the -35 and -10 regions 

  • Contains a helix-turn motif that gives tighter binding to the DNA 

steps of initiation

1. holoenzyme slides along the DNA until the sigma factor recognizes the promoter

2. binding of the sigma factor of the holoenzyme to the promoter forms the closed complex

3. an open complex is formed when the TATAAT box in the -10 region is unwound

4. a short RNA strand is made within the open complex

5. sigma factor is released —> makes transition to elongation phase

bacteria elongation

RNA polymerase transcribes in a 5’ to 3’ direction

• beta subunits form phosphodiester bonds between nucleotides

• nucleoside triphosphate enter through a pore

• DNA reforms helix with hydrogen bonds as exiting enzyme

template strand

antisense, used for RNA synthesis

coding strand

sense, has the same base sequence as the RNA

termination

end of RNA synthesis, occurs when the short RNA-DNA hybrid of the open complex is forced to separate

• releases the newly made RNA as well as the RNA polymerase

• 2 different mechanisms for bacteria

rho-dependent termination

requires rho protein that functions as a helicase