Transcription in prokaryotes Flashcards
Understand how the E.coli genome is packaged inside the cell Understand how genes are organised and the difference between coding and template strands Know the nature of the main promoter elements in E.coli and how they interact with RNA polymerase Explain the basics of RNA synthesis in transcription Appreciate the functions of intrinsic and Rho dependent terminators
What is the shape of an E.coli chromosome?
Cylinderical
Where is DNA stored in a bacteria and what else does it contain?
The nucleoid - DNA, HU and H1 packaging proteins
How is the DNA assembled?
Assembled in loops to coil, supercoiling is allowed
What is the definition of transcription?
Synthesis of RNA from a DNA template
What is the definition of a gene?
A region of double stranded DNA that encodes a peptide chain (protein)
What type of stranded DNA does transcription produce?
Single stranded RNA with complementary base pairing
Where is the translational start codon found on the mRNA?
Not at the start - untranslated region first
How can several genes be transcribed from one promoter?
An operon - controlled by one promoter
What are the 4 types of subunit in RNA polymerase?
2 alpha subunits - promoter recognition and binding
Beta subunit - catalytic center
B’ subunit - catalytic center
Sigma subunit - promoter specificity
Creates a Holoenzyme
What are the 3 components in a RNA promoter?
TTGACA (-35)
TATAAT (-10)
Startpoint
What happens at TTGACA (-35) and TATAAT (-10)?
RNA polymerase binds at -35
Unwinds at -10
What is different about RNA synthesis in a prokaryote compared to eukaryote?
No primer is needed
What is the active site like on the enzyme?
Short region of RNA product paired with template strand of DNA - stable
How does the terminator work?
It folds the mRNA into a hairpin structure which breaks and falls off due to weak bonds
What is the Rho factor-dependent termination? (4)
Rho is a hexametric RNA binding protein
Rho identifies rut (rich in c poor in G)
RNA pauses at hairpin and Rho catches up
Rho unwinds the DNA/RNA hybrid and all components are released
