Transcription! Flashcards
(26 cards)
Basic features of RNA
Contains the base uracil in place of thiamine
Has a ribose sugar bearing a hydroxyl group on it to prime carbon
Has tertiary structure
Can interact as functional units quaternary structure like in the ribosomes
Various structures of RNA resemble proteins
Why is RNA less stable than DNA?
The presence of the hydroxyl group on the two prime carbon on the sugar ribose causes it to react, intramolecularly with the three prime OH site, resulting in a phosphate bond breakage
Why use unstable RNA?
RNA evolved first
RNA can form many tertiary structures, allowing it to have different confirmations for different functions. Where has DNA generally only double stranded.
It offers a way of controlling it’s gene level, shutting off expression
Types of RNA
mRNA
And non-coding RNA (housekeeping and regulatory)
Housekeeping nc RNA
tRNA and rRNA
Transcription
Synthesis of RNA from DNA templates
all cellular RNAs are synthesized from DNA templateS
Exhibited as Christmas tree structure
What direction is RNA transcribed in? Which direction template is the template strand?
RNA synthesized in the five prime to three prime direction
The template strand is there for the three prime to five prime
RNA synthesis is complementary and anti-parallel to the DNA template strand
New nucleotides are added to the three prime OH group of the growing RNA
Which strand is utilized for transcription?
Oh, jeans can be located on either DNA strand
Transcription can utilize either DNA strand as the 3 to 5 template, but transcription always occurs in the five prime to three prime direction
Components needed for transcription
- DNA template
- 4 ribonucleotide triphosphates (rNTPs)
- DNA dependent polymerase
Differences btw rna and dna synthesis
Similar to DNA synthesis except:
the precursors RRNTs
Only one strand of DNA is used as a template
RNA chain can be initiated without a primer
RNA synthesis is catalyzed by RNA polymerase, and always proceeds in the five prime to three prime direction
What does DiNova mean?
Means no primer is required
What are the components of the RNA polymerase holoenzyme?
There’s only one RNA polymerase in prokaryotes, called the hollow enzyme
It contains
Alpha
Beta
Better prime
Omega
And sigma
Alpha function
Subunit of the holoenzyme
assembly of the tetrameric core
Function of beta
rNTP binding site
Function of beta prime
DNA template binding region
Function of omega
Helps to stabilize the tetrameric core
Function of sigma
Binds to the tetrameric core,
Many types of sigma factors allow for specificity
Recognizes and binds to the -35 and -10 consensus sequence in the promoter region
Positions RNA polymerase to begin transcription
Leaves once transcription starts at position this one
Initiation in prokaryotes
Once the hollow enzyme is attached to the promoter tightly
RNA polymerase is placed over the transcription start site add position +1
It unwinds DNA to produce a single strand a template
Joins the first two nucleotides
Does RNA synthesis/transcription require a primer?
No
Elongation in transcription in prokaryotes
Elongation occurs when the sigma factor is released, and RNA polymerase begins to move along the template strand
An rNTP complementary to the dna base of template +1 is the first nucleotide in the RNA mlc
Two phosphate groups are cleaved from each subsequent RNTP
Creates an RNA nucleotide that is added to the 3’ end of the growing RNA mlc
Termination
Transcription stops when rna polymerase reaches the terminator region of the gene
This is upstream of where the actual termination takes place
Two types in prokaryotes rho dependent and rho independent
How many polymerases do eukaryotes have
Most eukaryotes have at least 3
Promoter in eukaryotes
In eukaryotes, there are specific promoter sequences for genes transcribed by rna polymerase 1, 2 and 3
Accessory proteins recognize each of these specific types of promoters (through interaction with their dna sequence)
Pol I, Pol II and Pol III are only recruited to their promoter specific accessory proteins
Eukaryotic promoters
More complex than those in prokaryotes
Contain:
A regulatory promoter and a core promoter with
- TFIIB recognition element
- TATA box
- initiator element (transcription start site)
- downstream core promoter element
