Week 2 Flashcards
Amino acids and protein structure/ Protein synthesis and degredation
coding strand
5’ to 3’ strand mRNA would look just like this strand except T’s are U’s
template strand
3’ to 5’ strand Transcription starts at +1 BP
upstream
The bases before the the transcribed bases Houses the promoter
Downstream
the bases after the starting transcribed BP
numbering system
+ numbers indicated the start of transcription and movement downstream - numbers indicated upstream base pairs
Function RNA polymerase
Directs transcriptions Catalyzes the formation of phosphodiester bonds between nucleotides Synthesis occurs 5’ to 3’ direction and doesn’t require a free 3’ OH
Structure of RNA Polymerase
Classified as a Holoenzyme An enzyme with multiple subunits that each carry out specific structural, enzymatic, or regulatory functions
Promoters
Contains the TATA box A sequence of BPs that initiates transcription Tends to be highly conserved
Prokaryotic Transcription Initiation
Uses a protein called sigma factor to bind to the promotor region, which triggers RNA poly. to also bind. Initiation stage is completed when DNA strands separate near the promoter to form open complex
Promoters in prokaryotes
are recognized and binds to a sigma factor which triggers RNA polymerase to also bind
Do prokaryotes need assistance to unwind DNA
No. Prokaryotic RNA poly. opens the strands and the strands come back together at the rewinding point
Prokaryotic Transcription Elongation
Sigma factor falls off and RNA poly. continues to add nucleotides in a 5’-3’ direction
Prokaryotic transcription Termination
Require sequences tha signal RNA polymerase to pause, release the RNA transcript, and dissociate
Two types of Prokaryotic terminators
Intrinsic: RNA structures that do not require protein factors for function. “Hairpin structure” Extrinsic: factor-dependent . ATP-dependent Rho helices
Eukaryotic forms of RNA polymerase
RNA poly I, II, III
RNA polymerase I and III
transcribes nonstructural genes for rRNA and tRNA
RNA polymerase II
transcribes mRNA. Requires 5 general transcription factors to initiate transcription
Eukaryotic Transcription Initiation
promoter is recognized and bound by transcription factors and forms an initiation complex which is then recognized by RNA polymerase holoenzyme
Eukaryotic Transcription Termination
Different strategies depending on the RNA polymerase being used.
RNA Poly I terminates using DNA sequences and binding proteins.
RNA Poly II terminates RNA processing, cleavage and polyadenylation of the transcript
RNA Poly III terminates using RNA sequences
Splicing
Intron removal
Spliceosome structure
Composed of an RNA molecule and proteins called snRNPs (small nuclear ribonucleoprotein particles)
Spliceosome function
A portion of the RNA component of the spliceosome will recognize conserved signal sequences in the intron via complementarity
Several snRNP subunits will bind to the pre-mRNA, cause the intron loop, then excise the intron and re-litigate the exon pieces together
