Theme 2b Flashcards
What does an organisms phenotype depend on
Cell number, type and function
What is regenerative medicine
Growing a desired tissue type by turning on/off the appropriate genes using molecular techniques
What are the two main structures of a gene
Include promoter and transcriptional unit
What is the promoter
-DNA sequence (including TATA box) that specified where transcription begins on the chromosome
-located immediately upstream of the transcriptional start point of the nontemplate or coding strand
-recognized and bound by the transcriptional machinery (RNA polymerase and transcription factors) that initiate transcription
What is the transcriptional unit
Part of the genome that is copied into RNA
What does the RNA polymerase do
Synthesizes RNA transcript in a 5’ to 3’ direction
Unwinds and rewinds DNA helix during RNA synthesis
Does RNA need a primer
No just DNA
What are the 3 types of RNA polymerase s
1) RNA pol l: transcribes rRNA (noncoding)
2) RNA pol ll: transcribes mRNA (coding)
3) RNA pol lll: transcribes tRNA (noncoding)
What are the 3 steps of transcription
1) initiation
2) elongation
3) termination
What are the 2 types of transcriptional initiation
1) general transcription factors bind to RNA polymerase and recruit RNA polymerase ll resulting in low transcription levels
2) transcriptional activator proteins bind to enhancer regions resulting I high levels of transcription
What is the rate determining step on transcription
Initiation
What happens in transcriptional elongation
RNA transcript gets longer by RNA polymerase synthesis (3’ to 5’)
What happens in transcriptional termination
5’ sequence in DNA template causes termination after transcribed into RNA
What are the 3 termination factors and which type of cells do they occur
1) Rho-independent (prokaryotes)
2) Rho-dependent (prokaryotes)
3) cleavage and polyadenylation specific factor (eukaryotes)
How does Rho-independent termination work
-helicase enzyme
-terminator sequence in mRNA base pairs with itself to form G-C hairpin
-causes RNA polymerase to stall and dissociate
How does Rho-dependent termination work
-relies on Rho helicase
-terminator sequence in mRNA is recognized and bound by the Rho helicase which unwinds RNA from template DNA and RNA polymerase
How does the cleavage and polyadenlation specific factor work
-poly(A) sequence in mRNA signals the CPSF to cleave (pentose phosphate backbone) the completed mRNA transcript
Are all the termination factors sequence driven
Yes
What is the advantage of the 5’ and 3’ UTR’s
Regulate mRNA stability and translational efficiency
What is the open reading frame
Region of mRNA that is translated and included the start and stop codons at the borders
What is the 5’ cap
Modified guanosine triphosphate that is added to the 5’ end of the mRNA and acts as a ribosome binding site and protects mRNA from degradation
What is the poly(A) tail
Long string of adenine nucleotides added to the 3’ end of the mRNA to protect the mRNA from being degraded and increases translational efficiency
What are introns and exons
Introns: noncoding segments of DNA
Exons: coding segments of DNA
What is the difference between pre-mRNA and mature mRNA
Pre-mRNA has introns and exons mature mRNA only has exons that code for amino acids
What is the splicosome (snRNA)
Recognizes sequence on the introns and forms loops to remove them
What is alternative splicing
Generating different proteins from one gene
What percent of human genes are alternatively spliced
75%
How does the cell regulate genes
Post transcriptional regulation by RNA interference
What are microRNAs (miRNAs) and small interfering RNAs (siRNAs)
-precursors that are cleaved to 21-23 by double-stranded RNAs by the diver Rnase
-substrates of RISC (RNA induced-silencing complex)
What does RISC do
-unwinds one of the RNA strands which attract binding of the complementary mRNA
-this interferes with translation initiation or induces mRNA degradation
What is transcriptional regulation and what does it depend on
-control of mRNA synthesis
-depends on the speed of transcriptional initiation (promoter strength)
What is post transcriptional regulation
Processing of mRNA which affects wits stability and translational efficiency
