I. DNA & RNA | 14. Structure of the eukaryotic genes, initiation and termination of transcription in eukaryotes Flashcards
How many types of eukaryotic polymerases?
Eukaryotes have 3 types of RNA polymerases (I, II, III)
What is the difference in RNA polymerases between eukaryote and prokaryote?
1/ Eukaryotes have 3 types of RNA polymerases (I, II, III), while prokaryotes have only 1 type (α2ββ’).
2/
- In prokaryotes, transcription + translation occurs simultaneously i
- in eukaryotes, RNA is first transcribed in the nucleus and then translated in the cytoplasm.
RNA polymerase type I
-> What is the synthesized RNA?
Large pre-rRNA
RNA polymerase type I
-> What is the synthesized RNA?
Large pre-rRNA
RNA polymerase type II
-> What is the synthesized RNA?
hnRNAs
snRNAs
RNA polymerase type III
-> What is the synthesized RNA?
1/ pre-5s rRNA
2/ pre-tRNAs
3/ U6 snRNA
4/ SRP RNA
RNA polymerase type I
-> What is the mature RNA product?
28S, 18S and 5.8S
rRNAs
RNA polymerase type II
-> What is the mature RNA product?
1/ mRNAs (from hnRNAs)
2/ snRNAs
RNA polymerase type III
-> What is the mature RNA product?
5s rRNA
tRNAs
U6 snRNA
SRP RNA
Structure of eukaryotic genes
1/ Exons
2/ Introns
3/ Promoter sequences
What are exons?
coding sequence, transcribed + translated.
-> Coding for the amino acids in the polypeptide chain
What are introns?
non-coding sequence, transcribed but NOT translated (almost always have GU sequence in their 5’ end and AG in their 3’ end)
What are Promoter sequences?
DNA sequences that define where transcription of a gene by RNA polymerase II begins.
-> Typically located directly upstream or at the 5’end of the transcription initiation site.
Eukaryotic RNA polymerase II-dependent promoters are composed of 4 sequences which are ___
1) TATA box-TBP
2) BRE–TF2B (BRE = B recognition element)
3) DPE–TF2D (DPE = downstream promoter element)
4) INR–TF2D (INR = initiator element)
Eukaryotic RNA polymerase II-dependent promoters
-> Characteristics of TATA box
1/ Usually located 25-35 base pairs upstream of transcription start site
2/ TATA binding protein (TBP) binds to TATA-
box sequence -> unwinds the DNA
3/ Adenine (A) + thymine (T) = easiest place to unwind double helix, since only 2 H-bonds
between them