Rna & Transcription Flashcards
Mushroom poison
Amanita phalloides (the “death cap”).
These mushrooms contain the toxin
alpha amanitin.
sequence contains the genetic master plan. ‘ untouchable’
DNA
the “working copy” of the DNA.
RNA
by transcription
– 3 Major Types: mRNAs, rRNAs, tRNAs.
– Small RNA molecules:
• non-translated (non-coding - ncRNAs), snRNA, snoRNA, miRNA.
– Function
• protein-coding,structural,catalytic(Ribozymes), and regulatory.
Transcription Products
– Nucleotide polymer joined by phosphodiester bonds. – Considerably smaller than DNA. – Exist as single strands. – Contain ribose instead of deoxyribose. – Contain uracil instead of thymine. – They differ in size, function, and special structural shapes and modifications.
RNA characteristics
28S, 18S, 5.8S, and 5S.
Four rRNA species
which is related to the molecular weight and shape of the compound.]
“S”is the Svedberg unit
Together, rRNAs make up about
80% of the total RNA in the cell.
rRNA interacts with ribosomal proteins to form the
Ribosomes
Main function of rRNA is
mRNA Translation
The smallest of the 3 major types of RNA
tRNA
Make up about ___1___ the total RNA in the cell.
15%
tRNA contains
Modified bases
Forms secondary
and tertiary structures
tRNA
Main function of tRNA
mRNA decoding during translation.
There is at least one type of tRNA to transfer each of the
20 amino acids
Specific amino acid is covalently attached to its
3’ end
Most heterogeneous type of RNA in size and base sequence.
mRNA
It comprises about ___1___ of the total cellular RNA.
1- 3-5%
Eukaryotic mRNA is
Monocistronic
Monocistronic means that it
Carries information from just one gene.
mRNA structural characteristics
– 5’ Cap
– Untranslated regions (UTR) at its 5’- and 3’- ends.
– 3’ Poly A tail
- Chromatin structure remodeling to allow DNA access.
- Three RNA Polymerases for the synthesis of rRNA, tRNA, and mRNA.
- Transcription factors (TFs):regulatory proteins to initiate and regulate transcription.
Requirements for transcription of eukaryotic genes
Chromatin Remodeling affects the ability of the transcription machinery to access the DNA to be
transcribed
Relaxed form of DNA
Euchromatin
Most actively transcribed genes in
Euchromatin
Histone Acetyltransferase
HAT
HATs add acetyl group to
Lys
HATs add acetyl group to Lys —>
weak DNA/histone interaction
In, in euchromatin
Highly condensed chromatin
Heterochromatin
Most inactive segments of DNA
Heterochromatin
Histone Deacetylase
HDAC
HDAC removes acetyl group from Lys —>
strong DNA/histone interaction
RNA Pol I
Pre- rRNA: precursor of 28S, 18S, and 5.8S (in the
nucleolus)
RNA Pol II
mRNA and some ncRNA (snRNA, snoRNA, miRNA)
RNA Pol III
tRNA, 5S rRNA, some snRNA and snoRNA
Synthesis of all types of mtRNAs.
By One Mitochondrial RNA Polymerase
a region of DNA that initiates/promotes transcription of a particular gene.
Promoter
a region of DNA that initiates/promotes transcription of a particular gene.
DNA elements
– 25 nt upstream of the transcription start site (+1 nt).
• TATA or Hogness box
– 70 and 80 nucleotides upstream of the +1 nt.
CAAT Box
– Regulatory proteins that bind to DNA elements in promoters of RNA polymerase II genes.
Eukaryotic general transcription factors
CTF, SP1, TFIID.
Examples of TFs
– Assembly of the transcription initiation complex.
– Recruitment of RNA polymerases.
Function of TFs
Local unwinding of DNA caused by
RNA polymerase II
Local unwinding of DNA caused by RNA Pol II
and formation of an open initiation complex.
Transcription elongation
Alpha amanitin causes
-GI disturbances – Electrolyte imbalance – Fever – Liver and kidney dysfunction – 50-90% die within few days
