lecture 2 (30/09/24) Flashcards
The Pulse-Chase Experiment (scientists, dates, general idea)
Paul Zamecnik and Sydney Brenner
early 1950s
cells were exposed to radioactive uracil (a component of RNA)
RNA moved from nucleus to the cytoplasm
first clue RNA was a messenger
Where are proteins made?
in the ribosomes
What is the central dogma?
DNA –> RNA –> protein
Who discovered the enzymes responsible for synthesizing RNA and DNA?
Severo Ochoa and Arthur Kornberg
Nobel prize in 1959
What are some key differences between DNA and RNA?
DNA has deoxyribose (one less O than ribose), RNA has ribose
DNA has T, RNA has U
DNA is double stranded, RNA is single stranded
What are some consequences for the differences at the levels of sugar in DNA and RNA?
RNA is chemically more reactive than DNA - ribose has 2’ OH group
DNA is accurate and can be used as long-term storage, RNA can’t due to chemical activity
RNA is transient
describe the structure of RNA
RNA is largely single stranded
can form a variety of 3D shapes
can pair with other nucleic acids
What is the function of mRNAs?
code for proteins
What is the function of rRNAs?
form the core of the ribosome’s structure and catalyse protein synthesis
What is the function of miRNAs?
regulate gene expression
What is the function of tRNAs?
serve as adaptors between mRNA and amino acids during protein synthesis
What is the function of other non coding RNAs?
used in RNA splicing, gene regulation, telomere, maintenance, and other processes
What is the role of RNA polymerase I?
transcribes rRNAs
What is the role of RNA polymerase II?
transcribes mRNAs
What is the role of RNA polymerase III?
transcribes tRNAs
What is the direction of transcription?
5’ –> 3’
what is an NTP?
nucleoside containing nitrogenous base
ribose/ deoxyribose
3 phosphate groups bound to the sugar
What is needed for RNA synthesis?
enzyme (RNA polymerase)
DNA locally single stranded - one strand is template
NTPs (ATP, CTP, GTP, UTP)
pyrophosphate lost
5’ –> 3’ direction
Complementary base pairing pairs
DNA RNA
A ——> U
C ——> G
T ——> A
G ——> C
summarize RNA synthesis
complementary base pairing
5’ –> 3’ direction
breakage of phosphoanhydride bond of NTP releases energy
phosphodiester bonds are formed
(strands are antiparallel)
summarise mRNA processing idea
eukaryotic mRNA is processed before it leaves the nucleus
Pre mRNA –> mature mRNA
processing the ends of mRNAs is essential for stability
mRNA processing step by step
- 5’ cap w/ atypical nucleotide
- 3’ tail of poly-A-nucleotides
- introns removed
What are introns?
non-coding sequences
not in bacterial genes
removed in the spliceosome
What do the 5’, 3’ splice sites and branch point do?
help in the removal of introns
