Transcription, the central dogma and splicing Flashcards
what will be produced from transcription
RNA strand that is complimentary to one strand of DNA
transcription process
-rna is synthesised from a DNA template by RNA polymerase. -RNA polymerase targets a site on the DNA–> moving from left to right opening it it up -5’ to 3’ -as the enzyme moves along it adds nucleotides to the growing RNA strand
pyrophosphate
two phosphates e.g. lost during dna synthesis and transcription with nucleotides
simple transcription process
- RNA polymerase 2. DNA locally single stranded –> one strand is a template 3.NTPS (nucleotide triphosphate) 0ATP, CTP, GTP< TTP etc) 4. 2 phosphates are lost (pyrophosphate) 5. RNA synthesis 5’ to 3’ ALWAYs
which direction
5’ to 3’ always
transcriptome
set of all RNA molecules within a cell- including all mRNA- amount of RNA will depend on cell type
genome
all dna within cell
DNA vs RNA
-rna is unstable- so short term- more reactive due to extra hydroxyl group on 2 prime carbon -rna is only single stranded (no back up info) -rna is ore protein to mutations e.g. if cytosine losses amine group, it will change to URACIL–> would not be detected as a mutation since uracil is a base pair in RNA (however since U does not exist in DNA it would be detected by mismatch Mut protein -uracil instead of thymine -ribose although single stranded it can pair with itself, causing local regions of double helix
RNA can form..
double stranded regions, therefore a form 3D complexes
why is RNA more prone to mutations than DNA
if cytosine loses amine group, it will change to uracil this change would not be detected as a mutation since uracil is a base pair in RNA (however as it does not exist in DNA it would be detected
uracil instead of
thymine in RNA
ribose instead of
deoxyribose in RNA
why does ran polymerase know when to stop transcription
due to stop and start codons
what other proteins does RNA polymerase bind with when it binds to the promotor
transcription factors
what is the basic promoter required for
to shows the enzyme where to start
the structure and function of a cell depends on..
what proteins are produced and in what quantities
differences in gene expression is due to
differences in both translation and transcription
what happens when the polymerase reaches stop codon
it is released from the DNA
how is the new RNA chain formed??
by losing a pyrophosphate to forma a sugar phosphate back bone
RNA is more reactive due to..
an extra hydroxyl group on 2 carbon on the pentose
RNA doesn’t bind without..
transcription factors
there will be no transcription if there is no..
transcription factor
the transcription factors ill attach to..
the control region, just before the promotor region–>causes RNA polymerase to attach
what ion is found in the active site of polymerase
Mg2+
during transcription there will be a ….. in the polymerase
a short region of DNA/RNA helix
what is the central dogma
The central dogma of molecular biology describes the flow of genetic information in cells from DNA to messenger RNA (mRNA) to protein.
main flow idea of the central dogma
-DNA- transcription- RNA–translation– protein
transcription occurs in the
nucleus
translation occurs in the
cytoplasm
mRNA is processed before it leaves the nucleus and can be..
translated many times
what does processing of preRNA involve
nucleotides are added to the 5’ and 3’ end -5’ end:nucleotide is added via 5’5’ linkage- capped by an A typical nucleotide -3’ end: tail of nucleotides added (AAAAA)–> poly A nucleotides SPLICING also must occur to remove introns
what happens to the 5’ prime end of preRNA
nucleotide is added via 5’5’ linkage- capped by an A typical nucleotide
what happens to the 3’ end of preRNA
tail of nucleotides added (AAAAA)–> poly A nucleotides
splicing involves..
the removal of introns
why is splicing important
eukaryotic genes are interrupted by non-coding sequences –> prevents faulty proteins from being produced
which unit carries out splicing
spliceosome- catalyses the reaction too areas for ligation and cleavage are determined by the many sub-units of the spliceosome
what marks a mature RNA- s that it is allowed to be exported out of the nucleus
RNA binding proteins
afte rbeing translated many times over…
the cell degrades the mRNA
what effects the mRNA half life..
the sequence of the mRNA
in human transcripts how many genes exhibit alternative splicing
95%
alternative splicing
regulated process during gene expression that results in a single gene coding for multiple proteins. In this process, particular exons of a gene may be included within or excluded from the final, processed messenger RNA (mRNA) produced from that gene.
simple alternative splicing
where a single gene can code for many proteins due to the variability in splicing pattern e.g. exons of genes may be included or excluded production of multiple protein isoforms
RNA hypothesis
some believed RNA came before DNA- W.Gilberts -According to the RNA World Hypothesis, life later evolved to use DNA and proteins due to RNA’s relative instability and poorer catalytic properties, and gradually, ribozymes became increasingly phased out.
first stage of post transcriptional control
splicing-important regulatory step in determining which functional proteins are produced from gene expression. Thus, splicing is the first stage of post-transcriptional control.
splicing process
on either Side of the RNA there is a 5’ splice site and a 3’ splice site - the nucleosome will first cleave the rna on the 5’ end , and the the ran will form a loop attaching t the 3’ ran intron. -3’ end is now cleaved and a circular intron is formed called an INTRON LARIAT -exons on either side will then be rejoined by a ligase
